Surfing the wave, cycle, life history, and genes/proteins expressed by testicular germ cells. Part 5: Intercellular junctions and contacts between germs cells and Sertoli cells and their regulatory interactions, testicular cholesterol, and genes/proteins associated with more than one germ cell generation

Abstract

In the testis, cell adhesion and junctional molecules permit specific interactions and intracellular communication between germ and Sertoli cells and apposed Sertoli cells. Among the many adhesion family of proteins, NCAM, nectin and nectin-like, catenins, and cadherens will be discussed, along with gap junctions between germ and Sertoli cells and the many members of the connexin family. The blood-testis barrier separates the haploid spermatids from blood borne elements. In the barrier, the intercellular junctions consist of many proteins such as occludin, tricellulin, and claudins. Changes in the expression of cell adhesion molecules are also an essential part of the mechanism that allows germ cells to move from the basal compartment of the seminiferous tubule to the adluminal compartment thus crossing the blood-testis barrier and well-defined proteins have been shown to assist in this process. Several structural components show interactions between germ cells to Sertoli cells such as the ectoplasmic specialization which are more closely related to Sertoli cells and tubulobulbar complexes that are processes of elongating spermatids embedded into Sertoli cells. Germ cells also modify several Sertoli functions and this also appears to be the case for residual bodies. Cholesterol plays a significant role during spermatogenesis and is essential for germ cell development. Lastly, we list genes/proteins that are expressed not only in any one specific generation of germ cells but across more than one generation.

Cellular mechanisms regulating sperm–zona pellucida interaction

“…The majority of these changes occur during the final phase of cytodif-ferentiation, spermiogenesis, and are accompanied by protamine packaging of the DNA. Significantly, this latter event also results in silencing of the sperm's transcriptional machinery [9][10][11][12][13] .…”

Testicular connexin 43, a precocious molecular target for the effect of environmental toxicants on male fertility

“…At puberty, Cx43 is localized in the interstitial compartment, between Leydig cells, and also highly intermingled with proteins of tight and anchoring junctions between Sertoli cells at the level of the BTB 12,47,48 and between Sertoli cells and germ cells: spermatogonia and spermatocytes. 49 During the first wave of spermatogenesis, the levels of Cx43 protein measured in the seminiferous tubules increase.…”

Gene knockouts that affect Sertoli cell function

“…Phagocytosis is an important function of Sertoli cells, which are responsible for clearing apoptotic male germ cells during spermatogenesis and digesting cytoplasmic contents (i.e., residual body) shed by spermatozoa upon spermiation [1]. Increasing lines of evidence also suggest that Sertoli cell phagocytosis may target more than the two types of cells or cellular structures because developing male germ cells produce numerous vesicles containing unwanted or recyclable materials that can be phagocytized by Sertoli cells for processing and recycling [107].…”

“…Sertoli cells are functionally versatile because they not only provide physical, nutritional, and metabolic support to developing male germ cells, but they also direct and coordinate the complex spermatogenic program via endocrine (e.g., production of inhibin) and paracrine (e.g., secretion of growth factors and cytokines) mechanisms [1,2]. Consistent with the multitasking nature of Sertoli cells, the Sertoli cell transcriptome has been defined as abundant and dynamic [3,4].…”