Development of Neuropeptide Y-related Peptides in the Digestive Organs During the Larval Stage of Japanese Flounder, Paralichthys Olivaceus

cDNAs encoding three neuropeptide Y (NPY)-related peptides were identified from the Japanese flounder. One peptide corresponds to NPY, and its mRNA was expressed in the brain and retina. The second peptide corresponds to peptide YY (PYY), and its mRNA was expressed in the brain but surprisingly not in the digestive organs. This suggests that PYY lacks function as a digestive hormone in flounder. The third peptide corresponds to peptide Y (PY), and its mRNA occupied the brain and the endocrine cells of the intestine and the pancreatic accessory islets, but not of the principal islet. This suggests that PY has a dual role as a neuropeptide and a digestive hormone. In flounder larvae, PY cells appear in the intestinal epithelia at 3 days posthatching (dph), when larvae start feeding, in contrast to the endocrine pancreas at 30 dph. Therefore, the endocrine system of PY, which probably regulates the pancreatic enzyme secretion, develops synchronously with the start of feeding in the intestine but about 1 month later in the endocrine pancreas in flounder.