Androgen and progesterone receptors in shark (Squalus) testis: characteristics and stage-related distribution.

Abstract

Although testosterone (T) is essential for the normal completion of spermatogenesis, the exact T-sensitive control points are still unknown. Using staged tissues (premeiotic, PrM; meiotic, M; and postmeiotic, PoM) from zonal testes of the spiny dogfish Squalus acanthias, and standard [3H] steroid binding analysis, we characterized a T-binding component with physiochemical characteristics resembling classical androgen receptors (AR). [3H]T binding was of high affinity (dissociation constant = 4.4 x 10(-9) M), limited capacity (maximum binding, 94 fmol/g tissue) and relatively stable (t1/2 = 4 h at 4 C). The T-binding component was present in both cytosolic and nuclear extracts, adhered to DNA-cellulose, and displayed predicted sedimentation properties of an activated receptor in vivo or in vitro (5.06S). T, 5 alpha-dihydrotestosterone (DHT), and mibolerone (Mib), but not methyltrienelone (R1881), competed well for [3H]T binding; however, progesterone (P) was equivalent to T in its ability to displace tracer. Subsequent analysis of [3H] P binding revealed a P-binding component that was present in nuclear and cytosolic extracts, adhered to DNA, but differed from AR in its inability to bind Mib. Competition studies in which excess radioinert Mib was used to block AR revealed ligand specificity characteristics of progesterone receptors (PR): promegestone (R5020) greater than P greater than deoxycorticosterone, but T, DHT, dexamethasone, and corticosterone were ineffective competitors. Also, a nonlinear Scatchard plot was obtained, suggesting two P-binding activities, which differed in their binding affinities (dissociation constant = 0.88 vs. 5.9 x 10(-9) M) and capacities (66 vs. 210 fmol/g tissue). Conversely, using [3H]Mib to avoid interference from PR, we confirmed that T, DHT, and P were equivalent in their ability to displace ligand from AR. Comparison of tissues by stage of spermatogenesis revealed different distribution patterns for AR (PrM greater than M much greater than PoM) vs. PR (PoM much greater than M = PrM). These data provide definitive evidence for separate testicular T- and P-binding mechanisms and indicate the presence of temporally distinct sets of steroid-regulated genes.

Stage-dependent modulation of Sertoli cell steroid production in dogfish (Scyliorhinus canicula)

“…In our study, the optimum 22a-hydroxycholesterol concentration required to elicit the maximum rates of steroido¬ genesis (100-200 pmol l-1 depending on the steroid and on the nature of the lobule) was comparable to that required for rat Leydig cells (100 pmol 1" \ Risbridger et al, 1986 (Hall et al, 1969;Cooke et al, 1972) and that rat Sertoli cells cannot convert pregnenolone to progesterone (Wiebe et al, 1988 Kime (1978) and Cuevas and Callard (1992) (Sourdaine et al, 1990 (Dobson and Dodd, 1977), as observed in Torpedo marmorata and T. ocellata by Fasano et al (1989). This highlights the importance of the contribution of testicular paracrine mechanisms and, in particular, the effects of germ cells for the control of steroid production.…”

Cadmium accumulation and binding characteristics in intact Sertoli/germ cell units, and associated effects on stage‐specific functions in vitro: insights from a shark testis model

“…Although our findings provide no insight regarding the mechanism of the Cd-stimulated increase in the apoptosis of early-stage PrM cysts, the observed presence of a second nuclear-associated component of 109 Cd which is detected in greater amounts in PrM cysts than in PoM cysts (Betka and Callard, 1999), certainly implicates Cd in nuclear-associated activities in the intact spermatogonium/Sertoli cell units. Of interest, classic androgen and estrogen receptors are known to be concentrated in the PrM region of Squalus testis (Callard et al, 1985;Cuevas and Callard, 1992). In this regard, the potential for dysregulation of steroid-mediated activities is significant, given that Cd mimics the in vivo effects of estrogen in the uterus and mammary gland (Johnson et al, 2003), directly inhibits and/or activates androgen and estrogen receptors in mammalian (Martin et al, 2002;Takiguchi and Yoshihara, 2006) and fish (Guevel et al, 2000;Vetillard and Bailhache, 2005) steroidresponsive cells and tissues.…”

Stage and season effects on cell cycle and apoptotic activities of germ cells and Sertoli cells during spermatogenesis in the spiny dogfish (Squalus acanthias)

“…McClusky, unpublished observations). By extension and given that (1) mature spermatid cysts, which are absent in April -May, are major sites for the synthesis of androgen-binding protein and for the secretion of testosterone and its precursors (Simpson & Wardle 1967, Mak & Callard 1989, Sourdaine et al 1990, Cuevas & Callard 1992a, (2) classical nuclear oestrogen and androgen receptors are concentrated in the PrM region of the shark testis (Callard et al 1985, Cuevas & Callard 1992b, (3) the vascular pathway in Squalus is countercurrent to the spermatogenic progression, i.e. PoM cysts to GZ cysts (Cuevas et al 1992) and (4) hypophysectomy of male dogfish (Scyliorhinus) leads only to a small decrease in circulating androgen (Dobson & Dodd 1977a), overall reconciliation of all these observations in dogfish sharks suggests that the developmental advance of mature spermatogonial cysts in sharks is dependent not only on de novo testosterone and/or oestrogen synthesis in PrM cysts, but also on those synthesized in mature-spermatid cyst stages, when they are present in the spermatogenic progression.…”