Protooncogene c-ski is expressed in both proliferating and postmitotic neuronal populations

The cellular protooncogene, c-ski, is expressed in all cells of the developing mouse at low but detectable levels. In situ hybridization and Northern blot analyses reveal that some cells and tissues express this gene at higher levels at certain stages of embryonic and postnatal development. RT-PCR results indicate that alternative splicing of exon 2, known to occur in chickens (Sutrave and Hughes [1989] Mol. Cell. Biol. 9:4046-4051; Grimes et al. [1993] Oncogene 8:2863-2868) does not occur in adult mouse tissues. In the embryo, neural crest cells express the c-ski gene during migration at 8.5 to 9.5 days post coitum (p.c.). Neural crest derivatives such as dorsal root ganglia and melanocytes stain positively with an antibody to the ski protein. At 9 days p.c., the entire neural tube has high levels of c-ski gene expression. By 12-13.5 days only the ependymal layer expresses c-ski above background levels. At 14-16 days p.c., c-ski mRNAs are detected at high levels in the cortical layers of the brain and in the olfactory bulb. In 2 week and 6 week postnatal brains, c-ski gene transcripts are also detected in the hippocampus and in the granule cell layer of the cerebellum. The allantois and placenta exhibit high levels of c-ski mRNAs. Neonatal lung tissue increases c-ski gene expression approximately two-fold compared to prenatal levels. These results suggest that ski plays a role in both the proliferation and differentiation of specific cell populations of the central and peripheral nervous systems and of other tissues.