$$\rightleftharpoonup{xx}$$
$$\longleftharp{xx}$$,
$$\longrightharp{xx}$$,
Meiosis is one of the most important, highly rigid, evolutionary conserved events in eukaryotic organisms, and is essential for gametogenesis, sexual reproduction, genome integrity, and genetic diversity1,2,3. In mammals, the germ cells undergo two successive cell divisions, meiosis I and II, after a single round of DNA replication. Unlike sister chromatids in mitosis, duplicated homologous chromosomes pair up and segregate into two daughter cells during meiosis I4,5. In meiosis II, sister chromatids pull apart and segregate to form haploid gametes without DNA replication6. Mistakes in either of the two meiotic divisions, including spindle assembly defects and chromosome missegregation, can result in the loss of gametes, sterility or aneuploidy syndromes7,8,9.
Accumulating studies have shown that kinesin family motors play a crucial role in the regulation of chromosome alignment and segregation, spindle assembly, cytokinesis, and cell cycle progression in both mitotic and meiotic cells10,11,12. Kinesin-7 CENP-E (Centromere protein E) is a plus-end-directed kinetochore motor required for chromosome congression, chromosome transport and alignment, and the regulation of spindle assembly checkpoint in mitosis13,14,15,16,17,18. During meiosis, CENP-E inhibition by the specific inhibitor GSK923295 leads to cell cycle arrest, chromosome misalignment, spindle disorganization, and genome instability in spermatogenic cells19. The localization patterns and dynamics of CENP-E at the centromeres of dividing spermatocytes indicate that CENP-E interacts with kinetochore proteins for the sequential assembly of centromeres during meiosis I20,21. In oocytes, CENP-E is required for chromosome alignment and the completion of meiosis I13,22,23. Antibodies or morpholino injection of CENP-E results in misaligned chromosomes, abnormal kinetochore orientation, and meiosis I arrest in both mouse and Drosophila oocytes23. Compared with the essential roles of CENP-E in mitosis, the functions and mechanisms of CENP-E in meiosis remain largely unknown. Detailed mechanisms of CENP-E in chromosome congression and genome stability in male meiotic cells remain to be clarified.
Spermatogenesis is a complex and long-lasting physiology process, involving sequential spermatogonia proliferation, meiosis and spermiogenesis. Therefore, the whole process is extraordinarily difficult to be reproduced in vitro in mammals and other species24,25. It is impossible to induce spermatocytes differentiation after the pachytene stage in vitro. Studies on male meiotic divisions have been generally limited to experimental analyses of early meiotic prophase25,26. Despite many technological endeavors, including short-term culture of spermatocytes27,28 and organ culture methods25, there are few effective methods to study male meiotic division. Furthermore, genetic deletion of essential genes usually results in developmental arrest and embryonic lethality. For example, mouse embryos lacking CENP-E fail to implant and cannot develop past implantation29, which is an obstacle in mechanistic studies of CENP-E in meiosis. Taken together, establishing a practical and feasible system to study male meiotic division can greatly promote the research field of meiosis.
The small cell-permeable inhibitor is a powerful tool to study kinesin motors in cell division and developmental processes. The allosteric inhibitor, GSK923295, specifically binds to CENP-E motor domain, blocks the release of ADP (adenosine diphosphate), and finally stabilizes the interactions between CENP-E and microtubules30. In this study, an in vivo inhibition mouse model is presented through abdominal surgery and testicular injection of GSK923295. CENP-E inhibition results in chromosome misalignment in metaphase I of primary spermatocytes. Furthermore, CENP-E inhibition leads to meiotic arrest of spermatocytes and the disruption of spermatogenesis. A series of protocols are described for the analyses of spermatocytes and can be applied to observe meiotic spindle microtubules, homologous chromosomes, and subcellular organelles in spermatocytes. Our in vivo inhibition method is an effective method for the studies of meiotic division and spermatogenesis.