A sex-linked SNP mutation in amhr2 is responsible for male differentiation in obscure puffer ( Takifugu obscurus )

Background Anti-Mullerian hormone receptor type II (Amhr2) is a key receptor of Amh signaling in regulating gonad development. The amhr2 gene has been identified in numerous species, including a few teleost fishes. However, the roles of Amhr2 in Amh signaling in fish are poorly studied. Methods and results In this study, an amhr2 homolog from obscure puffer ( Takifugu obscurus ) was identified, and its molecular characteristics were systematically analyzed. Expression analysis revealed that amhr2 was highly expressed in the gonads of adult pufferfish and significantly upregulated during sex differentiation. Significantly, a sex-linked SNP site was verified in obscure puffer amhr2 . Females exhibited a homozygous genotype (C/C), while males possessed a heterozygous genotype (C/G), resulting in an amino acid variation (His/Asp384) in the kinase domain of Amhr2. Then, the functions of the different Amhr2 genotypes were further investigated. The male genotype protein (Amhr2 D384 ) showed an enhanced ability to interact with the type I receptor (Bmpr1a) compared to the female genotype (Amhr2 H384 ). The phosphorylation levels of Smads and activity of the target gene ( id3 ) induced by the male genotype were also much higher than those induced by the female genotype. These results confirmed that the male genotype had an enhanced effect on the Amh signaling pathway compared with the female genotype. Conclusions This study provides direct experimental evidence for the roles of different Amhr2 genotypes in pufferfish and suggests that amhr2 is responsible for male sex differentiation in obscure puffer.