Seasonal Changes in Immunoreactivity of Activin Signaling Component Proteins in Wild Ground Squirrel Testes

Abstract

Abstract. The seasonal spermatogenesis and localization of inhibin/activin subunits (alpha, betaA, betaB) in the testes of wild ground squirrel has been previously described; however, the expression pattern of activin receptors and cytoplasmic signaling SMADs has not been detected in any seasonal breeders. The objective of this study was to investigate the abundance and cellular localization of activin signaling components in testes of the wild ground squirrel during the breeding and nonbreeding seasons. The immunolocalizations of ActRIIB (activin type II receptor B) and activin-related SMADs (phospho-SMAD2/3, SMAD4 and SMAD7) were observed by immunohistochemistry. Total proteins were extracted from testicular tissues in the breeding and nonbreeding seasons and were used for Western blotting analysis for ActRIIB and SMADs. Immunoreactivities of activin signaling components were greater in the testes of the breeding season, and then decreased to a relatively low level in the nonbreeding season. ActRIIB and related SMADs were widely spread in the active testes, while spermatogonia were the predominant cellular sites of activin signal transduction during arrested spermatogenesis. The dynamic regulation of activin type II receptor and SMADs indicated that the activin signal pathway played an important paracrine role in seasonal spermatogenesis of the wild ground squirrel. Furthermore, the distinct localizations and immunoreactivity of ActRIIB and SMADs might suggest different functions of activin in seasonal spermatogenesis. . Seasonal changes of testicular function and spermatogenesis in wild animals are governed by the influence of many growth factors, including members of the transforming growth factor β (TGF-β) superfamily, which is defined as a group of over 40 ligands, such as TGF-βs, inhibins and activins, bone morphogenetic proteins (BMPs), Müllerian inhibiting substance (MIS) and growth and differentiation factors (GDFs) [2].Ligands of the TGF-β superfamily control many aspects of cell physiology through conserved signal transduction pathways [3]. Activin, which acts through two transmembrane serine/threonine kinases receptors, a type II receptor (ActRIIA or ActRIIB) and a type I receptor (ALK4 or ALK7), displays a high affinity for the type II receptors and does not interact with the isolated type I receptor [4,5]. Assembly and activation of the heteromeric receptor complex results in phosphorylation of the intracellular transducers of the activin signal, the SMAD proteins [6]. SMADs exist as three subgroups: the receptor-regulated SMADs (R-SMADs), the common SMAD (co-SMAD) and the inhibitory SMADs (ISMADs). Activin binds tightly to the ectodomain of the type II receptor first; this binding allows the subsequent incorporation of the type I receptor, forming a large ligand-receptor complex involving a ligand dimer and four receptor molecules. Thereafter, the phosphorylated receptors stimulate R-SMADs (SMAD2 and 3) to accumulate in the nucleus as heteromeric complexes with the Co-SMAD, of which SMAD4 is the ...

Seasonal Changes in Immunoreactivity of Vascular Endothelial Factor and its Receptors VEGFR1 and VEGFR2 in the Uterus of Wild Ground Squirrels (<i>Citellus dauricus</i> Brandt)

“…The background of each section in the different periods was used as the internal control during evaluation of the intensity of the immunostaining. Similar to our previous studies [21,22], immunoreactivity was shown as -for negative staining, + for the positive staining, ++ for the strongly positive staining and +++ for very strongly positive staining. …”

Seasonal Changes in Immunoreactivity of Inhibin/Activin Subunits in the Epididymis of Wild Ground Squirrels (<i>Citellus dauricus</i> Brandt)

“…Forty-six wild male ground squirrels (twenty six in the breeding season and twenty in the nonbreeding season) that were thought to be adults based on their body weights (general standard range of body weight for adult squirrel: 242–412 g) were captured in April to September (breeding season, April and May; nonbreeding season, June to September) of 2007 in Hebei Province, China [22, 23]. After anesthesia, all animals were euthanized by decapitation.…”

“…The testis and epididymis of this species exhibits distinct seasonal morphology changes from the breeding season to the nonbreeding season [21,22,23,24]. Our published results have indicated that seasonal changes in the distribution of inhibin/activin α, β A and β B subunits and activin signaling proteins were accompanied by changes in testicular activity in male ground squirrels and other mammals [21, 22, 25,26,27,28,29]. However, little is known about the role of inhibin/activin subunits in the epididymal tissue of this wild species.…”

Immunoreactivities of androgen receptor, estrogen receptors, p450arom, p450c17 proteins in wild ground squirrels ovaries during the nonbreeding and breeding seasons

“…From June to March, however, was the time of hibernation, or the nonbreeding season, in which the wild ground squirrel went through a long period of sexual dormancy [18-20]. The wild female ground squirrel provided us with a useful model to study the role of androgen in follicular development during the breeding and nonbreeding seasons.…”