Connexin43 gene expression and regulation in the rodent seminiferous epithelium.

Connexin43 (Cx43) is one of the most predominant gap junction proteins found in the testis. We used in situ hybridization and indirect immunofluorescence to study the distribution of Cx43 mRNA and protein in the rodent seminiferous epithelium. During mouse testis maturation, Cx43 mRNA and its corresponding protein were first detected in the adluminal compartment of the growing seminiferous tubules (early postnatal age: Day 12) to become progressively located in the basal compartment at later ages (Days 16, 19, 27). In seminiferous tubules of sexually mature animals, the intensity of the hybridization signal was stage-dependent, with a maximum at Stage VII compared with Stages V and IX of the spermatogenic cycle (p<0.05). The highest expression of Cx43 mRNA was observed in the supporting Sertoli cells and, to a lesser extent, in the most basally located and less mature germ cells (spermatogonia and spermatocytes). Consistent with these observations, in situ dye coupling was observed between Sertoli cells and basal germ cells. In a mutant mouse deficient for the retinoid X receptor beta, which exhibited abnormal spermatogenesis due to altered Sertoli cell function, Cx43 transcripts were markedly decreased in the seminiferous epithelium (p<0.01). The immunoreactive signal for Cx43 was significantly reduced in seminiferous tubules of the 3-month-old mutant mice (p<0.05) and undetectable in older animals. These data provide new information about the precise localization of Cx43 mRNA and protein in seminiferous tubules of immature and mature rodent testes. Moreover, they suggest that retinoids, through the RXRbeta receptors, could be involved in the control of Cx43 gene expression in Sertoli cells.

Modified expression of testicular gap-junction connexin 43 during normal spermatogenic cycle and in altered spermatogenesis.

In order to better understand the implications of gap junction proteins in spermatogenesis, connexin 43 (Cx43), the most abundant connexin in the testis, was evaluated in testes of wild-type mice and of two mutants with impaired spermatogenesis (ebo/ebo, and jun-d-/-mice). Reverse transcription-polymerase chain reaction (RT-PCR) amplification revealed a constitutive expression of mRNA for Cx43 in both wild-type mice and infertile mutants. In the seminiferous tubules of wild-type mice, indirect immunofluorescence revealed that Cx43 expression was stage-dependent and that the signal was mainly located in the region of Sertoli cell occluding junctions. Colocalization of Cx43 and of the tight-junction-associated protein zonula occludens 1 (ZO-1) was demonstrated in seminiferous tubules by using dual-label immunofluorescence in conjunction with confocal microscopy. The Cx43 staining analyzed by high-resolution confocal microscopy appeared as continuous, anastomozed ribbons and thin dots. The level of Cx43 immunoreactivity was reduced in seminiferous tubules of ebo/ebo and jun-d-/- mutants as compared to the respective wild-type mice. No staining for Cx43 was detected in Sertoli cell-only seminiferous tubules observed sometimes in jun-d-/- mice. The present study represents one of the first in vivo examples of alteration of seminiferous tubule Cx43 in testes with impaired spermatogenesis.

Ultrastructural and biochemical evidence for gap junction and connexin 43 expression in a clonal Sertoli cell line: a potential model in the study of junctional complex formation.

To clarify the exact role of Sertoli cells in testicular intercellular communications, a murine Sertoli cell line (42GPA9) has recently been established. Electron-microscopy studies indicate that the morphology of these immortalized cells strongly resembles that of mouse Sertoli cells in vivo with an indentend nucleus, elongated mitochondria and numerous lysosome-like structures. Ultrastructure analysis has also revealed that 42GPA9 cells form gap junctions as demonstrated by the presence of small electron-dense bridges that connect the plasma membranes of adjacent cells. The gap junction protein connexin 43 (Cx43) has been identified in cultured 42GPA9 cells by immunofluorescence and Western blot analysis. No immunostaining is detected in the absence of apparent intercellular contact. The anti-Cx43 antibody labels the contacts between 42GPA9 cells at confluency. This specific staining appears as small dots forming isolated rows of dots or surrounding the entire cell, suggesting that Cx43 is assembled into membrane plaques. The gap junctional communication capacity of the 42GPA9 cell line has been demonstrated by the dye-transfer technique. Exposure of 42GPA9 cells for 24 h to cAMP and 12-O-tetradecanoylphorbol-13-acetate greatly reduces the Cx43 staining at cell-cell contacts and concomitantly increases the cytoplasmic staining, suggesting that these agents alter the trafficking of Cx43 to the plasma membrane. Thus, the 42GPA9 line may provide a useful in vitro model for studying gap junction communication between Sertoli cells.