Spermatogenesis is an extremely complex and tightly regulated biological process that generates streamlined sperm capable of efficient fertilization, ensuring the reproductive success of the species. Spermatogenesis consists of an orderly series of mitotic events of spermatogonia, meiosis of spermatocytes, and spermiogenesis of spermatids to form sperm. Meiosis, distinct from mitosis, is a germ cell-specific cell division that involves two consecutive meiotic divisions to eventually generate haploid spermatids. Although the molecular mechanisms of mitosis have been extensively studied—for example, phosphorylation regulation of kinases is crucial for mitotic progression—mechanistic studies of meiotic progression remain limited in mammals.

HASPIN, a serine/threonine protein kinase, is highly expressed in germ cells (Soupsana et al., 2021), particularly in spermatocytes undergoing meiosis (Li et al., 2022). A well-known function of HASPIN is to phosphorylate the ‘Thr-3′ site of histone H3 (H3T3ph) (Kelly et al., 2010; Wang et al., 2010). H3T3ph is essential for mitosis, ensuring correct chromosome arrangement and accurate cell cycle progression (Yamagishi et al., 2010). By phosphorylating H3T3, HASPIN regulates the localization and activation of chromosomal passenger complex (CPC) at the centromeres (Wang et al., 2011; Zhou et al., 2014). Additionally, HASPIN is also important for meiosis. It controls microtubule-organizing center clustering and spindle pole integrity during mouse oocyte meiosis via Aurora kinase C (AURKC) (Balboula et al., 2016). Berenguer et al. demonstrated that HASPIN is essential for chromosome alignment by facilitating Aurora B (AURKB) recruitment to centromeres during male meiosis, highlighting its role in CPC dynamics (Berenguer et al., 2022). We previously found that Haspin deletion resulted in severe chromosome misalignment, primarily through dysregulation of H3T3ph and CPC function during male meiosis (Li et al., 2022). However, the detailed mechanisms underlying HASPIN-mediated meiotic regulation remain poorly characterized.

The HASPIN protein contains a C-terminal eukaryotic protein kinase domain and two intrinsically disordered regions (IDRs) in its N-terminal region (Higgins, 2003; Villa et al., 2009). Its kinase activity can be self-inhibited by binding to a conserved HASPIN Basic Inhibitory Segment (HBIS; 339–359 aa) located adjacent to the kinase domain (Ghenoiu et al., 2013). However, the functions of its N-terminal domain still require further investigation.

In this study, we characterized the functions of the N-terminal 1-243 region of HASPIN containing the first IDR region. Deletion of this region in HaspinΔ1-243/Δ1-243 mice caused chromosome misalignment at meiotic metaphase I, decreased sperm count, and male subfertility. Co-immunoprecipitation followed by proteomic analysis showed that HASPIN interacted with AURKA, a protein essential for chromosome alignment at meiotic metaphase I (Wellard et al., 2021). In addition, quantitative phosphoproteomics profiling revealed that deletion of amino acids 1-243 of HASPIN resulted in a defect in AURKA activation through inhibition of T279 phosphorylation. The N-terminal region of HASPIN is important for meiotic progression and male fertility.