Induction of Three Vitellogenins by 17beta-Estradiol with Concurrent Inhibition of the Growth Hormone-Insulin-Like Growth Factor 1 Axis in a Euryhaline Teleost, the Tilapia (Oreochromis mossambicus)1

Abstract

The objective of the present study was to utilize the male Mozambique tilapia (Oreochromis mossambicus) as a model for examining the molecular mechanisms that mediate the physiological transition between somatic and gonadal growth in female teleost fish, and in vertebrates in general. Partial cDNAs that encode multiple forms of vitellogenin (Vtg), which is the major precursor of yolk proteins, were cloned from estrogen-treated males and utilized to develop real-time quantitative RT-PCR assays, which were supplemented by an assay for Vtg immunoreactivity in the plasma. Alignment analyses of the amino acid sequences deduced from the vtg cDNAs revealed three distinct tilapia Vtgs, which were categorized as Aa-, Ab-, and C-type Vtgs. A single injection of male tilapias with 17beta-estradiol (E(2)) at 5 microg/g body weight significantly increased the plasma E(2) and hepatic levels of all three vtg transcripts within 1 day. Plasma E(2) levels declined after 3 days, whereas the plasma Vtg immunoreactivity and hepatic levels of the three vtg transcripts continued to increase. Hepatic expression of the estrogen receptor (esr) 1 gene, but not the esr2 gene, also increased markedly 1 day after E(2) injection and remained elevated for 5 days. While plasma growth hormone (Gh) levels were unaffected, hepatic expression of transcripts that encoded the Gh receptor and insulin-like growth factor 1 (Igf1) was suppressed by E(2), as were the plasma Igf1 levels. These results clearly suggest a distinct negative interplay between the growth and reproductive axes at the molecular level of key hepatic regulatory pathways involved in the control of energy utilization by gonadal and somatic growth processes.

Effects of steroid hormones on reproduction- and detoxification-related gene expression in adult male mosquitofish, Gambusia affinis

“…It is well known that the induction of Vtg mRNA expression in fish is achieved by ER activated by E2 (Atteke et al, 2003;Davis et al, 2007). In the present study, E2 also stimulated ERα transcription in concert with the activation of Vtg mRNA expression levels in the liver of male mosquitofish.…”

“…In combined hormone treatments, our present results have some differences compared with a previous study, where both P and T markedly inhibit the induction of hepatic Vtg mRNA in male turtles (Chrysemys picta) by E2, T being the most potent inhibitor (Custodia-Lora et al, 2004). Induction of Vtg gene expression by estrogens is closely related to ER regulation (Atteke et al, 2003;Davis et al, 2007). The present study also confirmed that E2 significantly increase the expression of ERα mRNA in the liver of …”

“…The results presented herein showed that ERα plays a dominant role in the up-regulation of Vtg mRNA expression in the liver of male mosquitofish. It has been shown that ERα plays a dominant role in the up-regulation of Vtg mRNA expression in the liver of female mosquitofish (Huang et al, 2012) and other fish (Sabo-Attwood et al, 2004;Davis et al, 2007) by E2. The lack of significant changes found in ERβ mRNA expression levels in the liver of male mosquitofish in response to E2 is consistent with other studies in which E2 treatment had no effects on zebrafish (Menuet et al, 2004) and male goldfish (Pomatto et al, 2011), suggesting that ERβ is unlikely to be the primary mediator of E2 actions on the liver associated with the induction of Vtg mRNA expression.…”

“…The presence of these steroid hormones may affect aquatic organisms (Miracle et al, 2006;Davis et al, 2007;Milla et al, 2011;Zucchi et al, 2012). Up to now, most studies in the literature focus on the biological effects caused by estrogens (Teles et al, 2006;Carrera et al, 2007;Davis et al, 2007;Henry et al, 2009;Marlatt et al, 2010;Del Giudice et al, 2011), with relatively few studies having examined the biological effects of other steroid hormones such as androgens and progestins.…”

Influência do horário de aplicação e da variedade genética em fêmeas de tilápias Oreochromis niloticus submetidas à indução hormonal com hCG

“…O hCG proporciona aumento dos níveis de gonadotrofinas, que estimulam o crescimento folicular e, consequentemente, os níveis de estradiol, que estão relacionados com a incorporação e a vitelogenina nos ovócitos (Davis et al, 2007). Esses ovos são maiores, proporcionando larvas maiores e com saco vitelino maior (Wootton, 1994;Gisbert et al, 2000) e maior sobrevivência larval.…”