Abstract
Fractionation and characterization of gonadotropins (GtH) from Fundulus heteroclitus pituitary extracts were carried out using a biocompatible liquid chromatographic procedure (Pharmacia FPLC system). Chromatographic fractions were monitored for gonadotropic activities (induction of oocyte maturation and steroid production) using homologous follicle bioassays in vitro. Size-exclusion chromatography eluted gonadotropic activity in one major protein peak (Mr ~ 30,000). Anion-exchange and hydrophobic-interaction chromatography (HIC) yielded two distinct peaks of 17beta-estradiol (E2)- and 17alpha-hydroxy,20beta-dihydroprogesterone (DHP)-promoting activity with associated oocyte maturation. Two-dimensional chromatography (chromatofocusing followed by HIC) resolved pituitary extracts into two active fractions; both induced E2 synthesis, but one was relatively poor in eliciting DHP and testosterone production. Thus, using homologous bioassays, at least two quantitatively different gonadotropic (steroidogenic) activities: an E2-promoting gonadotropin (GtH I-like) and a DHP-promoting gonadotropin (GtH II-like), which has a lower isoelectric point but greater hydrophobicity than the former, can be distinguished from F. heteroclitus pituitaries by a variety of chromatographic procedures. This study complements previous biochemical and molecular data in F. heteroclitus and substantiates the duality of GtH function in a multiple-spawning teleost.
Highlights
During a breeding season, many fish known as fractional spawners have been found to undergo periodic reproductive activity correlated with the lunar cycle [1], including Fundulus heteroclitus [2,3]
In order to understand the operant mechanisms involved in cyclic teleost reproduction and to provide a broader basis for comparative study of the teleost gonadotropic hormones (GtHs), we have focused our studies on the F. heteroclitus GtHs and their role in controlling the cyclic reproductive activity characteristic of this species and common to a large class of commercially important species other than salmonids
Each of the following chromatographic procedures has been performed at least ten times
Summary
Many fish known as fractional spawners have been found to undergo periodic reproductive activity correlated with the lunar cycle [1], including Fundulus heteroclitus (killifish) [2,3]. The presence of two distinct GtHs in teleosts has been demonstrated in several species including chum salmon [5,6], coho salmon [7], killifish [8,9,10], common carp [11], Atlantic croaker [12], tuna [13], bonito [14], red seabream [15], striped bass [16], yellowfin porgy [17], goldfish [18]and Japanese eel [19]. Fundulus is a fractional spawner and can act as an inexpensive, manipulated model system
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