Cell
Volume 81, Issue 1, 7 April 1995, Pages 85-94
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Article
Expression cloning of Siamois, a xenopus homeobox gene expressed in dorsal-vegetal cells of blastulae and able to induce a complete secondary axis

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Abstract

Using an expression cloning strategy that relies on a functional assay, we have cloned a novel Xenopus homeobox-containing gene, Siamois. Embryos injected in a ventral-vegetal blastomere with as little as 5 pg of Siamois mRNA develop a complete secondary axis, but the progeny of the injected cells do not participate in the secondary axis formation. In normal development, Siamois mRNA is first detected shortly after the midblastula transition, which is earlier than mRNAs for goosecoid or Xbrachyury, and is present most abundantly in the dorsal endoderm of early gastrulae. The activation of this gene can be obtained cell autonomously in dispersed embryo cells. These results indicate that Siamois may play an important role in the formation of the Nieuwkoop center.

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Present address: Institut de Biologie du Developpement de Marseille, Laboratoire de Ge̋nétique et Physiologie de Developpement, Case 907, Campus de Luminy, F-13288 Marseille Cedex 09, France.