Identification and Expression Profile of a Novel Alternative Splicing of Pax7 in Chick Skeletal Muscle

Pax7 is essential for skeletal muscle myogenesis. The alternative splicing forms of Pax7 were found in human and mouse. In this study, we identified a new alternative splicing of chick Pax7. We named it Pax7-2 and localized it in the nucleus of chick myoblast. In Pax7-2 mRNA, exon 8 of chick Pax7 gene was spliced out. That led to a 22-amino acid deletion in the COOH terminal of Pax7-2 protein compared with Pax7 protein. Luciferase assays demonstrated that chick Pax7 could act as a transactivator and the deleted 22 amino acids in Pax7-2 may belong to the transactivation domain of Pax7. Pax7-2 lost transactivation ability. We detected the expression levels of Pax7-2 in chick pectoralis muscles at different developmental stages and found that the expression of Pax7-2 was at its peak in d-12 chick embryos. The expression levels of Pax7 and Pax-2 in chick pectoralis muscles at different developmental stages had a similar trend across the period under study, although the changes of their expression levels were different. As chicks grew up, Pax7 and Pax7-2 were expressed at much lower levels.