Reproduction Abstracts

Introduction: The blood–testis barrier (BTB) remains semi-permeable to tracers of increasing molecular weight in an adult rat model of spermatogenic re-initiation. Complete closure of the BTB occurred when steps 2–7 round spermatids re-appeared in the epithelium, and coincided with the localisation of a new tight junction (TJ) protein claudin-12 (Cldn12) at the BTB. We hypothesise that meiotic and/or post-meiotic germ cells up-regulate Sertoli cell TJs, and aim to demonstrate isolated germ cells stimulate TJs in rat Sertoli cells in vitro.

Material and methods: Sertoli cells (d20) were cultured for 5 days, and then pachytene spermatocytes (PSC) or round spermatids (rST) were added in co-culture for 24 h. TJs were monitored by trans-epithelial electrical resistance (TER). Clnd11 and Cldn12 were examined by qPCR and immunofluorescence.

Results and discussion: TER increased two- to 2.7-fold with added PSC or rST to Sertoli cells, but only when cells were in direct contact. Tight junction protein Cldn11 mRNA expression decreased two- to 2.2-fold whilst Cldn12 expression was up-regulated 1.5- to 2.4-fold by germ cells. Cldn11 protein localisation was largely unaffected by germ cells, however Cldn12 localisation was intensely present at cell junctions when germ cells were added. This data provides strong evidence that an extra group of TJ proteins, in addition to the androgen-dependent claudins (Cldn11 and Cldn3) exist in rat Sertoli cells and are up-regulated by meiotic and post-meiotic germ cells. This data suggests a new mechanism by which BTB function may be regulated in normal spermatogenesis, of likely importance in diseases or conditions which impact these germ cell types.