title: Determination of the minimal domains of Mix.3/Mixer required for endoderm development.
abstract: The Mix/Bix family of Pax-like homeodomain transcription factors is expressed early in vertebrate development and play important roles in endoderm and mesoderm formation. Like other Pax-related homeodomain proteins, the Mix/Bix family binds DNA as monomers or dimers and dimerization is mediated by the homeodomain. While the Mix/Bix family shares extensive sequence homology within the DNA-binding homeodomain, ectopic expression of these proteins has profoundly different outcomes. Expression of Xenopus Mix.3/Mixer in explanted ectoderm results in endoderm differentiation, whereas Mix.1 expression does not. In this study we sought to define the domains of Mix.3/Mixer that are responsible for this endoderm inducing activity. We generated domain swap mutants between Mix.3/Mixer and Mix.1 and tested their ability to induce endoderm in explanted ectoderm. We demonstrate that the homeodomain and sixty-two amino acids in the carboxyl terminus are required to induce endoderm and that these domains must be on the same polypeptide and can not act in trans as a heterodimer. A Smad2 interaction motif in Mix.3/Mixer is involved in endoderm differentiation but is not essential. Thus, we have defined the regions of Mix.3/Mixer that confer endoderm-inducing activity. These studies reveal a novel co-operation between the homeodomain and a small domain in the carboxyl terminal region that is essential for Mix.3/Mixer function.
authors.affiliation: Department of Pathology, St Jude Children's Research Hospital, 332 North Lauderdale Street, Memphis, TN 38105, USA.
authors.forename: Joanne R
authors.initials: JR
authors.lastname: Doherty
authors.forename: Haiqing
authors.initials: H
authors.lastname: Zhu
authors.forename: Emin
authors.initials: E
authors.lastname: Kuliyev
authors.forename: Paul E
authors.initials: PE
authors.lastname: Mead
mesh_terms: D000818:Animals; D001483:Base Sequence; D004247:DNA / Q000235:genetics / Q000378:metabolism; D004627:Embryonic Induction; D004707:Endoderm / Q000378:metabolism*; D005326:Fetal Proteins / Q000235:genetics; D018507:Gene Expression Regulation, Developmental; D018398:Homeodomain Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D016296:Mutagenesis; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D051899:Smad2 Protein / Q000378:metabolism; D020825:T-Box Domain Proteins / Q000235:genetics; D014157:Transcription Factors / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D029867:Xenopus Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D014982:Xenopus laevis / Q000196:embryology / Q000235:genetics / Q000378:metabolism; D000098908:Brachyury Protein
chemical_list: D004247:DNA; D005326:Fetal Proteins; D018398:Homeodomain Proteins; D051899:Smad2 Protein; D020825:T-Box Domain Proteins; D014157:Transcription Factors; D029867:Xenopus Proteins; D000098908:Brachyury Protein; C497785:Smad2 protein, Xenopus; C405705:mixer protein, Xenopus