Submitted March 14, 2007
Returned for revision April 11, 2007
Accepted August 6, 2007
Mechanisms of Hormone Action
A Progestin and an Estrogen Regulate Early Stages of
Oogenesis in Fish
Chiemi Miura ,
Toshitsugu Higashino ,
and
Takeshi Miura *
* To whom correspondence should be addressed. E-mail: miutake{at}agr.ehime-u.ac.jp.
Abstract
Using two species of teleost fish, Japanese huchen (Hucho perryi) and common carp (Cyprinus carpio), we carried out experiments to investigate whether sex steroids are involved in early oogenesis in vitro. Ovarian fragments were cultured to examine the effects of a progestin, 17alpha, 20beta-dihydroxy-4-pregnen-3-one (DHP), and an estrogen, estradiol-17 beta (E2). DHP and E2 significantly promoted DNA synthesis in ovarian germ cells as shown by incorporation of BrdU into these cells. Furthermore, to detect the initiation of the first meiotic division in early oogenesis, we assessed ultrastructurally the occurrence of synaptonemal complexes (SC) and analyzed by immunohistochemistry the expression of a meiosis-specific marker, Spo11. In huchen, a higher percentage of oocytes with SC was seen in DHP-treated fragments than those in control or E2-treated fragments. Spo11 was expressed in germ cells after treatment of carp ovarian explants with DHP. These data suggest that the progression of germ cells through early oogenesis involves two sex steroids: E2 acts directly on oogonial proliferation while DHP acts directly on the initiation of the first meiotic division of oogenesis.
Key words:
Ovary •
Estradiol •
Gametogenesis •
Meiosis •
Progesterone
