XB-IMG-146176
Xenbase Image ID: 146176
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Figure 3. The NMC model for tailbud induction and tail inducing assays. (a) dorsal view of Stage 12.5 Xenopus embryo to show approximate location of the tailbud (TB) and tail forming region (TFR), cross-sectional drawing of same stage through the midline, anterior to left, showing the germ layers and location of the chordoneural hinge (cnh) at the dorsal blastopore lip (boxed). The location of C, N and M regions in the cnh are indicated. B) side view of Stage 24 embryo with dotted line outlining approximate limits of the TFR, cross section through midline to show germ layers (endoderm = yellow, mesoderm = red, and ectoderm = blue), tailbud (boxed), cnh and posterior wall (pw) and the location of the neurenteric canal (nec). Close up of box shows the location of N, M, and C in the tailbud following neurulation, as determined in Tucker and Slack.[29] (c) Grafts of the hinge region of exogastrulae, which contain unfolded NMC regions, or tailbuds, can induce formation of secondary tails if placed inside the blastopore cavity of a blastula stage embryo (einsteck graft).[29] NE, neuroectoderm and ME, mesendoderm. (d) 180° rotations of the neural plate at Stage 13 result in the formation of two new N/M boundaries. The posterior one lies over C and is induced to form a secondary tail in the normal location, the original N/M boundary has been exposed to C and so develops into a tail with reversed dorsal (d) ventral (v) polarity and the most anterior one does not form a tail, as it has not received a C signal. (e) Tailbud inducing activity assay, animal caps expressing test genes are removed at Stages 9–10 and trimmed into 100 × 600 μM rectangles before inserting into the neural plate of a host Stage 13 embryo.[27] Ectopic tails may be formed from the graft if they contain tailbud-like activity. In this case, the dorsal ventral polarity seems to come from the host. Germ layers in A and B are coloured as standard: Blue for ectoderm, red for mesoderm and yellow for endoderm. The M region is mesodermal in fate but ectodermal in origin and is therefore coloured purple. Data from Tucker and Slack, and Beck and Slack.[27, 29] Image published in: Beck CW (2015) Copyright © 2015. Image reproduced with permission of the Publisher, John Wiley & Sons. Larger Image Printer Friendly View |