Expression and distribution of CD151 as a partner of alpha6 integrin in male germ cells

Abstract

The physiological importance of CD151 tetraspanin is known from somatic cells and its outside-in signalling through integrins was described. In male germ cells, two tetraspanins, CD9 and CD81, are involved in sperm-egg membrane fusion, and similarly to integrins, they occupy characteristic regions. We report here on a newly discovered presence of CD151 in sperm, and present its expression and distribution during spermatogenesis and sperm transition during the acrosome reaction. We traced CD151 gene and protein expression in testicular cell subpopulations, with strong enrichment in spermatogonia and spermatids. The testicular and epididymal localization pattern is designated to the sperm head primary fusion site called the equatorial segment and when compared to the acrosome vesicle status, CD151 was located into the inner acrosomal membrane overlying the nucleus. Moreover, we show CD151 interaction with α6 integrin subunit, which forms a dimer with β4 as a part of cisprotein interactions within sperm prior to gamete fusion. We used mammalian species with distinct sperm morphology and sperm maturation such as mouse and bull and compared the results with human. In conclusion, the delivered findings characterise CD151 as a novel sperm tetraspanin network member and provide knowledge on its physiology in male germ cells.CD151 belongs to the tetraspanin superfamily, these proteins participate in many biological processes such as growth control, intracellular signalling, cell adhesion, migration, motility 1-4 and they also take place in pathogenesis of some human diseases 5,6 . Tetraspanins create a scaffolding multiprotein network in the membrane that anchors other proteins into specific domains with precise functions and moreover, they are indispensable players in the mammalian fertilization process. Tetraspanin CD9 expressed on mouse eggs is considered as an essential molecule for successful gamete fusion 7-9 as well as tetraspanin CD81 which is also involved in fertilization 10,11 . Our previous studies concerning species-specific traits of CD9 and CD81 in mouse, bull and porcine gametes during their functional maturation and fertilization, suggested the active participation of tetraspanins in these events [11][12][13][14] . With the ability of tetraspanins being part of signalling cascades involving cytoskeleton 5,15,16 they also play a crucial role in the organization of functional membrane protein cluster domains called a tetraspanin web, which were also described in oocyte and recently in sperm. The integral part of the tetraspanin web are integrins and the presence of α3β1, α6β1 and α6β4 integrins was shown in sperm [17][18][19][20] . Importantly, in somatic cells, tetraspanin CD151 was found to play a key role in regulating the adhesion strengthening of integrin α6β1 21 . CD151 has previously been linked with human gamete fusion 22 , associates specifically with α3, α6 and α7 integrins 1,3,23 and links α3β1 and α6β1 integrins to other tetraspanins, including CD9 [24][25][26][27] . Based on that knowledge we p...

Genetic instability and anti-HPV immune response as drivers of infertility associated with HPV infection

“…The equatorial segment (the EqS) of mammalian sperm is the site for sperm-egg fusion initiation, and the organizing center for assembly of molecular complexes required for gamete interaction and fusion. Sperm-egg membrane fusion involves three tetraspanins, CD9 and CD81 and, as lately discovered, also CD151 forming a novel tetraspanin network [ 51 ]. CD151 is highly expressed in the basal layers of cervical mucosa, where epithelial cells come into direct contact with the basement membrane.…”

“…The testicular and epididymal localization pattern is specifically enriched in the EqS as the primary sperm head fusion site. Prior to gamete fusion, CD151 interacts with α6 integrin subunit, which forms a dimer with β4 as a part of cis-protein interactions within sperm [ 51 ].…”

Tetraspanins, More than Markers of Extracellular Vesicles in Reproduction

“…Studies by van Niel et al [ 71 ] and Chairoungdua et al [ 72 ] indicated that tetraspanins may be crucial players in ESCRT-independent pathways of exosome biogenesis and secretion. It is well known that tetraspanins can modulate membranes by affecting their curvature [ 73 , 74 , 75 , 76 ], which directly predetermines their participation in EV formation. Considering the reversed cone-like molecular shape of CD9, Umeda et al [ 74 ] suggested that clustering of tetraspanin molecules could modulate membrane curvature to enable exosome budding and facilitate subsequent interaction of the C-terminal region of tetraspanins (cytoplasmic tail) with cytoskeletal actin through ezrin, radixin and moesin proteins [ 77 ], which may be involved in EV fission from the parent cell membrane.…”

αV Integrin Expression and Localization in Male Germ Cells

“…Within the oocyte tetraspanin web, integrins associate with members of the tetraspanin protein family and mediate mutual associations [5,6]. An analogous system is predicted to occur with sperm and CD9, CD81 [7,8], and CD151 [9]. αV integrin is also proposed to be involved in the formation of a multimolecular network [7][8][9][10].…”

“…An analogous system is predicted to occur with sperm and CD9, CD81 [7,8], and CD151 [9]. αV integrin is also proposed to be involved in the formation of a multimolecular network [7][8][9][10]. The αV integrin recognizes ligands with the arginine-glycine-aspartic Int.…”