Abstract
Chromobox homolog 2 (CBX2), a key member of the polycomb group (PcG) family, is essential for gonadal development in mammals. A functional deficiency or genetic mutation in cbx2 can lead to sex reversal in mice and humans. However, little is known about the function of cbx2 in gonadal development in fish. In this study, the cbx2 gene was identified in medaka, which is a model species for the study of gonadal development in fish. Transcription of cbx2 was abundant in the gonads, with testicular levels relatively higher than ovarian levels. In situ hybridization (ISH) revealed that cbx2 mRNA was predominately localized in spermatogonia and spermatocytes, and was also observed in oocytes at stages I, II, and III. Furthermore, cbx2 and vasa (a marker gene) were co-localized in germ cells by fluorescent in situ hybridization (FISH). After cbx2 knockdown in the gonads by RNA interference (RNAi), the sex-related genes, including sox9 and foxl2, were influenced. These results suggest that cbx2 not only plays a positive role in spermatogenesis and oogenesis but is also involved in gonadal differentiation through regulating the expression levels of sex-related genes in fish.
Highlights
The polycomb group (PcG) protein family was initially identified in Drosophila [1]
We identified medaka cbx2 via PCR cloning and sequencing, detected the relative expression of cbx2 mRNA in different tissues using real-time PCR, and established an expression profile of cbx2 mRNA in medaka gonads via digoxigenin (DIG)-labeled in situ hybridization (ISH) and fluorescent in situ hybridization (FISH)
A phylogenetic tree showed that Chromobox homolog 2 (CBX2) was evolutionarily conserved from fish to humans
Summary
The polycomb group (PcG) protein family was initially identified in Drosophila [1]. In higher eukaryotes, it is mainly involved in maintaining a series of cellular physiological activities, such as cell differentiation, cell cycle regulation, cell senescence, and X chromosome inactivation [2]. The CBX family contains five proteins, CBX2, CBX4, CBX6, CBX7, and CBX8 [9] They have a common conserved domain, their molecular size, tissue distribution, and biological functions are quite different. The functional role of cbx in gonadal development is still unclear in vertebrates other than mammals. The expression of cbx mRNA was knocked down using RNA interference (RNAi), the expression levels of cbx and sex-related genes, including foxl and sox, were analyzed to clarify the function of cbx in the gonadal development of fish
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