C-ski transcripts with and without exon 2 are expressed in skeletal muscle and throughout chick embryogenesis

Overexpression of v-ski or c-ski cDNAs has a pronounced effect on proliferation, morphological transformation and myogenic differentiation in cells in culture and in transgenic animals. Yet, little is known about expression of the c-ski locus or the relationship between c-ski cDNAs and alternatively spliced c-ski transcripts in chicken tissues, particularly in skeletal muscle or during embryogenesis. We developed a series of probes and oligonucleotide primers specific for the eight coding exons and the long 3' noncoding region found in chicken c-ski mRNAs. The most abundant chicken c-ski mRNAs in a vast array of tissues are 8.5 kb, with additional, but less abundant, mRNAs of 7.5, 6.5 and 4.4 kb. Steady-state levels of c-ski mRNAs, indistinguishable from transcripts in other tissues, accumulate in skeletal muscle from embryonic, newly hatched, and adult chicks. Only exon 2, a small exon of 111 bp, was found to be alternatively spliced in c-ski mRNAs. Transcripts with and without exon 2 appear in all tissues, in somites, and from the earliest stages of chick embryogenesis. Thus, c-ski cDNA sequences, which extend about 4.3 kb, represent either the least abundant form of c-ski mRNAs in tissues or a severely truncated form of the major 8.5 kb transcripts.