Divergent Regulatory Roles of Transcriptional Variants of the Chicken LDB3 Gene in Muscle Shaping.

LIM domain binding 3 ( LDB3 ) serves as a striated muscle-specific Z-band alternatively spliced protein that plays an important role in mammalian skeletal muscle development, but its regulatory role and molecular mechanism in avian muscle development are still unclear. In this study, we reanalyzed RNA sequencing data sets of 1415 samples from 21 chicken tissues published in the NCBI GEO database. First, three variants ( LDB3 -X, LDB3 -XN1, and LDB3 -XN2) generated by alternative splicing of the LDB3 gene were identified in chicken skeletal muscle, among which LDB3 -XN1 and LDB3 -XN2 are novel variants. LDB3 -X and LDB3 -XN1 are derived from exon skipping in chicken skeletal muscle at the E18-D7 stage and share three LIM domains, but LDB3 -XN2 lacks a LIM domain. Our results preliminarily suggest that the formation of three variants of LDB3 is regulated by RBM20 . The three splice isomers have divergent functions in skeletal muscle according to in vitro and in vivo assays. Finally, we identified the mechanism by which different variants play different roles through interactions with IGF2BP1 and MYHC , which promote the proliferation and differentiation of chicken myoblasts, in turn regulating chicken myogenesis. In conclusion, this study revealed the divergent roles of three LDB3 variants in chicken myogenesis and muscle remodeling and demonstrated their regulatory mechanism through protein-protein interactions.