CFAP161 is a microtubule inner protein (MIP) component of dynein-decorated doublet microtubules in the ciliary axoneme, essential for motile cilia beating and flagellar function. Based on limited published evidence, CFAP161 protein levels are dynamically regulated during sperm capacitation, a critical post-testicular maturation process required for fertilizing capacity 1. The protein localizes to axonemal structures and participates in sperm motility regulation, potentially through ubiquitin-proteasome system-mediated proteolysis.