Immunostainable Inhibin Subunits Are in Multiple Types of Testicular Cells*

Abstract

Immunostainable inhibin alpha-subunit has been demonstrated in rat testes in a pattern consistent with localization in Sertoli cells. In the present study the distribution of alpha-subunit immunostaining was compared to those of beta-A- and beta-B-subunits. Immunostaining of alpha-subunit was present in the seminiferous epithelium of fetal, neonatal, pubertal, and adult rats as well as in Sertoli cells in culture. The distribution of inhibin beta-B-subunit immunostaining in this epithelium was consistent with Sertoli cell localization similar to that of the alpha-subunit. The predominant staining with antibodies against the beta-A-subunit was in nuclei of immature germ cells around the periphery of each seminiferous tubule. The most probable localization of this staining was in the nuclei of pachytene and zygotene spermatocytes. Specific immunostaining with beta-A-subunit antiserum was also evident in the seminiferous epithelium adjacent to the tubular lumen. Immunoreactive alpha- and beta-A-subunit staining was present in a Leydig cell line, and beta-A immunoreactivity was present in interstitial cells of neonatal rat testes. After hypophysectomy, inhibin alpha-subunit immunostaining decreased, beta-A-subunit staining did not change, and beta-B-subunit staining increased. We conclude that immunoreactive inhibin subunits are present in multiple cells in the testis and that the amounts of immunostainable subunits in the seminiferous epithelium are differentially regulated.

Regulated production of activin A and inhibin B throughout the cycle of the seminiferous epithelium in the rat

“…Activin A is particularly associated with the Sertoli cells, but meiotic and postmeiotic germ cells also appear to contain activin b A immunoreactivity. Staining of b A in both Sertoli cells and in spermatogenic cells previously has been identified using rabbit polyclonal antibodies raised against b A synthetic peptides on frozen sections of adult rat testes (Roberts et al 1989, Shaha et al 1989, while b A mRNA has been localised to Sertoli cells, spermatocytes and spermatids (Kaipia et al 1992, Buzzard et al 2004. Both the expression of mRNA in these earlier studies and the release of activin A by tubule cultures observed in the present study were cyclic.…”

“…Whether this is due to the synthesis of activin A by these cell types themselves or uptake of activin A secreted from the Sertoli cells or from the circulation remains to be determined. Previous studies have not reported significant interstitial tissue b A staining in the adult testis (Roberts et al 1989, Shaha et al 1989, Majdic et al 1997, but it should be noted that both macrophages and mast cells produce activin A in other tissues (Erämaa et al 1992, Cho et al 2003 and may be important sources in the testis as well.…”

“…In addition, the cellular distribution of the b A -subunit of activin A was investigated using immunohistochemistry on whole testis sections. Immunohistological localisation of the inhibin B subunits in the testis of adult rats has been performed by several groups previously (Merchenthaler et al 1987, Roberts et al 1989, Shaha et al 1989, Majdic et al 1997 and was not repeated in the present study.…”

Follistatin-like immunoreactivity in the cytoplasm and nucleus of spermatogenic cells in the rat

“…The possibility still remains that follistatin is produced in Sertoli cells and then rapidly taken up by spermatocytes. In previous studies, the immunoreactive bA subunit of inhibin/activin has been detected in the cytoplasm (35) and the nucleus of spermatogenic cells (36). It is, therefore, conceivable that follistatin binds to activin in the cytoplasm and nucleus of spermatogenic cells.…”

Paracrine regulation of cellular interactions in the testis: factors in search of a function

“…The expression, processing and combination of at least four gene products (a-subunit, bA-subunit, bB-subunit and follistatin as binding protein) thus mediate the response. Most of the testicular cells produce all or at least several of these effectors (99,100). The expression and secretion of inhibin subunits is dependent on the spermatogenic cycle (101,102).…”