MOLECULAR MECHANISMS OF FISH REPRODUCTION

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(Hypothalamus) The two salmon gonadotropin-releasing horman genes (sGnRH-I and sGnRH-II) and their upstream regions were characterized in masu salmon. In the upstream regions, only the sGnRH-II gene has a large palindromic sequence. In contrast, the sGnRH-I gene is missing the large palindromic sequence. Changes in sGnRH synthetic activity in the brain during gonadal maturation were also examined by in situ hybridization in masu salmon. During gonadal maturation, the numbers of neurons expressing sGnRH mRNA increased in the preoptic area and the ventral telencephalon.(Pituitary) cDNA of II beta-subunit of gonadotropin (GTH) in Rusian stergeon was cloned. In addition, the possible involvement of somatolactin in acid-base regulation was suggested in rainbow trout.(Gonad) The two types of cDNA encoding P-450c17 and one type of 20 beta-IISD were isolated from rainbow trout ovary. Furthermore, cDNAs encoding several types of connexins which has the important role for the acquisition of oocyte maturational competence were also isolated from the atlantic croker.(Liver) Changes in levels of estrogen receptor gene expression in the liver were also examined by RT-PCR during gonadal maturation in eel.