Expression and regulatory mechanisms of ghrelin in blunt snout bream (Megalobrama amblycephala, ♀) × Topmouth culter (Culter alburnus, ♂) hybrid

Abstract Background Hybridization is a common strategy in fish breeding, particularly interspecific crosses, which can confer improved growth and feeding traits. The hybrid between blunt snout bream ( Megalobrama amblycephala , ♀) and topmouth culter ( Culter alburnus , ♂), known as BT, exhibits enhanced growth and herbivorous feeding preferences. Ghrelin , a conserved appetite-related peptide in teleosts, serves as an ideal gene for investigating gene regulation in hybrid fish. Results In the present study, we cloned and characterized the preproghrelin gene in BT and its paternal species, revealing high sequence similarity and typical functional domains. Ghrelin was among the highly expressed transcripts in the foregut of BT, showing maternal-biased allele expression. Allele-specific expression and regulatory analysis indicated compensatory cis - and trans -regulatory effects, reflecting regulatory balance from both parental genomes. To explore downstream pathways, BT individuals were intraperitoneally injected with acyl- ghrelin , followed by transcriptome analysis of brain and liver tissues. Acyl- ghrelin significantly modulated appetite and energy metabolism-related genes, notably downregulating lepa in the liver, and revealed distinct tissue-specific transcriptional responses. Conclusions These findings indicate that ghrelin expression patterns are consistent with the previously reported feeding and growth advantages of BT. The findings provide insights into the regulatory basis of gene expression dominance in interspecific hybrids and support the potential of targeting cis -regulatory elements for molecular breeding in aquaculture.