Figure 3

Lack of Sema6A and Sema6D in dorsal BCCs results in aberrant segregation of dorsal roots. (a) In control embryos axon bundles from each dorsal root ganglion extend to the DREZ in a well organized manner. Roots from adjacent DRGs are segregated and they are all of the same length (dashed bars). (b) In contrast, in embryos lacking Sema6A, roots from adjacent DRGs are no longer segregated (arrowheads). The arrangement of roots arising from individual DRGs is strongly disorganized and roots are often formed by fibers from two adjacent DRGs (arrowheads in (b)). (c) Similarly, roots are disorganized in embryos lacking Sema6D (arrowheads). In addition the length of the roots varied more in the absence of Sema6D (compare dashed bars in (c)). (d) Strong phenotypes were seen in 71% of the embryos lacking Sema6A and in 68% of the embryos lacking Sema6D. Only 13% of the embryos injected with an EGFP plasmid had a comparable phenotype. Downregulation of Sema6B resulted in aberrant DRG shapes and root arrangement in 30% of the embryos. (e) The shapes of DRGs were classified as arc-like when the distance between the most anterior and the most posterior fiber emanating from the DRG was the same as the anteroposterior diameter of the DRG; as bell-shaped when the fibers spread an anteroposterior length that was bigger than the diameter of the DRG; and as mushroom-like when the fibers entered the dorsal spinal cord in a segment that was shorter than the diameter of the DRG. Note that the diameter of the mushroom-like DRGs was smaller than the diameter of arc-like or bell-shaped DRGs. Bar: 200 μm.