When Brachyury meets Smad1: the evolution of bilateral symmetry during gastrulation.
Understanding the events that led to the emergence of the bilaterians is a daunting task, impaired by the huge evolutionary gap separating us from the pre-Cambrian. During gastrulation, the expression of the transcription factor Brachyury is remarkably well conserved around the blastopore of bilaterians and cnidarians. Only the bilaterian Brachyury proteins, however, share a distinctive N-terminal sequence not found in outgroups such as cnidarians, sponges or placozoans. We now know that, in vertebrates, this N-terminal domain confers specific transcriptional activity, by recruiting Smad1, the first identified co-factor for Brachyury. Smad1 is an effector of the BMP pathway, and has been isolated in bilaterians and cnidarians. Here, I propose that the protein-protein interaction between Brachyury and Smad1 represents an evolutionary novelty of the Urbilateria. The gain of the N-terminal domain might have been selected to spatially modulate the activity of Brachyury, thereby facilitating the establishment of bilateral symmetry during gastrulation movements.
Department of Zoology, University of Cambridge, Downing Street, Cambridge CB2 3EJ, UK. smarcellini@udec.cl
Sylvain
S
Marcellini
D000818:Animals; D005075:Biological Evolution; D019521:Body Patterning / Q000235:genetics / Q000502:physiology*; D005326:Fetal Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D005775:Gastrula / Q000502:physiology*; D005786:Gene Expression Regulation; D015398:Signal Transduction; D051898:Smad1 Protein / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D020825:T-Box Domain Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D000098908:Brachyury Protein
D005326:Fetal Proteins; D051898:Smad1 Protein; D020825:T-Box Domain Proteins; D000098908:Brachyury Protein