INCREASING PLATING DENSITY DURING A DEVELOPMENTAL WINDOW PREVENTS FATED ROD PRECURSORS DERAILMENT TOWARD HYBRID ROD-GLIA CELLS

In proliferating multipotent retinal progenitors, transcription factors dynamics set the fate of postmitotic daughter cells, but postmitotic cell fate redirection by extrinsic factors remains controversial. Intriguingly, transcriptome analysis of postmitotic rod precursors reveals the concurrent expression of genes critical for the Muller glia cell fate, which are rarely generated from terminally-dividing progenitors as a pair with rod precursors. By combining gene expression and functional characterization in single cultured rod precursors, we identified a time-restricted window where increasing plating density switches off the expression of genes critical for Muller glial cells. Intriguingly, rod precursors in low plating density cultures maintain the expression of genes common to both rod and glial cells and develop a mixed rod/Muller glial cells electrophysiological fingerprint, revealing rods derailment toward a hybrid rod-glial phenotype. The notion of plating density as an extrinsic factor critical for preventing rod cells diversion toward a hybrid cell state may provide a strategy to improve engraftment yield in regenerative approaches to retinal degenerative disease by stabilizing the fate of grafted rod precursors.