Genome-Wide Identification and Characterization of gh/prl/sl Family in Cynoglossus semilaevis

The Chinese tongue sole (<i>Cynoglossus semilaevis</i>) is a marine flatfish of significant economic value, characterized by pronounced female-biased sexual size dimorphism (SSD). Sexual differences of cell number and gene expression within the PIT-1 lineage of the pituitary gland may be crucial for interpreting the female-biased SSD of <i>C. semilaevis</i>. Among hormones secreted by PIT-1 cell lineage, growth hormone (<i>gh</i>), prolactin (<i>prl</i>), prolactin 2 (<i>prl2</i>), and somatolactin (<i>sl</i>) comprise a gene family within the extensive superfamily of class-1 helical cytokines. To better understand the function of the <i>gh/prl/sl</i> in teleost SSD, we firstly identified five genes of the <i>gh/prl/sl</i> family (<i>gh</i>, <i>sl</i>, <i>prl</i>, <i>prl2a</i>, and <i>prl2b</i>) and their receptors (<i>ghra</i>, <i>ghrb</i>, <i>prlra</i>, <i>prlrb</i>, and <i>prlr</i>-<i>like</i>) from <i>C. semilaevis</i> at the genome-wide level. Phylogenetic analyses revealed that the <i>gh</i>/<i>prl</i>/<i>sl</i> family and their receptors were each clustered into five distinct groups. More microsatellites were revealed in the intron 2 of <i>gh</i> gene of female rather than the male and pseudo-male individuals, which is positively correlated with its sexual expression pattern. Interaction network prediction indicated that <i>gh</i>, <i>prl</i>, and <i>sl</i> may collectively contribute to individual growth and development. A FRET experiment showed that <i>ghra</i> can act as a receptor for <i>sl</i>. Additionally, the transcripts of the <i>gh</i>/<i>prl/sl</i> family and their receptors exhibited varying abundances in the pituitary, brain, gonad, and liver of both female and male <i>C. semilaevis</i>, with most ligands showing the highest abundance in the female pituitary. Furthermore, <i>gh</i> and <i>sl</i> were found to be maternally expressed. The knock-down of <i>gh</i>, <i>prl</i>, and <i>sl</i> in the pituitary cells could lead to the expression change of <i>igf1</i>, <i>c-fos</i>, and <i>sos2</i>. This study provided a foundation for further functional characterization of the <i>gh</i>/<i>prl/sl</i> gene family, contributing to a deeper understanding of the growth and reproductive mechanisms in <i>C. semilaevis</i>.