51
|
Yin L, Zhu M, Knoll AH, Yuan X, Zhang J, Hu J. Doushantuo embryos preserved inside diapause egg cysts. Nature 2007; 446:661-3. [PMID: 17410174 DOI: 10.1038/nature05682] [Citation(s) in RCA: 261] [Impact Index Per Article: 15.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/08/2007] [Accepted: 02/13/2007] [Indexed: 11/08/2022]
Abstract
Phosphatized microfossils in the Ediacaran (635-542 Myr ago) Doushantuo Formation, south China, have been interpreted as the embryos of early animals. Despite experimental demonstration that embryos can be preserved, microstructural evidence that the Doushantuo remains are embryonic and an unambiguous record of fossil embryos in Lower Cambrian rocks, questions about the phylogenetic relationships of these fossils remain. Most recently, some researchers have proposed that Doushantuo microfossils may be giant sulphur-oxidizing bacteria comparable to extant Thiomargarita sp. Here we report new observations that provide a test of the bacterial hypothesis. The discovery of embryo-like Doushantuo fossils inside large, highly ornamented organic vesicles (acritarchs) indicates that these organisms were eukaryotic, and most probably early cleavage stage embryos preserved within diapause egg cysts. Large acanthomorphic microfossils of the type observed to contain fossil embryos first appear in rocks just above a 632.5 +/- 0.5-Myr-old ash bed, suggesting that at least stem-group animals inhabited shallow seas in the immediate aftermath of global Neoproterozoic glaciation.
Collapse
Affiliation(s)
- Leiming Yin
- State Key Laboratory of Paleobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, Nanjing 210008, China.
| | | | | | | | | | | |
Collapse
|
52
|
Hurlbut GD, Kankel MW, Lake RJ, Artavanis-Tsakonas S. Crossing paths with Notch in the hyper-network. Curr Opin Cell Biol 2007; 19:166-75. [PMID: 17317139 DOI: 10.1016/j.ceb.2007.02.012] [Citation(s) in RCA: 187] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/08/2007] [Accepted: 02/09/2007] [Indexed: 12/31/2022]
Abstract
The development of complex and diverse metazoan morphologies is coordinated by a surprisingly small number of evolutionarily conserved signaling mechanisms. These signals can act in parallel but often appear to function as an integrated hyper-network. The nodes defining this complex molecular circuitry are poorly understood, but the biological significance of pathway cross-talk is profound. The importance of such large-scale signal integration is exemplified by Notch and its ability to cross-talk with all the major pathways to influence cell differentiation, proliferation, survival and migration. The Notch pathway is, thus, a useful paradigm to illustrate the complexity of pathway cross-talk: its pervasiveness, context dependency, and importance in development and disease.
Collapse
Affiliation(s)
- Gregory D Hurlbut
- Department of Cell Biology, Harvard Medical School, Massachusetts General Hospital Cancer Center, Charlestown, Massachusetts, USA
| | | | | | | |
Collapse
|
53
|
Li CW, Chen JY, Lipps JH, Gao F, Chi HM, Wu HJ. Ciliated protozoans from the Precambrian Doushantuo Formation, Wengan, South China. ACTA ACUST UNITED AC 2007. [DOI: 10.1144/sp286.11] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/04/2022]
Abstract
AbstractCiliates, a major eukaryotic crown-group lineage with thousands of living species, are poorly represented in the fossil record. Ciliate biomarkers are known from the Precambrian, but only one group, the tintinnids, have an extensive fossil record dating back to the Ordovician. Thus, the occurrence of probable ciliate body fossils in Neoproterozoic rocks confirms their earlier appearance, so far inferred only from molecular sequence data and biomarkers. In this paper, we describe those fossils from the 580 million year old Precambrian Doushantuo phosphates, Guizhou, South China. Three new monospecific genera (100 µm to 200 µm in size) are represented by three-dimensional specimens with exceptionally well-preserved cell bodies including cilia, cytostome and tentacles. Two possess loricas and are referred to the tintinnids. The third has numerous tentacles, an apical cytostome and somatic cilia; it is interpreted as an ancestral early suctorian ciliate. These fossils indicate that the origin and evolutionary differentiation and specialization of ciliates took place before or along with the radiation of other crown-group eukaryotes, including metazoans.
Collapse
Affiliation(s)
- C.-W. Li
- Department of Life Sciences, National Tsing Hua University, Hsinchu, Taiwan, China (e-mail: )
| | - J.-Y. Chen
- Nanjing Institute of Geology and Paleontology, Nanjing 210008, China
| | - J. H. Lipps
- Divisions of Biology, California Institute of Technology, Pasadena, CA 91125, USA
| | - F. Gao
- Nanjing Institute of Geology and Paleontology, Nanjing 210008, China
- Department of Integrative Biology, Museum of Paleontology, University of California, Berkeley, CA 94720, USA
| | - H.-M. Chi
- Nanjing Institute of Geology and Paleontology, Nanjing 210008, China
| | - H.-J. Wu
- Department of Life Sciences, National Tsing Hua University, Hsinchu, Taiwan, China (e-mail: )
| |
Collapse
|
54
|
Wehner R, Fukushi T, Isler K. On Being Small: Brain Allometry in Ants. BRAIN, BEHAVIOR AND EVOLUTION 2007; 69:220-8. [PMID: 17108673 DOI: 10.1159/000097057] [Citation(s) in RCA: 63] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/24/2006] [Accepted: 05/15/2006] [Indexed: 11/19/2022]
Abstract
Comparative neurobiologists have provided ample evidence that in vertebrates small animals have proportionally larger brains: in a double-logarithmic plot of brain weight versus body weight all data points conform quite closely to a straight line with a slope of less than one. Hence vertebrate brains scale allometrically, rather than isometrically, with body size. Here we extend the phylogenetic scope of such studies and the size range of the brains under investigation to the insects, especially ants. We show that the principle of (negative) allometry applies as well, but that ants have considerably smaller brains than any ant-sized vertebrate would have, and that this result holds even if the relatively higher exoskeleton weights of ants (as compared to endoskeleton weights of mammals) are taken into account. Finally, interspecific comparisons within one genus of ants, Cataglyphis, show that species exhibiting small colony sizes (of a few hundred individuals) have significantly smaller brains than species in which colonies are composed of several thousand individuals.
Collapse
Affiliation(s)
- Rüdiger Wehner
- Institute of Zoology, University of Zurich, Zurich, Switzerland.
| | | | | |
Collapse
|
55
|
Moroz LL, Edwards JR, Puthanveettil SV, Kohn AB, Ha T, Heyland A, Knudsen B, Sahni A, Yu F, Liu L, Jezzini S, Lovell P, Iannucculli W, Chen M, Nguyen T, Sheng H, Shaw R, Kalachikov S, Panchin YV, Farmerie W, Russo JJ, Ju J, Kandel ER. Neuronal transcriptome of Aplysia: neuronal compartments and circuitry. Cell 2006; 127:1453-67. [PMID: 17190607 PMCID: PMC4024467 DOI: 10.1016/j.cell.2006.09.052] [Citation(s) in RCA: 247] [Impact Index Per Article: 13.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2006] [Revised: 07/12/2006] [Accepted: 09/25/2006] [Indexed: 02/05/2023]
Abstract
Molecular analyses of Aplysia, a well-established model organism for cellular and systems neural science, have been seriously handicapped by a lack of adequate genomic information. By sequencing cDNA libraries from the central nervous system (CNS), we have identified over 175,000 expressed sequence tags (ESTs), of which 19,814 are unique neuronal gene products and represent 50%-70% of the total Aplysia neuronal transcriptome. We have characterized the transcriptome at three levels: (1) the central nervous system, (2) the elementary components of a simple behavior: the gill-withdrawal reflex-by analyzing sensory, motor, and serotonergic modulatory neurons, and (3) processes of individual neurons. In addition to increasing the amount of available gene sequences of Aplysia by two orders of magnitude, this collection represents the largest database available for any member of the Lophotrochozoa and therefore provides additional insights into evolutionary strategies used by this highly successful diversified lineage, one of the three proposed superclades of bilateral animals.
Collapse
Affiliation(s)
- Leonid L. Moroz
- The Whitney Laboratory for Marine Bioscience, University of Florida, 9505 Ocean Shore Boulevard, St. Augustine, FL 32080, USA
- Department of Neuroscience and McKnight Brain Institute, 100 S. Newell Drive, Building 59, University of Florida, Gainesville, FL 32611, USA
| | - John R. Edwards
- Columbia Genome Center, College of Physicians and Surgeons, Columbia University, 1150 St. Nicholas Avenue, New York, NY 10032, USA
| | - Sathyanarayanan V. Puthanveettil
- Center for Neurobiology & Behavior and New York State Psychiatric Institute, Columbia University, 1051 Riverside Drive, Columbia University, New York, NY 10032, USA
| | - Andrea B. Kohn
- The Whitney Laboratory for Marine Bioscience, University of Florida, 9505 Ocean Shore Boulevard, St. Augustine, FL 32080, USA
| | - Thomas Ha
- The Whitney Laboratory for Marine Bioscience, University of Florida, 9505 Ocean Shore Boulevard, St. Augustine, FL 32080, USA
- Department of Neuroscience and McKnight Brain Institute, 100 S. Newell Drive, Building 59, University of Florida, Gainesville, FL 32611, USA
| | - Andreas Heyland
- The Whitney Laboratory for Marine Bioscience, University of Florida, 9505 Ocean Shore Boulevard, St. Augustine, FL 32080, USA
| | - Bjarne Knudsen
- The Whitney Laboratory for Marine Bioscience, University of Florida, 9505 Ocean Shore Boulevard, St. Augustine, FL 32080, USA
| | - Anuj Sahni
- The Whitney Laboratory for Marine Bioscience, University of Florida, 9505 Ocean Shore Boulevard, St. Augustine, FL 32080, USA
| | - Fahong Yu
- The Whitney Laboratory for Marine Bioscience, University of Florida, 9505 Ocean Shore Boulevard, St. Augustine, FL 32080, USA
- Interdisciplinary Center for Biotechnology Research, University of Florida, Gainesville, FL 32611, USA
| | - Li Liu
- The Whitney Laboratory for Marine Bioscience, University of Florida, 9505 Ocean Shore Boulevard, St. Augustine, FL 32080, USA
- Interdisciplinary Center for Biotechnology Research, University of Florida, Gainesville, FL 32611, USA
| | - Sami Jezzini
- The Whitney Laboratory for Marine Bioscience, University of Florida, 9505 Ocean Shore Boulevard, St. Augustine, FL 32080, USA
- Department of Neuroscience and McKnight Brain Institute, 100 S. Newell Drive, Building 59, University of Florida, Gainesville, FL 32611, USA
| | - Peter Lovell
- The Whitney Laboratory for Marine Bioscience, University of Florida, 9505 Ocean Shore Boulevard, St. Augustine, FL 32080, USA
| | - William Iannucculli
- Columbia Genome Center, College of Physicians and Surgeons, Columbia University, 1150 St. Nicholas Avenue, New York, NY 10032, USA
| | - Minchen Chen
- Columbia Genome Center, College of Physicians and Surgeons, Columbia University, 1150 St. Nicholas Avenue, New York, NY 10032, USA
| | - Tuan Nguyen
- Columbia Genome Center, College of Physicians and Surgeons, Columbia University, 1150 St. Nicholas Avenue, New York, NY 10032, USA
| | - Huitao Sheng
- Columbia Genome Center, College of Physicians and Surgeons, Columbia University, 1150 St. Nicholas Avenue, New York, NY 10032, USA
| | - Regina Shaw
- The Whitney Laboratory for Marine Bioscience, University of Florida, 9505 Ocean Shore Boulevard, St. Augustine, FL 32080, USA
- Interdisciplinary Center for Biotechnology Research, University of Florida, Gainesville, FL 32611, USA
| | - Sergey Kalachikov
- Columbia Genome Center, College of Physicians and Surgeons, Columbia University, 1150 St. Nicholas Avenue, New York, NY 10032, USA
| | - Yuri V. Panchin
- The Whitney Laboratory for Marine Bioscience, University of Florida, 9505 Ocean Shore Boulevard, St. Augustine, FL 32080, USA
| | - William Farmerie
- Interdisciplinary Center for Biotechnology Research, University of Florida, Gainesville, FL 32611, USA
| | - James J. Russo
- Columbia Genome Center, College of Physicians and Surgeons, Columbia University, 1150 St. Nicholas Avenue, New York, NY 10032, USA
| | - Jingyue Ju
- Columbia Genome Center, College of Physicians and Surgeons, Columbia University, 1150 St. Nicholas Avenue, New York, NY 10032, USA
- Department of Chemical Engineering, Columbia University, 500 West 120 Street, New York, NY 10027, USA
| | - Eric R. Kandel
- Center for Neurobiology & Behavior and New York State Psychiatric Institute, Columbia University, 1051 Riverside Drive, Columbia University, New York, NY 10032, USA
- Howard Hughes Medical Institute, 1051 Riverside Drive, Columbia University, New York, NY 10032, USA
- Kavli Institute for Brain Sciences, Columbia University, New York, NY 10032, USA
| |
Collapse
|
56
|
Bailey JV, Joye SB, Kalanetra KM, Flood BE, Corsetti FA. Evidence of giant sulphur bacteria in Neoproterozoic phosphorites. Nature 2006; 445:198-201. [PMID: 17183268 DOI: 10.1038/nature05457] [Citation(s) in RCA: 167] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2006] [Accepted: 11/20/2006] [Indexed: 11/09/2022]
Abstract
In situ phosphatization and reductive cell division have recently been discovered within the vacuolate sulphur-oxidizing bacteria. Here we show that certain Neoproterozoic Doushantuo Formation (about 600 million years bp) microfossils, including structures previously interpreted as the oldest known metazoan eggs and embryos, can be interpreted as giant vacuolate sulphur bacteria. Sulphur bacteria of the genus Thiomargarita have sizes and morphologies similar to those of many Doushantuo microfossils, including symmetrical cell clusters that result from multiple stages of reductive division in three planes. We also propose that Doushantuo phosphorite precipitation was mediated by these bacteria, as shown in modern Thiomargarita-associated phosphogenic sites, thus providing the taphonomic conditions that preserved other fossils known from the Doushantuo Formation.
Collapse
Affiliation(s)
- Jake V Bailey
- Department of Earth Sciences, University of Southern California, Los Angeles, California 90089, USA.
| | | | | | | | | |
Collapse
|
57
|
Liang MC, Hartman H, Kopp RE, Kirschvink JL, Yung YL. Production of hydrogen peroxide in the atmosphere of a Snowball Earth and the origin of oxygenic photosynthesis. Proc Natl Acad Sci U S A 2006; 103:18896-9. [PMID: 17138669 PMCID: PMC1672611 DOI: 10.1073/pnas.0608839103] [Citation(s) in RCA: 86] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2005] [Indexed: 11/18/2022] Open
Abstract
During Proterozoic time, Earth experienced two intervals with one or more episodes of low-latitude glaciation, which are probable "Snowball Earth" events. Although the severity of the historical glaciations is debated, theoretical "hard Snowball" conditions are associated with the nearly complete shutdown of the hydrological cycle. We show here that, during such long and severe glacial intervals, a weak hydrological cycle coupled with photochemical reactions involving water vapor would give rise to the sustained production of hydrogen peroxide. The photochemical production of hydrogen peroxide has been proposed previously as the primary mechanism for oxidizing the surface of Mars. During a Snowball, hydrogen peroxide could be stored in the ice; it would then be released directly into the ocean and the atmosphere upon melting and could mediate global oxidation events in the aftermath of the Snowball, such as that recorded in the Fe and Mn oxides of the Kalahari Manganese Field, deposited after the Paleoproterozoic low-latitude Makganyene glaciation. Low levels of peroxides and molecular oxygen generated during Archean and earliest Proterozoic non-Snowball glacial intervals could have driven the evolution of oxygen-mediating and -using enzymes and thereby paved the way for the eventual appearance of oxygenic photosynthesis.
Collapse
Affiliation(s)
- Mao-Chang Liang
- Division of Geological and Planetary Sciences, California Institute of Technology, 1200 East California Boulevard, Pasadena, CA 91125, USA.
| | | | | | | | | |
Collapse
|
58
|
Howard-Ashby M, Materna SC, Brown CT, Tu Q, Oliveri P, Cameron RA, Davidson EH. High regulatory gene use in sea urchin embryogenesis: Implications for bilaterian development and evolution. Dev Biol 2006; 300:27-34. [PMID: 17101125 PMCID: PMC1790870 DOI: 10.1016/j.ydbio.2006.10.016] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2006] [Revised: 10/13/2006] [Accepted: 10/13/2006] [Indexed: 01/13/2023]
Abstract
A global scan of transcription factor usage in the sea urchin embryo was carried out in the context of the Strongylocentrotus purpuratus genome sequencing project, and results from six individual studies are here considered. Transcript prevalence data were obtained for over 280 regulatory genes encoding sequence-specific transcription factors of every known family, but excluding genes encoding zinc finger proteins. This is a statistically inclusive proxy for the total "regulome" of the sea urchin genome. Close to 80% of the regulome is expressed at significant levels by the late gastrula stage. Most regulatory genes must be used repeatedly for different functions as development progresses. An evolutionary implication is that animal complexity at the stage when the regulome first evolved was far simpler than even the last common bilaterian ancestor, and is thus of deep antiquity.
Collapse
|
59
|
Abstract
The endomesoderm gene regulatory network (GRN) of C. elegans is a rich resource for studying the properties of cell-fate-specification pathways. This GRN contains both cell-autonomous and cell non-autonomous mechanisms, includes network motifs found in other GRNs, and ties maternal factors to terminal differentiation genes through a regulatory cascade. In most cases, upstream regulators and their direct downstream targets are known. With the availability of resources to study close and distant relatives of C. elegans, the molecular evolution of this network can now be examined. Within Caenorhabditis, components of the endomesoderm GRN are well conserved. A cursory examination of the preliminary genome sequences of two parasitic nematodes, Haemonchus contortus and Brugia malayi, suggests that evolution in this GRN is occurring most rapidly for the zygotic genes that specify blastomere identity.
Collapse
Affiliation(s)
- Morris F Maduro
- Department of Biology, University of California, Riverside, Riverside, CA 92521, USA.
| |
Collapse
|
60
|
Lankenau DH. Germline Double-Strand Break Repair and Gene Targeting in Drosophila: A Trajectory System throughout Evolution. Genome Integr 2006. [DOI: 10.1007/7050_019] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
|
61
|
Donoghue PCJ, Bengtson S, Dong XP, Gostling NJ, Huldtgren T, Cunningham JA, Yin C, Yue Z, Peng F, Stampanoni M. Synchrotron X-ray tomographic microscopy of fossil embryos. Nature 2006; 442:680-3. [PMID: 16900198 DOI: 10.1038/nature04890] [Citation(s) in RCA: 241] [Impact Index Per Article: 13.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2006] [Accepted: 05/10/2006] [Indexed: 11/08/2022]
Abstract
Fossilized embryos from the late Neoproterozoic and earliest Phanerozoic have caused much excitement because they preserve the earliest stages of embryology of animals that represent the initial diversification of metazoans. However, the potential of this material has not been fully realized because of reliance on traditional, non-destructive methods that allow analysis of exposed surfaces only, and destructive methods that preserve only a single two-dimensional view of the interior of the specimen. Here, we have applied synchrotron-radiation X-ray tomographic microscopy (SRXTM), obtaining complete three-dimensional recordings at submicrometre resolution. The embryos are preserved by early diagenetic impregnation and encrustation with calcium phosphate, and differences in X-ray attenuation provide information about the distribution of these two diagenetic phases. Three-dimensional visualization of blastomere arrangement and diagenetic cement in cleavage embryos resolves outstanding questions about their nature, including the identity of the columnar blastomeres. The anterior and posterior anatomy of embryos of the bilaterian worm-like Markuelia confirms its position as a scalidophoran, providing new insights into body-plan assembly among constituent phyla. The structure of the developing germ band in another bilaterian, Pseudooides, indicates a unique mode of germ-band development. SRXTM provides a method of non-invasive analysis that rivals the resolution achieved even by destructive methods, probing the very limits of fossilization and providing insight into embryology during the emergence of metazoan phyla.
Collapse
|
62
|
Conway Morris S. Darwin's dilemma: the realities of the Cambrian 'explosion'. Philos Trans R Soc Lond B Biol Sci 2006; 361:1069-83. [PMID: 16754615 PMCID: PMC1578734 DOI: 10.1098/rstb.2006.1846] [Citation(s) in RCA: 135] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
The Cambrian 'explosion' is widely regarded as one of the fulcrum points in the history of life, yet its origins and causes remain deeply controversial. New data from the fossil record, especially of Burgess Shale-type Lagerstätten, indicate, however, that the assembly of bodyplans is not only largely a Cambrian phenomenon, but can already be documented in fair detail. This speaks against a much more ancient origin of the metazoans, and current work is doing much to reconcile the apparent discrepancies between the fossil record, including the Ediacaran assemblages of latest Neoproterozoic age and molecular 'clocks'. Hypotheses to explain the Cambrian 'explosion' continue to be generated, but the recurrent confusion of cause and effect suggests that the wrong sort of question is being asked. Here I propose that despite its step-like function this evolutionary event is the inevitable consequence of Earth and biospheric change.
Collapse
Affiliation(s)
- Simon Conway Morris
- University of Cambridge, Department of Earth Sciences, Downing Street, Cambridge CB2 3EQ, UK.
| |
Collapse
|
63
|
Abstract
The comparison of DNA and protein sequences of extant species might be informative for reconstructing the chronology of evolutionary events on Earth. A phylogenetic tree inferred from molecular data directly depicts the evolutionary affinities of species and indirectly allows estimating the age of their origin and diversification. Molecular dating is achieved by assuming the molecular clock hypothesis, i.e., that the rate of change of nucleotide and amino acid sequences is on average constant over geological time. If paleontological calibrations are available, then absolute divergence times of species can be estimated. However, three major difficulties potentially hamper molecular dating : (1) a limited sample of genes and organisms, (2) a limited number of fossil references, and (3) pervasive variations of molecular evolutionary rates among genomes and species. To circumvent these problems, different solutions have been recently proposed. Larger data sets are built with more genes and more species sampled through the mining of an increasing number of genomes. Moreover, independent key fossils are identified to calibrate molecular clocks, and the uncertainty on their age is integrated in subsequent analyses. Finally, models of molecular rate variations are constructed, and incorporated in the so-called relaxed molecular clock approaches. As an illustration of these improvements, we mention that the debated age of the animal (bilaterian metazoans) diversification may have occurred between 642-761 million years ago (Mya), roughly 100 Ma before the Cambrian explosion. Among mammals, the initial diversification of major placental groups may have taken place around 100 Mya, well before the Cretaceous/Tertiary boundary marking the extinction of dinosaurs.
Collapse
Affiliation(s)
- Emmanuel J P Douzery
- Laboratoire de Paléontologie, Phylogénie et Paléobiologie-CC064, Institut des Sciences de l'Evolution UMR 5554/CNRS, Université Montpellier II, place E. Bataillon, 34095 Montpellier Cedex 05, France.
| | | | | |
Collapse
|
64
|
Broitman-Maduro G, Lin KTH, Hung WWK, Maduro MF. Specification of the C. elegans MS blastomere by the T-box factor TBX-35. Development 2006; 133:3097-106. [PMID: 16831832 DOI: 10.1242/dev.02475] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
In C. elegans, many mesodermal cell types are made by descendants of the progenitor MS, born at the seven-cell stage of embryonic development. Descendants of MS contribute to body wall muscle and to the posterior half of the pharynx. We have previously shown that MS is specified by the activity of the divergent MED-1,2 GATA factors. We report that the MED-1,2 target gene tbx-35, which encodes a T-box transcription factor, specifies the MS fate. Embryos homozygous for a putative tbx-35-null mutation fail to generate MS-derived pharynx and body muscle, and instead generate ectopic PAL-1-dependent muscle and hypodermis, tissues normally made by the C blastomere. Conversely, overexpression of tbx-35 results in the generation of ectopic pharynx and muscle tissue. The MS and E sister cells are made different by transduction of a Wnt/MAPK/Src pathway signal through the nuclear effector TCF/POP-1. We show that in E, tbx-35 is repressed in a Wnt-dependent manner that does not require activity of TCF/POP-1, suggesting that an additional nuclear Wnt effector functions in E to repress MS development. Genes of the T-box family are known to function in protostomes and deuterostomes in the specification of mesodermal fates. Our results show that this role has been evolutionarily conserved in the early C. elegans embryo, and that a progenitor of multiple tissue types can be specified by a surprisingly simple gene cascade.
Collapse
Affiliation(s)
- Gina Broitman-Maduro
- Department of Biology, University of California, Riverside, Riverside, CA 92521, USA
| | | | | | | |
Collapse
|
65
|
Chen JY, Bottjer DJ, Davidson EH, Dornbos SQ, Gao X, Yang YH, Li CW, Li G, Wang XQ, Xian DC, Wu HJ, Hwu YK, Tafforeau P. Phosphatized polar lobe-forming embryos from the Precambrian of southwest China. Science 2006; 312:1644-6. [PMID: 16778054 DOI: 10.1126/science.1125964] [Citation(s) in RCA: 68] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
In developing embryos of some extant spiralian animals, polar lobe formation is one of the symmetry-breaking mechanisms for segregation of maternal cytoplasmic substances to certain blastomeres and not others. Polar lobe formation leads to unique early cleavage morphologies that include trilobed, J-shaped, and five-lobed structures. Fossil embryos similar to modern lobeforming embryos are recognized from the Precambrian Doushantuo Formation phosphates, Weng'an, Guizhou Province, China. These embryos are abundant and form a developmental sequence comparable to different developing stages observed in lobe-forming embryos of extant spiralians. These data imply that lobe formation is an evolutionarily ancient process of embryonic specification.
Collapse
Affiliation(s)
- Jun-Yuan Chen
- Nanjing Institute of Geology and Paleontology, Institute of Evo/Developmental Biology, and State Key Laboratory of Pharmaceutical Biotechnology, Nanjing University, Nanjing 210093, China.
| | | | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
66
|
Abstract
In order to establish the portrait of Urbilateria, the common ancestor of triblastic metazoan, this paper focuses on the antero-posterior segmentation frequently considered as characterising the bilaterian bauplan. The synthesis presented here describes the morphological, anatomical and functional aspects of this organisation. Furthermore it analyses the conditions of its emergence during the ontogenesis of Annelids, Arthropods and Chordates and identifies its genetic bases. The provided data exhibit the unitary character of the segmentation modalities among protostomian and deuterostomian organisms. This process occurs in two phases, involving a posterior proliferative zone after the gastrulation. It shows the similarity of the expression patterns of orthologous genes, the implication of comparable signalisation and regulation pathways. The congruence of the results obtained at both structural and molecular levels reinforce the segmental organisation conception of the common ancestor of Bilaterians.
Collapse
Affiliation(s)
- Jean-Pierre Cornec
- EA 3781 EGEE (Evolution, Génome, Environnement). Université de Provence, Aix-Marseille I, Centre St-Charles, case 36, 3, place Victor-Hugo, 13331 Marseille, France.
| | | |
Collapse
|
67
|
Liu P, Yin C, Tang F. Microtubular metazoan fossils with multi-branches in Weng’an biota. ACTA ACUST UNITED AC 2006. [DOI: 10.1007/s11434-006-0630-6] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
|
68
|
Chi H, Xiao Z, Fu D, Lu Z. Analysis of fluorescence from algae fossils of the Neoproterozoic Doushantuo formation of China by confocal laser scanning microscope. Microsc Res Tech 2006; 69:253-9. [PMID: 16586481 DOI: 10.1002/jemt.20295] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
Chinese algae fossils can provide unique information about the evolution of the early life. Thin sections of Neoproterozoic algae fossils, from Guizhou, China, were studied by confocal laser scanning microscopy, and algae fossils were fluorescenced at different wavelengths when excited by laser light of 488 nm, 476 nm, and 568 nm wavelength. When illuminated by 488 nm laser light, images of the algae fossils were sharper and better defined than when illuminated by 476 nm and 568 nm laser light. The algae fossils fluoresce at a wide range of emission wavelengths. The three-dimensional images of the fluorescent algae fossils were compared with the transmission images taken by light microscope. We found that the fluorescence image of the confocal laser scanning microscope in a single optical section could pass for the transmission image taken by a light microscope. We collected images at different sample depths and made a three-dimensional reconstruction of the algae fossils. And on the basis of the reconstruction of the three-dimensional fluorescent images, we conclude that the two algae fossils in our present study are red algae.
Collapse
Affiliation(s)
- Huimei Chi
- State Key Laboratory of Bioelectronics, Southeast University, Nanjing 210096, China.
| | | | | | | |
Collapse
|
69
|
|
70
|
Abstract
The phylogenetic relationships among deuterostome animals have been debated for many years, and a diversity of hypotheses have been proposed based on both morphological and molecular data. Here we have assembled sequences of 217 nuclear-encoded proteins to address specific questions concerning their relationships and times of origin. We recovered significant support for urochordates as the closest relative of vertebrates with an analysis of 59 proteins (17,400 amino acids) and suggest that the basal position of urochordates found in previous molecular studies may have been the result of long-branch attraction biases. Our results also support Ambulacraria, the pairing of hemichordates with echinoderms (nine proteins; 2,382 amino acids), and Cyclostomata, the pairing of lampreys with hagfish (25 proteins; 6,895 amino acids). In addition, 325 shared proteins (102,110 amino acids) were obtained from the complete genomes of six vertebrates and a urochordate for phylogenetic analysis and divergence time estimation. An evolutionary timescale was estimated using a local (Bayesian) molecular clock method. We found that most major lineages of deuterostomes arose prior to the Cambrian Explosion of fossils (approximately 520 MYA) and that several lineages had originated before periods of global glaciation in the Precambrian.
Collapse
Affiliation(s)
- Jaime E Blair
- NASA Astrobiology Institute and Department of Biology, The Pennsylvania State University, University Park, USA.
| | | |
Collapse
|
71
|
COHEN BERNARDL. Not armour, but biomechanics, ecological opportunity and increased fecundity as keys to the origin and expansion of the mineralized benthic metazoan fauna. Biol J Linn Soc Lond 2005. [DOI: 10.1111/j.1095-8312.2005.00507.x] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
|
72
|
Abstract
Jaw shedding and replacement of Diopatra aciculata (Onuphidae, Eunicida), by the same process as arthropod molting, involving apolysis and ecdysis, is described here. These observations suggest that molting has either evolved convergently in eunicidan polychaetes and ecdysozoans or it was present in the last ecdysozoan/lophotrochozoan common ancestor and thus may not represent a synapomorphy of the ecdysozoans.
Collapse
Affiliation(s)
- Hannelore Paxton
- Department of Biological Sciences, Macquarie University, Sydney, NSW 2109, Australia.
| |
Collapse
|
73
|
Affiliation(s)
- Alexander O Vargas
- Departamento de Anatomía y Biología del Desarrollo, Facultad de Medicina, Universidad de Chile, Independencia 1027, Casilla 70.079-Santiago 7, Santiago, Chile.
| | | |
Collapse
|
74
|
Condon D, Zhu M, Bowring S, Wang W, Yang A, Jin Y. U-Pb Ages from the Neoproterozoic Doushantuo Formation, China. Science 2005; 308:95-8. [PMID: 15731406 DOI: 10.1126/science.1107765] [Citation(s) in RCA: 925] [Impact Index Per Article: 48.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
U-Pb zircon dates from volcanic ash beds within the Doushantuo Formation (China) indicate that its deposition occurred between 635 and 551 million years ago. The base records termination of the global-scale Marinoan glaciation and is coeval with similar dated rocks from Namibia, indicating synchronous deglaciation. Carbon isotopic and sequence-stratigraphic data imply that the spectacular animal fossils of the Doushantuo Formation are for the most part younger than 580 million years old. The uppermost Doushantuo Formation contains a pronounced negative carbonate carbon isotopic excursion, which we interpret as a global event at circa 551 million years ago.
Collapse
Affiliation(s)
- Daniel Condon
- Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
| | | | | | | | | | | |
Collapse
|
75
|
?Catalytically active Au on Titania:? yet another example of a strong metal support interaction (SMSI)? Catal Letters 2005. [DOI: 10.1007/s10562-004-0768-2] [Citation(s) in RCA: 165] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
|
76
|
Bengtson S, Budd G. Response to Comment on "Small Bilaterian Fossils from 40 to 55 Million Years Before the Cambrian". Science 2004; 306:1291; author reply 1291. [PMID: 15550644 DOI: 10.1126/science.1102328] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Affiliation(s)
- Stefan Bengtson
- Department of Palaeozoology, Swedish Museum of Natural History, Box 50007, SE-104 05 Stockholm, Sweden.
| | | |
Collapse
|
77
|
Bengtson S, Budd G. Comment on "Small Bilaterian Fossils from 40 to 55 Million Years Before the Cambrian". Science 2004. [DOI: 10.1126/science.1101338] [Citation(s) in RCA: 84] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Affiliation(s)
- Stefan Bengtson
- Department of Palaeozoology, Swedish Museum of Natural History, Box 50007, SE-104 05 Stockholm, Sweden
| | - Graham Budd
- Department of Earth Sciences, Palaeobiology Norbyvägen 22, SE-752 36 Uppsala, Sweden
| |
Collapse
|
78
|
Abstract
The fossil record has long supported the view that most animal phyla originated during a brief period approximately 520 MYA known as the Cambrian explosion. However, molecular data analyses over the past 3 decades have found deeper divergences among animals (approximately 800 to 1,200 MYA), with and without the assumption of a global molecular clock. Recently, two studies have instead reported time estimates apparently consistent with the fossil record. Here, we demonstrate that methodological problems in these studies cast doubt on the accuracy and interpretations of the results obtained. In the study by Peterson et al., young time estimates were obtained because fossil calibrations were used as maximum limits rather than as minimum limits, and not because invertebrate calibrations were used. In the study by Aris-Brosou and Yang, young time estimates were obtained because of problems with rate models and other methods specific to the study, and not because Bayesian methods were used. This also led to many anomalous findings in their study, including a primate-rodent divergence at 320 MYA. With these results aside, molecular clocks continue to support a long period of animal evolution before the Cambrian explosion of fossils.
Collapse
|
79
|
Douzery EJP, Snell EA, Bapteste E, Delsuc F, Philippe H. The timing of eukaryotic evolution: does a relaxed molecular clock reconcile proteins and fossils? Proc Natl Acad Sci U S A 2004; 101:15386-91. [PMID: 15494441 PMCID: PMC524432 DOI: 10.1073/pnas.0403984101] [Citation(s) in RCA: 364] [Impact Index Per Article: 18.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2004] [Accepted: 09/13/2004] [Indexed: 11/18/2022] Open
Abstract
The use of nucleotide and amino acid sequences allows improved understanding of the timing of evolutionary events of life on earth. Molecular estimates of divergence times are, however, controversial and are generally much more ancient than suggested by the fossil record. The limited number of genes and species explored and pervasive variations in evolutionary rates are the most likely sources of such discrepancies. Here we compared concatenated amino acid sequences of 129 proteins from 36 eukaryotes to determine the divergence times of several major clades, including animals, fungi, plants, and various protists. Due to significant variations in their evolutionary rates, and to handle the uncertainty of the fossil record, we used a Bayesian relaxed molecular clock simultaneously calibrated by six paleontological constraints. We show that, according to 95% credibility intervals, the eukaryotic kingdoms diversified 950-1,259 million years ago (Mya), animals diverged from choanoflagellates 761-957 Mya, and the debated age of the split between protostomes and deuterostomes occurred 642-761 Mya. The divergence times appeared to be robust with respect to prior assumptions and paleontological calibrations. Interestingly, these relaxed clock time estimates are much more recent than those obtained under the assumption of a global molecular clock, yet bilaterian diversification appears to be approximately 100 million years more ancient than the Cambrian boundary.
Collapse
Affiliation(s)
- Emmanuel J P Douzery
- Department of Paleontology, Phylogeny, and Paleobiology, Institut des Sciences de l'Evolution (Unité Mixte de Recherche 5554, Centre National de la Recherche Scientifique), Université Montpellier II, Montpellier Cedex 5, France.
| | | | | | | | | |
Collapse
|
80
|
Cameron RA. Hunting for Origins. Science 2004. [DOI: 10.1126/science.1100684] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
On the Origin of Phyla
. by James W. Valentine. University of Chicago Press, Chicago, 2004. 638 pp. $55, £38.50. ISBN 0-226-84548-6.
The authors provide a thorough and critical review and synthesis of recent research on the origin of species, covering both plants and animals.
Collapse
Affiliation(s)
- R. Andrew Cameron
- The reviewer is in the Division of Biology, Mail Code 139-74, 1200 East California Boulevard, California Institute of Technology, Pasadena, CA 91125, USA
| |
Collapse
|