Predominant expression of alternative PAX3 and PAX7 forms in myogenic and neural tumor cell lines

PAX3 and PAX7 are closely related paired box family members expressed durin g early neural and myogenic development. Assay of PAX3 and PAX7 mRNA expres sion in embryonal rhabdomyosarcoma, neuroblastoma, Ewing's sarcoma, and mel anoma cell lines revealed tumor-specific expression patterns similar to the corresponding embryonic lineages. Although the mammalian PAX3 and PAX7 gen es were reported to contain eight exons, we found that the predominant PAX3 and PAX7 transcripts in these tumor lines contain previously uncharacteriz ed ninth exons, These splicing events alter the COOH-terminal coding region s of the encoded products but do not alter the transcriptional activity as assayed using a reporter gene with a model PAX3/PAX7 binding site. However, the findings of nearly identical COOH-terminal regions within the correspo nding genes of the avian and fish genomes suggest conserved functional role s for these regions that require further investigation.