Germ Cell Degeneration in High-Temperature Treated Pufferfish, <i>Takifugu rubripes</i>

Abstract

Exogenous factors such as temperature, social behavior, and salinity play a crucial role during the critical sensitive period of sex differentiation in many vertebrates. In fishes, amphibians, and reptiles temperature treatment is known to induce all-male (or female) individuals, and genes related to sex differentiation have been studied. The Japanese pufferfish, Takifugu rubripes, possesses the most compact genome among vertebrates and has immense potential for studies focusing on comparative genome analysis. In this study, we describe gonadal morphology and vasa (germ cell marker) and dmrt1 (Sertoli cell marker) expression on a molecular level in relation to the development of temperature-treated pufferfish. To investigate the relationship between temperature and gonadal development, pufferfish were exposed to high-temperature conditions (32°C) during early gonadal development. Morphological observations showed that this high-temperature treatment did not influence sexual differentiation as determined by ovarian cavity characteristics; however, high-temperature treatment induces gonadal degeneration that is devoid of germ cells. RT-PCR results revealed no vasa expression within germ cell-degenerated gonads. In situ hybridization results showed that dmrt1 was expressed in somatic cells of germ cell-degenerated ovaries. These results suggest that high-temperature treatment during early gonadal development induces germ cell degeneration and masculinization of ovarian somatic cells in pufferfish.

Effect of Rearing Temperatures during Embryonic Development on the Phenotypic Sex in Zebrafish <i>(Danio rerio)</i>

“…When the germline was absent, the gonad underwent a testis fate, and normal somatic structures were developed. As the primordial germ cells are sensitive to high water temperatures [Lee et al, 2009;Selim et al, 2009], apoptosis might lead to the development of male somatic tissues [Baroiller et al, 2009b]. The fact that in the present study the major trigger on the sex ratios of the progeny could be seen already during the period from 5 to 10 hpf might emphasize the susceptibility of germ cells to high water temperatures and their importance for the sex differentiation process in zebrafish.…”

“…Lee et al [2009] found that in the Pufferfish, Takifugu rubripes , an early high temperature treatment (32 ° C) induced a degeneration of the gonads, shown by a complete lack of germ cells. Morphologically, high-temperature treatments had no effect on sexual differentiation, and female ovary characteristics were maintained.…”

High temperature-induced sterility in the female Nile tilapia, Oreochromis niloticus

“…In medaka, high temperature (32-34°C) inhibited germ cell proliferation and caused a female-to-male sex reversal, which was found to be mediated by increased levels of circulating cortisol (Hayashi et al, 2010). In fugu, high temperature-induced degeneration of germ cells with concomitant increase in expression of male somatic cell marker Dmrt1 (Lee et al, 2009). In mammals, administration of androgens or estrogen inhibitors induced apoptosis of gonadal cells (Billig et al, 1993;Lue et al, 1999b), suggesting that sex hormones play important role in maintenance of germ cells in the gonad.…”

The Reversible Sex of Gonochoristic Fish: Insights and Consequences

“…The presence of germ cells is indeed necessary for ovarian formation and differentiation in some fish species [Nishimura and Tanaka, 2014]. Loss of germ cells induced by high temperatures or by other means in zebrafish [Uchida et al, 2004;Slanchev et al, 2005], medaka [Kurokawa et al, 2007], and fugu [Lee et al, 2009] induced sex reversal of females into males, with somatic cells seemingly predisposed to develop into male cells [Nishimura and Tanaka, 2014]. However, this was not the case in the goldfish [Goto et al, 2012].…”