CHARACTERATION OF THE DUPLICATED 20β-HSD GENES IN PELTEOBAGRUS FULVIDRACO AND THEIR EXPRESSION PATTERNS AND REGULATIONS

Maturation inducing hormone (MIH) plays pivotal roles in gamete maturation, ovulation and spermiation of fish. In most teleost species, 17α, 20β-dihydroxy-4-pregnen-3-one (DHP) is the major MIH. The steroidogenic enzyme, named 20β-hydroxysteroid dehydrogenase (20β-HSD), is responsible for DHP production in several teleost species. To date, only one copy of 20β-hsd has been characterized in vertebrates, including fish. In this study, two copies of 20β-hsd genes were identified in genomes of several fish species. Phylogenetic and syntenic analyses revealed that the duplication of 20β-hsd gene may not result from the teleost specific genome duplication (TSGD). Multiple-alignment re- sults indicated that these two enzymes might possess similar spatial structures and co-enzyme/substrate binding motifs, whereas, their catalytic activities might differ. The duplicated copy of 20β-hsd was further cloned from yellow catfish (Pelteobagrus fulvidraco). Tissue distribution results showed that, 20β-hsd Ⅰ mRNA was mainly expressed in testis, ovary, head kidney and kidney, while 20β-hsd Ⅱ mRNA was mainly located in testis, ovary, heart, head kidney, kidney, intestine, pituitary and liver. Seasonal expression results revealed that, lower 20β-hsd Ⅰ expression and higher 20β-hsd Ⅱ expression were observed in male fish during reproductive time window (in May). Three hours after injection of hCG (1000 IU/kg body weight), the expression of 20β-hsd Ⅰ was up-regulated and then suppressed signifi- cantly, while the expression of 20β-hsd Ⅱ was up-regulated in a time dependent manner in male fish. These results demonstrated the differential regulation pattern of 20β-hsd Ⅰ and 20β-hsd Ⅱ in response to hCG.