Analysis of the coding activity and stability of messenger RNA in Drosophila oocytes.

The coding activity of the messenger RNA in the ooplasm of late stage 14 (S14) oocytes of Drosophila melanogaster was analyzed by labeling the oocytes in vitro with ³⁵S]methionine and examining the labeled products by two-dimensional gel electrophoresis and fluorography. This analysis was done both with newly formed S14 oocytes from rapidly laying females and with S14 oocytes stored for about 10 days in females that were prevented from laying. Comparison of the fluorographs showed that the proteins labeled in the newly formed oocytes were also labeled in the stored oocytes. Thus, the coding activity of S14 oocyte messenger RNA appears to remain stable during prolonged storage in utero. The oocyte proteins synthesized during oogenesis and incorporated into S14 oocytes were labeled in vivo by injecting ³⁵S]methionine into newly eclosed females, and the S14 oocytes were removed 2 days later for gel electrophoresis and fluorography. Comparison of the fluorographs produced by the in vivo and in vitro labeling procedures showed that most of the oocyte proteins labeled in vivo were also labeled in vitro. The S14 oocytes, therefore, appear to contain messenger RNA for most of the oocyte proteins synthesized during oogenesis. There were also several additional proteins detected only in the fluorographs of the in vivo labeled oocytes; the most prominent of these were identified by immunoprecipitation tests as vitellogenin proteins of yolk granules, which are known to be synthesized outside the oocyte, in fat bodies. The occurrence of stable S14 oocyte messenger RNA for most of the oocyte proteins suggests that the synthesis of those proteins during oogenesis occurs in the developing oocytes, specified by a stable population of oocyte messenger RNA.