As expected, no Myoc+ astrocytes are found embryonically but start to emerge at P4, when 4.6% of all cortical GLS astrocytes are Myoc+. This drastically increases to 91.6% at P8 and 96.6% at P12 to ultimately reach 99.2% in adulthood. In the spinal cord, 99.8% of all GLS astrocytes are Myoc+. A small subpopulation of white matter astrocytes in the corpus collosum is also Myoc+. At no point in development do we observe Myoc+ astrocytes in the parenchyma, suggesting that they are instructed locally at the surface. Values in (B) represent adjusted p values (padj; see below). Boxplots represent the median, with hinges showing the first and third quartiles and whiskers showing the interquartile range. Statistical tests in (B) were performed using a one-way ANOVA and post-hoc Tukey HSD (honestly significant difference) to calculate padj. A padj of <0.05 was considered statistically significant.