Gene regulation of melatonin and dopamine receptors during eye development

To gain insight into the role of melatonin and dopamine in retinal development, gene expression of two melatonin receptors, MT1, and MT2, as well as five dopamine receptors, D-1, D-2, D-3, D-4 and D-5, in the rat eye was analyzed by reverse transcription-polymerase chain reaction across various developmental stages. MT1, transcript levels reached maximum levels at embryonic day (E) 16 and then decreased gradually until reaching adult levels by postnatal day (P) 14. MT2 transcript levels similarly peaked at E16, but then decreased dramatically until birth to its lowest levels, which were maintained throughout the postnatal period. Thus, gene expression of both the MT1 and MT2 receptors showed a striking inverse correlation with maturation of the eye. In contrast to melatonin receptors, gene expression of all dopamine receptor subtypes, except for D-3, showed only an increase as development proceeds with highest levels in adulthood. The D-3 message was not detected throughout the developmental period examined. Gene expression of D-1-like receptors, D-1 and D-5, showed a substantial increase to adult levels during the fetal period at E16 and E20, respectively. Transcript levels of D-2-like receptors, D-2 and D-4, on the other hand, were not detected before birth but increased significantly to adult levels by P7 and P14, respectively. The present findings suggest the presence of unique developmental mechanisms by which transcription of various G protein-coupled receptors are regulated in the eye. (C) 2003 IBRO. Published by Elsevier Science Ltd. All rights reserved.