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Figure 4


Fig. 4. Tangential, mediolateral and trans-median defects in cell body migration occur in Tbx20 mutants. (A,B) Isl1 (green) and Hb9 (red) expression in flat-mounted hindbrains from E11.5 Tbx20 mutant and control. Trigeminal neurons (Isl1+/Hb9-) at r2 fail to migrate laterally and radially in Tbx20 mutants. Facial BM neurons (Isl1+/Hb9-) at r4 do not migrate caudally past the Isl1+/Hb9+ abducens cells (yellow, r5) in Tbx20 mutants. (C-H) Comparison of Isl1 (green) and Phox2b (red) expression in transverse sections between E11.5 Tbx20 mutants and controls (in r2, r4 and r6). Dashed line in C,D indicates the border between medial (m) and lateral (l) regions of the hindbrain used for quantification. (I) Quantification of mediolateral (M-L) cell movement determined by measuring the ratio of BM neurons (Isl1+/Phox2b+) located in the medial (m) versus lateral (l) region. Cell counts were performed on transverse sections taken at r2 levels containing trigeminal neurons at E11.5 in Tbx20 mutants and controls. Each bar represents the average of at least six sections from three different embryos; mean±s.e.m. (J) Quantification of rostrocaudal (R-C) migration of facial neurons marked by Isl1/Phox2b double labeling (yellow). Cell counts were taken from transverse sections at r4 and r6 in Tbx20 mutants and controls. Each bar represents the average of at least eight sections from three different embryos; mean±s.e.m. (K,L) The SE1::gfp transgenic reporter was crossed into the Tbx20 mutant background to reveal vestibuloacoustic (VIII) motor neuron cell bodies and axons. In E11.5 control embryos, GFP-labeled cells and axons cross the r4 midline (bracket). In Tbx20 mutants, midline crossing fails to occur. (M,N) Summary diagram comparing the cell body movements of trigeminal (V), vestibuloacoustic (VIII) and facial (VII) motor neuron migration in Tbx20 mutants and controls. Images shown are representative of four or more embryos of each genotype. Scale bars: in B, 400 µm for A,B; in H, 80 µm for C-H; in L, 160 µm for K,L.





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