Meeting Abstract
The advent of single cell RNAseq has enabled the transcriptomic comparison of cell types within and between species. By characterizing the cell type diversity of phylogenetically diverse animals, we can identify how and when key innovations in cell types have occurred in various lineages. Here, we present progress in documenting the diversity of photoreceptor cell types in the sea lamprey Petromyzon marinus, a basal branching jawless vertebrate. We dissociated retinas and brains of larval and adult lamprey, generating ~15,000 retinal cell transcriptomes for each stage with Chromium 10X technology, clustered them with Seurat in R, and validated markers for key cell type clusters with in situ staining methods. The adult lamprey retina showed overt cell type conservation with jawed vertebrates, although canonical markers of retinal ganglion cells and amacrine cells labeled both populations variably, suggesting that these cell types are not yet fully distinct in jawless fishes. Additionally, the photoreceptors and bipolar cells expressed deep brain opsins highly, suggestive of nonvisual photoreceptive roles. In stark contrast, the histologically simple retinas of the larval lamprey lacked most markers for bipolar cells, suggesting that larvae lack this cell type. Additionally, the larval photoreceptors were devoid of visual opsins, expressing only deep brain opsins, suggesting that larval retinal photoreceptors first differentiate as ambient light sensors resembling pineal and deep brain photoreceptors. Together, our data support the photoreceptor origin of bipolar cells, and the evolution of retinal, pineal, and deep brain photoreceptors by division of labor.
