ENDOCRINE REGULATION OF GAMETOGENESIS IN FISH
Transcript of ENDOCRINE REGULATION OF GAMETOGENESIS IN FISH
Bull. Inst. Zool., Academia Sinica, Monograph 16: 139-172 (1991)
ENDOCRINE REGULATION OF GAMETOGENESIS IN FISH
lvi. YOSHIKUNI and Y. NAGAHAMA Laboratory of Reproductive Biology, National Institute for Basic Biology,
Okazaki 444, Japan
It is well established that in
teleosts, as in other vertebrates, the
pituitary-gonadal axis plays an
important role in regulating gameto
genesis. In most cases, gonadotropins
act through the biosynthesis of
gonadal steroid hormones which In
turn mediate various stages of
gametogenesis including oocyte
growth, oocyte maturation, spermato
genesis and spermiation. Thus, the
determination of steroid hormones in
volved in each process is a significant
research goal for scientists interested
in the fish reproduction. This article
reviews some of recent findings on
the identification of steroidal regu
lators in gametogenesis and the sites
and mechanisms of these regulators.
GONADOTROPIN
The question of whether fish
possess one or two gonadotropins in
the pituitary gland has been con
troversial (Burza wa -Gerard, 1982;
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Van Oordt and Peute, 1983; Idler and
Ng, 1983). There is now, however,
biochemical evidence that teleosts,
similar to other vertebrates, possess
two gonadotropins. Idler and his
colleagues (Idler and N g, 1983) have
isolated two gonadotropins, carbo
hydrate-rich ((maturational" gonado
tropin and carbohydrate-poor Hvitello
genic" gonadotropin. More recently,
two distinct carbohydrate gonado
tropins, designated as GTH I and
GTH II, have been isolated and
characterized from pituitaries of
spawning chum salmon, Oncorhynchus
keta (Suzuki et al., 1988a, 1988b; Itoh
et al., 1988; Kawauchi -et al., 1989).
Each of these gonadotropins consists
of a and f3 subunits, the f3 subunits
ha ving amino acid sequence identities
of 31%. GTH I and GTH II have
also been purified in coho salmon,
Oncorhynchus kisutch, (Dickhoff and
Swanson, 1990) and they are chemi
cally similar to the chum salmon
gonadotropins. Both GTH I and GTH