| |
Fig. 1. Onset of Xsna expression in Xenopus mesoderm and ectoderm. Distribution of Xsna blastulae and gastrulae shown by in situ hybridisation under dark field illumination, with corresponding bright field
views below. A-D, and F are sagittal sections with the most dorsal side on the left in D and on the right in F. Scale bar = 400 pm in A-D, F; 190 pm in E. A: Stage 9. First appearance of Xsna transcripts, in most-
vegetal tier of marginal zone (z) on dorsal side (d), before external blastopore formation. B: Stage 10. Labelling is more intense and extensive on
dorsal side (d) in involuted mesoderm (i) above forming blastopore lip (b).
Arrows indicate movement of mesoderm. Xsna transcripts are also in
most-vegetal tier of ventral (v) marginal zone (2). C: Stage 10.5. Xsna
transcripts detected in involuting suprablastoporal endoderm (superficial
layer of marginal zone; se, small arrowheads) and in all involuted mesoderm (i), but not in un-involuted mesoderm (u), with a sharp boundary to
the labelling (large arrowheads) in blastopore lip (b). D: Stage 11. Involuting suprablastoporal endoderm (se, small arrowheads) and involuted
mesoderm (i) are labelled. First appearance of Xsna transcripts in ectoderm (ec, arrows). E: Stage 11.5. Sharp boundary (large arrowheads)
between expressing involuted mesoderm (i) and non-expressing un-involuted prospective mesoderm (u) still found in blastopore lip in mid-gastrulation. Ectoderm (ec) containing Xsna transcripts indicated (arrows). F: Stage 12. Mesoderm (m) lining nearly entire late-gastrula
contains Xsna transcripts, including pre-chordal mesoderm (pm) anteriorly (a). Arrows indicate ectodermal (ec) Xsna expression. a = anterior;
ac = animal cap; b = blastopore lip; bc = blastocoel: d = dorsal; e = endoderm; ec = ectoderm; i = involuted mesoderm; m = mesoderm; p = posterior; pm = pre-chordal mesoderm; se = suprablastoporal endoderm; u = un-involuted prospective mesoderm; v = ventral; z = marginal zone.
|
