Abstract Smad (mothers against decapentaplegic homologue) proteins are the downstream signalling factors involved in TGFβ (transforming growth factor beta) pathways. The present study was aimed to reveal the estradiol feedback regulation of Smad signalling in one of the endangered sturgeon species Acipenser dabyanus. Two receptor‐activated (R‐) smad paralogues, smad2 and smad3 were identified in Yangtze sturgeon, whose full‐length cDNA sequences were 1,824 and 1,876 base pairs, encoding 467 and 426 amino acids respectively. Multiple sequence alignment suggested that both Smad2 and Smad3 were highly conserved among vertebrates. Phylogenetic analysis indicated that Smad2 was more conserved than Smad3 in Yangtze sturgeon. Tissue distribution analysis revealed that both smad2 and smad3 transcribed ubiquitously in heart, liver, spleen, kidney, intestine, testis, ovary, midbrain and pituitary. Transcription levels of smad2 and smad3 in the ovary were increased significantly after 17β‐estradiol (E2) intraperitoneal injection (p < 0.05). Besides, transcriptions of aromatase (cyp19a1a), and oestrogen receptor beta (erβ) were decreased due to E2 injection (p < 0.05). These results indicate that E2 exerts positive feedback effect on R‐smad signalling, potentially through the downregulation of aromatase and ERβ, in the ovary of sturgeons.
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