Hepatic transcriptome analysis provides new insights into ghrelin regulation of the liver in Nile tilapia ( Oreochromis niloticus ).

Ghrelin is a growth-promoting hormone produced by the gastrointestinal tract that plays a crucial role through the ghrelin-growth hormone secretagogue receptor (GHS-R) and growth hormone/insulin-like growth factor-1 (GH/IGF-1) axes. To explore the effect of ghrelin on the transcriptomic profile of tilapia liver, the hepatic transcriptome of tilapia was sequenced for two groups, including saline-injected control (CL) and ghrelin-injected (GL; 2 μg/g body weight) tilapia. The transcriptome of livers from the two groups was sequenced using an Illumina HiSeqTM 2000 platform and yielded approximately 310.53 million raw reads. Subsequently, approximately 308.51 million clean reads were obtained from the total raw reads using in-house Perl scripts. Approximately 92.36% clean reads were mapped to the Nile tilapia genome using RSEM. Using the DESeq package, 250 differentially expressed genes (DEGs) were identified. Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis showed enrichment of two pathways related to RNA transcription (ribosome biogenesis in eukaryotes pathway and RNA transport pathway), with a total of 14 functional DEGs. ATP-binding and muscle contraction terms were identified as enriched using Gene Ontology (GO), yielding a total of 28 DEGs. Finally, real-time quantitative PCR (RT-qPCR) was used to confirm the accuracy of the transcriptomic results. The results of RT-qPCR were highly consistent with the RNA-seq, indicating that results of RNA-seq were valid. The differences in gene expression between the groups indicated that ghrelin-injection altered energy metabolism and RNA transcription in the tilapia liver, which provides new information to help promote the growth of tilapia.