In Lhx2 deletion mutant embryos, thalamic axons are not able to enter the ventral telencephalon and aberrant topography exists in vitro.
Despite their abnormal positioning in r4, FBM neurons in fh131 mutant embryos extend axons to the correct target muscles in the second branchial arch (see Fig. S1 in the supplementary material).
Therefore, in mutant embryos, dense BP102 staining of axons beyond the CNS/PNS boundary clearly delineates a novel phenotype, herein termed an AEP defect (Axon Exiting to Periphery).
We also show normal extension of the hypoglossal, dorsal vagal and spinal cord motoneuron axons in ATF2 mutant embryos.
We used a combination of behavioral, anatomical and physiological techniques to elucidate the causes of pathfinding errors of motoneuron axons in narrowminded mutant embryos.
We found that the Robo1 rescue transgene was able to restore wild-type levels of midline repulsion to FasII-positive axons in robo1 null mutant embryos.
Dwyer et al. subjected mice of the TCA-TLZ line to random mutagenesis with N-ethyl-N-nitrosourea (ENU), followed by a breeding strategy of two intercrosses and one backcross, in order to identify thalamocortical axon phenotypes in homozygote mutant embryos at E18.5.
We found that pan-neural mis-expression of Robo1R2Ig1+2 in comm mutant embryos strongly suppressed the commissureless phenotype and restored midline crossing of many axons, as assayed by anti-HRP antibody staining, while mis-expression of Robo2R1Ig1+2 had a much milder effect.
Analysis of HS treated embryos revealed that transgenic overexpression of Tg(hsp70l:unplugged SV1-myc) in wildtype or unplugged mutant embryos did not affect the location of the AChR prepattern (Figure 5A F), or motor axons guidance (Figure 5I and J).
Genetic mosaic analysis indicates that Topped function is non-cell autonomous for motoneurons, and when wild-type cells are transplanted into topped mutant embryos, ventromedial fast muscle are the only cell type able to rescue the CaP axon defect.
