Abstract
Purpose :
The Crumbs complex is crucial for cell polarity and epithelial tissue function with Crumbs homologue-1 mutations causing severe inherited retinal dystrophies. Removal of Crb2 from photoreceptors causes retinal degeneration mimicking retinitis pigmentosa (RPE), whereas removal of Crb1 from Müller cells mimics late onset RPE. Here we study the loss of Crb2 in photoreceptors with concurrent loss of Crb1 in Müller cells to allude to the role of CRB levels in these adjacent cells.
Methods :
Crb1 KO mice were crossed with a retinal Crb2-Crx-Cre KO mice allowing ablation of Crb2 in photoreceptor precursor cells and of Crb1 in Müller cells during retinal development. Animals from different ages were analysed. Immunohistochemistry was carried out to allude to any ectopic localization of cells and proteins. Using electron microscopy (EM) and toluidine blue stained plastic-embedded sections we evaluated retinal morphology. We studied the retinal function by electroretinography (ERG) in vivo.
Results :
With Crb2 remaining in Müller cells but concurrent loss of Crb2 from photoreceptors and of Crb1 in Müller cells, the retinas showed severe disruption in retinal architecture. With onset starting at E15.5 these retina exhibit a rapid and early onset degeneration never forming an outer plexiform layer. EM at E17.5 shows the disruption of the outer limiting membrane and the loss of the subretinal space separating the photoreceptors from the retinal pigment epithelium. At 1month of age there is a combined outer and inner nuclear layer which protrudes sporadically through the inner plexiform layer (IPL) to the ganglion cell layer (GCL) which is thickened by these ectopic cells. The ectopic cells are mostly rod and cone photoreceptors, rhodopsin and cone arrestin positive respectively, largely displaced into the GCL but also the IPL. At early time points an increase in OTX2 positive photoreceptor precursors is seen suggesting an overproliferation of its lineage. ERG under scotopic conditions showed an attenuation of the a-wave and b-wave as well as the b-wave photopically.
Conclusions :
Loss of both Crb2 from photoreceptors with concomitant loss of Crb1 from Müller cells mimics Leber congenital amaurosis, whereas loss of Crb2 from photoreceptors mimics retinitis pigmentosa. Adjacently located CRB proteins in these cell types therefore are pivotal for maintenance of retinal structure and function.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.