Cytoskeletal dynamics and spermatogenesis

Abstract

Different cellular events occur during spermatogenesis, and these include (i) mitosis for self-renewal of spermatogonia, (ii) differentiation of type A spermatogonia into type B and commitment of type B spermatogonia to develop into preleptotene primary spermatocytes, (iii) transit of preleptotene/leptotene spermatocytes across the blood-testis barrier in coordination with germ cell cycle progression and meiosis, (iv) spermiogenesis and spermiation. These events also associate with extensive changes in cell shape and size, and germ cell movement. The cytoskeleton, which comprises actin, microtubules and intermediate filaments, is believed to function in these cellular events. However, few studies have been conducted by investigators in the past decades to unfold the role of the cytoskeleton during spermatogenesis. This review summarizes recent advances in the field relating to cytoskeletal dynamics in the testis, and highlights areas of research that require additional emphasis so that new approaches for male contraception, as well as therapeutic approaches to alleviate environmental toxicant-induced reproductive dysfunction in men, can possibly be developed.

Figure 1.

A schematic drawing to illustrate the organization of F-actin and microtubules (MTs) in Sertoli cells in the seminiferous epithelium and their possible crosstalk during spermatogenesis. F-actin is abundantly found at sites of cell–cell contact, including the basal ES and TBC at the BTB formed between Sertoli cells, and the apical ES and TBC at the Sertoli cell–spermatid interface. Actin filaments found at the ES and the TBC are arranged in a different manner, being packed in hexagonal arrays in the ES, but exist as a branched network at the TBC. MTs run vertically in parallel to the longitudinal axis of Sertoli cells with their minus ends pointing apically. The translocation of the apical ES in both directions in the seminiferous epithelium is proposed to be mediated by MT-based motors using MTs as tracks. Based on studies in other epithelial cells, MT minus ends may interact with junction protein complexes at the apical ES.

Figure 2.

Co-localization of Eps8 and F-actin in Sertoli cells cultured in vitro. Sertoli cells isolated from 20-day-old rat testes were cultured on Matrigel-coated glass coverslips for 4 days at 0.04 × 10⁶ cells cm⁻². Eps8 (green) and F-actin (red) were visualized with an anti-Eps8 antibody and rhodamine conjugated phalloidin, respectively. Sertoli cell nuclei were visualized by DAPI (blue). Eps8 is concentrated at the cell–cell interface, co-localizing with the tips of cortical F-actin. Orderly bundles of actin filaments are also found inside the Sertoli cell. Scale bar, (a) 20 µM, which applies to (b) and (c).