Fascin 1 is an actin filament-bundling protein that regulates ectoplasmic specialization dynamics in the rat testis

Abstract

is an actin filament-bundling protein that regulates ectoplasmic specialization dynamics in the rat testis.

Fascin – An actin binding and bundling protein in the testis and its role in ectoplasmic specialization dynamics

“…This postulate is supported by findings that fascin 1 is associated (and also co-localized) with actin cross-linking and bundling protein palladin (Fig. 2) and also branched actin polymerization protein Arp3 (actinrelated protein 3, which together with Arp2 forms the Arp2/3 complex that is known to induce barbed end nucleation, effectively convert an actin microfilament to a branched configuration), 8 both of which are also found in the testis, displaying similar spatiotemporal expression as of fascin 1. 36,37 In short, the concerted efforts of actin bundling proteins fascin 1 and palladin, as well as branched actin-inducing protein Arp3, thus re-organize actin filalment bundles at the ES in response the transition of epithelial cycle from VII-IX, facilitating the transport of preleptotene spermatocytes (at stage VIII) and elongated spermatids (from stage VII to early VIII) as well as the release of sperm at spermiation (at late stage VIII).…”

“…2), but considerably diminished in IX tubules. 8 This tightly regulated spatiotemporal expression at the apical and basal ES during the epithelial cycle suggests the likely involvement of fascin 1 in regulating actin bundling activity at the ES. This postulate is supported by findings that fascin 1 is associated (and also co-localized) with actin cross-linking and bundling protein palladin (Fig.…”

“…An earlier report based on studies using in situ hybridization and immunofluorescence microscopy suggest that fascin 3 is a spermatid-specific actin bundling protein in the mouse testis and it is also associated with epididymal and ejaculated spermatozoa, 12 perhaps being used in the assembly of actin filament bundles that are involved in the shaping of the spermatid head and also the acrosomeacroplaxome-manchette complex during spermiogenesis. 12 However, fascin 3 is not expressed by Sertoli cells 8,12 and spermatids and sperms are metabolically quiescent cells versus Sertoli cells. Also, apical ES is a dynamic ultrastructure at the Sertoli-spermatid interface but the actin microfilament bundles are limited to the Sertoli cell, and as such, the Sertoli cell is considered to be the major contributor of apical ES function during spermatogenesis.…”

“…Fascin 1 is expressed in multiple mammalian cells, known to be involved in inducing actin bundling 6 including Sertoli and germ cells. 8 Fascin 2 is mostly expressed in retina restricted to photoreceptors for the assembly of lamellipodial extension of photoreceptor disks, known as retinal fascin, [9][10][11] but it is also expressed in the testis by Sertoli and germ cells. 8 In contrast, fascin 3 is highly expressed in the testis, mostly in spermatids and spermatozoa, but not in Sertoli cells, 12 and it is called testis fascin.…”

“…8 Fascin 2 is mostly expressed in retina restricted to photoreceptors for the assembly of lamellipodial extension of photoreceptor disks, known as retinal fascin, [9][10][11] but it is also expressed in the testis by Sertoli and germ cells. 8 In contrast, fascin 3 is highly expressed in the testis, mostly in spermatids and spermatozoa, but not in Sertoli cells, 12 and it is called testis fascin. Based on these findings, it is likely that fascin 3 is used for the assembly of actin filament-rich ultrastructures surrounding the spermatid nucleus 13 and the acrosome-acroplaxome-manchette complex 14,15 during spermiogenesis 12 since these ultrastructures require rapid but precise organization of actin filaments for their assembly during spermatogenesis.…”