Yellow catfish (Pelteobagrus fulvidraco) lacking of germ cells exhibited gonadal sexual dimorphism

Abstract

Yellow catfish (Pelteobagrus fulvidraco) is a valuable freshwater aquaculture species in China, characterized by an XX/XY sex determination system and pronounced sexual dimorphism in growth. Primordial germ cells (PGCs), progenitors of germ cells, play an essential roles in gonadal sex differentiation and development. In order to reveal the function of germ cells in the sexual differentiation of yellow catfish, PGCs were ablated during embryogenesis through the morpholino-mediated knockdown of the dead end (dnd) gene. The PGCs-depleted gonads exhibited two distinct histological types: one characterized by an ovarian cavity structure (type I gonad) and the other by seminiferous lobule-like structures (type II gonad). Additionally, the expression profiles of germ cell-specific and gonadal somatic cell-related genes were analyzed in the 12-month-old wild-type (WT) fish and dnd morphants. Germ cell-specific genes, dnd, vasa, and dmc1, were identified in the gonads of WT fish but were absent in the gonads of morphants. Genes associated with ovarian somatic cells, cyp19a1 and foxl2, were primarily found in the ovaries of WT fish and in type I gonads. Conversely, testicular somatic cell-related genes, amh, cyp11b, and dmrt1, exhibited predominant or elevated expression levels in the testes of WT fish and in type II gonads. These findings suggested that the differentiation of gonadal somatic cells in yellow catfish occurs independently of germ cells. Our study holds significant importance for advancing the understanding of sex differentiation in yellow catfish, and making an ideal candidate recipient for germline stem cell transplantation within the Bagridae family.