We have described the expression of three nuclear protooncogenes, c-myc, c-myb and c-ets-1 during feather morphogenesis in the chick embryo. In parallel with the expression patterns obtained by in situ hybridization, we have mapped the spatial distribution of S-phase cells by monitoring the incorporation of 5-bromodeoxyuridine. We do not detect c-myc or c-myb transcripts during the early stages when S-phase cells are scattered in the dermis and in the epidermis. Rather c-ets-1 transcripts are abundant in the dermal cells which divide and accumulate under the uniform epidermis. At the onset of the formation of the feather bud, cells within each rudiment cease DNA replicative activities and c-myc transcripts are detected both in the epidermis and in the underlying dermis. This expression precedes the reentry into the S phase. The transcription of c-myb, which has been previously tightly linked to hemopoietic cells is also detected in the developing skin. This expression is essentially located in proliferating epidermal cells on and after the beginning of feather outgrowth. As feather outgrowth proceeds, the distribution of c-myc and c-myb transcripts is restricted to the highly proliferating epidermis. In contrast c-ets-1 transcripts are never detected in the epidermis. During the later stages of skin morphogenesis, the transcription of c-ets-1 is restricted to the endothelial cells of blood vessels, as previously described. We suggest that the differential expression of these nuclear oncogenes reflects the activation of different mitotic controlling pathways during the development of the skin.
Elimination of Keratinocytes Atagnant in S Phase Through Epidermal Turnover Instead of In Situ Apoptosis