Retinoschisin Is Expressed In A Developmental Wave Through The Retina Following Neuron Birth And Retinal Layer Formation

Abstract

Abstract: : Purpose: Juvenile X–linked retinoschisis (XLRS) affects retinal structural integrity and impairs neural signal generation by inner retinal neurons, with ERG a–wave preservation but b–wave loss. We studied the localization and time course of retinoschisin (RS) expression in postnatal retinal development. Methods: Rabbit anti–mouse RS polyclonal antisera was generated against mouse RS amino acid residues 24–37. Developmental expression of RS was studied with immunohistochemistry and in situ hybridization in mouse retinal sections and by RT–PCR in tissue dissected from specific retinal layers by laser capture microscopy (LCM). Terminally differentiated neuronal classes were identified by specific homeobox gene expression. ERGs identified the developmental time of functional synapse activity between photoreceptors and proximal retinal layers. Results: Retinal ganglion cells (RGCs) immunolabeled for RS by postnatal day 1 (P1) and showed RS message by in situ hybridization before photoreceptors appeared from the undifferentiated neuroblastic layer. RGCs dissected at P1 by LCM yielded RS message by RT–PCR. Amacrine cells (AC) labeled for RS by P3 and showed RS message by in situ hybridization. The OPL synaptic zone labeled for RS during P10–14, coincident with the appearance of the ERG b–wave, and RS localized to the post–synaptic elements. RGC and AC labeling subsided by P10–14, but adult RGCs showed continued expression by LCM and RT–PCR. Mueller cells and processes did not label for RS or carry RS message. Conclusions: RS expression occurs in a "developmental wave" through the retina, first appearing in RGC and then in progressively more posterior retinal neuronal classes as they are born and the retinal layers develop. This is consistent with local expression of RS without need for transport from distant sites. Its localization to the post–synaptic elements in the OPL suggests a role in synapse formation or stabilization. Continued expression of RS by essentially all adult retinal neurons supports a therapeutic strategy of RS protein replacement even after retinal development is complete.

Keywords: retinal degenerations: cell biology • retinal development • degenerations/dystrophies