Partial formation of sperm dimorphism from spermatocytes of the cottoid fish, Hemilepidotus gilberti in cell culture

Abstract

Polymorphism of sperm is considered to be significant for the reproductive strategy in some animal species. The phenomenon is thought to occur in the species-specific stage of spermatogenesis, but how the identical germ cells are differentiated towards polymorphic sperm remains unknown. We here performed a germ cell culture in the cottoid fish, Hemilepidotus gilberti, whose sperm exhibit dimorphism with fertilizable eusperm and unfertilizable parasperm. In the culture, germ cells, which were obtained with an identical morphology, a spherical shape of 5-7 microm in diameter, differentiated into smaller spherical cells with a single nucleus, a moving flagellum and localized mitochondria. In addition, large retroflex-shaped cells with two elongated nuclei were also observed in the cell culture. Germ cells that had each morphological feature were histologically also observed in some cysts of the spermatogenetic testis, suggesting that the former type of cell corresponded to developing eusperm and the latter corresponded to developing parasperm. When BrdU was incorporated into germ cells in the culture, it was detected in both cells with eusperm-like and those with parasperm-like morphologies. These findings suggest that DNA-duplicating spermatocytes are potent to autonomously progress a part of spermatogenesis to form dimorphic sperm.

Two states of active spermatogenesis switch between reproductive and non‐reproductive seasons in the testes of the medaka, Oryzias latipes

“…The testis culture system has been established in some lower vertebrates, which has contributed greatly to the study of spermatogenic control at cellular and molecular levels (Miura et al 1991;Yazawa et al 2000;Miura & Miura 2003;Hayakawa et al 2007). In O. latipes, although testis culture had been reported by Song & Gutzeit (2003), we succeeded in establishing a long-term culture in which proliferation of A-and B-gonia, as well as differentiation of P-cytes to tids, was constantly maintained for at least 10 days.…”

“…Since FSH and LH are known to promote spermatogenesis through different pathways (Dierich et al 1998;Lei et al 2001;Ohta et al 2007), those gonadotropins may be a key for understanding the mechanism for inducing the spermatogenic state specific to the M-J or O-J period. The testis culture system has been established in some lower vertebrates, which has contributed greatly to the study of spermatogenic control at cellular and molecular levels (Miura et al 1991;Yazawa et al 2000;Miura & Miura 2003;Hayakawa et al 2007). In O. latipes, although testis culture had been reported by Song & Gutzeit (2003), we succeeded in establishing a long-term culture in which proliferation of A-and B-gonia, as well as differentiation of P-cytes to tids, was constantly maintained for at least 10 days.…”