Müller Glia-Vasculature Interactions in the Developing Retina.

Coordinated signaling among neurons, glia, and the vasculature is essential for nervous system development. In the developing retina, spontaneous cholinergic retinal waves are the primary source of neural activity during the early maturation of the vasculature. Here, we test the hypothesis that retinal waves influence angiogenesis and the maturation of the glial-vascular interface. We first found that retinal vasculature grew normally in mice lacking β2-containing nicotinic acetylcholine receptor-mediated retinal waves, demonstrating that early spontaneous activity is not required for angiogenesis. We next examined how Müller glia establish and signal at the developing glial-vascular interface. Sparse labeling and immunohistochemistry revealed that Müller glial lateral processes closely associate with endothelial tip cells during intermediate and deep layer angiogenesis and establish Aquaporin-4-enriched endfeet at vascular contact sites from the earliest stages of vascular growth. These associations were stable across development and persisted even when diving-vessel trajectories were disrupted in Piezo2 conditional knockouts. To determine whether glial signaling at the vascular interface is coupled to retinal waves, we combined two-photon calcium imaging with simultaneous retinal ganglion cell voltage-clamp recordings. Müller glial endfeet exhibited robust, compartmentalized calcium transients that were largely uncorrelated with retinal waves. Although blocking GABA-A receptors with gabazine increased wave-correlated activity in all glial compartments, the majority of endfoot calcium signaling remained wave-independent. Together, these findings support a model in which both angiogenesis and establishment of the Müller glial-vascular interface proceed through wave-independent developmental programs.