Relaxin receptor-like proteins in Scylla paramamosain: Two distinct types and their roles in ovarian development

Scylla paramamosain, a vital marine economic crab species along the southeast coast of China, has been insufficiently studied regarding its reproductive regulation. Relaxin and its receptors play crucial roles in regulating animal reproductive processes. However, their functions and mechanisms of action in crustaceans remain unclear. In this study, two relaxin receptor-like proteins genes (SpRRLP) from S. paramamosain were cloned and designated as SpRRLP1 and SpRRLP2. Sequence analysis revealed that both belong to the C1 type of leucine-rich repeat type G-protein coupled receptors (LGR), with SpRRLP1 classified as an LGR4-type and SpRRLP2 as an RXFP/LGR3-type relaxin receptor. Temporal and spatial expression profiles demonstrated that both genes are most highly expressed in the ovary and eyestalk of mature crabs, with their expression levels significantly increasing during the middle and late stages of ovarian development. RNAi experiment combined with transcriptome analysis indicated that SpRRLP1 may be involved in ovarian development through pathways such as immunity, autophagy, and estrogen signaling, while SpRRLP2 primarily regulates ovarian development via pathways including the synthesis of sex steroid-like hormones and arachidonic acid metabolism. This study provides valuable insights into elucidating the mechanisms underlying gonadal development and reproductive regulation in crustaceans.