The Role of Transcription Factors in Gonad Development and Sex Differentiation of a Teleost Model Fish—Guppy (Poecilia reticulata)

SIMPLE SUMMARY: The research was carried out to determine differences in gonadal development in female and male guppies (Poecilia reticulata) at the molecular level. Fish from the Poeciliidae family is an excellent model for gonadal differentiation studies due to their fertility and the occurrence of sexual dimorphism. Due to exceptional exposure of the aquatic environment to xenobiotics and other pollutants released into water, it becomes necessary to consider their influence on fish and other aquatic organisms’ reproductive capacity. To better understand the processes occurring during gonadal development in guppies, we conducted our research on animals of different ages: 1, 60, and 360 dph (day post-hatching). By examining the basic mechanisms of sex determination in guppies, it will be possible to identify disorders in gonadal development caused by exposure to pollutants in the water. ABSTRACT: The guppy (Poecilia reticulata) is one of the world’s most popular ornamental fish. Due to lecithotrophic viviparous, it is commonly used in toxicological studies and environmental monitoring. This study aimed to investigate the molecular mechanisms of gonad development and differentiation during guppy ontogenesis. The study mainly focused on the role and localization of potential specific sex markers and transcription factors: Sox9, Dmrt1, Erβ. For histological analysis, guppies of both sexes were collected at 1, 60, and 360 dph (day post-hatching). The gonads morphology and immunohistochemistry detection of mentioned markers localization were performed. The expression of Sox9 protein was compared between sexes. Histological analysis revelated all types of male germinal cells in 60 dph guppy’s testes. Maturated oocytes were visible in the ovaries of 360 dph fish. The Sox9 expression varied in spermatocytes and spermatids, from cellular to nuclear localization, and was higher in ovaries. Dmrt1 was detected in all testes groups and 360 dph ovaries. The Erβ was observed in both sexes at 60 and 360 dph. For the first time, the localization of transcription factors in guppy during ontogenesis was traced. The Sox9 designation as a factor regulating the development of germinal cells in adult guppies may facilitate the analysis of xenobiotics’ influence on fish’s reproductive system.