Neuropeptide F and Its Receptor Genes in the Cuttlefish Sepiella japonica: Identification, Characterization, Expression, and Potential Role in Food Intake

Neuropeptide F (NPF), an invertebrate homolog of vertebrate neuropeptide Y (NPY), exerts pleiotropic functions through its interaction with the G protein-coupled receptor (GPCR) neuropeptide F receptor (NPFR). However, the role of the NPF/NPFR system in the Chinese common cuttlefish Sepiella japonica Sasaki, 1929—a commercially and scientifically important cephalopod species in East China Sea aquaculture—remains unclear. In the present study, SjNPF/SjNPFR genes were cloned from S. japonica. Multiple alignments demonstrated that SjNPF/SjNPFR exhibited a high identity with that of other cephalopods. Spatio-temporal expression patterns revealed that SjNPF and SjNPFR transcripts were relatively highly expressed in the central nervous and digestive systems across all developmental stages. In situ hybridization (ISH) monitored clear and stable positive signals of SjNPF and SjNPFR mRNA at the junction of the subvertical lobe and the vertical lobe, as well as in the brachial lobe, pedal lobe and the palleovisceral lobe. Subcellular localization studies showed that SjNPF was primarily localized in the cytoplasm, whereas SjNPFR was membrane-localized. Moreover, under feeding-regulatory conditions (5-day starvation followed by 3-day refeeding), mRNA expression levels of SjNPF and SjNPFR in the treated group were positively correlated with starvation and negatively correlated with refeeding. These findings provide valuable insights for future investigations into the pleiotropic functional roles of the NPF/NPFR system in S. japonica and the peptidergic regulation of this system in cephalopods.