Structural relationship and posttranslational modification of stage-specific proteins synthesized during early...

The synthesis of stage-related proteins characteristic of meiotic maturation and early preimplantation development occurs in the absence of significant transcription. Previous work indicated that some of the stage-related proteins typical of the early postfertilization period are synthesized in unfertilized oocytes at the same time that they are detected in fertilized eggs. This observation has led to the suggestion that protein synthesis in newly fertilized eggs is regulated by an intrinsic developmental program initiated during the resumption of meiosis (meiotic maturation) and supported in part by previously untranslated mRNA. It also has been proposed that the rapid and complex changes in protein synthesis that characterize this period may involve differential gene expression or selective protein degradation, or both. To date, cell-free translation of oocyte RNA has not demonstrated the existence of a sizeable population of preformed mRNA that could support the observed changes in protein synthesis. I have tested the notion that the apparent changes in protein synthesis during early development in the mouse may be derived from families of proteins related both in amino acid sequence and posttranslational modification. The findings show that many changes in protein synthetic patterns related to early development after fertilization are independent of fertilization and involve the posttranslational modification of proteins with identical or very similar primary structures. The results are discussed with respect to current interpretations of quantitative and qualitative changes in protein synthesis during early mammalian development as they relate to differential gene expression and presumed activation of preformed mRNA.