MOLECULAR CHARACTERISTICS, GENOMIC STRUCTURE AND EXPRESSION PATTERNS OF DIVERSE BMP15 ALLELES IN POLYPLOID GIBEL CARP CLONE F

Bone morphogenetic protein 15 (bmp15) plays key roles in regulating development and function maintenance of reproductive system in vertebrates. In this study, we first identified two divergent bmp15 homeologs from gibel carp (Carassius gibelio Bloch) clone F. Both Cgbmp15a and Cgbmp15b possess 3 different alleles, which were obtained from ovary cDNA by using rapid-amplification of cDNA ends (RACE). Multiple sequence alignment of Bmp15 protein in vertebrates and phylogenetic analysis of gibel carp, crucian carp, and zebrafish bmp15 genomic sequences indicated that two rounds of polyploidization had been occurred during allo-hexaploid gibel carp evolution. The early polyploidy produced the two divergent bmp15a and bmp15b, and the late polyploidy generated the 6 Cgbmp15 alleles of gibel carp. Synteny analysis of genomic regions around bmp15 gene in vertebrates suggested that the complex genomic changes might occur after the polyploidization in gibel carp, such as the loss of bmp15 adjacent genes. Cgbmp15a and Cgbmp15b were predominantly expressed in ovary with the highest level in cortical alveolus oocytes. The Cgbmp15a level is remarkably higher than Cgbmp15b in adult tissues and oocytes at different developmental stages (P<0.05). Moreover, Cgbmp15a increased at 6 hours and reached peak level at 8 hours after DHP induction in vitro, while Cgbmp15b slightly increased at 8 hours after DHP induction. These results indicate that Cgbmp15a play a major role in gibel carp oocyte development and maturation.