CATSPER3 is a pore-forming subunit of the CatSper complex, a sperm-specific voltage-gated calcium channel essential for male fertility 1. Unlike other CatSper proteins that show testis-restricted expression, CATSPER3 exhibits broader tissue distribution while maintaining high testicular expression 2. The protein contains a single channel-forming domain with a characteristic pore-loop sequence (TxDxW) and a C-terminal coiled-coil domain that enables interaction with other CatSper subunits to form a functional hetero-tetrameric channel 1. CATSPER3 plays a crucial role in sperm hyperactivation, capacitation, and acrosome reaction, which are essential for successful fertilization 3. Reduced CATSPER3 mRNA expression is significantly associated with asthenoteratozoospermia, correlating positively with sperm motility, mitochondrial membrane potential, and fertilization rates in ICSI procedures 4. The protein shows regional expression patterns, with tail localization being particularly important for sperm function 5. CATSPER3 expression increases substantially during sexual maturation, beginning around day 60 in pigs and maintaining high levels through adulthood 2. Clinical studies identify CATSPER3 as a potential biomarker for male infertility, particularly in cases of nonobstructive azoospermia where it serves as a diagnostic indicator of spermatogenesis dysfunction 6.