Fig. 4.

Dbx1-derived OLs myelinate axons of PV⁺ and PV⁻ neurons in cell clusters. a, c Confocal images of two YFP⁺ cell clusters composed of YFP⁺/DsRed⁺ OLs (white arrowheads) and YFP⁺ interneurons at PN19 in the somatosensory cortex of Dbx1^CRE;Rosa26^YFP;PLP^DsRed mice. Insets: magnification of a YFP⁺/DsRed⁺ OL and a YFP⁺ interneuron of the same clusters (asterisks). Scale bars: 25 and 5 µm. b The DsRed⁺ branches of OLs belonging to the cluster in a (top, white arrowheads) co-localize with the axonal marker SMI-312 (middle) and MBP (bottom), confirming that these cells are myelinating cells (n = 24 firstOLs from n = 3 mice). d The DsRed⁺ branches of OLs belonging to the cluster in c (top, white arrowheads) co-localize with the axonal marker SMI-312 (middle) and PV, the specific marker of FSI (bottom), confirming that some branches myelinate PV⁺ interneurons. The asterisk indicates the soma of the PV⁺/YFP⁺ interneuron in the cluster (mean area occupied by YFP⁺/DsRed⁺ OL: 13419 ± 698 µm²; mean diameter: 155.57 ± 7.88 µm; n = 9 from 9 clusters). Scale bars in b and d: 50 µm. e Spatial distribution of YFP⁺/DsRed⁺ OLs (red) and YFP⁻/DsRed⁺ OLs (gray) with respect to YFP⁺ interneurons (green) in YFP⁺ cell clusters (n = 22 clusters). Note the shorter intersomatic distances for OLs and interneurons from the Dbx1 lineage, but the lack of a specific orientation of OLs. f Box plots of distances (d) of YFP⁺/DsRed⁺ OLs (red) and YFP⁻/DsRed⁺ OLs (gray) to YFP⁺ interneurons (mean intersomatic distance: 44.2 ± 3.5 µm for n = 33 YFP⁺/DsRed⁺ OLs compared to 53.5 ± 2.1 µm for n = 99 YFP⁻/DsRed⁺ OLs, respectively, in 22 clusters; Mann–Whitney U test; significant p-value is indicated). Boxes show interquartile ranges and medians; whiskers indicate 10% and 90% percentile values. g Dot plots of percentages of PV⁺ and PV⁻ axons co-localizing with SMI-312 and DsRed⁺ branches of YFP⁺/DsRed⁺ OLs (red; n = 7 clusters from 3 mice) and YFP⁻/DsRed⁺ OLs (gray; n = 7 clusters from 3 mice) (two-way ANOVA, F = 0.978 and DF = 1; significant p-values are indicated). Data in g are presented as mean ± SEM