TUB-like protein 2, a substrate of CCT8, is essential for the intraflagellar transport during spermiogenesis in mice

Abstract Male infertility is a significant global health challenge. We previously found that TUB-like protein 2 (TULP2), a member of the TULPs family, is indispensable for male fertility. In this study, we demonstrate the essential role of TULP2 in sperm function, including capacitation, acrosome reaction, and fertilization. Mechanistic investigations revealed TULP2 as a critical coordinator of protein transport during spermatogenesis. Specifically, TULP2 interacts with several intraflagellar transport (IFT) components, and quantitative analyses revealed significant dysregulation of some IFT-related molecules including IFT20, IFT80, IFT70A, BBS7, DYNLT2B, and HDAC6 in Tulp2−/− mice. Furthermore, localization analyses revealed pronounced abnormalities in the distribution of IFT20 in both testicular spermatids and spermatozoa, while IFT70A and IFT80 mislocalization was specifically observed in spermatozoa of Tulp2−/− mice. Our findings reveal that the apical domain of chaperonin containing TCP1 subunit 8 (CCT8) appears to recognize and interact with TULP2. Knockdown of CCT8 results in the formation of TULP2 aggregates in the cytoplasm, thereby impairing its function in ciliogenesis. We identified a homozygous missense variant in TULP2 (c.C832 > T [p.R278W]) in one individual with asthenoteratozoospermia. Interestingly, the sperm flagella of this individual exhibited abnormalities that closely resembled those observed in knockout (KO) mice. Overall, we propose that TULP2, as a CCT8 substrate, is a crucial protein for sperm function and may regulate spermatogenesis through its interactions with IFT components.