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.

Actin-binding protein drebrin E is involved in junction dynamics during spermatogenesis

“…[13][14][15] Thus, it is conceivable that there is extensive junction restructuring taking place at the cellcell interface, involving constant remodeling of the cytoskeleton to facilitate these events. [16][17][18] Interestingly, the basal ES which is found at the Sertoli-Sertoli cell interface at the site of the BTB and the apical ES which is restricted to the Sertoli cellspermatid (from step 8-19 spermatids in rats) interface, share similar ultrastructural features, that is, actin filament bundles sandwiched in between cisternae of endoplasmic reticulum and the apposing Sertoli cell or Sertoli cell-spermatid plasma membranes. 1,16,18 Earlier studies have shown that these actin filament (F-actin) bundles are maintained by actin bundling and capping proteins [e.g., epidermal growth factor receptor pathway substrate 8 (Eps8)], 19 and actin nucleation proteins [e.g., actinrelated protein 3 (Arp3) of the Arp2/3 complex].…”

“…[16][17][18] Interestingly, the basal ES which is found at the Sertoli-Sertoli cell interface at the site of the BTB and the apical ES which is restricted to the Sertoli cellspermatid (from step 8-19 spermatids in rats) interface, share similar ultrastructural features, that is, actin filament bundles sandwiched in between cisternae of endoplasmic reticulum and the apposing Sertoli cell or Sertoli cell-spermatid plasma membranes. 1,16,18 Earlier studies have shown that these actin filament (F-actin) bundles are maintained by actin bundling and capping proteins [e.g., epidermal growth factor receptor pathway substrate 8 (Eps8)], 19 and actin nucleation proteins [e.g., actinrelated protein 3 (Arp3) of the Arp2/3 complex]. 20 Interestingly, these actin-associated proteins are also known to participate in endocytic vesicle-mediated trafficking at the cell-cell interface to "stabilize" or "de-stabilize" cell adhesion protein complexes, facilitating spermatid movement.…”

Autophagy is required for ectoplasmic specialization assembly in sertoli cells

“…54,55 They therefore could not present the exogenous constriction force, and so the precise function remains controversial. 13 Autophagy is active in Sertoli cells, [26][27][28][29] and early morphology studies found that the lysosomes of the seminiferous epithelium show cyclical variations.…”

“…F-actin is packed in hexagonal arrays in the ES, while it appears as a branched network surrounding the tubular portion of TBCs. 43,55 As PDLIM1 could work as a scaffold to recruit other molecules to bind the F-actin bundles, and the binding of PDLIM1 to ACTN1 and PALLD may offer more actin binding site in a smaller volume, facilitating the F-actin interconnectivity, 9,60,61 so the accumulation of PDLIM1 may facilitate the branched F-actin network formation in TBCs rather than affecting their assembly. The disordered distribution of TBCs might be caused by the abnormal structure of apical ES or malformed sperm head, and these possibilities still need further experimental data to be distinguished in the future.…”

Actin binding proteins and spermiogenesis

“…1). As noted above, virtually all the proteins that are involved in these processes have been identified in the testis during the past decade and localized to the apical and basal ES at sites where actin filament bundles are present, 52,53 illustrating that they are involved in actin remodeling to facilitate spermiogenesis.…”