Hormonal induction of all stages of spermatogenesis in vitro in the male Japanese eel (Anguilla japonica).

Abstract

The importance of gonadotropins and androgens for spermatogenesis is generally accepted in vertebrates, but the role played by specific hormones has not been clarified. Under cultivation conditions, male Japanese eels (Anguila japonica) have immature testes containing only premitotic spermatogonia, type A and early-type B spermatogonia. In the present study, a recently developed organ-culture system for eel testes was used to determine in vitro effects ofvarious steroid hormones on spermatogenesis. After 9 days of culture in serum-free, chemically defined medium. containing 11-ketotestosterone (10 ng/ml), a major androgen in male eels, type A and early-type B spermatogonia began mitosis, producing late-type B spermatogonia. After 18 days, zygotene spermatocytes with synaptonemal complexes appeared, indicating that melosis had already started by this time. In testis fragments cultured for 21 days, round spermatids and spermatozoa were observed with spermatogenic cells at all stages of development. Addition of 11-ketotestosterone to the culture medium also caused a marked cytological activation of Sertoli cells. No other steroid hormones tested had such stimulatory effects. These results, together with our earlier observations, suggest the following sequence for the hormonal induction of spermatogenesis Wi eel testes; gonadotropin stimulates the Leydig cells to produce 11-ketotestosterone, which, in turn, activates the Sertoli cells leading to the completion of spermatogenesis. This is, thus, an example of an animal system in which all stages of spermatogenesis have been induced by hormonal manipulation in vitro.The formation of sperm, spermatogenesis, is an extended process that begins with the proliferation of spermatogonia and proceeds through the extensive morphological changes that convert the haploid spermatid into a mature, functional spermatozoon. Although it is generally accepted that the principal stimuli for vertebrate spermatogenesis are pituitary gonadotropins and androgens, the specific role played by individual hormones has not been clarified (1-4). A number of factors complicating in vivo investigations of the mechanisms involved in the spermatogenesis can be eliminated in in vitro organ (5, 6) and cell (7-10) culture systems in which the direct effects of various factors, including hormonal influences, upon the spermatogenic cells and testes can be investigated.Under conditions of cultivation, male Japanese and European eel have immature testes containing only premitotic spermatogonia, type A and early-type B spermatogonia (11)(12)(13)(14)(15). It has been reported that in both species a single injection of exogenous human chorionic gonadotropin induces all stages of spermatogenesis in vivo (12,14,15). This injection also caused an increase in plasma levels of 11-ketotestosterone (12, 15). Thus, the eel testis provides an excellent system for studying the mechanism by which spermatogenesis is regulated. In the present study, we have used a recently developed organ culture system for eel te...

Morphometric changes and sex steroid levels during the annual reproductive cycle of the Lusitanian toadfish, Halobatrachus didactylus

“…Similar observations have been made for other species specially those that display conspicuous reproductive behaviour: e.g., garibaldi, Hypsypops rubinculus (Girard) (Sikkel, 1993), bluegill, Lepomis macrochirus (Rafinesque) (Kindler et al, 1989), and demoiselle Chromis dispilus (Griffin) (Barnett and Pankhurst, 1994). For many other teleosts (rainbow trout, Salmo gairdneri (Richardson), Scott et al, 1980; white sucker, Catostomus commersoni (Lacepe ede), Scott et al, 1984; Artic charr, Salvelinus alpinus (L.), Mayer et al, 1992) 11-KT and T peak during the pre-spawning period possibly related to the role of 11-KT in spermatogenesis (Miura et al, 1991a). Furthermore, type I males had significantly higher plasma levels of 11-KT than type II males.…”

Molecular mechanisms underlying sex change in hermaphroditic groupers

“…Androgens have been shown to play roles in sex differentiation (Baroiller et al 1998) and sex change (Cardwell and Liley 1991) in protogynous hermaphrodites. In males, 11-KT, teleost-specific androgen, is considered a principal androgen in teleostean fish, and it plays a central role in sexual maturation, development of secondary sexual characteristics and reproductive behaviour (Miura et al 1991;Borg 1994). In many sexchanging fish, the levels of circulating 11-KT have been reported to increase with the progression of sex change (Nakamura et al 1989;Johnson et al 1998;Kroon and Liley 2000;Bhandari et al 2003), and exogenous 11-KT treatment can induce sex reversal (Kroon and Liley 2000;Yeh et al 2003).…”

Cloning of cDNAs and the differential expression of A‐type cyclins and Dmc1 during spermatogenesis in the Japanese eel, a teleost fish

“…In particular, the Japanese eel testis provides an excellent model for the clarification of the molecular mechanism involved in the initiation of spermatogenesis, because only spermatogonial stem cells are present in the testis of the cultivated eel, and hormonal induction of spermatogenesis in vivo and in vitro already has been accomplished (Miura et al, 1991;Kobayashi et al, 1998). However, no available information on cell cycle-related genes during spermatogenesis is reported for nonmammalian vertebrates.…”