Cylicin-1 (CYLC1)

Cylicin-1 is a **testis-specific cytoskeletal protein**, primarily localized to the **perinuclear theca (PT) and calyx at the posterior region of mature sperm nuclei**[2][3][5]. It is exclusively expressed during spermiogenesis in mammals, and is characterized by a high lysine content, resulting in a very basic isoelectric point (pI ~10.5)[2][5]. Cylicin-1 displays a dynamic localization: initially in the subacrosomal layer of round spermatids and later migrating to the postacrosomal region as spermatids elongate, finally concentrating in the sperm calyx[3][1]. Functional studies in knockout mice and human genetic analysis have demonstrated that **cylicin-1 is critical for proper sperm head morphology, anchoring the acrosome to the nucleus, and maintaining PT integrity**[1][3][5]. Loss or mutation of CYLC1 leads to severe male infertility due to sperm deformities such as acrosome detachment, altered head shape, and defective flagellum. Cylicin-1 can interact with itself and with other PT proteins (including CCIN, ACTRT1, CAPZA3, ACTL7A, and FAM209), forming structural complexes crucial for sperm head formation and stability[3]. Currently, Cylicin-1 is not considered a **therapeutic target** (such as a receptor, enzyme, or transporter) and has no known drug interactions. Its main biomedical relevance is as a structural and possibly diagnostic marker in the study of male infertility, where CYLC1 variants may help identify patients with structural sperm defects[3][1].

Other names

Cylicin-1CYLC1CYL1CYLCYCL1SPGFX8Multiple-band polypeptide Ibasic protein of sperm head cytoskeleton 1cylicin Imultiple-band polypeptide I