Essential for male fertility and sperm mitochondrial sheath formation (PubMed:33536340). Required for proper mitochondrial elongation and coiling along the flagellum during the formation of the mitochondrial sheath (PubMed:33536340). Facilitates the growth and aggressiveness of neuroblastoma cells (By similarity). Increases the EZH2 activity and H3K27me3 levels in a RBBP4-dependent manner, and facilitates the enrichment of polycomb repressive complex 2 and H3K27me3 on gene promoters, resulting in transcriptional repression of tumor suppressors affecting the proliferation, invasion, and metastasis of tumor cells (By similarity). Interacts with TBC1D15, TBC1D21, GK2 and IMMT (PubMed:33536340). Interacts with VDAC2 and VDAC3 in a TBC1D21-dependent manner (PubMed:33536340). Interacts (via ARM domains) with RBBP4 (By similarity). Testis-specific. Expression begins around postnatal day 20, which roughly corresponds to the haploid, round spermatid stage of spermatogenesis. Male mice are infertile due to reduced sperm motility and abnormal sperm morphology.