Single-cell spatially resolved transcriptomic characterization of the developing mouse cochlea

The cochlea, the sensory organ of hearing, functions as a frequency analyzer, analogous to a musical instrument. During development, while the medio-lateral axis supports differentiation of sensory cells and their surrounding supporting cells, the longitudinal axis underlies frequency-dependent properties of the cochlea. The combination of these two gene expression gradients defines unique physiological attributes of each cell intimately linked to its position within the cochlea. To determine which cochlear cell-types have a transcriptomic signature sensitive to these two gradients and identify the underlying gene regulatory networks, we took advantage of the advent of spatial single cell transcriptomics methodologies. We therefore generated a spatial transcriptomic atlas reaching single cell resolution based on the Visium HD technique, a sequencing-based technology that employ arrays of spatially barcoded probes to capture RNA molecules unbiasedly from histological tissue sections. Spatial transcriptional changes during embryonic stages, E14 and E16, as well as during postnatal development, P1 and P8, were investigated. Based on this dataset, not only cell-type assignment in single cell RNA-seq experiments could be validated, but the classification for some cell-types could be refined. Gradients of gene expression along the medio-lateral and longitudinal axes in multiple cell-types together with their temporal dynamics across development were also uncovered. Altogether, this atlas paves the way for deciphering gene regulatory networks controlling gene expression as a function of position in the cochlear cell types, providing a valuable resource for the design of efficient, robust and safe gene therapy strategies.