Role of microtubule plus TIPs and -TIPs in spermatogenesis - Insights from studies of toxicant models

During spermatogenesis, preleptotene spermatocytes and haploid spermatids, lacking lamellipodia and filopodia to initiate cell movement per se, but rely on Sertoli cells for transport across the blood-testis barrier (BTB) and the adluminal compartment of the seminiferous epithelium, respectively. Tracks provided by microtubules (MTs) that lay across the epithelium are essential to support germ cell and other cargo transports, but the mechanism(s) remain elusive. Studies have provided insightful information through the use of toxicant models. Herein, we summarize findings based on studies of the microtubule plus (+)-end tracking proteins (+ TIPs) and the microtubule minus (-)-end targeting proteins (-TIPs), at the corresponding plus (+)-end and minus (-)-end of the polarized MTs in rat testes. We also provide a model by which + TIPs and -TIPs that work in concert with microtubule-associated proteins (MAPS; e.g., MAP-1a), MARKs (microtubule affinity-regulating kinases), and microtubule-specific motor proteins (e.g., dynein 1) to support germ cell and cargo transports. This thus provides a framework to design experiments for future studies.