Multiple Isoforms of Olive Flounder (Paralichthys olivaceus) Pax3a and Pax3b Display Differential Regulations on Myogenic Differentiation

Paired box 3 (Pax3) is a critical upstream regulator of the onset of myogenesis. We have previously identified two spliced isoforms of pax3a (pax3a-1 and pax3a-2) and three spliced isoforms of -pax3b (pax3b-1, pax3b-2, and pax3b-3) in olive flounder, but their roles in myogenesis are unknown. In this study, we investigated their cellular localization, transcriptional activity on myod gene regulation, and roles in myogenesis. Different Pax3a and Pax3b isoforms revealed various subcellular localizations, which were related to their corresponding protein structures. Pax3a-1, Pax3a-2, and Pax3b-1 promoted the transcriptional activity of myod to different degrees, whereas Pax3b-2 and Pax3b-3 had a slight inhibitory or no effect. The pairwise interaction analysis demonstrated the synergistic effect of Pax3b-1 and Pax3b-3 on myod transcriptional activity. The overexpression of different pax3a and pax3b isoforms differentially altered the spatial expression patterns of myod and differentially regulated the expression levels of their target genes (myod, myf5, and c-met) in zebrafish embryonic myogenesis. In addition, the different flounder myod promoter-driven pax3a/3b isoform expression vectors were successfully introduced into the skeletal muscles of juvenile flounder by electroporation. However, none of them could change the mRNA expression levels of mstn, myf5, myod, myogenin, pax7a, and pax7b in the electroporated muscles. These results suggest that different Pax3a and Pax3b isoforms may precisely and collaboratively regulate embryonic myogenesis, but their roles in juvenile myogenesis are uncertain.

Automated summary

This study investigated the roles of different isoforms of Pax3a and Pax3b in myogenesis. The results showed that different isoforms have different subcellular localizations and transcriptional activities, and they regulate the expression of different target genes during embryonic myogenesis. These findings contribute to a better understanding of the functions of Pax3a and Pax3b in muscle development.