Located in the BTB inside the rat testis (Kaitu’u-Lino et al., 2007). As a result, substantially work is required to define the function(s) of unique claudin(s) inside the cyclic restructuring events of the BTB in the course of spermatogenesis. 2.1.two. Occludin–Occludin is definitely the very first integral membrane protein identified in the TJ (Furuse et al., 1993). Although occludin shares a similar topography with claudins by having 4 transmembrane domains, two extracellular loops plus a cytoplasmic tail, there’s no sequence homology among the two TJ proteins (Cummins, 2012; Furuse et al., 1998). In contrast to claudins, which are composed of several members within the mAChR5 manufacturer claudin gene household, no occludin-related gene has been identified therefore far, but two occludin isoforms are created by option IL-6 Molecular Weight splicing. Also, in contrast to claudins, occludin features a relative lengthy cytoplasmic tail. Ser and Thr residues of its cytoplasmic tail are heavily phosphorylated; and research have shown that phosphorylations at these web sites via protein kinases are essential for regulating occludin localization and distribution in epithelia/endothelia. As an example, a study making use of key Sertoli cell cultures in vitro has demonstrated that focal adhesion kinase (FAK) is structurally connected with occludin and additionally, it regulates the structural interaction amongst occludin and ZO-1 (Siu et al., 2009a, 2009b). Additionally, a knockdown of FAK in Sertoli cells led to a reduce in phosphorylation of Ser and Tyr, but not Thr in occludin, which, in turn, possibly resulted in an increase within the internalization of occludin, thereby perturbing the TJ barrier (Siu et al., 2009a). Apart from FAK, c-Yes is another nonreceptor protein tyrosine kinase known to become structurally associated with occluding in the Sertoli cell BTB (Xiao et al., 2011). When the intrinsic activity of c-Yes in Sertoli cells with an establishedInt Rev Cell Mol Biol. Author manuscript; accessible in PMC 2014 July 08.Mok et al.Pagefunctional TJ-permeability barrier that mimicked the BTB in vivo was inhibited by SU6656, a selective c-Yes inhibitor, redistribution of occludin from cell ell interface to cell cytosol was identified, contributing for the disruption on the Sertoli cell TJ barrier (Xiao et al., 2011). In addition to FAK and c-Yes, protein kinase C (PKC) also plays a function in modulating the localization of occludin at TJs by means of its effects to confer the phosphorylation status in occludin. Study reported that upon stimulation of PKC by phorbol 12-myristate 13-acetate (PMA) and 1,two dioctanoylglycerol (DiC8), phosphorylation of occludin was induced, leading to a rise in occludin localization at the cell ell interface (Andreeva et al., 2001). The importance of occludin in spermatogenesis was also addressed by studies making use of synthetic occludin peptide. It was demonstrated that when occludin ccludin interaction amongst adjacent Sertoli cells was disrupted through intratesticular injection of peptide corresponding to a segment of the second extracellular loop of occludin, the BTB was compromised, leading to germ cell loss from the epithelium (Chung et al., 2001). Interestingly, when occludin was deleted, occludin knockout mice remained fertile by age six weeks at the time the initial wave of spermatogenesis occurred (Saitou et al., 2000). Nevertheless, these occludin knockout mice have been found to be infertile by 400 weeks of age, with their seminiferous tubules displayed atrophy and devoid of germ cells (Saitou et al., 2000). Subsequent research by producing a further genetic model of occludin knockdo.