Uptake of tricarboxyli acid cycle intermediates by preimplantation mouse embryos in vitro

Preimplantation embryo gene expression: 56 years of discovery, and counting

The biology of preimplantation embryo gene expression began 56 years ago with studies of the effects of protein synthesis inhibition and discovery of changes in embryo metabolism and related enzyme activities. The field accelerated rapidly with the emergence of embryo culture systems and progressively evolving methodologies that have allowed early questions to be re-addressed in new ways and in greater detail, leading to deeper understanding and progressively more targeted studies to discover ever more fine details. The advent of technologies for assisted reproduction, preimplantation genetic testing, stem cell manipulations, artificial gametes, and genetic manipulation, particularly in experimental animal models and livestock species, has further elevated the desire to understand preimplantation development in greater detail. The questions that drove enquiry from the earliest years of the field remain drivers of enquiry today. Our understanding of the crucial roles of oocyte-expressed RNA and proteins in early embryos, temporal patterns of embryonic gene expression, and mechanisms controlling embryonic gene expression has increased exponentially over the past five and a half decades as new analytical methods emerged. This review combines early and recent discoveries on gene regulation and expression in mature oocytes and preimplantation stage embryos to provide a comprehensive understanding of preimplantation embryo biology and to anticipate exciting future advances that will build upon and extend what has been discovered so far.

Truth in science: experimental design and the legacy of John D Biggers, PhD., DSc

The current article presents a brief historical perspective on Professor John D Biggers, PhD, DSc. who died on 7 April, 2018. His interests covered reproductive physiology, embryo culture, cryobiology, sperm preservation, statistics and experimental design, and the history and ethics of human reproductive biology. Emphasis is placed on John Biggers' approach to the development of media for the culture of mammalian preimplantation embryos and to correct several minor misconceptions that have arisen in recent years regarding some of his studies. Much can be learned from his detailed approach to scientific investigation and experimental design. His scientific accomplishments and seminal contributions are important, but the tapestry of his life and legacy continue to be woven through the many students, fellows, and collaborators with whom he worked with over many years. The present article builds on a previous conversation that Michael Summers and Catherine Racowsky had with John Biggers that was published in 2008 [1].

Role of the mitochondrial genome during early development in mice. Effects of ethidium bromide and chloramphenicol

The role of the mitochondrial genome in early development and differentiation was studied in mouse embryos cultured in vitro from the two to four cell stage to the blastocyst (about 100 cells). During this period the mitochondria undergo morphological differentiation: progressive enlargement followed by an increase in matrix density, in number of cristae, and in number of mitochondrial ribosomes. Mitochondrial ribosomal and transfer RNA synthesis occurs from the 8 to 16 cell stage on and contributes to the establishment of a mitochondrial protein-synthesizing system. Inhibition of mitochondrial RNA- and protein-synthesis by 0.1 microg/ml of ethidium bromide or 31.2 microg/ml of chloramphenicol permits essentially normal embryo development and cellular differentiation. Mitochondrial morphogenesis is also nearly normal except for the appearance of dilated and vesicular cristae in blastocyst mitochondria. Such blastocysts are capable of normal postimplantation development when transplanted into the uteri of foster mothers. Higher concentrations of these inhibitors have general toxic effects and arrest embryo development. It is concluded that mitochondrial differentiation in the early mouse embryo occurs through the progressive transformation of the preexisting mitochondria and is largely controlled by the nucleocytoplasmic system. Mitochondrial protein synthesis is required for the normal structural organization of the cristae in blastocyst mitochondria. Embryo development and cellular differentiation up to the blastocyst stage are not dependent on mitochondrial genetic activity.