Transcriptional activator of MEF2C involved in the regulation of adult muscle fiber type identity and skeletal muscle regeneration (PubMed:19914232). Plays an important role in spermatogenesis (PubMed:27739607). Required for the survival of spermatogonia and participates in spermatocyte meiosis (PubMed:27739607). Highly expressed in spermatogonia, spermatocytes, and round spermatids within the testis (at protein level). Accumulates in the testis starting at postnatal day 3, and remains at a steady level from 1 to 3 weeks in age. Increased markedly during skeletal muscle differentiation (at protein level). Null mice have an abnormal skeletal muscle fiber type ratio in males as well as defects in muscle regeneration following injury (PubMed:19914232). Male germ-cell-specific conditional knockout results in complete male infertility, early loss of spermatogonia and meiotic arrest in spermatocytes (PubMed:27739607). Spermatocytes show significantly reduced expression meiotic arrest-related genes (PubMed:27739607).