Expression Characteristics and Putative Functions of KIF3A/KIF3B During Spermiogenesis of Phascolosoma Esculenta

The microtubule（MT）-associated proteins KIF3A and KIF3B are ubiquitously expressed in a wide range of taxa. This study investigated the functions of these proteins in spermiogenesis, which involves various MT-dependent processes, in Phascolosoma esculenta. We cloned the complete c DNA of Pe-KIF3A/3B. Structural predictions showed that Pe-KIF3A/3B are composed of a highly conserved motor domain, a coiled-coil domain, and a tail domain. Real-time quantitative PCR showed that Pe-kif3a/3b are expressed in all tissues evaluated, with the highest levels in sperm masses. Fluorescence in situ hybridization and immunofluorescence were employed to analyze the dynamic expression patterns of KIF3A/3B during spermiogenesis. Pe-KIF3A/3B consistently co-localized with MTs at all stages of spermiogenesis, indicating their potential functions in cargo trafficking. Pe-KIF3A/3B colocalized with mitochondria, suggesting that they may mediate mitochondrial movement. In late-stage spermatids and mature sperm, co-localization was detected in the midpiece, suggesting that Pe-KIF3A/3B could facilitate midpiece formation. The co-localization of Pe-KIF3A and Pe-KIF3B at all stages of spermiogenesis suggests their function as the heterodimeric KIF3AB. Basing on the observed temporal and spatial expression patterns of Pe-KIF3A/3B, MTs, and mitochondria in our study, we suggest that heterodimer KIF3AB has a potential role in acrosome biogenesis, sperm head remodeling, enflagellation, and mitochondrial migration during spermiogenesis in P. esculenta. In addition, our study on the morphological characteristics of spermatogenic cells provided fundamental data on the reproductive biology of P. esculenta.