RIMBP3 (RIMS binding protein 3) is a manchette-associated protein essential for male fertility through its role in sperm morphogenesis. During spermiogenesis, RIMBP3 localizes to the manchette, a transient microtubular structure critical for converting round spermatids into mature sperm 1. The protein functions as a component of a multiprotein complex involving HOOK family proteins, KLC3, and other cargo adapter proteins that regulate microtubule dynamics 2. RIMBP3 phosphorylation is regulated by HIPK4 kinase during spermiogenesis, with these phosphorylation events essential for proper sperm head shaping 3. Targeted deletion of RIMBP3 in mice causes male infertility characterized by abnormal sperm morphology, including deformed nuclei and detached acrosomes 1. RIMBP3 interacts directly with Hook1, a manchette protein required for proper sperm head morphogenesis, suggesting this interaction is critical for manchette function 1. In humans, RIMBP3 is significantly downregulated in non-obstructive azoospermia (NOA) and is among eight genes implicated in impaired spermatogenesis 4. These findings establish RIMBP3 as a key molecular component whose dysfunction contributes to male infertility.