A study to assess the assembly of a functional blood-testis barrier in developing rat testes

Abstract

the blood-testis barrier (BtB) is an important ultrastructure in the seminiferous tubule of the mammalian testis that segregates the events of spermatogenesis, in particular post-meiotic germ cell development, from the harmful substances in the environment including toxicants and drugs, as well as from the unwanted hormones and biomolecules in the systemic circulation. It is known that the BtB is assembled by ~15-21 days postpartum (dpp) in rats coinciding with the onset of late cell cycle progression, namely the formation of zygotene and pachytene spermatocytes by day 15-18 dpp. this is to prepare for: (1) the differentiation/transformation of pachytene spermatocytes to diplotene and dictyate spermatocytes and (2) meiosis I and II, which take place by 23-26 and 26 dpp, respectively. Recent findings have shown spermatogonia/spermatogonial stem cells (SSC) in the tubules failed to re-initiate spermatogenesis by differentiating spermatogonia beyond type A spermatogonia in the absence of a functional BtB, leading to meiotic arrest. these studies thus illustrate that a functional BtB is crucial to the initiation and/or re-initiation of spermatogenesis. Herein, we sought to examine the precise time window when a functional and intact BtB is established in the developing rat testis during the final stage of cell cycle progression and meiosis. Using the techniques of: (1) dual-labeled immunofluorescence analysis to assess the distribution of integrated proteins at the tight junction (tJ), basal ectoplasmic specialization [basal eS, a testis-specific atypical adherens junction (AJ) type] and gap junction (GJ) at the BtB, (2) functional assay to assess the BtB integrity in vivo, (3) immunoblot analysis to monitor changes in steady-state levels of adhesion proteins at the BtB, and (4) co-immunoprecipitation to assess changes in protein-protein interactions at the BtB, it was shown that a BtB was being assembled by day 15-20 dpp, but a functional BtB was not fully established until day 25 dpp in Sprague-Dawley rats, tightly associated with the onset of meiosis I and II. these findings thus illustrate the significance of the BtB on cell cycle progression and the preparation for meiosis, such as germ cell differentiation beyond type A spermatogonia.

P-glycoprotein regulates blood–testis barrier dynamics via its effects on the occludin/zonula occludens 1 (ZO-1) protein complex mediated by focal adhesion kinase (FAK)

“…Based on the findings reported herein, although the TJ permeability barrier at the BTB after P-glycoprotein knockdown was transiently disrupted as a result of TJ protein redistribution at the BTB, the basal ES proteins N-cadherin and β-catenin, which are capable of conferring the immunological barrier, were unaffected (25). This latter finding explains the maintenance of fertility in mdr1 −/− mice (22,23), and it is also consistent with a recent study showing that an intact BTB is necessary for spermatogonial stem cell differentiation beyond type A spermatogonia to initiate spermatogenesis (26). Additionally, other efflux drug transporters that are also present in Sertoli cells (9) (SI Discussion) can likely supersede the lost function of P-glycoprotein at the BTB in the mdr1 −/− mice.…”

Prenatal and lactation nicotine exposure affects Sertoli cell and gonadotropin levels in rats

“…However, a functional BTB is not fully established until 25 dpp. This phenomenon is closely associated with the onset of meiosis I and II (Mok et al 2011). At around 60 dpp, rats are in late puberty (Stumpp et al 2006) when spermatozoa begin to be found in the epididymis (Robb et al 1978).…”

Blood–testis barrier and Sertoli cell function: lessons from SCCx43KO mice

“…They separate the seminiferous epithelium into a basal and an adluminal compartment through the formation of the blood-testis barrier (BTB) that is located around the basal third of the seminiferous tubule. This barrier is established through tight, adherens and gap junction proteins that form the so called SC-SC junctional complex with gap junctions being believed to play a vital role in its formation and dynamic regulation (Pelletier 1995, Cyr et al 1999, Mok et al 2011, Gerber et al 2014, Jiang et al 2014, Gerber 2015, Rode et al 2015.…”