The Small GTPase RhoA Is Required for Proper Locomotor Circuit Assembly
Figure 5
Abnormal morphology and incorrect innervation in the spinal cord of RhoA cKO mice.
(A) Dark field photos demonstrated that the dorsal funiculi of RhoA cKO mutant mice at the cervical spinal cord were more shallow and widened compared to the control and heterozygous mice. RhoA cKO mice exhibited a remarkable increase in the amount of gray matter at the midline. The width (horizontal line in A, left panel) and the height (vertical line in A, left panel) of funiculi were measured. Scale bar: 500 µm. (B) The ratio of width to height measurements for the dorsal funiculus of RhoA cKO mice was significantly greater than that of control and heterozygous mice (p<0.001). No significant differences were observed between control and heterozygous mice (p>0.05) (C). At the midline, the space between the dorsal column and ventral column of gray matter of RhoA cKO mice was significantly greater compared to control and heterozygous mice (p<0.001). n = 3–4 mice per group. Data are represented as the mean ± SD. *** = p<0.001 (ANOVA followed by the Student-Newman-Keuls test). (D) Schematic drawing illustrating the strategy used for labeling spinal interneurons. Crystals of rhodamine dextran were applied unilaterally to control and RhoA cKO isolated mouse spinal cords at L4 (red rectangle). Contralateral projections were then visualized by imaging the labeled spinal cords at L2 (black dashed box) with an epifluorescence microscope. (E) Many spinal interneuron axons aberrantly cross the midline at L2 in the spinal cords of RhoA cKO mice, but not control littermates. Lower panels show an enlarged image of the area boxed in the upper panels. Scale bar represents 200 µm. Three sections per animal and N = 4 animals were analyzed per genotype.