Expression of the c-ski proto-oncogene during cell cycle arrest and myogenic differentiation.

Although the ski oncogene plays a role in cell proliferation, morphological transformation, and myogenic differentiation, the myogenic activities of the proto-oncogene c-ski have yet to be elucidated. c-ski is expressed within myoblasts during embryogenesis. Transcripts from the proto-oncogene can be detected in somites early in myogenic commitment, as well as in terminally differentiated skeletal muscle. However, c-ski mRNAs expressed in cells of the myogenic lineage are indistinguishable from c-ski transcripts in other cell types, raising the possibility that muscle-specific c-ski transcripts are expressed transiently. Avian cell lines QM7 and QM5 were used as a model to analyze changes in expression and alternative exon usage of c-ski during synchronous muscle differentiation. Upon serum deprivation, QM7 cells undergo myogenic differentiation. In contrast, QM5 cells cease proliferation but do not differentiate. Results show that levels of expression and alternative splicing of c-ski transcripts remain unchanged during cell cycle arrest or myogenic differentiation.

Molecular evolution of the F glycoprotein of human parainfluenza virus type 1.

Human parainfluenza virus type 1 (hPIV1) is a major cause of upper and lower respiratory tract infections among children. Immunity is mediated at least in part by antibody to the fusion (F) surface glycoprotein. Thus, genetic variation in the F gene could influence host range, virulence, and immunity. To examine the genetic diversity among hPIV1 isolates, the F genes of hPIV1 isolates from a single geographic location were sequenced and compared with the F gene of a strain isolated in 1957. Genetic variation was 2.2%-3.4%, averaging 0.8 amino acid changes per year. Changes were progressive over time, and virus evolution was dominated by a single lineage. Three of 7 isolates tested did not induce syncytium formation in tissue culture. This phenotype could not be ascribed to a single unique mutation in the F gene, but these 3 isolates had mutations in the transmembrane region of the HN gene. It is unlikely that the limited genetic evolution of the F gene will be an obstacle to vaccine development.

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.