Fig. 6. Pre-placodal markers are upregulated following grafting adjacent to the anterior-most neural plate, but not the trunk neural plate. (A) Anterior epiblast was isolated from HH stage 3⁺-4 quail embryos and grafted into chick hosts of between 0-4 ss at the level of either the most anterior part of the pre-placodal region (at the level of the presumptive nasal and lens placodes) or adjacent to the neural plate in the trunk (posterior to the pre-placodal region). Embryos were examined after 8 hours with a pan-Distalless antibody (pan-Dll) or an Eya2 probe, together with QCPN antibody to label quail tissue. Grafts adjacent to the anterior neural plate express both markers, but grafts adjacent to trunk level neural plate - which lie posterior to the pre-placodal region - do not. (B) Trunk ectoderm from young (0-2 ss) or old (7-9 ss) quail embryos was grafted into the pre-placodal region of 0-4 ss chick hosts. Embryos were examined after 8 hours with a pan-Distalless antibody (pan-Dll) or an Eya2 probe, together with QCPN antibody to label quail tissue. Young trunk ectoderm expresses both markers, but older ectoderm does not.