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Edda Kastenhuber, Andreas Staeuble, Matthias Gesemann, Stephanie Niklaus, Marion Haug, Stephan C. Neuhauss; Characterization of TRPM and TRPC Channels in the Zebrafish Retina. Invest. Ophthalmol. Vis. Sci. 2012;53(14):4311.
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© ARVO (1962-2015); The Authors (2016-present)
Glutamate, the major neurotransmitter of vertebrate photoreceptors, is released at higher rates in the dark. Light increments are detected by ON bipolar cells (BCs) expressing the metabotropic glutamate receptor mGluR6. Binding of glutamate to mGluR6 leads to the closure of the constitutively open transient receptor channel TRPM1. This inhibition is released by decreased binding of glutamate in light. It is very likely that other TRP channels, particularly of the TRPM and TRPC family, play additional roles in the retina. We therefore analyzed both TRP subfamilies in the zebrafish and focused on those with retinal expression.
Phylogenetic comparison to mammalian TRPM and TRPC genes was used to identify zebrafish orthologs. Expression was analyzed by in situ hybridization (ISH) in whole mount zebrafish larvae and retinal sections. The function of those genes expressed in the retina is characterized by morpholino gene knockdown experiments.
We found four out of eleven trpm genes to be expressed in the zebrafish eye. Of these only the two trpm1 paralogs (trpm1a and trpm1b) displayed retinal expression.Both genes are expressed in the retinal pigment epithelium and in the inner nuclear layer (INL). Trpm1a is additionally expressed in photoreceptors and the ciliary marginal zone. The role of TRPM1 in the ON pathway seems to be conserved in the zebrafish, as cells in the INL co-express trpm1 and mglur6 orthologs in ON BCs. Electroretinograms of morpholino injected larvae will confirm trpm1 function in the ON response.The expression of trpm1a in the ciliary margin hints at a role in retinal development. We compare trpm1a morphants with wild-type siblings concerning proliferation rate of retinal stem cells and number of differentiated retinal neurons. Interestingly, we discovered a novel mechanism regulating the expression of trpm1a in photoreceptors.The zebrafish TRPC family consists of twelve members. Preliminary analysis located trpc1 expression to the INL and ganglion cell layer.
As a summary, TRPM and TRPC channels are expressed in different cell types of the zebrafish retina and play a role in development and function.
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