[Frontiers in Bioscience 12, 1552-1562, January 1, 2007]
Junction interaction in the seminiferous epithelium: regulatory roles of connexin-based gap junction
Nikki P. Y. Lee1, William S. B. Yeung2, and John M. C. Luk1
1 Department of Surgery, and 2 Department of Obstetrics and Gynecology, Jockey Club Clinical Research Centre, The University of Hong Kong, Pokfulam, Hong Kong, SAR, China
FIGURES
Figure 1. The intermingled relationship of AJ, TJ, and GJ in the testis. This is a schematic diagram presenting the localizations of junctions in the seminiferous tubules in the adult rat testis. Sertoli and various germ cells are found in the seminiferous tubules (ST), whereas Leydig cells (LC) situate in the inter-tubular compartments. Myoid cells are located in the peripheral area of the seminiferous tubules adjacent to tunica propria. During spermatogenesis, germ cells, such as spermatogonium, migrate from the basal compartment to the adluminal compartment, passing the blood-testis barrier (BTB), before releasing into lumens as mature spermatozoa. The movement of germ cells across the seminiferous epithelium involves rapid cell-cell associations and dissociations, which in turn activate restructuring of junctions, including GJ.
Figure 2. Morphology of the testes and junction structures of the blood-testis barrier (BTB) after treatment with pan-connexin peptide. Using pan-connexin peptide as a model, the interactive relationships of different junction types at the sites of BTB are demonstrated schematically (28). This is a speculative model based on the study using pan-connexin peptide, attempting to illustrate the BTB integrity after perturbation of the connexin structures in the testes (28). In normal rat testes, the intact epithelium contains several germ cell layers, composed of spermatogonia (SPG), preleptotene or leptotene spermatocytes (PLS), pachytene spermatocytes (PS), round spermatids (RS), and elongated spermatids (ES). BTB, physically dividing the seminiferous epithelium into adluminal and basal compartment, harbors hybrid junctions with AJ (N-cadherin-based), TJ (occludin-based), and GJ (connexin-based). After blocking GJ function by using pan-connexin peptide, multi-nucleated giant cells are generated within the seminiferous epithelium. The dysregulation of GJ concomitantly perturbs occludin-based TJ complex, leading to a subsequent elimination of occludin at the sites of BTB (indicated by the blunted arrow). At this time, most of the germ cells are lost, leaving behind the Sertoli cells, spermatogonia, and few spermatocytes in the seminiferous epithelium. However, no change in the level of N-cadherin is observed at the site of BTB. From this, it is known that occludin-based TJ is more susceptible to the depletion of connexin function in the testes. GJ, gap junction; N, Sertoli cell nucleus; SC, Sertoli cell; TJ, tight junction; TP, tunica propria; ZO, zonula occludens.