Embryonic teratocarcinoma mouse cells (P19) and embryonic NIH3T3 fibroblasts were induced chemically to differentiate along neurogenic or myogenic lineages. The expression profiles of Pax7 alternate transcripts were then assessed by RNA isolation and RT-PCR. Only two transcripts, Pax7b and Pax7d, were expressed in the neurogenic lineage. By contrast, in adult skeletal muscle, four transcripts, Pax7a-d, were expressed in the myogenic lineage. Moreover, P19 cells were shown to undergo neural cell differentiation when stably transfected with a single Pax7 transcript, PAX7b, generated from human skeletal muscle. Our results suggest a key role for Pax7 transcripts in lineage determination. (C) 2001 Academic Press.