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 prol iferation, morphological transformation and myogenic differentiation i n cells in culture and in transgenic animals. Yet, little is known abo ut expression of the c-ski locus or the relationship between c-ski cDN As and alternatively spliced c-ski transcripts in chicken tissues, par ticularly in skeletal muscle or during embryogenesis. We developed a s eries of probes and oligonucleotide primers specific for the eight cod ing exons and the long 3' noncoding region found in chicken c-ski mRNA s. The most abundant chicken c-ski mRNAs in a vast array of tissues ar e 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 trans cripts 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 wit h and without exon 2 appear in all tissues, in somites, and from the e arliest stages of chick embryogenesis. Thus, c-ski cDNA sequences, whi ch 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.