Figure 6

Sfrp1 partially restores a commissural axonal phenotype. (a-c) Chicken neural tubes electroporated at HH12-13 with pCAGGS::Sfrp1-IRES-EGFP (a), pCAGGS::Phox2b-IRES-EGFP (b) or pCAGGS::Sfrp1-IRES-EGFP plus pCAGGS::Phox2b-IRES-EGFP (c) were analyzed by anti-GFP immunohistochemistry. Expression of Sfrp1 did not grossly alter the morphology of neuroepithelial cells, neither did it prevent Phox2b from promoting relocation to the ML. However, Sfrp1 prevented Phox2b from repressing the growth of commissural axons (arrowheads). (d-d") Chicken neural tubes electroporated with pCAGGS::Sfrp1-IRES-EGFP and a Phox2b expression vector were analyzed by anti-GFP and anti-Phox2b immunohistochemistry as indicated. Virtually all the transfected cells express both GFP and Phox2b. (e-e") Chicken neural tubes electroporated with pCAGGS::Sfrp1-IRES-EGFP plus pCAGGS::Phox2b-IRES-EGFP were analyzed by anti-GFP and anti-Islet1,2 immunohistochemistry as indicated. Co-expression of Sfrp1 did not prevent Phox2b from inducing Islet1,2 (bracket). (f-h') Chicken neural tubes electroporated with pCAGGS::Phox2b-IRES-EGFP (f, f'), pCAGGS::Sfrp1-IRES-EGFP (g, g') or with pCAGGS::Sfrp1-IRES-EGFP plus pCAGGS::Phox2b-IRES-EGFP (h, h') were analyzed by anti-axonin-1 and anti-GFP immunohistochemistry. In (f, g, h), the anti-axonin-1 staining is shown alone, and in (f', g', h') it is merged with the anti-GFP immunofluorescence. The fascicle formed by the commissural fibers en route to the floor plate is marked by an asterisk; it is absent after Phox2b transfection and partially restored by co-expressing Sfrp1.