Seasonal Changes in mRNA Levels of Gonadotropin and Thyrotropin Subunits in the Goldfish,Carassius auratus

Activin is an important regulator of gonadotropin expression and production in the vertebrate pituitary, and its activity is fine-tuned by its binding protein follistatin. In the present study, a full-length cDNA for follistatin was cloned in the goldfish, which shows 74% amino acid sequence identity with that of mammals. Recombinant goldfish follistatin expressed in the Chinese hamster ovary cells significantly blocked activin-induced F5-5 cell differentiation. Goldfish follistatin is expressed in a wide range of tissues including the brain, pituitary, ovary, and testis. The expression of follistatin mRNA in the pituitary is regulated by both activin and gonadal steroids in vitro. Treatment with goldfish activin B for 48 h significantly up-regulated follistatin expression in cultured pituitary cells, suggesting a closed activin-follistatin feedback loop in the pituitary. In agreement with this, both human and goldfish follistatin down-regulated the expression of follistatin itself, probably due to the neutralization of endogenous activin. Examination of FSHb and LHb expression in the same samples supports the role of activin and follistatin in the differential regulation of FSH and LH as demonstrated previously. Since the expression level of activin b B in the pituitary is rather stable both in vitro and in vivo, it is conceivable that follistatin may play a pivotal regulatory role in the intra-pituitary activin system. Both estradiol and testosterone up-regulated follistatin expression in vitro, suggesting a mediating role for follistatin in steroid feedback on pituitary hormones. These results provide clues to the potential physiological roles of activin-follistatin system in the regulation of gonadotropin biosynthesis in teleosts.

Section: Annual Expression Profiles Of Follistatin Activin B B Fshsupporting

confidence: 90%

Evidence for the existence of a local activin–follistatin negative feedback loop in the goldfish pituitary and its regulation by activin and gonadal steroids

Cheng¹,

Yuen²,

Ge³

2007

“…It is very likely that the reduction in plasma fT 4 levels is the result of a reduced activity of the thyroid gland caused by a negative feedback of T 3 on pituitary thyrotropes. As in mammals, T 3 represses tsh b-subunit gene expression in fish pituitaries in vitro in a classical negative feedback system (Pradet-Balade et al 1997, Schmitz et al 1998, Sohn et al 1999. Moreover, thyroid hormone economy is complicated by the presence of specific thyroid hormone-binding proteins that facilitate vectorial plasma transport (reviewed by Klaren et al (2007a)).…”

Section: Discussionmentioning

confidence: 99%

Effects of cortisol and thyroid hormone on peripheral outer ring deiodination and osmoregulatory parameters in the Senegalese sole (Solea senegalensis)

Arjona¹,

Vargas‐Chacoff²,

Río³

et al. 2011

The thyroid gland in fish mainly secretes the thyroid prohormone 3,5,3 0 ,5 0 -tetraiodothyronine (T 4 ), and extrathyroidal outer ring deiodination (ORD) of the prohormone to 3,5,3 0 -triiodothyronine (T 3 ) is pivotal in thyroid hormone economy. Despite its importance in thyroid hormone metabolism, factors that regulate ORD are still largely unresolved in fish. In addition, the osmoregulatory role of T 3 is still a controversial issue in teleosts. In this study, we investigated the regulation of the ORD pathway by cortisol and T 3 in different organs (liver, kidney, and gills) of Solea senegalensis and the involvement of T 3 in the control of branchial and renal Na C , K C -ATPase activity, a prime determinant of the hydromineral balance in teleosts. Animals were treated with i.p. slow-release coconut oil implants containing cortisol or T 3 . Hepatic and renal ORD activities were up-regulated in cortisol-injected animals. T 3 -treated fish showed a prominent decrease in plasma-free T 4 levels, whereas ORD activities did not change significantly. Branchial and renal Na C , K C -ATPase activities were virtually unaffected by T 3 , but were transiently up-regulated by cortisol. We conclude that cortisol regulates local T 3 bioavailability in S. senegalensis via ORD in an organ-specific manner. Unlike T 3 , cortisol appears to be directly implicated in the up-regulation of branchial and renal Na

“…In fish, GTHs are differentially secreted in the plasma during the reproductive cycle suggesting that they have specific functions (Prat et al 1996, Gomez et al 1999, Sohn et al 1999. FSH may play a determinant role in regulating early gametogenesis.…”

Section: Introductionmentioning

confidence: 99%

Functional specificity of the rainbow trout (Oncorhynchus mykiss) gonadotropin receptors as assayed in a mammalian cell line

Sambroni¹,

Gac²,

Breton³

et al. 2007

In vertebrates, gonadotropins (GTHs) (FSH and LH) are two circulating pituitary glycoprotein hormones that play a major role in the regulation of gonadal functions, including gonadal cell proliferation/differentiation and steroidogenesis. In mammals, it is well known that their biological effects are mediated by highly specific membrane-bound receptors expressed preferentially on the somatic cells of the gonads. However, in fish, binding and functional studies have shown that cross-reactivity may occur in GTH receptors depending on the species. To understand the molecular mechanisms involved in GTH actions, functional characterization of trout GTH receptors and their gonadal gene expression pattern has been carried out. The present study describes the presence of two distinct GTH receptors in trout showing similarities with those of higher vertebrates but also differences in their structural determinants. In vitro functional studies demonstrate that rtLH specifically activates its cognate receptor (EC 50 Z117 ng/ml), whereas purified rainbow trout FSH (rtFSH) activates FSHR but also LHR at supraphysiological doses (EC 50 Z38 vs 598 ng/ml for FSHR and LHR respectively). The high doses of rtFSH required to activate LHR put into question the physiological relevance of this interaction. The use of heterologous chinook GTHs confirms the strong preference of each hormone for its cognate receptor. The gonadal expression pattern of the GTH receptor genes suggests that FSH may play an important role in regulating gonadal functions, not only at the early stages but also at the final stages of the male and female reproductive cycles, in addition to the LH pathway.