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.
Marcellini
Sylvain
S
Department of Zoology, University of Cambridge, Downing Street, Cambridge CB2 3EJ, UK. smarcellini@udec.cl
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