The transport of germ cells across the seminiferous epithelium is composed

The transport of germ cells across the seminiferous epithelium is composed of a series of cellular events during the epithelial cycle essential to the completion of spermatogenesis. removed by the Sertoli cell via phagocytosis to form phagosomes and be degraded by lysosomes leading to subfertility and/or infertility. However the biology of spermatid transport in particular the final events that lead to spermiation remain elusive. Based on recent data in the field we critically evaluate the biology of spermiation herein by focusing on the actin binding proteins (ABPs) that regulate the organization of actin microfilaments at the Sertoli-spermatid interface which is crucial for spermatid transport during this event. The hypothesis we put forth herein also highlights some specific areas of research Rabbit polyclonal to ACSM5. that can be pursued by investigators in the years to come. the basal ES are quite different [29 40 Apical ES appears to mechanically grasp the head of spermatids which undergo rapid elongation and maturation via spermiogenesis and to confer spermatid polarity so that the head of spermatids are pointing toward the basement membrane [20 41 On the other hand TBC consists of a cylindrical double-membrane core composed of the plasma membranes of two Glycitein adjacent cells cuffed by a network of actin microfilaments [8 30 42 (Figure 1). Basal TBC develops Glycitein between adjacent Sertoli cells which undergoes regressive changes during the epithelial cycle. Most membranous complexes arise during the early stages of the epithelial cycle at II-V and develop into large bulbous endings. At midcycle namely stages VI-VII most basal TBC display regressive changes and are eventually resorbed by Sertoli cell lysosomes. Basal TBC resorption is related to the impending breakdown of the Glycitein “old” BTB above spermatocytes as these cells are being transported upward crossing the BTB [30] (Figure 1). It is noted that basal TBC is not clustered at any specific and predictable location at the belt-like junctions somewhat difficult to distinguish from elements of other junctional complexes [43]. Since both ES and TBC are actin-based ultrastructures and the regulation of actin dynamics in unique testicular junctions are crucial to spermatogenesis we focus on actin-binding and actin regulating proteins and their relationship with actin and other proteins at the ES in this review. We also focus our discussion herein on the spermatid transport across the seminiferous epithelium utilizing the apical ES since the biology of preleptotene spermatocyte transport at the basal ES/BTB has recently Glycitein been reviewed [21 44 45 3 Actin binding proteins (ABPs) Actin is an essential component of the cytoskeleton it is found in mammalian cells including Sertoli cells in the testis existing in one of the two forms: globular monomeric actin (G-actin) and filamentous polymeric actin (F-actin) [46-50]. G-actin Glycitein is polymerized and assembled into double helices forming F-actin. F-actin also known as microfilament has inherent polarity in which the rapidly growing end is the “barbed end” and the slow growing end the “pointed end” [51] which acts as the “vehicle” to transport the “cargo” which is the spermatid. Microfilaments can be cross-linked into higher order structures of meshes bundles or composite bundled networks. These changes in the organization of the actin cytoskeleton thus confers plasticity to cells besides mechanical integrity which also induces changes in the localization of the adhesion protein complexes at the TJ such as occludin-ZO-1(zonula occludens-1) and claudin-ZO-1 apical ES such as integrin-laminin and nectin-afadin which all use F-actin for their attachment [44]. Actin re-organization also enable cells to carry out various functions including cell division motility contraction phagocytosis and endocytic vesicle-mediated protein trafficing besides conferring cell shape polarity adhesion and signal transduction [46 52 Actin dynamics are tightly regulated by over 150 actin binding proteins (ABPs) that modulate localization polymerization cleavage cross-linking and organization of microfilaments and they can be classified into two broad groups. One is proteins that regulate F-actin assembly and disassembly such as nucleation barbed end capping depolymerization and monomer-binding. The other group is proteins that regulate higher-order F-actin structures including F-actin bundling and F-actin cross-linking. Actin bundling proteins confer either parallel or antiparallel alignment of actin microfilaments and bundle F-actin into linear arrays. Some cross-linking proteins (e.g. filamin A) generate Glycitein branched arrays of actin [46.