| |
Fig. 6. Xsna expression during neural crest migration in Xenopus.
Distribution of Xsna mRNA shown by in situ hybridisation under dark field
illumination, with corresponding bright field views below (A-F) or to the
right (G-I). Scale bar = 400 pm in E, G; 200 pm in A-D,F; 100 pm in H,I.
A: Stage 23. Transverse head section showing strongly labelled mandib-
ular aggregates of cephalic neural crest (c) migrating around the pro-
spective brain (nt) and eye primordia (ee). B: Stage 22. Transverse head
section. Arrows indicate Xsna expression in ventral prospective forebrain.
C: Stage 24. Horizontal head section showing hyoid and branchial ag-
gregates of cephalic neural crest (c) migrating into the prospective bran-
chial arch region (ba). The hybridisation signal in the surrounding visceral
arch mesoderm (v) conceals the outline of the aggregates. D: Stage 21.
Anterior of sagittal section. Distinct expression in neural tube roofplate
(rp) and trunk neural crest (c) above. Labelling in mesoderm (pm) and
endoderm of pre-chordal plate also. E: Stage 23. Transverse anterior
trunk section. No labelling in notochord (n), myotomes (my) and proneph-
roi primordia in dorsal lateral plate (pn), while transcripts are still detected
in sclerotome (s), dermatome (dm), and the rest of lateral plate (Ip).
Labelling in neural tube roofplate (rp) and trunk neural crest (c). F: Stage
23. Extreme posterior transverse section of embryo in (E). Paraxial me-
soderm not yet segmented (us) and notochord (n) is undifferentiated
mesoderm. G: Stage 28. Horizontal trunk section. Strong expression in
pre-migratory trunk neural crest cells (c) along midline between muscle
blocks (my). H: Stage 28. Transverse trunk section. Strong expression in
pre-migratory trunk neural crest cells (c) above the neural tube (nt). I:
Stage 35. Transverse trunk section. Strongly labelled trunk neural crest
cells (c) migrating (arrows) dorsally into fin (df) and ventrally around
neural tube (nt) and notochord (n). a = anterior: ba = branchial arch
region: c = neural crest; df = dorsal fin; dm = dermatome; e = endo-
derm; ee = eye; ep = epidermis; Ip = lateral plate mesoderm: my =
myotome; n = notochord; nt = neural tube; p = posterior; pm = pre-
chordal mesoderm; pn = pronephros; rp = roofplate; s = sclerotome; us
= unsegmented paraxial mesoderm; v = visceral arch mesoderm. |
