Biology subjects

Valdez-Lopez, J. C.

Publications and source records attributed to Valdez-Lopez, J. C..

3 recordsLinked to original sources

bioRxiv2026

Retinal degeneration in a mouse model of CRB1 disease rescued by the photoreceptor-specific CRB1-B isoform

Many genes involved in inherited diseases produce alternate mRNA isoforms that remain poorly characterized. Functional assessment of these isoforms could therefore unlock new insights into disease pathobiology or treatment. Here we investigated the function of the newly discovered B isoform of CRB1, a gene implicated in inherited retinal degenerations. CRB1-B is the most abundant retinal isoform, and differs from the canonical CRB1-A isoform in several important ways. Crucially, CRB1-B is the only isoform expressed by photoreceptors -- the cells vulnerable to degeneration. Using a mouse model of CRB1-associated degeneration with degraded visual acuity, we find that restoring CRB1-B to photoreceptors prevents degeneration and completely rescues visual function, despite the absence of other isoforms. The therapeutic mechanism involves preservation of adherens junctions between photoreceptors and supporting glia: We establish that progressive loss of these junctions is a key pathobiological mechanism underlying photoreceptor death, and that junction loss is prevented by restoring photoreceptor expression of CRB1-B. Our findings nominate CRB1-B replacement as a promising gene therapy strategy. More broadly, they suggest that exploring disease gene isoform diversity offers an untapped opportunity to devise novel therapeutics.

neuroscience↗

bioRxiv2025

Microglia and myeloid cell populations of the developing mouse retina

Microglia make important contributions to central nervous system (CNS) development, but the breadth of their distinct developmental functions remain poorly understood. The mouse retina has been a key model system for understanding fundamental mechanisms controlling assembly of the CNS. To gain insight into where and how microglia might influence retinal development, here we identified molecularly unique myeloid cell populations that are selectively present during development, and characterized their anatomical locations. Development-specific transcriptional states were identified using single-cell (sc) and single-nucleus RNA-sequencing (RNA-seq) across multiple timepoints. Transcriptional states were validated in vivo by histological staining for key RNA and/or protein markers. Several of these development-specific myeloid populations have been described before in brain scRNA-seq atlases but not validated in vivo, while others are unique to our retinal dataset. We identify two closely-related microglial populations, labeled by the Spp1 and Hmox1 genes, that are distinguished mainly by activity of the NRF2 transcription factor. Both types are present selectively within the developing retinal nerve fiber layer where they engulf neurons and astrocytes undergoing developmental cell death. Hmox1+ microglia were also localized selectively at the wavefront of developing vasculature during retinal angiogenesis, suggesting that developmental events associated with angiogenesis modulate NRF2 activity and thereby induce microglia to switch between the Spp1+ and Hmox1+ states. Overall, our results identify transcriptional profiles that define specific populations of retinal microglia, opening the way to future investigations of how these programs support microglial functions during development.

neuroscience↗

bioRxiv2020

The C-terminus and Third Cytoplasmic Loop Cooperatively Activate Mouse Melanopsin Phototransduction

Melanopsin, an atypical vertebrate visual pigment, mediates non-image forming light responses including circadian photoentrainment and pupillary light reflexes, and contrast detection for image formation. Melanopsin-expressing intrinsically photosensitive retinal ganglion cells (ipRGCs), are characterized by sluggish activation and deactivation of their light responses. The molecular determinants of mouse melanopsins deactivation have been characterized (i.e. C-terminal phosphorylation and {beta}-arrestin binding), but a detailed analysis of melanopsins activation is lacking. We propose that an extended 3rd cytoplasmic loop is adjacent to the proximal C-terminal region of mouse melanopsin in the inactive conformation which is stabilized by ionic interaction of these two regions. This model is supported by site-directed spin labeling and electron paramagnetic resonance (EPR) spectroscopy of melanopsin, the results of which suggests a high degree of steric freedom at the 3rd cytoplasmic loop, which is increased upon C-terminus truncation, supporting the idea that these two regions are close in 3-dimensional space in wild-type melanopsin. To test for a functionally critical C-terminal conformation, calcium imaging of melanopsin mutants including a proximal C-terminus truncation (at residue 365) and proline mutation of this proximal region (H377P, L380P, Y382P) delayed melanopsins activation rate. Mutation of all potential phosphorylation sites, including a highly conserved tyrosine residue (Y382), into alanines also delayed the activation rate. A comparison of mouse melanopsin with armadillo melanopsin--which has substitutions of various potential phosphorylation sites and a substitution of the conserved tyrosine--indicates that substitution of these potential phosphorylation sites and the tyrosine residue result in dramatically slower activation kinetics, a finding that also supports the role of phosphorylation in signaling activation. We therefore propose that melanopsins C-terminus is proximal to intracellular loop 3 and C-terminal phosphorylation permits the ionic interaction between these two regions, thus forming a stable structural conformation that is critical for initiating G-protein signaling. STATEMENT OF SIGNIFICANCEMelanopsin is an important visual pigment in the mammalian retina that mediates non-image forming responses such as circadian photoentrainment and pupil constriction, and supports contrast detection for image formation. In this study, we detail two critical structural features of mouse melanopsin--its 3rd cytoplasmic loop and C-terminus--that are important in the activation of melanopsins light responses. Furthermore, we propose that these two regions directly participate in coupling mouse melanopsin to its G-protein. These findings contribute to further understanding of GPCR-G-protein coupling, and given recent findings suggesting flexibility of melanopsin signal transduction in the retina (possibly by coupling more than one G-protein type), these findings provide insight into the molecular basis of melanopsin function in the retina.

neuroscience↗