Stage‐specific protein synthesis during early embryogenesis in Drosophila melanogaster.

The changes in protein species synthesized during early Drosophila embryogenesis were characterized by two‐dimensional electrophoresis. Of the 261 proteins scored, 68 (26%) show dramatic changes in rates of synthesis during the first 8 h of embryogenesis. These stage‐specific proteins can be classified into three categories: early, detected at 1, 2 and 3 h but not later; late, not detected at 1 h, but appearing later; and discontinuous, detected before and after, but not at 3 and 4 h. RNA was extracted from three representative stages, translated in vitro, and the translation products separated on two‐dimensional gels. There was a strong correlation between the patterns of synthesis in vivo and in vitro, suggesting that the early proteins are translated from maternal mRNA, and the late proteins from zygotic mRNA. A thorough comparison was made between the proteins synthesized in wild‐type and dorsal embryos, in which virtually only dorsal hypoderm differentiates. The first observed difference was a reduced synthesis of actin I at 8 h, indicating that the absence of mesodermal and endodermal tissues is not detectable at the level of moderately abundant protein until the onset of differentiation.