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Fig. 2 (Fig. 2 appears on page 111). Expression pattern of Xsna
shown by whole mount in situ hybridisation. A: Stage 10.25, vegetal view.
Mesodermal Xsna expression is in a ring around the bottom of the em-
bryo, with intensity of signalling decreasing towards the ventral side (v).
b = blastopore lip. B: Stage 11. Lateral aspect of embryo showing me-
soderm (m) and broad band of ectodermal expression (e). d = dorsal. C:
Stage 11, view from dorsal side showing break in the expression of Xsna
in the involuted mesoderm behind the blastopore lip (b) and the arc of
ectodermal expression (e). D: Stage 12, view from dorsal side showing
lack of mesodermal expression where the notochord is starting to differ-
entiate (n) and with pre-chordal mesoderm in the upper dorsal mid-line
(pc). Ectodermal expression (e) in the prospective cranial folds is now
further from the blastopore (compared with Fig. 2C) as a result of con-
vergent extension. E: Stage 12.5, top dorsal side. Bottom, side view.
Expression in the prospective cranial folds (d) and in a contiguous stripe
of cells that is probably superficial ectoderm (s) extending to the blasto-
pore (b). Notochord is visible as an unstained region (n). Down regulation
of mesoderm expression towards anterior is visible. F: Stage 14, strong
Xsna expression in the cranial neural folds (cf), and a weaker longitudinal
stripe in the superficial layer (t). Note lack of mesodermal expression
below anterior neural plate but increasing towards posterior. Strong me-
sodermal expression in the lateral plate mesoderm. G: Stage 17, neural
tube almost closed with Xsna expression on roof of the neural tube (r).
Mesoderm shows indications of segmentation (s) in mid-dorsal region.
Cranial folds strongly labelled (c). H: Tailbud stage (cleared). Labelling in
sclerotorne persisting together with posterior mesoderm (p). I: Tailbud
stage. Branchial arches (b). Trunk neural crest (t). Mesoderm in tailbud
(m). |