GENETIC CONTROL OF VERY EARLY MAMMALIAN DEVELOPMENT

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Abstract
Summary: The overall picture of mammalian preimplantation development is one of complex but integrated molecular activity. As development progresses from the 1 cell stage, blastomeres acquire properties that differ from those of cells of previous stages and eventually differ from one another even at the same stage. The evidence concerning the role of the embryonic genome during this process can be summarized under two headings:(1) Expression of embryonic genome(a) Quantitative and qualitative changes in RNA and protein synthesis begin to occur soon after fertilization.(b) Changes in structural proteins (enzyme activities, transport systems and intercellular junctions) occur throughout early development.(c) Paternal gene products can be detected as early as the 2‐cell stage.(2) The need for expression of the embryonic genome(a) Inhibitors of RNA and protein synthesis result in abnormal and lethal development.(b) Several mutations (T/t, Ay, Os, c25H, Om, Ts) are lethal during early development.(c) Chromosomal imbalance (monsomy, haploidy, nullisomy) has adverse effects on early development.Even though studies in vitro on the inhibition of translation indicate that stable maternal messenger RNAs are present in the developing mouse embryo, the evidence outlined in this article strongly supports the belief that embryonic gene expression occurs very early in development (at least by the 2 cell stage) and that this expression is required for normal development.