Project description:Stargardt disease (STGD1) is an inherited retinopathy affecting approximately 1:8,000 individuals. It is characterised by biallelic mutations in ABCA4, and encodes a vital protein for the recycling of retinaldehyde in the retina. Despite its prevalence and impact, there are currently no treatments available for this condition. Furthermore, 35% of STGD1 cases remain genetically unsolved. Efforts have been directed towards comprehending the fundamental disease mechanisms and identifying all disease-causing variants in the extensive 150kb gene, to better aid with the development of effective therapeutic strategies. In this study, we generated iPSC lines from two monoallelic (PT1 & PT2), late onset STGD1 cases with the heterozygous complex allele - c.[5461-10T>C;5603A>T]. We differentiated these cells alongside a biallelic affected control (AC) - c.4892T>C, and c.4539+2001G>A, to retinal organoids (ROs) allowing us to investigate cellular and molecular characteristics associated with STGD1. We hypothesized that the missing inheritance in our monoallelic cases is due to an RNA defect. Consequently, we utilised a myriad of sequencing strategies including WGS, single-cell RNA sequencing (scRNAseq) and long-read RNA sequencing (LRS) to address this. ROs were grown for 230 days and developed all key retinal neurons with photoreceptor outer segments capable of ABCA4 expression. We observed patient-specific disruption to lamination with OPN1MW/LW+ cone photoreceptor retention in the RO centre during differentiation. Retention was more severe in the AC case affecting both cones and rods, suggesting a genotype/phenotype correlation. scRNAseq suggests retention may be due to the induction of apoptosis in photoreceptors. WGS successfully identified the missing alleles in both cases; PT1 reported c. 5603A>T in homozygous state and PT2 uncovered a rare hypomorph - c.4865T>C. Furthermore, ROs were able to recapitulate the retina-specific splicing defect in PT1 as shown by LRS data. Collectively, these results highlight the suitability of ROs in STGD1 modelling. Their ability to display genotype-phenotype correlations enhances their utility as a platform for therapeutic development. Importantly, both PT1 and PT2 cases were genetically resolved in this study, providing two more individuals their confirmed genetic diagnosis.
Project description:Stargardt disease is an inherited retinopathy affecting approximately 1:8000 individuals. It is characterised by biallelic variants in ABCA4 which encodes a vital protein for the recycling of retinaldehydes in the retina. Despite its prevalence and impact, there are currently no treatments available for this condition. Furthermore, 35% of STGD1 cases remain genetically unsolved. To investigate the cellular and molecular characteristics associated with STGD1, we generated iPSCs from two monoallelic unresolved (PT1 & PT2), late-onset STGD1 cases with the heterozygous complex allele - c.[5461-10 T > C;5603 A > T]. Both patient iPSCs and those from a biallelic affected control (AC) carrying -c.4892 T > C and c.4539+2001G > A, were differentiated to retinal organoids, which developed all key retinal neurons and photoreceptors with outer segments positive for ABCA4 expression. We observed patient-specific disruption to lamination with OPN1MW/LW+ cone photoreceptor retention in the retinal organoid centre during differentiation. Photoreceptor retention was more severe in the AC case affecting both cones and rods, suggesting a genotype/phenotype correlation. scRNA-Seq suggests retention may be due to the induction of stress-related pathways in photoreceptors. Whole genome sequencing successfully identified the missing alleles in both cases; PT1 reported c.-5603A > T in homozygous state and PT2 uncovered a rare hypomorph - c.-4685T > C. Furthermore, retinal organoids were able to recapitulate the retina-specific splicing defect in PT1 as shown by long-read RNA-seq data. Collectively, these results highlight the suitability of retinal organoids in STGD1 modelling. Their ability to display genotype-phenotype correlations enhances their utility as a platform for therapeutic development.
Project description:Coevolutionary change requires reciprocal selection between interacting species, i.e., that the partner genotypes that are favored in one species depend on the genetic composition of the interacting species. Coevolutionary genetic variation is manifested as genotype ´ genotype (G ´ G) interactions for fitness from interspecific interactions. Although quantitative genetic approaches have revealed abundant evidence for G ´ G interactions in symbioses, the molecular basis of this variation remains unclear. Here we study the molecular basis of G ´ G interactions in a model legume-rhizobium mutualism using gene expression microarrays. We find that, like quantitative traits such as fitness, variation in the symbiotic transcriptome may be partitioned into additive and interactive genetic components. Our results suggest that plant genetic variation is the largest influence on nodule gene expression, and that plant genotype and the plant genotype ´ rhizobium genotype interaction determine global shifts in rhizobium gene expression that in turn feedback to influence plant fitness benefits. Moreover, the transcriptomic variation we uncover implicates regulatory changes in both species as drivers of symbiotic gene expression variation. Our study is the first to partition genetic variation in a symbiotic transcriptome, and illuminates potential molecular routes of coevolutionary change. We assayed gene expression using three biological replicates for each plant genotype × rhizobium genotype combination (4 combinations) for a total of 12 chips.