E-MTAB-6058
Single cell RNA-seq of isolated human foetal L/M-opsin cone photoreceptor populations labelled using the AAV2/9.pR2.1.GFP reporter
Human cone photoreceptors represent a rare cell population of the human retina and are largely outnumbered by other retinal cell types. Despite their rarity, cone photoreceptors are critical for optimal daylight vision and their loss has the greatest impact on sight during the progression of retinal dystrophies. This is most applicable to the L/M-opsin cone populations which form the largest proportion of cones in the human retina and are the only cone types present within the fovea, which is responsible for fine detailed vision. Better understanding of the early genesis of these cells within the human developing retina, particularly in relation to the expression of genes that could be involved in regulating early events such as cell fate decision, is required. These molecular determinants could be exploited in vitro to generate more cone photoreceptors within human stem cell-derived retinal differentiation culture systems, suitable for use in cell transpantation therapies or disease modelling purposes. Additionally, the nature of this cell population in terms of their gene expression heterogeneity remains to be defined.  State of the art technology has now advanced so that mRNA sequencing can be performed on individual cells, which means the transcriptome of rare cell populations such as cone photoreceptor cells can be interrogated without the need for ample material. Using the AAV2/9 pR2.1:GFP reporter, containing a synthetic promoter region previously characterised to drive expression in cone photoreceptors, we label and isolate human foetal L/M-opsin cone photoreceptors within the 15pcw human retinal retina. Isolated GFP+ cells were separated into individual cells using the Fluidigm C1 microfludics system, before RNA extraction and cDNA library preparation was performed. In total, 74 single cells were captured and processed for RNA sequencing; quality control of the data led to the inclusion of 65 individual cells for the downstream analysis. Principal component analysis revealed a very subtle heterogeneity across the cells, with the highest variability observed according to the first principal component (PC1). Differential gene expression analysis correlated to PC1 led to the identification of 503 significantly differentially expressed genes. Notably, some genes increase in expression across the cells when ordered according to PC1 which have previous associations with photoreceptor maturation, whereas other genes associated with developmental processes became downregulated across the cells. This led to the hypothesis that at this single timepoint in the human foetal retina, developing L/M-opsin cone photoreceptors exist at different stages of maturation. Overlapping genes were identified from comparing RNA seq data from 15pcw single cells and population samples at early and late timepoints of pR2.1:GFP+ cells, which showed the same gene expression trend between experiments. This suggests differences in cell maturation at a single timepoint of development could be representative of their true developmental trajectory. This overlapping gene dataset is also highly useful to define new gene that could be involved in cone photoreceptor development.
Human cone photoreceptors represent a rare cell population of the human retina and are largely outnumbered by other retinal cell types. Despite their rarity, cone photoreceptors are critical for optimal daylight vision and their loss has the greatest impact on sight during the progression of retinal dystrophies. This is most applicable to the L/M-opsin cone populations which form the largest proportion of cones in the human retina and are the only cone types present within the fovea, which is responsible for fine detailed vision. Better understanding of the early genesis of these cells within the human developing retina, particularly in relation to the expression of genes that could be involved in regulating early events such as cell fate decision, is required. These molecular determinants could be exploited in vitro to generate more cone photoreceptors within human stem cell-derived retinal differentiation culture systems, suitable for use in cell transpantation therapies or disease modelling purposes. Additionally, the nature of this cell population in terms of their gene expression heterogeneity remains to be defined.  State of the art technology has now advanced so that mRNA sequencing can be performed on individual cells, which means the transcriptome of rare cell populations such as cone photoreceptor cells can be interrogated without the need for ample material. Using the AAV2/9 pR2.1:GFP reporter, containing a synthetic promoter region previously characterised to drive expression in cone photoreceptors, we label and isolate human foetal L/M-opsin cone photoreceptors within the 15pcw human retinal retina. Isolated GFP+ cells were separated into individual cells using the Fluidigm C1 microfludics system, before RNA extraction and cDNA library preparation was performed. In total, 74 single cells were captured and processed for RNA sequencing; quality control of the data led to the inclusion of 65 individual cells for the downstream analysis. Principal component analysis revealed a very subtle heterogeneity across the cells, with the highest variability observed according to the first principal component (PC1). Differential gene expression analysis correlated to PC1 led to the identification of 503 significantly differentially expressed genes. Notably, some genes increase in expression across the cells when ordered according to PC1 which have previous associations with photoreceptor maturation, whereas other genes associated with developmental processes became downregulated across the cells. This led to the hypothesis that at this single timepoint in the human foetal retina, developing L/M-opsin cone photoreceptors exist at different stages of maturation. Overlapping genes were identified from comparing RNA seq data from 15pcw single cells and population samples at early and late timepoints of pR2.1:GFP+ cells, which showed the same gene expression trend between experiments. This suggests differences in cell maturation at a single timepoint of development could be representative of their true developmental trajectory. This overlapping gene dataset is also highly useful to define new gene that could be involved in cone photoreceptor development.