Elsevier

Developmental Biology

Volume 343, Issues 1–2, 1–15 July 2010, Pages 138-152
Developmental Biology

Evolution of Developmental Control Mechanisms
A conserved mechanism for vertebrate mesoderm specification in urodele amphibians and mammals

https://doi.org/10.1016/j.ydbio.2010.04.002Get rights and content
Under an Elsevier user license
open archive

Abstract

Understanding how mesoderm is specified during development is a fundamental issue in biology, and it has been studied intensively in embryos from Xenopus. The gene regulatory network (GRN) for Xenopus is surprisingly complex and is not conserved in vertebrates, including mammals, which have single copies of the key genes Nodal and Mix. Why the Xenopus GRN should express multiple copies of Nodal and Mix genes is not known. To understand how these expanded gene families evolved, we investigated mesoderm specification in embryos from axolotls, representing urodele amphibians, since urodele embryology is basal to amphibians and was conserved during the evolution of amniotes, including mammals. We show that single copies of Nodal and Mix are required for mesoderm specification in axolotl embryos, suggesting the ancestral vertebrate state. Furthermore, we uncovered a novel genetic interaction in which Mix induces Brachyury expression, standing in contrast to the relationship of these molecules in Xenopus. However, we demonstrate that this functional relationship is conserved in mammals by showing that it is involved in the production of mesoderm from mouse embryonic stem cells. From our results, we produced an ancestral mesoderm (m)GRN, which we suggest is conserved in vertebrates. The results are discussed within the context of a theory in which the evolution of mechanisms governing early somatic development is constrained by the ancestral germ line–soma relationship, in which germ cells are produced by epigenesis.

Keywords

Mesoderm induction
Gene regulatory networks

Cited by (0)

1

These two authors contributed equally to this work.