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Fig. 1. Organizer grafts result in induction of a secondary axis. (A)
Schematic of the organizer graft created by Spemann and Mangold, using a
light-gray newt donor (Triturus cristatus) grafted into a dark-gray
host (Triturus taeniatus). The gastrulae are shown in hemisection for
illustrative purposes only (dorsal is towards the right, and the dimensions of
these embryos are more Xenopus-like than Triturus-like).
(B) The famous result of an optimal grafting experiment
(Spemann and Mangold, 1924),
showing a section through the trunk of a twinned embryo. The light-gray graft
has contributed to the notochord, medial somite and floor plate of the
secondary axis. The graft has an induced neural tube, somites, a pronephros
and a secondary archenteron cavity. (C, D) Contemporary organizer
grafts from Andrea E. Wills (UC Berkeley, CA, USA). (C) The section shows a
rafted organizer labeled with lacZ mRNA and stained with Red-Gal; the
section is taken through the trunk of a stage 28 Xenopus laevis
embryo, where the axial tissues are also stained with Tor70 antibody. (D)
Twinned Xenopus embryo, resulting from an organizer graft carried out
at stage 10.
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