A Sertoli Cell-Specific Knockout of Connexin43 Prevents Initiation of Spermatogenesis

Abstract

The predominant testicular gap junctional protein connexin43 (cx43) is located between neighboring Sertoli cells (SCs) and between SCs and germ cells. It is assumed to be involved in testicular development, cell differentiation, initiation, and maintenance of spermatogenesis with alterations of its expression being correlated with various testicular disorders. Because total disruption of the cx43 gene leads to perinatal death, we generated a conditional cx43 knockout (KO) mouse using the Cre/loxP recombination system, which lacks the cx43 gene solely in SCs (SCCx43KO), to evaluate the SC-specific functions of cx43 on spermatogenesis in vivo. Adult SCCx43KO(-/-) mice showed normal testis descent and development of the urogenital tract, but testis size and weight were drastically lower compared with heterozygous and wild-type littermates. Histological analysis and quantitation of mRNA expression of germ cell-specific marker genes revealed a significant reduction in the number of spermatogonia but increased SC numbers/tubule with only a few tubules left showing normal spermatogenesis. Thus, SC-specific deletion of cx43 mostly resulted in an arrest of spermatogenesis at the level of spermatogonia or SC-only syndrome and in intratubular SC clusters. Our data demonstrate for the first time that cx43 expression in SCs is an absolute requirement for normal testicular development and spermatogenesis.

Connexin 43 is critical to maintain the homeostasis of the blood–testis barrier via its effects on tight junction reassembly

“…Because maturation of spermatogenesis requires the establishment of BTB along with differentiation of Sertoli cells, normal spermatogenesis cannot take place in the absence of a functional BTB. A malfunctioning BTB thus leads to infertility or reduced fertility in rodents and humans (18,(20)(21)(22). This postulate is further supported by the findings in claudin-11 −/− mice (claudin-11 is an integral membrane protein at the BTB) wherein Sertoli cells in claudin-11 −/− mice are similarly found to be proliferating and sloughed off into the lumen (23).…”

“…These findings are also supported by the phenotypes observed in mice and humans with lower levels of Cx43. Adult Sertoli cellspecific Cx43 knockout (SC-Cx43 KO) mice displayed spermatogenic arrest at the spermatogonial level (18,19). Sertoli cells were found to undergo mitotic proliferation without differentiation and sloughing of Sertoli cell clusters can be found at the lumen of the seminiferous tubule (18).…”

“…Adult Sertoli cellspecific Cx43 knockout (SC-Cx43 KO) mice displayed spermatogenic arrest at the spermatogonial level (18,19). Sertoli cells were found to undergo mitotic proliferation without differentiation and sloughing of Sertoli cell clusters can be found at the lumen of the seminiferous tubule (18). In humans, testes with Sertoli cell only syndrome or spermatogenic arrest at the spermatogonial level in infertile men were also correlated with lower levels of Cx43 in seminiferous tubules (20,21).…”

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

“…Furthermore, it has been verified in numerous publications that the lack of even a single junctional protein localised at the BTB results in distinct testicular phenotypes and mostly causes sterility; see also Table 1 for more details (Reaume et al 1995, Gow et al 1999, Juneja et al 1999, Saitou et al 2000, Brehm et al 2007, Sridharan et al 2007, Weider et al 2011a,b, Chojnacka et al 2012, Giese et al 2012, Gerber et al 2014, Jiang et al 2014, 2015, Gerber 2015, Noelke et al 2015. It may also be mentionable in this context that it was reported in different studies that BTB components may act as early targets of environmental and reproductive toxicants mostly leading to testicular disorders (Defamie et al 2001, Sobarzo et al 2006, 2009, Li et al 2009a, Salian et al 2009, Pointis et al 2011.…”

“…This process is believed to coincide with the termination of SC proliferation and their functional maturation. The direct cell-cell interactions within the seminiferous tubules are mainly dependent upon tight, adherens, and gap junctions as these different junction types have been identified and located between SC (Cyr et al 1999, Mruk & Cheng 2004, Brehm et al 2007, Sridharan et al 2007, Weider et al 2011a, Gerber et al 2014, Gerber 2015, Noelke et al 2015.…”