Oxygen-dependent alternative mRNA splicing and a cone-specific motor protein revealed by single-cell RNA sequencing in hypoxic retinas.

Restricted oxygen supply in the aging eye may lead to hypoxic conditions in the outer retina and contribute not only to physiological aging but also to nonhereditary degenerative retinal diseases. To understand the hypoxic response of specific retinal cell types, we performed single-cell RNA sequencing of retinas isolated from mice exposed to hypoxia. Significantly upregulated expression of marker genes in hypoxic clusters confirmed a general transcriptional response to hypoxia. By focusing on the hypoxic response in photoreceptors, we identified and confirmed a kinesin motor protein (Kif4) that was specifically and strongly induced in hypoxic cones. In contrast, RNA-binding proteins Rbm3 and Cirbp were differentially expressed across clusters but demonstrated isoform switching in hypoxia. The resulting short variants of these gene transcripts are connected to epitranscriptomic regulation, a notion supported by the differential expression of writers, readers and erasers of m6A RNA methylations in the hypoxic retina. Our data indicate that retinal cells adapt to hypoxic conditions by adjusting their transcriptome at various levels including gene expression, alternative splicing and the epitranscriptome. Adaptational processes may be cell-type specific as exemplified by the cone-specific upregulation of Kif4 or general like alternative splicing of RNA binding proteins.