1
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Pfeffer PL. The first lineage determination in mammals. Dev Biol 2024; 513:12-30. [PMID: 38761966 DOI: 10.1016/j.ydbio.2024.05.011] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2023] [Revised: 03/15/2024] [Accepted: 05/16/2024] [Indexed: 05/20/2024]
Abstract
This review describes in detail the morphological, cytoskeletal and gene expression events leading to the gene regulatory network bifurcation point of trophoblast and inner cell mass cells in a variety of mammalian preimplantation embryos. The interrelated processes of compaction and polarity establishment are discussed in terms of how they affect YAP/WWTR activity and the location and fate of cells. Comparisons between mouse, human, cattle, pig and rabbit embryos suggest a conserved role for YAP/WWTR signalling in trophoblast induction in eutherian animals though the mechanisms for, and timing of, YAP/WWTR activation differs among species. Downstream targets show further differences, with the trophoblast marker GATA3 being a direct target in all examined mammals, while CDX2-positive and SOX2-negative regulation varies.
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Affiliation(s)
- Peter L Pfeffer
- School of Biological Sciences, Victoria University of Wellington, Wellington, New Zealand.
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2
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Kidwai FK, Canalis E, Robey PG. Induced pluripotent stem cell technology in bone biology. Bone 2023; 172:116760. [PMID: 37028583 PMCID: PMC10228209 DOI: 10.1016/j.bone.2023.116760] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/19/2023] [Revised: 03/31/2023] [Accepted: 04/04/2023] [Indexed: 04/09/2023]
Abstract
Technologies on the development and differentiation of human induced pluripotent stem cells (hiPSCs) are rapidly improving, and have been applied to create cell types relevant to the bone field. Differentiation protocols to form bona fide bone-forming cells from iPSCs are available, and can be used to probe details of differentiation and function in depth. When applied to iPSCs bearing disease-causing mutations, the pathogenetic mechanisms of diseases of the skeleton can be elucidated, along with the development of novel therapeutics. These cells can also be used for development of cell therapies for cell and tissue replacement.
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Affiliation(s)
- Fahad K Kidwai
- Skeletal Biology Section, National Institute of Dental and Craniofacial Research, National Institutes of Health, Department of Health and Human Services, Bethesda, MD 20892, United States of America
| | - Ernesto Canalis
- Center for Skeletal Research, Orthopedic Surgery and Medicine, UConn Musculoskeletal Institute, UConn Health, Farmington, CT 06030-4037, United States of America
| | - Pamela G Robey
- Skeletal Biology Section, National Institute of Dental and Craniofacial Research, National Institutes of Health, Department of Health and Human Services, Bethesda, MD 20892, United States of America.
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3
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Covarrubias A, Aguilera-Olguín M, Carrasco-Wong I, Pardo F, Díaz-Astudillo P, Martín SS. Feto-placental Unit: From Development to Function. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2023; 1428:1-29. [PMID: 37466767 DOI: 10.1007/978-3-031-32554-0_1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 07/20/2023]
Abstract
The placenta is an intriguing organ that allows us to survive intrauterine life. This essential organ connects both mother and fetus and plays a crucial role in maternal and fetal well-being. This chapter presents an overview of the morphological and functional aspects of human placental development. First, we describe early human placental development and the characterization of the cell types found in the human placenta. Second, the human placenta from the second trimester to the term of gestation is reviewed, focusing on the morphology and specific pathologies that affect the placenta. Finally, we focus on the placenta's primary functions, such as oxygen and nutrient transport, and their importance for placental development.
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Affiliation(s)
- Ambart Covarrubias
- Health Sciences Faculty, Universidad San Sebastián, Concepción, Chile
- Department of Medicine, Cedars-Sinai Medical Center, Los Angeles, CA, USA
- Group of Research and Innovation in Vascular Health (GRIVAS Health), Chillán, Chile
| | - Macarena Aguilera-Olguín
- Biomedical Research Centre, School of Medicine, Universidad de Valparaíso, Viña del Mar, Chile
- Cellular Signalling and Differentiation Laboratory (CSDL), Medicine and Science Faculty, Universidad San Sebastián, Santiago, Chile
| | - Ivo Carrasco-Wong
- Cellular Signalling and Differentiation Laboratory (CSDL), School of Medical Technology, Medicine and Science Faculty, Universidad San Sebastián, Santiago, Chile
| | - Fabián Pardo
- Metabolic Diseases Research Laboratory, Interdisciplinary Centre of Territorial Health Research (CIISTe), Biomedical Research Center (CIB), San Felipe Campus, School of Medicine, Faculty of Medicine, Universidad de Valparaíso, San Felipe, Chile
| | - Pamela Díaz-Astudillo
- Biomedical Research Centre, School of Medicine, Universidad de Valparaíso, Viña del Mar, Chile
| | - Sebastián San Martín
- Biomedical Research Centre, School of Medicine, Universidad de Valparaíso, Viña del Mar, Chile.
- Group of Research and Innovation in Vascular Health (GRIVAS Health), Chillan, Chile.
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4
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Thowfeequ S, Srinivas S. Embryonic and extraembryonic tissues during mammalian development: shifting boundaries in time and space. Philos Trans R Soc Lond B Biol Sci 2022; 377:20210255. [PMID: 36252217 PMCID: PMC9574638 DOI: 10.1098/rstb.2021.0255] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
The first few days of embryonic development in eutherian mammals are dedicated to the specification and elaboration of the extraembryonic tissues. However, where the fetus ends and its adnexa begins is not always as self-evident during the early stages of development, when the definitive body axes are still being laid down, the germ layers being specified and a discrete form or bodyplan is yet to emerge. Function, anatomy, histomorphology and molecular identities have been used through the history of embryology, to make this distinction. In this review, we explore them individually by using specific examples from the early embryo. While highlighting the challenges of drawing discrete boundaries between embryonic and extraembryonic tissues and the limitations of a binary categorization, we discuss how basing such identity on fate is the most universal and conceptually consistent. This article is part of the theme issue 'Extraembryonic tissues: exploring concepts, definitions and functions across the animal kingdom'.
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Affiliation(s)
- Shifaan Thowfeequ
- Department of Physiology, Anatomy and Genetics, University of Oxford, South Parks Road, Oxford OX1 3QX, UK
| | - Shankar Srinivas
- Department of Physiology, Anatomy and Genetics, University of Oxford, South Parks Road, Oxford OX1 3QX, UK
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5
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Pfeffer PL. Alternative mammalian strategies leading towards gastrulation: losing polar trophoblast (Rauber's layer) or gaining an epiblast cavity. Philos Trans R Soc Lond B Biol Sci 2022; 377:20210254. [PMID: 36252216 PMCID: PMC9574635 DOI: 10.1098/rstb.2021.0254] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Using embryological data from 14 mammalian orders, the hypothesis is presented that in placental mammals, epiblast cavitation and polar trophoblast loss are alternative developmental solutions to shield the central epiblast from extraembryonic signalling. It is argued that such reciprocal signalling between the edge of the epiblast and the adjoining polar trophoblast or edge of the mural trophoblast or with the amniotic ectoderm is necessary for the induction of gastrulation. This article is part of the theme issue 'Extraembryonic tissues: exploring concepts, definitions and functions across the animal kingdom'.
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Affiliation(s)
- Peter L. Pfeffer
- School of Biological Sciences, Victoria University of Wellington, Kelburn Parade, Wellington 6010, New Zealand
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6
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Abstract
Analogies between placentation, in particular the behavior of trophoblast cells, and cancer have been noted since the beginning of the twentieth century. To what degree these can be explained as a consequence of the evolution of placentation has been unclear. In this review, we conclude that many similarities between trophoblast and cancer cells are shared with other, phylogenetically older processes than placentation. The best candidates for cancer hallmarks that can be explained by the evolution of eutherian placenta are mechanisms of immune evasion. Another dimension of the maternal accommodation of the placenta with an impact on cancer malignancy is the evolution of endometrial invasibility. Species with lower degrees of placental invasion tend to have lower vulnerability to cancer malignancy. We finally identify several areas in which one could expect to see coevolutionary changes in placental and cancer biology but that, to our knowledge, have not been explored. Expected final online publication date for the Annual Review of Animal Biosciences, Volume 10 is February 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.
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Affiliation(s)
- Günter P Wagner
- Systems Biology Institute, Yale University, West Haven, Connecticut, USA; , , .,Department of Ecology and Evolutionary Biology, Yale University, New Haven, Connecticut, USA.,Department of Obstetrics, Gynecology and Reproductive Sciences, Yale University, New Haven, Connecticut, USA.,Department of Obstetrics and Gynecology, Wayne State University, Detroit, Michigan, USA
| | - Kshitiz
- Department of Biomedical Engineering, University of Connecticut Health, Storrs, Connecticut, USA;
| | - Anasuya Dighe
- Systems Biology Institute, Yale University, West Haven, Connecticut, USA; , , .,Department of Ecology and Evolutionary Biology, Yale University, New Haven, Connecticut, USA
| | - Andre Levchenko
- Systems Biology Institute, Yale University, West Haven, Connecticut, USA; , , .,Department of Biomedical Engineering, Yale University, New Haven, Connecticut, USA
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7
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Wu Y, Zhang W. The Role of E3s in Regulating Pluripotency of Embryonic Stem Cells and Induced Pluripotent Stem Cells. Int J Mol Sci 2021; 22:1168. [PMID: 33503896 PMCID: PMC7865285 DOI: 10.3390/ijms22031168] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/25/2020] [Revised: 01/15/2021] [Accepted: 01/20/2021] [Indexed: 12/14/2022] Open
Abstract
Pluripotent embryonic stem cells (ESCs) are derived from early embryos and can differentiate into any type of cells in living organisms. Induced pluripotent stem cells (iPSCs) resemble ESCs, both of which serve as excellent sources to study early embryonic development and realize cell replacement therapies for age-related degenerative diseases and other cell dysfunction-related illnesses. To achieve these valuable applications, comprehensively understanding of the mechanisms underlying pluripotency maintenance and acquisition is critical. Ubiquitination modifies proteins with Ubiquitin (Ub) at the post-translational level to monitor protein stability and activity. It is extensively involved in pluripotency-specific regulatory networks in ESCs and iPSCs. Ubiquitination is achieved by sequential actions of the Ub-activating enzyme E1, Ub-conjugating enzyme E2, and Ub ligase E3. Compared with E1s and E2s, E3s are most abundant, responsible for substrate selectivity and functional diversity. In this review, we focus on E3 ligases to discuss recent progresses in understanding how they regulate pluripotency and somatic cell reprogramming through ubiquitinating core ESC regulators.
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Affiliation(s)
| | - Weiwei Zhang
- College of Life Sciences, Capital Normal University, Beijing 100048, China;
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8
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Mulholland CB, Nishiyama A, Ryan J, Nakamura R, Yiğit M, Glück IM, Trummer C, Qin W, Bartoschek MD, Traube FR, Parsa E, Ugur E, Modic M, Acharya A, Stolz P, Ziegenhain C, Wierer M, Enard W, Carell T, Lamb DC, Takeda H, Nakanishi M, Bultmann S, Leonhardt H. Recent evolution of a TET-controlled and DPPA3/STELLA-driven pathway of passive DNA demethylation in mammals. Nat Commun 2020; 11:5972. [PMID: 33235224 PMCID: PMC7686362 DOI: 10.1038/s41467-020-19603-1] [Citation(s) in RCA: 31] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2020] [Accepted: 10/22/2020] [Indexed: 12/12/2022] Open
Abstract
Genome-wide DNA demethylation is a unique feature of mammalian development and naïve pluripotent stem cells. Here, we describe a recently evolved pathway in which global hypomethylation is achieved by the coupling of active and passive demethylation. TET activity is required, albeit indirectly, for global demethylation, which mostly occurs at sites devoid of TET binding. Instead, TET-mediated active demethylation is locus-specific and necessary for activating a subset of genes, including the naïve pluripotency and germline marker Dppa3 (Stella, Pgc7). DPPA3 in turn drives large-scale passive demethylation by directly binding and displacing UHRF1 from chromatin, thereby inhibiting maintenance DNA methylation. Although unique to mammals, we show that DPPA3 alone is capable of inducing global DNA demethylation in non-mammalian species (Xenopus and medaka) despite their evolutionary divergence from mammals more than 300 million years ago. Our findings suggest that the evolution of Dppa3 facilitated the emergence of global DNA demethylation in mammals.
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Affiliation(s)
- Christopher B Mulholland
- Department of Biology II and Center for Integrated Protein Science Munich (CIPSM), Human Biology and BioImaging, Ludwig-Maximilians-Universität München, Planegg-Martinsried, Germany
| | - Atsuya Nishiyama
- Division of Cancer Cell Biology, The Institute of Medical Science, The University of Tokyo, 4-6-1 Shirokanedai, Minato-ku, Tokyo, 108-8639, Japan
| | - Joel Ryan
- Department of Biology II and Center for Integrated Protein Science Munich (CIPSM), Human Biology and BioImaging, Ludwig-Maximilians-Universität München, Planegg-Martinsried, Germany
| | - Ryohei Nakamura
- Department of Biological Sciences, Graduate School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-0033, Japan
| | - Merve Yiğit
- Department of Biology II and Center for Integrated Protein Science Munich (CIPSM), Human Biology and BioImaging, Ludwig-Maximilians-Universität München, Planegg-Martinsried, Germany
| | - Ivo M Glück
- Physical Chemistry, Department of Chemistry, Center for Nanoscience, Nanosystems Initiative Munich and Center for Integrated Protein Science Munich, Ludwig-Maximilians-Universität München, Munich, Germany
| | - Carina Trummer
- Department of Biology II and Center for Integrated Protein Science Munich (CIPSM), Human Biology and BioImaging, Ludwig-Maximilians-Universität München, Planegg-Martinsried, Germany
| | - Weihua Qin
- Department of Biology II and Center for Integrated Protein Science Munich (CIPSM), Human Biology and BioImaging, Ludwig-Maximilians-Universität München, Planegg-Martinsried, Germany
| | - Michael D Bartoschek
- Department of Biology II and Center for Integrated Protein Science Munich (CIPSM), Human Biology and BioImaging, Ludwig-Maximilians-Universität München, Planegg-Martinsried, Germany
| | - Franziska R Traube
- Center for Integrated Protein Science (CIPSM) at the Department of Chemistry, Ludwig-Maximilians-Universität München, Munich, Germany
| | - Edris Parsa
- Center for Integrated Protein Science (CIPSM) at the Department of Chemistry, Ludwig-Maximilians-Universität München, Munich, Germany
| | - Enes Ugur
- Department of Biology II and Center for Integrated Protein Science Munich (CIPSM), Human Biology and BioImaging, Ludwig-Maximilians-Universität München, Planegg-Martinsried, Germany
- Department of Proteomics and Signal Transduction, Max Planck Institute for Biochemistry, Am Klopferspitz 18, 82152, Martinsried, Germany
| | - Miha Modic
- The Francis Crick Institute and UCL Queen Square Institute of Neurology, London, UK
| | - Aishwarya Acharya
- Department of Biology II and Center for Integrated Protein Science Munich (CIPSM), Human Biology and BioImaging, Ludwig-Maximilians-Universität München, Planegg-Martinsried, Germany
| | - Paul Stolz
- Department of Biology II and Center for Integrated Protein Science Munich (CIPSM), Human Biology and BioImaging, Ludwig-Maximilians-Universität München, Planegg-Martinsried, Germany
| | - Christoph Ziegenhain
- Department of Biology II, Anthropology and Human Genomics, Ludwig-Maximilians-Universität München, Planegg-Martinsried, Germany
| | - Michael Wierer
- Department of Proteomics and Signal Transduction, Max Planck Institute for Biochemistry, Am Klopferspitz 18, 82152, Martinsried, Germany
| | - Wolfgang Enard
- Department of Biology II, Anthropology and Human Genomics, Ludwig-Maximilians-Universität München, Planegg-Martinsried, Germany
| | - Thomas Carell
- Center for Integrated Protein Science (CIPSM) at the Department of Chemistry, Ludwig-Maximilians-Universität München, Munich, Germany
| | - Don C Lamb
- Physical Chemistry, Department of Chemistry, Center for Nanoscience, Nanosystems Initiative Munich and Center for Integrated Protein Science Munich, Ludwig-Maximilians-Universität München, Munich, Germany
| | - Hiroyuki Takeda
- Department of Biological Sciences, Graduate School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-0033, Japan
| | - Makoto Nakanishi
- Division of Cancer Cell Biology, The Institute of Medical Science, The University of Tokyo, 4-6-1 Shirokanedai, Minato-ku, Tokyo, 108-8639, Japan
| | - Sebastian Bultmann
- Department of Biology II and Center for Integrated Protein Science Munich (CIPSM), Human Biology and BioImaging, Ludwig-Maximilians-Universität München, Planegg-Martinsried, Germany.
| | - Heinrich Leonhardt
- Department of Biology II and Center for Integrated Protein Science Munich (CIPSM), Human Biology and BioImaging, Ludwig-Maximilians-Universität München, Planegg-Martinsried, Germany.
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9
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Davidian A, Koshel E, Dyomin A, Galkina S, Saifitdinova A, Gaginskaya E. On some structural and evolutionary aspects of rDNA amplification in oogenesis of Trachemys scripta turtles. Cell Tissue Res 2020; 383:853-864. [PMID: 32897424 DOI: 10.1007/s00441-020-03282-x] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2020] [Accepted: 08/12/2020] [Indexed: 10/23/2022]
Abstract
The features of rDNA amplification have been studied in oocytes of the red-eared slider Trachemys scripta using a number of specific histochemical and cytomolecular methods. A single nucleolus in early diplotene oocytes is associated with the nucleolus organizer region (NOR). With oocyte growth, the number of nucleoli increases dramatically and reaches hundreds by the lampbrush chromosome stage (pre-vitellogenesis). RNA-polymerase I, fibrillarin, and PCNA immunodetection in the amplified nucleoli and FISH of the 5'ETS probe to the oocyte nuclear content suggest pre-rRNA and rDNA synthesis in the nucleoli at all stages studied. This implies a continuous reproduction of the nucleoli during oocyte development from early diplotene up to vitellogenesis. The data obtained offer a different way for rDNA amplification and formation of extrachromosomal nucleoli in turtle oocytes compared with the amplified nucleoli formation in amphibian and fish oocytes. In the Sauropsida clade of Archelosauria, which includes turtles, crocodiles, and birds, rDNA function is known to be suppressed in avian oogenesis during the lampbrush stage (Gaginskaya et al. in Cytogenet Genome Res 124:251-267, 2009).
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Affiliation(s)
- Asya Davidian
- St Petersburg University, St Petersburg, 199034, Russia
| | | | - Alexander Dyomin
- St Petersburg University, St Petersburg, 199034, Russia.,Saratov State Medical University, Saratov, 410000, Russia
| | | | - Alsu Saifitdinova
- Herzen State Pedagogical University of Russia, St Petersburg, 191186, Russia
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10
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Abstract
Mammals evolved from oviparous reptiles that laid eggs in a dry, terrestrial environment, thus requiring large amounts of yolk to support development and tough, outer coats to protect them. Eutherian mammals such as humans and mice exhibit an "extreme" form of viviparity in which yolk and conceptus coats have become largely redundant. However, the "other" mammals-monotremes and marsupials-have retained and modified some features of reptilian development that provide valuable insights into the evolution of viviparity in mammals. Most striking of these are the conceptus coats, which include the zona pellucida, the mucoid coat, and the shell coat. We discuss current knowledge of these coats in monotremes and marsupials, their possible roles, and recently identified components such as the zona pellucida protein ZPAX, conceptus coat mucin (CCM), and nephronectin (NPNT).
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Affiliation(s)
| | - Marilyn B Renfree
- School of BioSciences, University of Melbourne, Parkville, VIC, Australia.
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11
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Abstract
We present an overview of symmetry breaking in early mammalian development as a continuous process from compaction to specification of the body axes. While earlier studies have focused on individual symmetry-breaking events, recent advances enable us to explore progressive symmetry breaking during early mammalian development. Although we primarily discuss embryonic development of the mouse, as it is the best-studied mammalian model system to date, we also highlight the shared and distinct aspects between different mammalian species. Finally, we discuss how insights gained from studying mammalian development can be generalized in light of self-organization principles. With this review, we hope to highlight new perspectives in studying symmetry breaking and self-organization in multicellular systems.
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Affiliation(s)
- Hui Ting Zhang
- European Molecular Biology Laboratory, 69117 Heidelberg, Germany;
| | - Takashi Hiiragi
- European Molecular Biology Laboratory, 69117 Heidelberg, Germany;
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12
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Pfeffer PL. Building Principles for Constructing a Mammalian Blastocyst Embryo. BIOLOGY 2018; 7:biology7030041. [PMID: 30041494 PMCID: PMC6164496 DOI: 10.3390/biology7030041] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 06/13/2018] [Revised: 07/19/2018] [Accepted: 07/20/2018] [Indexed: 12/16/2022]
Abstract
The self-organisation of a fertilised egg to form a blastocyst structure, which consists of three distinct cell lineages (trophoblast, epiblast and hypoblast) arranged around an off-centre cavity, is unique to mammals. While the starting point (the zygote) and endpoint (the blastocyst) are similar in all mammals, the intervening events have diverged. This review examines and compares the descriptive and functional data surrounding embryonic gene activation, symmetry-breaking, first and second lineage establishment, and fate commitment in a wide range of mammalian orders. The exquisite detail known from mouse embryogenesis, embryonic stem cell studies and the wealth of recent single cell transcriptomic experiments are used to highlight the building principles underlying early mammalian embryonic development.
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Affiliation(s)
- Peter L Pfeffer
- School of Biological Sciences, Victoria University of Wellington, Wellington 6012, New Zealand.
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13
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Abstract
Marsupials and monotremes differ from eutherian mammals in many features of their reproduction and development. Some features appear to be representative of transitional stages in evolution from therapsid reptiles to humans and mice, particularly with respect to the extraembryonic tissues that have undergone remarkable modifications to accommodate reduced egg size and quantity of yolk/deutoplasm, and increasing emphasis on viviparity and placentation. Trophoblast and hypoblast contribute the epithelial layers in most of the extraembryonic membranes and are the first two lineages to differentiate from the embryonic lineage. How they are specified varies greatly among mammals, perhaps largely due to heterochrony in the stage at which they must function. Differences probably also exist in the stage at which lineages are specified relative to the stage at which they fully commit to differentiation. The dogma of sequential commitment to trophoblast and hypoblast with progressive loss of potency may not be a fundamental feature of early mammalian development, but merely a recently acquired developmental pattern in eutherians, or at least mice.
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14
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Tseng WC, Munisha M, Gutierrez JB, Dougan ST. Establishment of the Vertebrate Germ Layers. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2017; 953:307-381. [PMID: 27975275 DOI: 10.1007/978-3-319-46095-6_7] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
The process of germ layer formation is a universal feature of animal development. The germ layers separate the cells that produce the internal organs and tissues from those that produce the nervous system and outer tissues. Their discovery in the early nineteenth century transformed embryology from a purely descriptive field into a rigorous scientific discipline, in which hypotheses could be tested by observation and experimentation. By systematically addressing the questions of how the germ layers are formed and how they generate overall body plan, scientists have made fundamental contributions to the fields of evolution, cell signaling, morphogenesis, and stem cell biology. At each step, this work was advanced by the development of innovative methods of observing cell behavior in vivo and in culture. Here, we take an historical approach to describe our current understanding of vertebrate germ layer formation as it relates to the long-standing questions of developmental biology. By comparing how germ layers form in distantly related vertebrate species, we find that highly conserved molecular pathways can be adapted to perform the same function in dramatically different embryonic environments.
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Affiliation(s)
- Wei-Chia Tseng
- Department of Cellular Biology, University of Georgia, Athens, GA, 30602, USA
| | - Mumingjiang Munisha
- Department of Cellular Biology, University of Georgia, Athens, GA, 30602, USA
| | - Juan B Gutierrez
- Department of Mathematics, University of Georgia, Athens, GA, 30602, USA.,Institute of Bioinformatics, University of Georgia, Athens, GA, 30602, USA
| | - Scott T Dougan
- Department of Cellular Biology, University of Georgia, Athens, GA, 30602, USA.
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15
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Conserved and divergent expression patterns of markers of axial development in the laboratory opossum,Monodelphis domestica. Dev Dyn 2016; 245:1176-1188. [DOI: 10.1002/dvdy.24459] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2016] [Revised: 09/14/2016] [Accepted: 09/14/2016] [Indexed: 11/07/2022] Open
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16
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Roberts RM, Green JA, Schulz LC. The evolution of the placenta. Reproduction 2016; 152:R179-89. [PMID: 27486265 DOI: 10.1530/rep-16-0325] [Citation(s) in RCA: 111] [Impact Index Per Article: 13.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2016] [Accepted: 08/01/2016] [Indexed: 01/23/2023]
Abstract
The very apt definition of a placenta is coined by Mossman, namely apposition or fusion of the fetal membranes to the uterine mucosa for physiological exchange. As such, it is a specialized organ whose purpose is to provide continuing support to the developing young. By this definition, placentas have evolved within every vertebrate class other than birds. They have evolved on multiple occasions, often within quite narrow taxonomic groups. As the placenta and the maternal system associate more intimately, such that the conceptus relies extensively on maternal support, the relationship leads to increased conflict that drives adaptive changes on both sides. The story of vertebrate placentation, therefore, is one of convergent evolution at both the macromolecular and molecular levels. In this short review, we first describe the emergence of placental-like structures in nonmammalian vertebrates and then transition to mammals themselves. We close the review by discussing the mechanisms that might have favored diversity and hence evolution of the morphology and physiology of the placentas of eutherian mammals.
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Affiliation(s)
- R Michael Roberts
- C.S. Bond Life Sciences CenterUniversity of Missouri, Columbia, Missouri, USA Division of Animal SciencesUniversity of Missouri, Columbia, Missouri, USA
| | - Jonathan A Green
- Division of Animal SciencesUniversity of Missouri, Columbia, Missouri, USA
| | - Laura C Schulz
- Department of ObstetricsGynecology and Women's Health, University of Missouri School of Medicine, Columbia, Missouri, USA
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17
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Yoshida M, Kajikawa E, Kurokawa D, Noro M, Iwai T, Yonemura S, Kobayashi K, Kiyonari H, Aizawa S. Conserved and divergent expression patterns of markers of axial development in reptilian embryos: Chinese soft-shell turtle and Madagascar ground gecko. Dev Biol 2016; 415:122-142. [DOI: 10.1016/j.ydbio.2016.05.005] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2016] [Revised: 05/06/2016] [Accepted: 05/06/2016] [Indexed: 12/18/2022]
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18
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Familari M, Au PCK, de Iongh RU, Cruz Y, Selwood L. Expression analysis of Cdx2 and Pou5f1 in a marsupial, the stripe-faced dunnart, during early development. Mol Reprod Dev 2016; 83:108-23. [PMID: 26613191 DOI: 10.1002/mrd.22597] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/24/2015] [Accepted: 11/26/2015] [Indexed: 11/06/2022]
Abstract
The first lineage allocation during mouse development forms the trophectoderm and inner cell mass, in which Cdx2 and Pou5f1 display reciprocal expression. Yet Cdx2 is not required for trophectoderm specification in other mammals, such as the human, cow, pig, or in two marsupials, the tammar and opossum. The role of Cdx2 and Pou5f1 in the first lineage allocation of Sminthopsis macroura, the stripe-faced dunnart, is unknown. In this study, expression of Cdx2 and Pou5f1 during oogenesis, development from cleavage to blastocyst stages, and in the allocation of the first three lineages was analyzed for this dunnart. Cdx2 mRNA was present in late antral-stage oocytes, but not present again until Day 5.5. Pou5f1 mRNA was present from primary follicles to zygotes, and then expression resumed starting at the early unilaminar blastocyst stage. All cleavage stages and the pluriblast and trophoblast cells co-expressed CDX2 and POU5F1 proteins, which persisted until early stages of hypoblast formation. Hypoblast cells also show co-localisation of POU5F1 and CDX2 once they were allocated, and this persisted during their division and migration. Our studies suggest that CDX2, and possibly POU5F1, are maternal proteins, and that the first lineage to differentiate is the trophoblast, which differentiates to trophectoderm after shell loss one day before implantation. In the stripe-faced dunnart, cleavage cells, as well as trophoblast and pluriblast cells, are polarized, suggesting the continued presence of CDX2 in both lineages until late blastocyst stages may play a role in the formation and maintenance of polarity.
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Affiliation(s)
- Mary Familari
- School of Biosciences, University of Melbourne, Parkville, Victoria, Australia
| | - Phil Chi Khang Au
- School of Biosciences, University of Melbourne, Parkville, Victoria, Australia
| | - Robb U de Iongh
- Department of Anatomy and Neuroscience, University of Melbourne, Parkville, Victoria, Australia
| | - Yolanda Cruz
- Department of Biology, Oberlin College, Oberlin, Ohio
| | - Lynne Selwood
- School of Biosciences, University of Melbourne, Parkville, Victoria, Australia
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Frankenberg SR, de Barros FR, Rossant J, Renfree MB. The mammalian blastocyst. WILEY INTERDISCIPLINARY REVIEWS-DEVELOPMENTAL BIOLOGY 2016; 5:210-32. [DOI: 10.1002/wdev.220] [Citation(s) in RCA: 39] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/12/2015] [Revised: 10/22/2015] [Accepted: 10/29/2015] [Indexed: 11/10/2022]
Affiliation(s)
| | - Flavia R.O. de Barros
- Program in Developmental and Stem Cell Biology; Peter Gilgan Centre for Research and Learning, Hospital for Sick Children; Toronto Canada
- Department of Molecular Genetics; University of Toronto; Toronto Canada
| | - Janet Rossant
- Program in Developmental and Stem Cell Biology; Peter Gilgan Centre for Research and Learning, Hospital for Sick Children; Toronto Canada
- Department of Molecular Genetics; University of Toronto; Toronto Canada
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20
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Abstract
The placenta sits at the interface between the maternal and fetal vascular beds where it mediates nutrient and waste exchange to enable in utero existence. Placental cells (trophoblasts) accomplish this via invading and remodeling the uterine vasculature. Amazingly, despite being of fetal origin, trophoblasts do not trigger a significant maternal immune response. Additionally, they maintain a highly reliable hemostasis in this extremely vascular interface. Decades of research into how the placenta differentiates itself from embryonic tissues to accomplish these and other feats have revealed a previously unappreciated level of complexity with respect to the placenta's cellular composition. Additionally, novel insights with respect to roles played by the placenta in guiding fetal development and metabolism have sparked a renewed interest in understanding the interrelationship between fetal and placental well-being. Here, we present an overview of emerging research in placental biology that highlights these themes and the importance of the placenta to fetal and adult health.
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Early Developmental and Evolutionary Origins of Gene Body DNA Methylation Patterns in Mammalian Placentas. PLoS Genet 2015; 11:e1005442. [PMID: 26241857 PMCID: PMC4524645 DOI: 10.1371/journal.pgen.1005442] [Citation(s) in RCA: 79] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2015] [Accepted: 07/14/2015] [Indexed: 12/11/2022] Open
Abstract
Over the last 20-80 million years the mammalian placenta has taken on a variety of morphologies through both divergent and convergent evolution. Recently we have shown that the human placenta genome has a unique epigenetic pattern of large partially methylated domains (PMDs) and highly methylated domains (HMDs) with gene body DNA methylation positively correlating with level of gene expression. In order to determine the evolutionary conservation of DNA methylation patterns and transcriptional regulatory programs in the placenta, we performed a genome-wide methylome (MethylC-seq) analysis of human, rhesus macaque, squirrel monkey, mouse, dog, horse, and cow placentas as well as opossum extraembryonic membrane. We found that, similar to human placenta, mammalian placentas and opossum extraembryonic membrane have globally lower levels of methylation compared to somatic tissues. Higher relative gene body methylation was the conserved feature across all mammalian placentas, despite differences in PMD/HMDs and absolute methylation levels. Specifically, higher methylation over the bodies of genes involved in mitosis, vesicle-mediated transport, protein phosphorylation, and chromatin modification was observed compared with the rest of the genome. As in human placenta, higher methylation is associated with higher gene expression and is predictive of genic location across species. Analysis of DNA methylation in oocytes and preimplantation embryos shows a conserved pattern of gene body methylation similar to the placenta. Intriguingly, mouse and cow oocytes and mouse early embryos have PMD/HMDs but their placentas do not, suggesting that PMD/HMDs are a feature of early preimplantation methylation patterns that become lost during placental development in some species and following implantation of the embryo.
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22
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Sheng G. Epiblast morphogenesis before gastrulation. Dev Biol 2015; 401:17-24. [DOI: 10.1016/j.ydbio.2014.10.003] [Citation(s) in RCA: 52] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2014] [Revised: 09/24/2014] [Accepted: 10/08/2014] [Indexed: 12/21/2022]
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Abstract
Pluripotent cells in embryos are situated near the apex of the hierarchy of developmental potential. They are capable of generating all cell types of the mammalian body proper. Therefore, they are the exemplar of stem cells. In vivo, pluripotent cells exist transiently and become expended within a few days of their establishment. Yet, when explanted into artificial culture conditions, they can be indefinitely propagated in vitro as pluripotent stem cell lines. A host of transcription factors and regulatory genes are now known to underpin the pluripotent state. Nonetheless, how pluripotent cells are equipped with their vast multilineage differentiation potential remains elusive. Consensus holds that pluripotency transcription factors prevent differentiation by inhibiting the expression of differentiation genes. However, this does not explain the developmental potential of pluripotent cells. We have presented another emergent perspective, namely, that pluripotency factors function as lineage specifiers that enable pluripotent cells to differentiate into specific lineages, therefore endowing pluripotent cells with their multilineage potential. Here we provide a comprehensive overview of the developmental biology, transcription factors, and extrinsic signaling associated with pluripotent cells, and their accompanying subtypes, in vitro heterogeneity and chromatin states. Although much has been learned since the appreciation of mammalian pluripotency in the 1950s and the derivation of embryonic stem cell lines in 1981, we will specifically emphasize what currently remains unclear. However, the view that pluripotency factors capacitate differentiation, recently corroborated by experimental evidence, might perhaps address the long-standing question of how pluripotent cells are endowed with their multilineage differentiation potential.
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Affiliation(s)
- Kyle M. Loh
- Department of Developmental Biology and the Stanford Institute for Stem Cell Biology & Regenerative Medicine, Stanford University School of Medicine, Stanford, California; Genome Institute of Singapore, Stem Cell & Regenerative Biology Group, Agency for Science, Technology & Research, Singapore; and Department of Medicine and the Beth Israel Deaconess Medical Center, Division of Hematology/Oncology, Harvard Medical School, Boston, Massachusetts
| | - Bing Lim
- Department of Developmental Biology and the Stanford Institute for Stem Cell Biology & Regenerative Medicine, Stanford University School of Medicine, Stanford, California; Genome Institute of Singapore, Stem Cell & Regenerative Biology Group, Agency for Science, Technology & Research, Singapore; and Department of Medicine and the Beth Israel Deaconess Medical Center, Division of Hematology/Oncology, Harvard Medical School, Boston, Massachusetts
| | - Lay Teng Ang
- Department of Developmental Biology and the Stanford Institute for Stem Cell Biology & Regenerative Medicine, Stanford University School of Medicine, Stanford, California; Genome Institute of Singapore, Stem Cell & Regenerative Biology Group, Agency for Science, Technology & Research, Singapore; and Department of Medicine and the Beth Israel Deaconess Medical Center, Division of Hematology/Oncology, Harvard Medical School, Boston, Massachusetts
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24
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Dudley JS, Murphy CR, Thompson MB, McAllan BM. Desmoglein-2 during pregnancy and its role in the evolution of viviparity in a marsupial (Sminthopsis crassicaudata; Dasyuridae). J Morphol 2014; 276:261-72. [DOI: 10.1002/jmor.20333] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2014] [Revised: 09/28/2014] [Accepted: 10/02/2014] [Indexed: 11/09/2022]
Affiliation(s)
- Jessica S. Dudley
- School of Medical Sciences and Bosch Institute; University of Sydney; Sydney NSW 2006 Australia
| | - Christopher R. Murphy
- School of Medical Sciences and Bosch Institute; University of Sydney; Sydney NSW 2006 Australia
| | - Michael B. Thompson
- School of Biological Science (A08); University of Sydney; Sydney NSW 2006 Australia
| | - Bronwyn M. McAllan
- School of Medical Sciences and Bosch Institute; University of Sydney; Sydney NSW 2006 Australia
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25
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Irie N, Tang WWC, Azim Surani M. Germ cell specification and pluripotency in mammals: a perspective from early embryogenesis. Reprod Med Biol 2014; 13:203-215. [PMID: 25298745 PMCID: PMC4182624 DOI: 10.1007/s12522-014-0184-2] [Citation(s) in RCA: 52] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2014] [Accepted: 05/19/2014] [Indexed: 12/01/2022] Open
Abstract
Germ cells are unique cell types that generate a totipotent zygote upon fertilization, giving rise to the next generation in mammals and many other multicellular organisms. How germ cells acquire this ability has been of considerable interest. In mammals, primordial germ cells (PGCs), the precursors of sperm and oocytes, are specified around the time of gastrulation. PGCs are induced by signals from the surrounding extra-embryonic tissues to the equipotent epiblast cells that give rise to all cell types. Currently, the mechanism of PGC specification in mammals is best understood from studies in mice. Following implantation, the epiblast cells develop as an egg cylinder while the extra-embryonic ectoderm cells which are the source of important signals for PGC specification are located over the egg cylinder. However, in most cases, including humans, the epiblast cells develop as a planar disc, which alters the organization and the source of the signaling for cell fates. This, in turn, might have an effect on the precise mechanism of PGC specification in vivo as well as in vitro using pluripotent embryonic stem cells. Here, we discuss how the key early embryonic differences between rodents and other mammals may affect the establishment of the pluripotency network in vivo and in vitro, and consequently the basis for PGC specification, particularly from pluripotent embryonic stem cells in vitro.
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Affiliation(s)
- Naoko Irie
- Wellcome Trust/Cancer Research UK, Gurdon InstituteUniversity of CambridgeTennis Court RoadCB2 1QNCambridgeUK
| | - Walfred W. C. Tang
- Wellcome Trust/Cancer Research UK, Gurdon InstituteUniversity of CambridgeTennis Court RoadCB2 1QNCambridgeUK
| | - M. Azim Surani
- Wellcome Trust/Cancer Research UK, Gurdon InstituteUniversity of CambridgeTennis Court RoadCB2 1QNCambridgeUK
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26
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Hayashi K, Saitou M. Perspectives of germ cell development in vitro in mammals. Anim Sci J 2014; 85:617-26. [PMID: 24725251 PMCID: PMC4271675 DOI: 10.1111/asj.12199] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2014] [Accepted: 02/14/2014] [Indexed: 01/15/2023]
Abstract
Pluripotent stem cells, such as embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs) are able to differentiate into all cell lineages of the embryo proper, including germ cells. This pluripotent property has a huge impact on the fields of regenerative medicine, developmental biology and reproductive engineering. Establishing the germ cell lineage from ESCs/iPSCs is the key biological subject, since it would contribute not only to dissection of the biological processes of germ cell development but also to production of unlimited numbers of functional gametes in vitro. Toward this goal, we recently established a culture system that induces functional mouse primordial germ cells (PGCs), precursors of all germ cells, from mouse ESCs/iPSCs. The successful in vitro production of PGCs arose from the study of pluripotent cell state, the signals inducing PGCs and the technology of transplantation. However, there are many obstacles to be overcome for the robust generation of mature gametes or for application of the culture system to other species, including humans and livestock. In this review, we discuss the requirements for a culture system to generate the germ cell lineage from ESCs/iPSCs.
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Affiliation(s)
- Katsuhiko Hayashi
- Graduate School of Medicine, Kyoto University, Kyoto, Japan; CiRA, Graduate School of Medicine, Kyoto University, Kyoto, Japan; PRESTO, Japan Science and Technology Agency, Saitama, Japan
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27
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Sheng G. Day-1 chick development. Dev Dyn 2013; 243:357-67. [DOI: 10.1002/dvdy.24087] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/09/2013] [Revised: 10/22/2013] [Accepted: 10/22/2013] [Indexed: 02/04/2023] Open
Affiliation(s)
- Guojun Sheng
- Laboratory for Early Embryogenesis; RIKEN Center for Developmental Biology; Kobe Hyogo Japan
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28
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Morrison JT, Bantilan NS, Wang VN, Nellett KM, Cruz YP. Expression patterns of Oct4, Cdx2, Tead4, and Yap1 proteins during blastocyst formation in embryos of the marsupial,Monodelphis domesticaWagner. Evol Dev 2013; 15:171-85. [DOI: 10.1111/ede.12031] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Affiliation(s)
- J. T. Morrison
- Department of Biology; Oberlin College; Oberlin, OH 44074; USA
| | - N. S. Bantilan
- Department of Biology; Oberlin College; Oberlin, OH 44074; USA
| | - V. N. Wang
- Department of Biology; Oberlin College; Oberlin, OH 44074; USA
| | - K. M. Nellett
- Department of Biology; Oberlin College; Oberlin, OH 44074; USA
| | - Y. P. Cruz
- Department of Biology; Oberlin College; Oberlin, OH 44074; USA
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29
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Frankenberg S, Shaw G, Freyer C, Pask AJ, Renfree MB. Early cell lineage specification in a marsupial: a case for diverse mechanisms among mammals. Development 2013; 140:965-75. [DOI: 10.1242/dev.091629] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
Abstract
Early cell lineage specification in eutherian mammals results in the formation of a pluripotent inner cell mass (ICM) and trophoblast. By contrast, marsupials have no ICM. Here, we present the first molecular analysis of mechanisms of early cell lineage specification in a marsupial, the tammar wallaby. There was no overt differential localisation of key lineage-specific transcription factors in cleavage and early unilaminar blastocyst stages. Pluriblast cells (equivalent to the ICM) became distinguishable from trophoblast cells by differential expression of POU5F1 and, to a greater extent, POU2, a paralogue of POU5F1. Unlike in the mouse, pluriblast-trophoblast differentiation coincided with a global nuclear-to-cytoplasmic transition of CDX2 localisation. Also unlike in the mouse, Hippo pathway factors YAP and WWTR1 showed mutually distinct localisation patterns that suggest non-redundant roles. NANOG and GATA6 were conserved as markers of epiblast and hypoblast, respectively, but some differences to the mouse were found in their mode of differentiation. Our results suggest that there is considerable evolutionary plasticity in the mechanisms regulating early lineage specification in mammals.
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Affiliation(s)
| | - Geoff Shaw
- Department of Zoology, University of Melbourne, 3010 Victoria, Australia
| | - Claudia Freyer
- Department of Zoology, University of Melbourne, 3010 Victoria, Australia
| | - Andrew J. Pask
- Department of Zoology, University of Melbourne, 3010 Victoria, Australia
| | - Marilyn B. Renfree
- Department of Zoology, University of Melbourne, 3010 Victoria, Australia
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30
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Sheng G, Foley AC. Diversification and conservation of the extraembryonic tissues in mediating nutrient uptake during amniote development. Ann N Y Acad Sci 2013; 1271:97-103. [PMID: 23050970 PMCID: PMC3499656 DOI: 10.1111/j.1749-6632.2012.06726.x] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
The transfer of nutrients from the mother through the chorioallantoic placenta meets the nutritional needs of the embryo during human prenatal development. Although all amniotes start with a similar “tool kit” of extraembryonic tissues, an enormous diversity of extraembryonic tissue formation has evolved to accommodate embryological and physiological constraints unique to their developmental programs. A comparative knowledge of these extraembryonic tissues and their role in nutrient uptake during development is required to fully appreciate the adaptive changes in placental mammals. Here, we offer a comparative embryological perspective and propose that there are three conserved nutrient transfer routes among the amniotes. We highlight the importance of the yolk sac endoderm, thought to be a vestigial remnant of our amniote lineage, in mediating nutrient uptake during early human development. We also draw attention to the similarity between yolk sac endoderm-mediated and trophectoderm-mediated nutrient uptake.
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Affiliation(s)
- Guojun Sheng
- Lab for Early Embryogenesis, RIKEN Center for Developmental Biology, Kobe, Hyogo, Japan.
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31
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Abstract
Specific cells within the early mammalian embryo have the capacity to generate all somatic lineages plus the germline. This property of pluripotency is confined to the epiblast, a transient tissue that persists for only a few days. In vitro, however, pluripotency can be maintained indefinitely through derivation of stem cell lines. Pluripotent stem cells established from the newly formed epiblast are known as embryonic stem cells (ESCs), whereas those generated from later stages are called postimplantation epiblast stem cells (EpiSCs). These different classes of pluripotent stem cell have distinct culture requirements and gene expression programs, likely reflecting the dynamic development of the epiblast in the embryo. In this chapter we review current understanding of how the epiblast forms and relate this to the properties of derivative stem cells. We discuss whether ESCs and EpiSCs are true counterparts of different phases of epiblast development or are culture-generated phenomena. We also consider the proposition that early epiblast cells and ESCs may represent a naïve ground state without any prespecification of lineage choice, whereas later epiblasts and EpiSCs may be primed in favor of particular fates.
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Affiliation(s)
- Jennifer Nichols
- Wellcome Trust Centre for Stem Cell Research, Stem Cell Institute University of Cambridge, Cambridge CB2 1QR, United Kingdom
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32
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Abstract
Pluripotency is a "blank" cellular state characteristic of specific cells within the early embryo (e.g., epiblast cells) and of certain cells propagated in vitro (e.g., embryonic stem cells, ESCs). The terms pluripotent cell and stem cell are often used interchangeably to describe cells capable of differentiating into multiple cell types. In this review, we discuss the prevailing molecular and functional definitions of pluripotency and the working parameters employed to describe this state, both in the context of cells residing within the early embryo and cells propagated in vitro.
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Affiliation(s)
- Marion Dejosez
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, Texas 77030, USA.
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33
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Abstract
When amniotes appeared during evolution, embryos freed themselves from intracellular nutrition; development slowed, the mid-blastula transition was lost and maternal components became less important for polarity. Extra-embryonic tissues emerged to provide nutrition and other innovations. One such tissue, the hypoblast (visceral endoderm in mouse), acquired a role in fixing the body plan: it controls epiblast cell movements leading to primitive streak formation, generating bilateral symmetry. It also transiently induces expression of pre-neural markers in the epiblast, which also contributes to delay streak formation. After gastrulation, the hypoblast might protect prospective forebrain cells from caudalizing signals. These functions separate mesendodermal and neuroectodermal domains by protecting cells against being caught up in the movements of gastrulation.
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Affiliation(s)
- Claudio D Stern
- Department of Cell and Developmental Biology, University College London, GowerStreet (Anatomy Building), London WC1E 6BT, UK.
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34
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Johnson M. Decisions, decisions: how are they made in the early embryo – and does it matter? Reprod Biomed Online 2011; 22:509-11. [DOI: 10.1016/j.rbmo.2011.03.001] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
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35
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Switching stem cell state through programmed germ cell reprogramming. Differentiation 2011; 81:281-91. [PMID: 21330045 DOI: 10.1016/j.diff.2011.01.003] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2010] [Revised: 12/29/2010] [Accepted: 01/11/2011] [Indexed: 01/27/2023]
Abstract
Depending on their origin, embryo-derived stem cells have distinct properties that largely correspond to their counterpart in vivo. Mouse epiblast stem cells derived from post-implantation embryos differ from embryonic stem cells derived from blastocysts in their transcriptional and epigenetic profile, their morphology and culture requirements. When maintained in appropriate conditions, the cells keep self-renewing and do not adopt a different state. Recent studies, however, show that it is possible to convert between stem cell states. Here we review recent advances to induce stem cell state changes and we consider the potential of germ cell-mediated reprogramming for the conversion. Since the properties of mouse epiblast stem cells are similar to human embryonic stem cells, we discuss the significance of stem cell conversion and germ cell-mediated reprogramming in humans.
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36
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Renfree MB, Pask AJ. Reproductive and developmental manipulation of the marsupial, the tammar wallaby Macropus eugenii. Methods Mol Biol 2011; 770:457-473. [PMID: 21805276 DOI: 10.1007/978-1-61779-210-6_18] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
The developing marsupial is an ideal animal for use in biomedical research. Marsupials are mammals that have been separated from eutherian mammals for over 130-140 million years. They all deliver altricial young that complete their growth and development after birth usually in a pouch, but not all marsupials have a pouch. Their lactation changes dynamically throughout the period of pouch life, and the mother controls their growth via the production of milk that is tailor-made for each stage of development. The tammar wallaby, Macropus eugenii, has been the experimental marsupial of choice for over five decades, as it is highly amendable to handling and breeds well in captivity. The tammar is especially interesting because it has both a lactational and a seasonal control of its reproduction and embryonic diapause that normally lasts 11 months. Standard molecular techniques can be used for most manipulations in marsupials. However, there are several special techniques for treating the young for experimental surgery and for organ culture that we detail below.
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Affiliation(s)
- Marilyn B Renfree
- Department of Zoology, The University of Melbourne, Melbourne, VIC 3010, Australia.
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37
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Nagai H, Mak SS, Weng W, Nakaya Y, Ladher R, Sheng G. Embryonic development of the emu, Dromaius novaehollandiae. Dev Dyn 2010; 240:162-75. [DOI: 10.1002/dvdy.22520] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
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38
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Leitch HG, Blair K, Mansfield W, Ayetey H, Humphreys P, Nichols J, Surani MA, Smith A. Embryonic germ cells from mice and rats exhibit properties consistent with a generic pluripotent ground state. Development 2010; 137:2279-87. [PMID: 20519324 PMCID: PMC2889601 DOI: 10.1242/dev.050427] [Citation(s) in RCA: 113] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 05/11/2010] [Indexed: 02/02/2023]
Abstract
Mouse and rat embryonic stem cells can be sustained in defined medium by dual inhibition (2i) of the mitogen-activated protein kinase (Erk1/2) cascade and of glycogen synthase kinase 3. The inhibitors suppress differentiation and enable self-renewal of pluripotent cells that are ex vivo counterparts of naïve epiblast cells in the mature blastocyst. Pluripotent stem cell lines can also be derived from unipotent primordial germ cells via a poorly understood process of epigenetic reprogramming. These are termed embryonic germ (EG) cells to denote their distinct origin. Here we investigate whether EG cell self-renewal and derivation are supported by 2i. We report that mouse EG cells can be established with high efficiency using 2i in combination with the cytokine leukaemia inhibitory factor (LIF). Furthermore, addition of fibroblast growth factor or stem cell factor is unnecessary using 2i-LIF. The derived EG cells contribute extensively to healthy chimaeric mice, including to the germline. Using the same conditions, we describe the first derivations of EG cells from the rat. Rat EG cells express a similar marker profile to rat and mouse ES cells. They have a diploid karyotype, can be clonally expanded and genetically manipulated, and are competent for multilineage colonisation of chimaeras. These findings lend support to the postulate of a conserved molecular ground state in pluripotent rodent cells. Future research will determine the extent to which this is maintained in other mammals and whether, in some species, primordial germ cells might be a more tractable source than epiblast for the capture of naïve pluripotent stem cells.
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Affiliation(s)
- Harry G. Leitch
- Wellcome Trust Cancer Research UK Gurdon Institute, The Henry Wellcome Building of Cancer and Developmental Biology, University of Cambridge, Tennis Court Road, Cambridge CB2 1QN, UK
- Wellcome Trust Centre for Stem Cell Research, University of Cambridge, Tennis Court Road, Cambridge CB2 1QN, UK
- Department of Physiology, Development, and Neuroscience, University of Cambridge, Tennis Court Road, Cambridge CB2 1QN, UK
| | - Kate Blair
- Wellcome Trust Centre for Stem Cell Research, University of Cambridge, Tennis Court Road, Cambridge CB2 1QN, UK
- Department of Biochemistry, University of Cambridge, Tennis Court Road, Cambridge CB2 1QN, UK
| | - William Mansfield
- Wellcome Trust Centre for Stem Cell Research, University of Cambridge, Tennis Court Road, Cambridge CB2 1QN, UK
| | - Harold Ayetey
- Wellcome Trust Centre for Stem Cell Research, University of Cambridge, Tennis Court Road, Cambridge CB2 1QN, UK
- Department of Biochemistry, University of Cambridge, Tennis Court Road, Cambridge CB2 1QN, UK
| | - Peter Humphreys
- Wellcome Trust Centre for Stem Cell Research, University of Cambridge, Tennis Court Road, Cambridge CB2 1QN, UK
| | - Jennifer Nichols
- Wellcome Trust Centre for Stem Cell Research, University of Cambridge, Tennis Court Road, Cambridge CB2 1QN, UK
- Department of Physiology, Development, and Neuroscience, University of Cambridge, Tennis Court Road, Cambridge CB2 1QN, UK
| | - M. Azim Surani
- Wellcome Trust Cancer Research UK Gurdon Institute, The Henry Wellcome Building of Cancer and Developmental Biology, University of Cambridge, Tennis Court Road, Cambridge CB2 1QN, UK
- Department of Physiology, Development, and Neuroscience, University of Cambridge, Tennis Court Road, Cambridge CB2 1QN, UK
| | - Austin Smith
- Wellcome Trust Centre for Stem Cell Research, University of Cambridge, Tennis Court Road, Cambridge CB2 1QN, UK
- Department of Biochemistry, University of Cambridge, Tennis Court Road, Cambridge CB2 1QN, UK
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39
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Abstract
This review describes the three classical models (mosaic, positional, and polarization) proposed to explain blastocyst formation and summarizes the evidence concerning them. It concludes that the polarization model incorporates elements of the other two models and best explains most known information. I discuss key requirements of a molecular basis for the generation and stabilization of polarity and identify ezrin/E-cadherin, PAR proteins, and Cdx2 as plausible key molecular players. I also discuss the idea of a network process operating to build cell allocations progressively into committed differences. Finally, this review critically considers the possibility of developmental information being encoded within the oocyte and zygote. No final decision can be reached on a mechanism of action underlying any encoded information, but a cell interaction process model is preferred over one that relies solely on differential inheritance.
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Affiliation(s)
- Martin H Johnson
- Department of Physiology, Development, and Neuroscience and Center for Trophoblast Research, The Anatomy School, Cambridge CB2 3DY, United Kingdom.
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40
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The evolution of class V POU domain transcription factors in vertebrates and their characterisation in a marsupial. Dev Biol 2010; 337:162-70. [DOI: 10.1016/j.ydbio.2009.10.017] [Citation(s) in RCA: 67] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2009] [Revised: 10/07/2009] [Accepted: 10/08/2009] [Indexed: 11/18/2022]
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41
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Axial differentiation and early gastrulation stages of the pig embryo. Differentiation 2009; 78:301-11. [DOI: 10.1016/j.diff.2009.07.006] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2009] [Revised: 07/20/2009] [Accepted: 07/23/2009] [Indexed: 11/23/2022]
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Silva J, Nichols J, Theunissen TW, Guo G, van Oosten AL, Barrandon O, Wray J, Yamanaka S, Chambers I, Smith A. Nanog is the gateway to the pluripotent ground state. Cell 2009; 138:722-37. [PMID: 19703398 PMCID: PMC3437554 DOI: 10.1016/j.cell.2009.07.039] [Citation(s) in RCA: 760] [Impact Index Per Article: 50.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/12/2009] [Revised: 06/10/2009] [Accepted: 07/23/2009] [Indexed: 01/04/2023]
Abstract
Pluripotency is generated naturally during mammalian development through formation of the epiblast, founder tissue of the embryo proper. Pluripotency can be recreated by somatic cell reprogramming. Here we present evidence that the homeodomain protein Nanog mediates acquisition of both embryonic and induced pluripotency. Production of pluripotent hybrids by cell fusion is promoted by and dependent on Nanog. In transcription factor-induced molecular reprogramming, Nanog is initially dispensable but becomes essential for dedifferentiated intermediates to transit to ground state pluripotency. In the embryo, Nanog specifically demarcates the nascent epiblast, coincident with the domain of X chromosome reprogramming. Without Nanog, pluripotency does not develop, and the inner cell mass is trapped in a pre-pluripotent, indeterminate state that is ultimately nonviable. These findings suggest that Nanog choreographs synthesis of the naive epiblast ground state in the embryo and that this function is recapitulated in the culmination of somatic cell reprogramming.
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Affiliation(s)
- Jose Silva
- Wellcome Trust Centre for Stem Cell Research, University of Cambridge, Tennis Court Road, Cambridge CB2 1QR, UK
- Department of Biochemistry, University of Cambridge, Tennis Court Road, Cambridge CB2 1QR, UK
- Corresponding author
| | - Jennifer Nichols
- Wellcome Trust Centre for Stem Cell Research, University of Cambridge, Tennis Court Road, Cambridge CB2 1QR, UK
- Department of Physiology, Development, and Neuroscience, University of Cambridge, Tennis Court Road, Cambridge CB2 1QR, UK
| | - Thorold W. Theunissen
- Wellcome Trust Centre for Stem Cell Research, University of Cambridge, Tennis Court Road, Cambridge CB2 1QR, UK
- Department of Biochemistry, University of Cambridge, Tennis Court Road, Cambridge CB2 1QR, UK
| | - Ge Guo
- Wellcome Trust Centre for Stem Cell Research, University of Cambridge, Tennis Court Road, Cambridge CB2 1QR, UK
- Department of Biochemistry, University of Cambridge, Tennis Court Road, Cambridge CB2 1QR, UK
| | - Anouk L. van Oosten
- Wellcome Trust Centre for Stem Cell Research, University of Cambridge, Tennis Court Road, Cambridge CB2 1QR, UK
- Department of Biochemistry, University of Cambridge, Tennis Court Road, Cambridge CB2 1QR, UK
| | - Ornella Barrandon
- Wellcome Trust Centre for Stem Cell Research, University of Cambridge, Tennis Court Road, Cambridge CB2 1QR, UK
- Department of Biochemistry, University of Cambridge, Tennis Court Road, Cambridge CB2 1QR, UK
| | - Jason Wray
- Wellcome Trust Centre for Stem Cell Research, University of Cambridge, Tennis Court Road, Cambridge CB2 1QR, UK
- Department of Biochemistry, University of Cambridge, Tennis Court Road, Cambridge CB2 1QR, UK
| | - Shinya Yamanaka
- Department of Stem Cell Biology, Institute for Frontier Medical Sciences, Kyoto University, Kyoto 606-8507, Japan
| | - Ian Chambers
- MRC Centre for Regenerative Medicine, Institute for Stem Cell Research, School of Biological Sciences, University of Edinburgh, King's Buildings, Edinburgh EH9 3JQ, UK
| | - Austin Smith
- Wellcome Trust Centre for Stem Cell Research, University of Cambridge, Tennis Court Road, Cambridge CB2 1QR, UK
- Department of Biochemistry, University of Cambridge, Tennis Court Road, Cambridge CB2 1QR, UK
- Corresponding author
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43
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Abstract
After maternal predetermination gives way to zygotic regulation, a ground state is established within the mammalian embryo. This tabula rasa for embryogenesis is present only transiently in the preimplantation epiblast. Here, we consider how unrestricted cells are first generated and then prepared for lineage commitment. We propose that two phases of pluripotency can be defined: naive and primed. This distinction extends to pluripotent stem cells derived from embryos or by molecular reprogramming ex vivo.
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Affiliation(s)
- Jennifer Nichols
- Wellcome Trust Centre for Stem Cell Research, Department of Physiology, University of Cambridge, Tennis Court Road, Cambridge CB2 1QR, UK
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44
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Abstract
Over two centuries after the first platypus specimen stirred the scientific community in Europe, the whole-genome sequence of the duck-billed platypus has been completed and is publicly available. After publication of eutherian and marsupial genomes, this is the first genome of a monotreme filling an important evolutionary gap between the divergence of birds more that 300 million years ago and marsupials more than 140 million years ago. Monotremes represent the most basal surviving branch of mammals and the platypus genome sequence allows unprecedented insights into the evolution of mammals and the fascinating biology of the egg-laying mammals. Here, we discuss some of the key findings of the analysis of the platypus genome and point to new findings and future research directions, which illustrate the broad impact of the platypus genome project for understanding monotreme biology and mammalian genome evolution.
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Keyte AL, Smith KK. Opossum (Monodelphis domestica): A Marsupial Development Model. ACTA ACUST UNITED AC 2008; 2008:pdb.emo104. [PMID: 21356687 DOI: 10.1101/pdb.emo104] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
INTRODUCTIONMonodelphis domestica is the most commonly used laboratory marsupial. In addition to the many factors that make it a convenient laboratory animal (small size, ease of care, nonseasonal breeding), it is the first marsupial whose genome has been sequenced. In this article, we present an overview of aspects of its biology and its use as a model organism. We also discuss basic care, breeding, embryo manipulation, and modifications of common techniques for the study of the development of this species.
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Affiliation(s)
- Anna L Keyte
- Department of Biology, Duke University, Durham, NC 27708, USA
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46
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Abstract
The strategic importance of the genome sequence of the gray, short-tailed opossum, Monodelphis domestica, accrues from both the unique phylogenetic position of metatherian (marsupial) mammals and the fundamental biologic characteristics of metatherians that distinguish them from other mammalian species. Metatherian and eutherian (placental) mammals are more closely related to one another than to other vertebrate groups, and owing to this close relationship they share fundamentally similar genetic structures and molecular processes. However, during their long evolutionary separation these alternative mammals have developed distinctive anatomical, physiologic, and genetic features that hold tremendous potential for examining relationships between the molecular structures of mammalian genomes and the functional attributes of their components. Comparative analyses using the opossum genome have already provided a wealth of new evidence regarding the importance of noncoding elements in the evolution of mammalian genomes, the role of transposable elements in driving genomic innovation, and the relationships between recombination rate, nucleotide composition, and the genomic distributions of repetitive elements. The genome sequence is also beginning to enlarge our understanding of the evolution and function of the vertebrate immune system, and it provides an alternative model for investigating mechanisms of genomic imprinting. Equally important, availability of the genome sequence is fostering the development of new research tools for physical and functional genomic analyses of M. domestica that are expanding its versatility as an experimental system for a broad range of research applications in basic biology and biomedically oriented research.
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47
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Bromfield J, Messamore W, Albertini DF. Epigenetic regulation during mammalian oogenesis. Reprod Fertil Dev 2008; 20:74-80. [PMID: 18154701 DOI: 10.1071/rd07181] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
Abstract
The advent of the epigenetic era has sparked a new frontier in molecular research and the understanding of how development can be regulated beyond direct alterations of the genome. Thus far, the focal point of epigenetic regulation during development has been chromatin modifications that control differential gene expression by DNA methylation and histone alterations. But what of events that alter gene expression without direct influence on the DNA itself? The present review focuses on epigenetic pathways regulating development from oogenesis to organogenesis and back that do not involve methylation of cytosine in DNA. We discuss target components of epigenetic modification such as organelle development, compartmentalisation of maternal factors and molecular mediators in the oocyte and how these factors acting during oogenesis impact on later development. Epigenetic regulation of development, be it via cytosine methylation or not, has wide-ranging effects on the subsequent success of a pregnancy and the intrinsic health of offspring. Perturbations in epigenetic regulation have been clearly associated with disease states in adult offspring, including Type II diabetes, hypertension, cancers and infertility. A clear understanding of all epigenetic mechanisms is paramount when considering the increased use of assisted reproductive techniques and the risks associated with their use.
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Affiliation(s)
- John Bromfield
- Department of Molecular and Integrative Physiology, University of Kansas Medical Center, Kansas City, KS 66160, USA
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48
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Au PCK, Whitley J, Vaux D, Selwood L, Familari M. Identification of novel and known ovary-specific genes including ZP2, in a marsupial, the stripe-faced dunnart. Mol Reprod Dev 2008; 75:318-25. [PMID: 17597472 DOI: 10.1002/mrd.20708] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
During the early stages of oogenesis, oocyte-specific factors, synthesized by and stored within the oocyte, play critical roles during oogenesis, folliculogenesis, fertilization and early embryonic development in the mouse. The identification of marsupial maternal factors, expressed specifically in the ovary or oocyte, may provide an insight into the conserved evolutionary mechanisms that drive mammalian oocyte development to cleavage stages. In this study, 10 clones including dunnart ZP2 and c-mos, isolated by cDNA representational difference analysis, were validated by RT-PCR for ovary-specific expression. This novel combination of techniques to isolate ovary-specific genes has identified three novel genes with ovary-specific expression. Both dunnart ZP2 and c-mos exhibited ovary-specific expression, making this study the first isolation of c-mos in a marsupial species. Dunnart ZP2 expression was examined in detail by in situ hybridization and results indicate oocyte-specific expression of dunnart ZP2 in the cytoplasm of oocytes of primordial, primary and secondary follicles with expression being highest in oocytes of primary follicles. ZP2 was not expressed in granulosa cells of any follicles.
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Affiliation(s)
- Phil Chi Khang Au
- Department of Zoology, University of Melbourne, Parkville, Victoria, Australia
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49
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Kress A, Selwood L. Marsupial Hypoblast: Formation and Differentiation of the Bilaminar Blastocyst in Sminthopsis macroura. Cells Tissues Organs 2006; 182:155-70. [PMID: 16914918 DOI: 10.1159/000093965] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 04/24/2006] [Indexed: 11/19/2022] Open
Abstract
Hypoblast formation in Sminthopsis macroura starts in blastocysts with a size between 1.0 and 1.4 mm, in which cells appear to be similar to each other, and finishes at the complete 2.6- or 2.7-mm bilaminar blastocyst, which is fully lined with hypoblast cells. When hypoblast cells begin allocation, the pluriblast region progressively differentiates from the trophoblast. Some pluriblast cells, which are otherwise undistinguished, lying on one side near the boundary of the circular pluriblast, move to the inside as hypoblast cells by mitosis or migration. They initially line the pluriblast and then the trophoblast. Hypoblast cells continue to leave the pluriblast/epiblast and intercalate into the underlying hypoblast layer until the advanced stages of bilaminar blastocysts. Associated with the origin of the hypoblast cells, the residual surface epiblast cells become less flatted and more cuboidal or rounded in shape. Characteristics are increased density of ribosomes, granular endoplasmic reticulum and a marked apical-basal polarity related to apical microvilli and endocytosis and more vesicles with flocculent content and a loss of the crystalloid deposits that were typical for earlier stages. Trophoblast cells become flat and elongated with only few vesicles, and they transform into extra-embryonic ectoderm cells, which are broader, rather square and with a higher density of ribosomes. Hypoblast cells are characterized by a relatively high level of ribosomes and endoplasmic reticulum, fewer small vesicles and no noticeable endocytotic processes and initially form a reticulum because the cells preferentially migrate along cell-cell boundaries by extension of long filopodia. Once hypoblast cells reach the boundary of the embryonic area and extend to line the trophoblast, they progressively consolidate into a squamous epithelium. It is suggested that the origin of the hypoblast from one side of the pluriblast and its invasion under the trophoblast from proliferating centres at the edge of the embryonic area provide mechanisms for patterning epiblast, hypoblast, trophoblast and extra-embryonic ectoderm.
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Affiliation(s)
- Annetrudi Kress
- Department of Anatomy, University of Basel, Basel, Switzerland.
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50
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Abstract
The traditional way to study the immunology of pregnancy follows the classical transplantation model, which views the fetus as an allograft. A more recent approach, which is the subject of this Review, focuses on the unique, local uterine immune response to the implanting placenta. This approach requires knowledge of placental structure and its variations in different species, as this greatly affects the type of immune response that is generated by the mother. At the implantation site, cells from the mother and the fetus intermingle during pregnancy. Unravelling what happens here is crucial to our understanding of why some human pregnancies are successful whereas others are not.
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