Figure 4.

KCC2 overexpression impairs the growth and maturation of brain and hindbrain structures. A, In control embryos, the acetylated tubulin staining highlights the postoptic, anterior, and posterior commissures (open arrowheads), the ventral and dorsal longitudinal tracts (filled arrowheads), the trigeminal ganglion (open arrow), and the pigmented optic cup forming the retina (filled arrow). In contrast, only the ventral longitudinal tract (filled arrowhead) and the optic vesicle (filled arrow) can be seen in KCC2-overexpressing embryos. B, Top-down view of the large Mauthner cells, which are easily discernable in control embryos. When KCC2 is overexpressed, the Mauthner cells appear less well defined but their axons cross the midline and project caudally as in control embryos. C, The hindbrain reticulospinal neurons (side view) are present in KCC2 embryos. However, their axon projections to the spinal cord (top-down view) are much less elaborated in KCC2-overexpressing embryos.