Melatonin Receptor RNA Expression in Xenopus Neural Retina and Pigment Epithelium

Document Type

Article

Publication Date

12-1-1997

Description

Purpose. Melaionin is an Indolamine hormone presumably synthesized by retinaî photoreceptors, and may act as a para:rine signal of darkness wilhin the retina. Previous studies have suggested that rrelatonin may be involved in photoreceptor outer segment disc shedding and phago:ytosis, and modulation of neurotransmitter release in the inner retina. The goal of his study was to determine if melatonin receptor mRNA is expressed in the neural retina and retinal pigment epithelium (RPE) of Xenopus laevis. Methods. Sheets oi RPE, devoid of contaminating cells, were obtained from Xenopus eyes by Dûpase treatment. Epithelial cultures were subsequently established on microporc us membrane filters in a defined medium. Total RNA was isolated from neural r;tina, fresh RPE sheets, and cultured RPE cells. RNA expression of the three know n Xenopus melatonin receptor subtypes was determined by reverse-transcription/pol] merase chain reaction (RT/PCR) amplification, followed by Southern hybridizati )n with cDNA and RNA probes. Results. PCR-amplified cDNA encoding melator in receptor subtypes l B and 1C, but not 1 A, were detected in reverse-transcribed R VA obtained from brain, neural retina and RPE. RPE cells grown in culture fur two weeks also demonstrated IB and 1C receptor RNA expression. Conclusions. RNA encoding the IB and 1C melatonin receptor subtypes is expressed in the nf ural retina and RPE of Xenopus retina, and expression persists in RPE cells when giown in culture. The expression of melatonin receptor RNA in the RPE may reflect a icgulatory role for melatonin in some diurnal events that occur in this tissue, such as r hagocytosis of photoreceptor outer segmenl membranes, and intracellular migration cf pigment granules.

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