Figure 4.

ATM-like microglia are induced by morphogenetic constraints and tissue mechanical lesions

(A and B) Coronal E18.5 brain hemisections immunostained with IBA1 and Spp1 showing a marked recruitment of Spp1-expressing microglia at the CSA of Emx1^cre/+;RhoA^fl/fl mice, with approximately 75% of Spp1-positive CSA microglia in mutants, but 8% of CSA cells detected in controls at this stage (n = 4 at least for each condition, from a minimum of two distinct litters).

(C and D) Coronal E15.5 brain hemisections immunostained for IBA1 and Spp1 showing a significantly diminished percentage of CSA microglia expressing Spp1 in E15.5 Brn4^cre/+; Wnt3a^dta/+ mutant mice compared to controls, despite a conserved number of accumulating cells (n = 4 at least for each condition, from a minimum of two distinct litters).

(E) Schematic representation of in utero lesion (IUL) procedure induced by mechanical poking of the neocortex using a glass capillary.

(F) Coronal sections through the E14.5 neocortex of control and IUL embryos collected 2.5 h after lesion induction, showing amoeboid Cx3cr1^gfp-positive cells accumulating at the lesion site and the co-expression of Spp1 and Mac2 (solid arrowheads) in IUL embryos but dispersed Cx3cr1^gfp-positive cells and no expression of ATM markers in controls (n_controls = 9, n_IUL = 8, from at least two distinct litters). Quantification of the percentage of Cx3cr1^gfp-positive cells at the lesion site co-expressing ATM markers (n_SPP1 = 4, n_MAC2 = 3, n_GPNMB = 4 from at least two distinct litters).

Graphs show means ± SEM. Mann-Whitney U tests were performed for statistical comparison, ^∗p < 0.05. Scale bars: 200 μm in (A) and 100 μm in (C) and (F).

Am, amygdala; CSA, cortico-striato-amygdalar boundary; Ncx, neocortex; Str, striatum.