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To address the roles of doublesex and mab-3-related transcription factor 1 (Dmrt1), forkhead transcription factor gene 2 (Foxl2), and aromatase in sex differentiation of Southern catfish, the cDNA sequences of these genes were isolated from the gonads. Dmrt1a and Dmrt1b were found to be expressed in the gonads, being higher in the testis. A low expression level of Dmrt1b was also detected in the intestine and kidney of the male. Foxl2 was found to be expressed extensively in the brain (B), pituitary (P), gill and gonads (G), with the highest level in the ovary, indicating the possible involvement of Foxl2 in the B-P-G axis. Cytochrome P450 (Cyp)19b was found to be expressed in the brain, spleen, and gonads, while Cyp19a was only expressed in the gonads and spleen. All-female Southern catfish fry were treated with fadrozole (F), tamoxifen (TAM), and 17b-estradiol (E 2 ) respectively, from 5 to 25 days after hatching (dah).The expression levels of these genes were measured at 65 dah. In the F-, TAM-, and FCTAM-treated groups, Dmrt1a and Dmrt1b were up-regulated in the gonad, whereas Foxl2 and Cyp19a were down-regulated, while the expression of Cyp19b in the gonad remained unchanged. Furthermore, downregulation of Foxl2 and Cyp19b was also detected in the brain.In the E 2 -treated group, Dmrt1a and Dmrt1b were downregulated to an undetectable level in the gonad, whereas Foxl2 and Cyp19b were up-regulated in the brain. Consistent with the observed changes in the expressions of these genes, 56, 70, and 80% sex-reversed male individuals were obtained in the F-, TAM-, and FCTAM-treated groups respectively. These results indicate the significant roles of Dmrt1, Foxl2, and Cyp19 in the sex differentiation of Southern catfish.

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A newly synthetic allopolyploid strain (SAS) was selected and established from gynogenetic offspring of gibel carp clone A + with 156 chromosomes induced by common carp sperm with 50 chromosomes. In this study, the allopolyploid strain was detected to contain 206 chromosomes, and the growth trait was evaluated to have 25.15% growth faster than that of clone A + . Genetic marker analyses of transferrin (Tf) alleles, ITS1 sequences and mtDNA D-loop sequences indicated that the allopolyploid strain was synthetized from maternal gibel carp clone A + and paternal common carp, and the synthetic chromosome sets were further confirmed by genomic in situ hybridization (GISH) and chromosome localization of 45S rDNA. Significantly, the synthetic allopolyploid strain has tended to be stable by five successive generations of gynogenesis, because it still keeps unisexual reproduction mode of gynogenesis. Therefore, it will become a novel variety for gibel carp aquaculture in future. K E Y W O R D SCarassius gibelio, fluorescent in situ hybridization, genomic in situ hybridization, gynogenesis, synthetic allopolyploid strain | INTRODUCTIONSince the discovery of gynogenesis in natural polyploid gibel carp from the last century (Cherfas, 1981;Golovinskaya, Romashov & Cherfas, 1965;Jiang, Yu, Chen & Liang, 1983), artificial allogynogenesis activated by heterologous sperm from red common carp had been used to propagate allogynogenetic gibel carp (Gui, 1997;Gui & Zhou, 2010;Liu et al., 2017;Mei & Gui, 2015;, and the resulted allogynogenetic gibel carp populations had been extensively cultured throughout China . Intriguingly, a few of allopolyploid individuals (about 0.5%) with an extra chromosome set of common carp were found from the allogynogenetic populations (Fan et al., 1997;Gui, Liang, Zhu & Jiang, 1991, 1993aZhao, Liu, Chen, Qing & Dong, 2004). These findings implicate that eggs of polyploid gibel carp not only have the capability to maintain all chromosomes itself, but also possess the ability to form higher ploidy allopolyploids by incorporating an alien sperm chromosome set (Gui, 1997;Gui & Zhou, 2010;Li, Liang, Wang, Zou & Gui, 2016;Yang, Gui, Zhu, Liang & Jiang, 1994;Yi et al., 2003; Zhang et al., 2015). Moreover, several allopolyploid clones or strains have been synthetic because they still maintain unisexual gynogenesis ability (Gui & Zhou, 2010;Zhu & Gui, 2007), and some of them have been applied to aquaculture practice because of the growth superiority (Li, Liang, et al., 2016).Recently, a nucleo-cytoplasmic hybrid clone A + has been created in polyploid gibel carp via androgenesis (Wang et al., 2011). Because the clone A + still maintains unisexual gynogenesis ability and manifests desirable economic traits, it has been used as a novel strain