Identification of ActivinβA and Gonadotropin Regulation of the Activin System in the Ovary of Chinese Sturgeon <i>Acipenser sinensis</i>

Activin is a dimeric growth factor with diverse biological activities in vertebrates. This study aimed to investigate the regulatory role of the <i>activin</i> signaling pathway in the ovary of the endangered, cultured sturgeon species <i>Acipenser sinensis</i>. One <i>activinβA</i> subunit was identified, with a full-length complementary DNA (cDNA) sequence of 1572 base pairs. Multiple sequence alignment suggested that ActivinβA shared high sequence identities with its counterparts in four other sturgeon species. Phylogenetic analysis indicated the conserved evolution of ActivinβA among vertebrates from mammals to fish species. Transcripts of <i>activinβA</i> were distributed ubiquitously in the liver, kidney, intestine, ovary, midbrain, hypothalamus, and pituitary, with the highest transcription found in the pituitary. In Chinese sturgeon ovarian cells, in vitro human recombinant Activin A incubation stimulated the <i>activin</i> system-related gene transcriptions of <i>activinβA</i>, <i>follistatin</i>, its receptors -<i>activinRIIA</i> and <i>activinRIIB</i>, and drosophila mothers against decapentaplegic proteins (<i>smads</i>) <i>smad2</i>, <i>smad3,</i> and <i>smad4</i>. Ovary development-related mRNA levels of <i>cyp19a1a</i> and aromatase receptors of <i>erα</i> and <i>erβ</i> were enhanced by Activin A or human chorionic gonadotropin (hCG) incubation. Furthermore, 15 IU/mL hCG treatment increased the transcription levels of <i>activinβA</i>, <i>follistatin</i>, <i>activinRIIA</i>, and <i>smad2</i>. This suggested that the <i>activin</i> system was functional for the regulation of ovary development in Chinese sturgeon, possibly under the regulation of gonadotropin, by recruiting <i>activinβA</i>, <i>follistatin</i>, <i>activinRIIA</i>, and <i>smad2</i>. These results were helpful for the molecular exploration of activin signaling in fish species, as well as the ovarian maturation regulation of <i>A. sinensis</i>.