Seasonal Changes in Spermatogenesis and Immunolocalization of Inhibin/Activin Subunits in the Wild Male Ground Squirrel (<i>Citellus dauricus Brandt</i>)

Abstract

Abstract. The objective of this study was to investigate the seasonal changes in spermatogenesis and the immunolocalization of the inhibin α and inhibin/activin (βA and βB) subunits during the breeding and non-breeding seasons in the wild male ground squirrel. The testicular weight and size and seminiferous tubule diameter were measured, and histological observations of testes were performed. The sections of the testes were immunostained by the avidin-biotin-peroxidase complex method (ABC) using polyclonal antisera raised against porcine inhibin α, inhibin/activin βA and inhibin/activin βB during the breeding and non-breeding seasons. There were marked variations in testicular weight and size and seminiferous tubule diameter between the breeding and non-breeding seasons, and all types of spermatogenic cells, including spermatozoa, were found in the breeding season. In addition, immunoreactivity was also detected for the inhibin α, βA and βB subunits in Sertoli and Leydig cells during the breeding season, but immunostaining was only present for the inhibin α and inhibin/activin βB subunits in Sertoli cells during the non-breeding season. These results suggest that seasonal changes in testicular weight and size and seminiferous tubule diameter of wild ground squirrels are correlated with changes in spermatogenesis, and the cellular localization of the inhibin/activin subunits showed season related changes in the breeding and non-breeding seasons. Key words: Ground squirrel (Citellus dauricus Brandt), Immunohistochemistry, Inhibin, Spermatogenesis, Testis (J. Reprod. Dev. 54: [460][461][462][463][464] 2008) he inhibin/activin subunits are members of the transforming growth factor β (TGF β) superfamily. They are produced in the testes and are postulated to have paracrine and autocrine roles in the regulation of steroidogenesis and spermatogenesis in addition to endocrine regulatory effects on FSH secretion [1][2][3][4]. Inhibin consists of an α subunit linked by a disulfide bridge to one of the 2 highly homologous β subunits (βA and βB) to form inhibin A (α and βA) or inhibin B (α and βB) [5]. In the male, inhibin is produced in the testis, principally by Sertoli cells. The various inhibin/activin subunits have been localized in testes as messenger RNA and proteins. The expression of mRNA in Sertoli cells varies with the stage of the seminiferous cycle [6], with differences between the various subunits possibly reflecting differential production of activin and inhibin [7]. Some seasonal male breeders, such as stallions [5,8,9], rams [10] and Japanese monkeys [11][12][13], show seasonal changes in circulating inhibin concentrations in accordance with testicular activity. Furthermore, in Japanese black bears [14] and raccoon dogs [15], there are temporal changes in inhibin expression and secretion with the changing role of Sertoli cells in the breeding and non-breeding seasons.The wild male ground squirrel (Citellus dauricus Brandt) is a typical seasonal breeder with a short sexually active period in April and May ...

Immunolocalization of Inhibin/Activin Subunit Proteins During the Breeding Season in Testes and Scented Glands of Muskrats (Ondatra zibethicus)

“…These findings are not unique to the muskrats, as similar observations had been found in other seasonal breeders, such as rams [15], Japanese black bears [31], raccoon dogs [32], ground squirrels [21] and stallions [16]. In rams, the presence of mRNA and protein of all three inhibin/activin subunits in adult testes was confirmed by Northern blot analysis and immunocytochemistry, respectively, showing that the testes could produce and secrete dimeric inhibin during the reproductive cycle [15].…”

“…In rams, the presence of mRNA and protein of all three inhibin/activin subunits in adult testes was confirmed by Northern blot analysis and immunocytochemistry, respectively, showing that the testes could produce and secrete dimeric inhibin during the reproductive cycle [15]. In our studies on seasonal breeders [21,31,32], positive staining for inhibin α, β A and β B was observed in both Sertoli and Leydig cells in the breeding season, suggesting that Sertoli and Leydig cells of these seasonal breeders could secrete bioactive inhibins and activins in the breeding season. Previous studies suggested that inhibin/activin subunits might play some important roles in spermatogonial development [13,28], such as Sertoli cell proliferation [2] and steroid biosynthesis [5,6,14].…”

“…The control sections were treated with normal rabbit serum (Sigma, St. Louis, MO, U.S.A.) instead of the primary antisera. The specificity of the inhibin  and inhibin/activin ( A and  B ) subunits has been described for rat [17] and golden hamster testes [10] and for wild ground squirrels [21].…”

Immunohistochemical Localization of Inhibin/Activin Subunits in the Wild Ground Squirrel (<i>Citellus dauricus brandt</i>) Ovary

“…The control sections were treated with normal rabbit serum (Sigma) instead of the primary antisera. The specificity of inhibin α and inhibin/activin β A and β B subunit antibodies has been described for several wild rodents before, including the wild ground squirrel [16] and muskrat (Ondatra zibethicus) [20]. …”

“…The wild ground squirrel (Citellus dauricus Brandt) is a typical seasonal breeder with a short sexually active period in April and May, followed by a long period of sexual dormancy from June to the following March [15]. Previously, we have detected the immunoreactivity of inhibin/activin subunits, activin type II receptor, activin-related SMADs and steroidogenic enzymes (P450c17 and P450arom) in the testis of the wild ground squirrel and revealed an important paracrine role of the activin signal in seasonal spermatogenesis [16][17][18]. The present study aimed to investigate the immunoreactivity of inhibin/activin subunits in the ovarian recrudescence and regression during the breeding and nonbreeding seasons, and to explore the potential roles of the most substantial ovarian peptide hormones in the seasonal folliculogenesis of the wild ground squirrel.…”