Expression of Maternal and Embryonic Genes during Sea Urchin Development
We have investigated the patterns of protein synthesis during embryonic development using two-dimensional electrophoresis. The recruitment of a large amount of new maternal mRNA into polysomes following fertilization is accompanied by very few changes in the relative rates of synthesis of about 1000 polypeptides detected. Between the time of hatching and invagination, many polypeptides become undetectible and many others appear. A variety of other developmental changes occur in this period as well, indicating that a key transition has occurred from early development, dominated by expression of the maternal genome to late development, which requires participation of the embryonic genome. About 20% of the newly synthesized polypeptides, mostly minor ones, undergo changes in relative rates of synthesis during development, and far fewer change detectibly in mass. A variety of patterns of metabolism are observed for different polypeptides. Cloned cDNAs have been identified which correspond to mRNAs coding for some of these developmentally regulated proteins. Some of the newly synthesized polypeptides are enriched in one of the three primary tissue layers, and these increase in relative rates of synthesis during development. A comparison of polypeptides enriched in ectoderm or endoderm demonstrates little evolutionary conservation among three genera. Few prevalent paternal mRNAs are detectible in comparable abundance in interspecies hybrid embryos even at the mature pluteus stage. For some genes this may be because the stored maternal RNA persists throughout embryonic development without being replenished by new synthesis. We have identified several cloned DNAs complementary to transcripts which normally accumulate extensively during embryogenesis of the paternal species but are barely detectible in the hybrid embryos. The possible defects in expression of these paternal genes in foreign cytoplasm are discussed.
KeywordsEmbryonic Development Germinal Vesicle Histone Gene Hybrid Embryo Paternal Genome
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