Sox8 and Sox9 regulate differentiation and nuclear positioning of retinal Müller glia

Temporal patterning of retinal progenitor cells governs the sequential generation of retinal cell types, with gliogenesis occurring late in development. Sox8 and Sox9, members of the SoxE transcription factor family, are highly expressed in late-stage retinal progenitor cells and mature Müller glia, yet their functional roles remain incompletely defined. Here, we have employed gain- and loss-of-function approaches, single-cell multiomic profiling, and injury models to investigate Sox8 and Sox9 function. Overexpression of human SOX8 and SOX9 in early-stage mouse retinal progenitor cells both suppressed generation of early-born cells, consistent with a role in late-stage temporal identity, and induced ectopic generation of oligodendrocyte lineage-like cells. Conversely, conditional deletion of Sox8 and/or Sox9 in late-stage progenitors did not impair Müller glia specification, but caused radial displacement of glial nuclei into the outer retina and reduced expression of multiple markers of mature Müller glia. Loss of Sox8 and/or Sox9 in mature Müller glia modestly increased proliferation post-injury without inducing neurogenic competence. These findings suggest that Sox8 and Sox9 are dispensable for gliogenesis and repression of neurogenic competence, but are essential for proper laminar positioning and full terminal differentiation of retinal Müller glia.