Augmentation of dmrt1 leads to gonadal differentiation towards testis in cyp17a1−/−;XX common carp

Although the essential role of estrogen in ovarian differentiation has been documented in several species of fish, this remains unknown in allotetraploid common carp ( Cyprinus carpio ). Here, the gonads from common carp with the cytochrome P450 family 17 subfamily A member 1 ( cyp17a1 ) −/− genotype (knockout, KO), which exhibited complete testicular differentiation regardless of their genetic sex determination (GSD) system (XX or XY), were analyzed for transcriptional profiles at various stages during gonadal differentiation. At 25, 32 and 60 days post-hatching (dph), the doublesex and mab-3 related transcription factor 1 ( dmrt1 )- ovarian aromatase ( cyp19a1a ) loop pattern could be clustered into high dmrt1 -low cyp19a1a and low dmrt1 -high cyp19a1a clusters, depending on the presence or absence of the male-determining gene on the Y chromosome ( mdy ) in genetic male and female cyp17a1 +/+ carp (Control, Con), respectively. The transcriptional profile of KO;XY carp continuously exhibited similar patterns to those of Con;XY carp in the dmrt1 - cyp19a1a loop (high dmrt1 -low cyp19a1a ). However, the gene expression profiles of KO;XX carp deviated from those of Con;XX carp and skewed towards those of Con;XY and KO;XY carp from 25 to 60 dph, and clustered with those of Con;XY carp at 90 dph. At the same stage from 25 to 60 dph, Con;XX exhibited upregulated meiosis-related genes, including synaptonemal complex central element protein 2 ( syce2 ), REC8 meiotic recombination protein b ( rec8b ), and DNA meiotic recombinase 1 ( dmc1 ), among which only dmc1 was observed to be upregulated in KO;XX carp. Administering 17β-estradiol restored ovarian differentiation in KO;XX carp. Antagonism between Dmrt1 and cyp19a1a /17β-estradiol was observed in fish gonads due to a direct interaction between Dmrt1 and Steroidogenic factor 1 (Sf-1), whereby Dmrt1 repressed Sf-1's ability to activate the cyp19a1aA and cyp19a1aB promoters. The Con;XX fish at 90 dph exhibited comprehensively advanced meiotic processes. We uncovered the genetic basis of a two-phase checkpoint regulatory mechanism of the putative mdy and estrogen sufficiency and elucidated the association between dmrt1 and estrogen signaling in sustaining gonadal differentiation and the meiotic process in juvenile common carp during the period of 32–90 dph. • Gonadal differentiation in common carp involves checkpoints of mdy and estrogen. • Constant dmrt1 reticence is required for ovarian differentiation in common carp. • Carp Dmrt1 blocks Sf-1-mediated cyp19a1a transcription by binding to its promoter. • Dmrt1 and cyp19a1a /estrogen determine their respective downstream cascades.