Fig. 3

SIX1 expression in quail-chick chimeras of the cephalic NC. a Schematic representation of the cranial NC grafting procedure. The chick neural fold/premigratory NC from midbrain to anterior rhombencephalic level was unilaterally replaced by its quail counterpart (in red) at stage HH8 (5ss); the resulting chimeras were analyzed at HH15 (25ss) for SIX1 immunoreactivity, nuclear staining (DAPI) and the presence of QCPN+ quail cells (red dotted lines indicate orientation and position of the sections shown in b-i and j-m). b-e In the prosencephalic region, SIX1 (c) is expressed in the olfactory placode (op) and the adjacent cranial mesenchyme surrounding the prosencephalon, in which quail NCC, positive for QCPN are located (d); b’-e’ Highlighting of the area boxed in b-e, showing engrafted quail cells that are either positive (arrows) or negative (arrowhead) for SIX1. f-i SIX1 and QCPN are both expressed in the head mesenchyme around the eye. f’-i’ (magnified region indicated by a boxed area in f-i) Some NCC engrafted in the periocular mesenchyme co-stain with SIX1 and QCPN (arrow), while others do not express SIX1 protein (arrowhead). j-m In the maxillary region, SIX1 expression (k) is present in the mesenchyme dorsal to the foregut, in the foregut endoderm and the core region of BA1 (ba in j) whereas the grafted QCPN+ cells (l) are located in the peripheral mesenchyme of the BA and do not express SIX1 (m Merge of SIX1 and QCPN). Scale bars, 25 μm (b-i) and (b’-i’) and 50 μm (j-m)