Transcriptome analysis and CRISPR-Cas9-mediated mutagenesis identify gpr116 as a candidate gene for growth promotion in grass carp (Ctenopharyngodon idella)

Grass carp (Ctenopharyngodon idella) is an economically important aquaculture species known for its considerable variability in growth performance. In this study, we investigated the growth phenotype by comparing fast-growing and slow-growing groups. Microstructural analyses revealed that slow-growing fish exhibited significantly larger myofibrillar gaps and lower muscle fiber density. To elucidate the underlying molecular basis, we performed transcriptome (RNA-Seq) analysis of brain and dorsal muscle tissues. 328 differentially expressed genes (DEGs) were identified in dorsal muscle tissue (33 up and 295 down-regulated) and 228 in brain tissue (17 up and 211 down-regulated). Gene Ontology and KEGG enrichment analyses indicated that the DEGs were closely associated with apoptosis and angiogenesis pathways. Among the candidate genes, gpr116 was significantly up-regulated in the brain and dorsal muscle tissue of the fast-growing group. Finally, CRISPR-Cas9-mediated knockout in a zebrafish model confirmed that gpr116 deletion significantly restricted growth, underscoring its pivotal role in the growth regulation of grass carp. These discoveries lay significant groundwork for deeper exploration of growth regulation mechanisms in grass carp and offer important clues for selective breeding of key growth marker genes in this species.