Abstract
Purpose :
Polycomb-group (PcG) complexes are evolutionarily conserved epigenetic machineries that remodel chromatin through histone modifications for silencing targeted genes. Recently, PcG complexes have been shown to alter retinal neurogenesis and lineage differentiation. BCOR is part of Polycomb Repressive Complex 1 that ubiquitinates lysine 119 on histone H2A. Dysregulation of BCOR is associated with eye and retinal disorders, including lens microphthalmia, oculofaciocardiodental syndrome, and retinoblastoma; however, its role in retinal neurogenesis is not well understood. We hypothesize that BCOR suppresses early retinal progenitor genes.
Methods :
We designed and validated a morpholino targeting the 5’ untranslated region of BCOR (BCOR-MO. Using Xenopus laevis and tropicalis, we injected15ng of BCOR-MO (N=21) or of Control-MO (N=21) at the two-cell stage, and then observed ocular phenotypes in the tailbuds at Stage 46.Tailbuds were assessed for the ratio of the area of the injected vs. uninjected eye and retinal layers were visualized using H&E staining. In situ hybridization was used for probing characteristic retinal lineage-specific genes and structural differences were compared by histology. The effect of BCOR expression levels on the percent of cells expressing early retinal progenitor genes (PAX6, SIX3, SIX6, LHX2, RAX, VSX2, SOX2, VIM) and lineage-specific genes (RHO, OPN1SW, VSX1, TFAP2A, PROX1) was assessed by single-cell RNA-sequencing (scRNA-seq) data from retinal organoids and fetal retina samples. Wilcoxon Rank Sum test was used for statistical analysis.
Results :
In both developmental animal models, depletion of BCOR in cell lineages giving rise to the eye led to a discrete microphthalmia phenotype without disrupting normal retinal layers. scRNA-seq analysis revealed that cells expressing BCOR had a statistically greater percentages of cells expressing the aforementioned markers (p < 0.0001). Data also revealed that BCOR expression level within the subset of cells expressing BCOR was negatively correlated with the percent of cells expressing the markers of interest.
Conclusions :
Our results indicate BCOR normally functions to regulate critical steps in retinal development. We provide evidence that appropriate homeostatic BCOR expression is required for normal eye development, suggesting that alterations in BCOR expression may contribute to progression and development of retinal disorders.
This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.