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Diana M Mitchell, Timothy McGinn, Ruth Frey, Deborah L Stenkamp; Regulation of the tandemly duplicated LWS opsin genes during development and regeneration in zebrafish. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):450.
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© ARVO (1962-2015); The Authors (2016-present)
Retinoic Acid (RA) regulates photoreceptor fate, differentiation, and survival. Our microarray analysis revealed upregulation of LWS-1 in embryonic zebrafish eyes treated with RA during photoreceptor differentiation. LWS-1 is the upstream member of the tandemly duplicated LWS array also containing LWS-2, orthologous to the human L/M array. Normally, LWS-1 is expressed in red-sensitive cones located mainly in ventral retina, but not until larval stages. Adult retinas show specific spatial patterns of LWS-1 and LWS-2 cones, but how these patterns are achieved is not known. Understanding how the LWS array functions during development and regeneration is important for achieving long-term goals that aim to regenerate proper photoreceptor subtype ratios and high acuity color vision in damaged retinas.
We used the transgenic line LWS-PAC(H) reporting LWS-1:GFP and LWS-2:RFP expression to examine individual cones of RA treated and control retinas by confocal microscopy and spatial pattern analysis. To determine if LWS cones recapitulate spatial patterns following regeneration, we examined LWS-1 and LWS-2 expression by in situ hybridization in regenerated adult retinas following ouabain damage that destroys all retinal neurons.
Confocal imaging of LWS-PAC(H) retinas revealed that RA treatment results in ventrally located LWS-1 expressing cones, and a large proportion of these cones co-express GFP and RFP, indicating that RA induced a switch from LWS-2 to LWS-1 in individual cones. Spatial pattern analysis of cone mosaics indicated that LWS-1 cones present in RA-treated eyes did not disrupt the LWS-2 cone mosaic, providing further evidence that LWS-1 cones following RA treatment are post-mitotic LWS-2 cones that switched opsin expression. We find that cones expressing LWS-1 and LWS-2 in regenerated retinas do not recapitulate the topographic distribution seen in undamaged retinas.
Our results suggest that RA signaling may act as a molecular toggle regulating the LWS gene array to promote the proper patterning of LWS-1 and LWS-2 cones during development. However, the patterning mechanism(s) regulating the LWS array during development is not similarly engaged during regeneration. This is the first indication that global topographic patterning cues during regeneration do not function in the same manner as during development.
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