Figure 8

Sox13 overexpression partly antagonizes Phox2b activity. (a-m") Chicken neural tubes electroporated at HH 12–13 either separately with pCAGGS::Phox2b-IRES-EGFP (a-a", d-d", g-g", j-j") or pCAGGS::Sox13-IRES-EGFP (b-b", e-e", h-h", k-k") or with pCAGGS::Phox2b-IRES-EGFP plus pCAGGS::Sox13-IRES-EGFP (c-c", f-f", i-i", l-l", m-m") were analyzed 48 h after electroporation. Transverse sections were stained with anti-GFP antibodies in combination with anti-NeuN (a-c"), anti-Sox2 (g-i"), anti-Islet1/2 (j-l") or anti-Lhx1,5 immunohistochemistry (m-m") or in combination with anti-BrdU antibodies (d-f") after BrdU injection into the amniotic cavity 2 h before fixation. Phox2b induces and Sox13 represses NeuN (asterisks in (a', a", b')) in the ML. When co-expressed with Sox13, Phox2b is still capable of inducing NeuN, which, however, is now also switched on in the VZ (c', c"). Cells electroporated with Phox2b are BrdU-negative whether Sox13 was co-transfected (f) or not (d). Cells electroporated with Sox13 whether co-transfected with Phox2b (i) or not (h) express Sox2, while cells electroporated with Phox2b alone are always Sox2-negative (g). Islet1,2 induction by Phox2b (j) is abolished by co-transfection of Sox13 (l). Repression of Lhx1,5 by Phox2b is not prevented by co-expressing Sox13 (m). Co-transfection of Sox13 together with Phox2b inhibits relocation to the ML (c, f, i, l, m) implemented by expression of Phox2b alone (a, d, g, j).