Investigating the possibility of Notch signalling in the adult retina




Ronellenfitch, Kara

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The Notch signalling pathway is a highly conserved cell-to-cell signalling pathway involved in developmental cell fate determination in all metazons. When Notch is signalling, differentiation is inhibited and a progenitor-like state is favoured. This signalling pathway has been implicated in the developing retina, where the inhibition of Notch has been shown to skew the proportion of different retinal neuronal cell types. Although functional knockout studies have allowed us to characterize some of the roles of Notch in the retina, low protein levels have made it difficult to characterize the location of Notch receptors and ligands in neuronal tissue. Here we sought to characterize the localization of the Notch signalling pathway components in both the developing and the adult mouse retina. Using RT-PCR we were able to show the presence of mRNA for Notch receptors, ligands, and DNA binding cofactors for the Notch intracellular domain, CBF1, throughout postnatal development as well as in the adult retina. In situ hybridization confirmed the presence of Notch1, Notch2, and CBF1 mRNA in the embryonic (E14.5) and early postnatal (P1.5) retina similar to what has been reported in earlier studies, but in the adult retina (P40), levels were below detection. To further explore the role of Notch in the adult retina we used two transgenic mouse reporter models in which a Notch responsive element directs the expression of EGFP or Venus. In the adult retina of the NTR line (Tg(Cp-EGFP)25Gaia/J) reporter expression was detected in rod ON and cone type 2 OFF bipolar cells, as well as in a subset of both amacrine and ganglion cells. In the CBFRE:H2B-Venus line adult reporter expression was detected in photoreceptors, and a large proportion of both amacrine and ganglion cells. Together this data supports the conclusion that Notch is expressed and actively signalling in the retina throughout development and possibly in the adult retina, although below levels of in situ hybridization detection. These results represent the possibility of a previously unknown role for Notch in the adult retina.



retina, notch