title: Modular evolution of DNA-binding preference of a Tbrain transcription factor provides a mechanism for modifying gene regulatory networks.
abstract: Gene regulatory networks (GRNs) describe the progression of transcriptional states that take a single-celled zygote to a multicellular organism. It is well documented that GRNs can evolve extensively through mutations to cis-regulatory modules (CRMs). Transcription factor proteins that bind these CRMs may also evolve to produce novelty. Coding changes are considered to be rarer, however, because transcription factors are multifunctional and hence are more constrained to evolve in ways that will not produce widespread detrimental effects. Recent technological advances have unearthed a surprising variation in DNA-binding abilities, such that individual transcription factors may recognize both a preferred primary motif and an additional secondary motif. This provides a source of modularity in function. Here, we demonstrate that orthologous transcription factors can also evolve a changed preference for a secondary binding motif, thereby offering an unexplored mechanism for GRN evolution. Using protein-binding microarray, surface plasmon resonance, and in vivo reporter assays, we demonstrate an important difference in DNA-binding preference between Tbrain protein orthologs in two species of echinoderms, the sea star, Patiria miniata, and the sea urchin, Strongylocentrotus purpuratus. Although both orthologs recognize the same primary motif, only the sea star Tbr also has a secondary binding motif. Our in vivo assays demonstrate that this difference may allow for greater evolutionary change in timing of regulatory control. This uncovers a layer of transcription factor binding divergence that could exist for many pairs of orthologs. We hypothesize that this divergence provides modularity that allows orthologous transcription factors to evolve novel roles in GRNs through modification of binding to secondary sites.
authors.affiliation: Department of Biological Sciences, Carnegie Mellon University.
authors.forename: Alys M
authors.initials: AM
authors.lastname: Cheatle Jarvela
authors.affiliation: Department of Biological Sciences, Carnegie Mellon University.
authors.forename: Lisa
authors.initials: L
authors.lastname: Brubaker
authors.affiliation: Division of Genetics, Department of Medicine, Brigham and Women's Hospital and Harvard Medical School, Boston, MA.
authors.forename: Anastasia
authors.initials: A
authors.lastname: Vedenko
authors.affiliation: Department of Chemistry, Carnegie Mellon University.
authors.forename: Anisha
authors.initials: A
authors.lastname: Gupta
authors.affiliation: Department of Chemistry, Carnegie Mellon University.
authors.forename: Bruce A
authors.initials: BA
authors.lastname: Armitage
authors.affiliation: Division of Genetics, Department of Medicine, Brigham and Women's Hospital and Harvard Medical School, Boston, MA Department of Pathology, Brigham and Women's Hospital and Harvard Medical School, Boston, MA.
authors.forename: Martha L
authors.initials: ML
authors.lastname: Bulyk
authors.affiliation: Department of Biological Sciences, Carnegie Mellon University veronica@cmu.edu.
authors.forename: Veronica F
authors.initials: VF
authors.lastname: Hinman
mesh_terms: D000818:Animals; D001665:Binding Sites; D004247:DNA / Q000378:metabolism*; D019143:Evolution, Molecular; D053263:Gene Regulatory Networks; D008969:Molecular Sequence Data; D010802:Phylogeny; D040081:Protein Array Analysis; D012617:Sea Urchins / Q000235:genetics / Q000378:metabolism*; D017422:Sequence Analysis, DNA; D013215:Starfish / Q000235:genetics / Q000378:metabolism*; D020825:T-Box Domain Proteins / Q000235:genetics* / Q000378:metabolism*
chemical_list: D020825:T-Box Domain Proteins; D004247:DNA
keywords: T-box; echinoderm; evo-devo; evolution; gene regulatory networks; transcription factors