Human organoids recapitulating the cell-type diversity and function of their target organ are valuable for basic and translational research. We developed light-sensitive human retinal organoids with multiple nuclear and synaptic layers and functional synapses. We sequenced the RNA of 285,441 single cells from these organoids at seven developmental time points and from the periphery, fovea, pigment epithelium and choroid of light-responsive adult human retinas, and performed histochemistry. Cell types in organoids matured in vitro to a stable "developed" state at a rate similar to human retina development in vivo. Transcriptomes of organoid cell types converged toward the transcriptomes of adult peripheral retinal cell types. Expression of disease-associated genes was cell-type-specific in adult retina, and cell-type specificity was retained in organoids. We implicate unexpected cell types in diseases such as macular degeneration. This resource identifies cellular targets for studying disease mechanisms in organoids and for targeted repair in human retinas.
Calcium is a messenger ion that controls all aspects of cone photoreceptor function, including synaptic release. The dynamic range of the cone output extends beyond the activation threshold for voltage-operated calcium entry, suggesting another calcium influx mechanism operates in cones hyperpolarized by light. We have used optical imaging and whole-cell voltage clamp to measure the contribution of store-operated Ca2+ entry (SOCE) to Ca2+ homeostasis and its role in regulation of neurotransmission at cone synapses. Mn2+ quenching of Fura-2 revealed sustained divalent cation entry in hyperpolarized cones. Ca2+ influx into cone inner segments was potentiated by hyperpolarization, facilitated by depletion of intracellular Ca2+ stores, unaffected by pharmacological manipulation of voltage-operated or cyclic nucleotide-gated Ca2+ channels and suppressed by lanthanides, 2-APB, MRS 1845 and SKF 96365. However, cation influx through store-operated channels crossed the threshold for activation of voltage-operated Ca2+ entry in a subset of cones, indicating that the operating range of inner segment signals is set by interactions between store- and voltage-operated Ca2+ channels. Exposure to MRS 1845 resulted in ∼40% reduction of light-evoked postsynaptic currents in photopic horizontal cells without affecting the light responses or voltage-operated Ca2+ currents in simultaneously recorded cones. The spatial pattern of store-operated calcium entry in cones matched immunolocalization of the store-operated sensor STIM1. These findings show that store-operated channels regulate spatial and temporal properties of Ca2+ homeostasis in vertebrate cones and demonstrate their role in generation of sustained excitatory signals across the first retinal synapse.
Adenine and uridine nucleotides and adenosine are proposed to act as neuromodulators and other nucleotides and nucleosides are also suggested to be involved in brain function. A following major step towards the verification of the functional role of nucleotides and nucleosides in the brain would be the examination of regional distribution of purines, pyrimidines and the enzymes involved in their metabolism. Using our recently developed chromatography-based assay for nucleosides from tissue homogenates, we analysed nucleosides in microdissected samples derived from various regions of human brain. Marked differences in the levels of nucleosides were measured in the cerebral cortex, cerebellar cortex, thalamus and white matter. The greatest levels of most nucleosides were found in the cerebral cortex, followed by the cerebellar cortex and the white matter while the smallest concentrations were found in the thalamus, although adenosine and xanthine showed a different distribution pattern in these brain areas. Within the cerebral cortex, the measured substances showed little variations except certain high levels in the cingulate and low levels in the frontal cortex. Even distribution of nucleosides was found in the thalamic nuclei while relative high values were measured in the medial geniculate body. Since a dramatic change in nucleoside concentrations occurs after death, the measured nucleoside concentrations are an interplay of original nucleotide and nucleoside concentrations and enzyme reactions following death. Thus our results suggest regional differences in nucleotide and nucleoside composition and nucleotide metabolising enzyme activities between brain areas.
