Fig. 4From: Rac1 plays an essential role in axon growth and guidance and in neuronal survival in the central and peripheral nervous systemsReduced diameters of limb nerves and reduction in the number of LMC motor neurons in Olig2-Cre;Rac1 CKO/− embryos. a Diagrams traced from Fig. 2e’, g’ showing where the nerve diameters were measured. D Proximal and D Distal, measurements of dorsal nerve diameter immediately proximal and distal, respectively, to the point where Fz3 −/− dorsal axons stall. V, measurement of ventral nerve diameter at a similar distance from the plexus. b At the locations shown in (a), the nerve diameters were measured from neurofilament-immunostained whole-mount forelimbs (top) and hindlimbs (bottom) from one litter at E12.5 and a second litter at E13.5 (left and right, respectively, separated by gray dashed lines). Numbers above each set of data points are as follows: (top) P values for the WT littermate vs. Olig2-Cre;Rac1 CKO/− comparison (Student’s two-tailed two-sample unequal variance t-tests) and (bottom) the average thickness of Olig2-Cre;Rac1 CKO/− nerves as a percentage of the WT controls. c Motor neuron apoptosis visualized with cleaved caspase3 and Islet1/2 immunostaining in cross sections of E11.5 lumbar spinal cords. The ventrolateral region of the spinal cord is shown with the left border of the spinal cord demarcated by a white dashed line. Very few apoptotic cells are present in Rac1 CKO/+ controls (left), whereas cleaved caspase3 is seen in multiple Islet1/2+ cells in the Olig2-Cre;Rac1 CKO/− ventral spinal cord (right). N = 3 for each genotype. Scale bar, 500 μm. d Diagram showing the expression pattern of transcription factors in LMCL and LMCM motor neurons. SC spinal cord, D dorsal, V ventral. Adopted from Figure 5A of Hua et al. [17]. e LMCM and LMCL motor neurons in the ventrolateral spinal cord were identified as Islet1+/Foxp1+ and Islet1−/Foxp1+ populations, respectively, in cross sections of E12.5 Rac1 CKO/− (left panel; lateral is to the left) and Olig2-Cre;Rac1 CKO/− (right panel; lateral is to the right) lumbar spinal cords. White dashed lines encircle the LMC. The solid white line demarcates the border of the spinal cord. L lateral, M medial. Scale bar, 100 μm. f Quantification of the number of LMCM (top) and LMCL (bottom) motor neurons per 14-μm-thick cross section of E12.5 lumbar spinal cords. Motor neurons were counted from 10 serial sections and averaged from three pairs of WT (blue) and Olig2-Cre;Rac1 CKO/− (red) littermates, with adjacent counted sections separated by four uncounted sections. g Top, GFP immunostaining shows defects in axon growth among primary spinal cord motor neurons in dissociated cell cultures from E11.5 Hb9-GFP;Olig2-Cre;Rac1 CKO/− (right) and littermate control Hb9-GFP;Olig2-Cre;Rac1 CKO/+ (left) embryos. Red arrows, axons and axon branches. Bottom, quantification of axon lengths. Scale bar, 100 μmBack to article page