Microglia-astrocyte crosstalk regulates synapse remodeling via Wnt signaling

Unilateral whisker lesioning at age P4 leads to removal of thalamocortical synapses in layer IV of the barrel cortex over the course of the next 6 days. Synapse removal is mediated by microglia and induced by CX3CL1-CX3CR1 signaling between neurons and microglia. Downstream of CX3CL1-CX3CR1 activation, microglia induce astrocyte morphological changes and activation of canonical Wnt signaling in astrocytes. To explore the spatial pattern of microglia Wnt ligand expression and astrocyte Wnt receptor expression in astrocytes, we analyzed coronal sections containing the barrel cortex from 4 wild-type mice and 4 CX3CL1 knockout mice at 24 hours after whisker lesioning by multiplexed error-robust fluorescent in situ hybridization (MERFISH). Brains were isolated from P5 mice at 24 hours after unilteral whisker lesioning of the right side of the mouse's snout at age P4. Brains were extracted and embedded in OCT for sectioning onto specialized coverslips. Coronal sections containing the barrel cortex were collected for analysis by MERFISH. Each coverslip contained 1 coronal section from a wild-type mouse and 1 coronal section from a CX3CL1 knockout mouse.