Expression of c-fos and c-jun mRNA in the developing chicken lens: relationship to cell proliferation, quiescence, and differentiation.

The in vivo developmental pattern of c-fos and c-jun mRNA expression has been examined in the embryonic chicken lens using a coupled reverse transcription/polymerase chain reaction assay. Levels of each mRNA were measured in the central epithelium, equatorial epithelium, and fiber cell mass at 6, 10, 14, and 19 days of development. The results showed that c-fos and c-jun mRNAs accumulated during development of the embryonic chicken lens epithelium as the proportion of proliferating cells decreased, suggesting that quiescent epithelial cells express high levels of both protooncogene mRNAs. Cells in the early stages of terminal differentiation near the lens equator also contained relatively high levels of c-fos and c-jun mRNA. As lens fiber cells matured, the number of copies of c-fos mRNA per cell decreased markedly, while c-jun mRNA increased. These findings demonstrate that c-fos and c-jun are differentially regulated during terminal differentiation of lens fiber cells and suggest that these protooncogenes are expressed in lens epithelial cells following cell cycle arrest.