11-Ketotestosterone and IGF-I increase the size of previtellogenic oocytes from shortfinned eel, Anguilla australis, in vitro

Abstract

Previtellogenic ovarian fragments from eel, Anguilla australis, were cultured in vitro in a chemically defined medium containing steroids and/or peptide hormones for 18 days in order to investigate their involvement in control of early oocyte growth. 11-Ketotestosterone (11-KT), but not estradiol-17b, induced a significant 10-20% increase in diameters of previtellogenic oocytes and oocyte nuclei in a dose-dependent manner. Effects were greatest for 100 nM 11-KT, a dose that is within the physiological range seen in very early vitellogenic eels in the wild. The effect was not accompanied by obvious ultrastructural changes in the oocytes other than an apparent increase in nuclear size. Similarly, treatment with recombinant human IGF-I resulted in increased oocyte diameters, whereas no such effect was seen after treatment with heterologous insulin, GH, leptin, or human chorionic gonadotropin. Interestingly, lipid supplementation also resulted in an increase in oocyte diameter, and greater radioactivity in ovarian explants following incubation with 14 C-triglycerides and 11-KT, but not FSH, suggesting that the androgen may play a role in lipid accumulation into the oocyte. Our results implicate hormones from both the reproductive and the metabolic axes in control of previtellogenic oocyte growth in a teleost fish.Reproduction (2007) 133 955-967

Identification and Transcriptional Modulation of the Largemouth Bass, Micropterus salmoides, Vitellogenin Receptor During Oocyte Development by Insulin and Sex Steroids1

“…Short-term in vitro studies have reported successful incorporation of radiolabeled Vtg into fish oocytes [17,18]. Several publications have explored the signals controlling Vtg uptake and suggest control by various hormones including gonadotropin I [19], insulin (INS) and thyroxine [20], a pituitary glycoprotein fraction from salmon [21], 11-ketotestosterone (11-KT), and INS-like growth factor hormone I (IGF-I) [22]. Some of these factors have also been shown to regulate uptake of VLDL and other lipids during early stages of fish ovarian development [22,23].…”

“…VLDL and lipid incorporation, as measured by oocyte diameter increase, is the only related process that has been shown to be under the control of 11-KT, and it is possible that it dually regulates repression of vtgr mRNA while enhancing receptor cycling and function. The addition of IGF-I combined with 11-KT enhanced oocyte growth, which additionally suggests that multiple factors likely control these processes [22,23].…”

“…Although the functional role of nuclear hormone receptors in the teleost ovaries is not well characterized, a few studies have investigated the contribution of estrogens and androgens during primary oocyte growth and showed that sex steroids affect sex differentiation, cell growth, and gene expression changes related to steroidogenesis [22,23,[56][57][58][59]. Here we set out to determine whether E 2 or 11-KT could modulate the transcriptional levels of vtgr in early growth stage follicles.…”

“…We previously observed that patterns of expression for LMB esr2a and esr2b [34] share a similar trend to vtgr expression during the reproductive cycle in the ovary with maximal expression in previtellogenic tissues. Because both estrogens and androgens have been suggested to contribute to primary growth of follicles in other teleosts [22,23,56], we also cloned the ar cDNA and determined its temporal expression profile. We reveal here for the first time that the mRNA levels of LMB ar follow the same trend as esr and vtgr.…”

“…The precise functions of INS during these time frames, particularly during primary ovarian growth, have been described by measuring DNA synthesis and binding receptor studies [61,62]. INS and INSlike growth factor-I (IGF-I) have been shown to bind to fish ovaries primarily in previtellogenic oocytes of carp [62], and recombinant human IGF-I increased the diameter of shortfinned eel previtellogenic oocytes [22]. These studies support a role for INS in directing primary growth events in developing oocytes, and our data further suggest a specific role for controlling vtgr mRNA production during this window.…”