title: Critical Roles of the LIM Domains of Lhx3 in Recruiting Coactivators to the Motor Neuron-Specifying Isl1-Lhx3 Complex.
abstract: During spinal cord development, the LIM domains of the LIM homeodomain factor Lhx3 bind to either the LIM cofactor nuclear LIM interactor (NLI) or another LIM homeodomain factor, Isl1, assembling the tetrameric V2 interneuron-specifying Lhx3 complex (2NLI:2Lhx3) or the hexameric motor neuron-specifying Isl1-Lhx3 complex (2NLI:2Isl1:2Lhx3). However, the detailed molecular basis by which the Lhx3-LIM domains contribute to motor neuron specification still remains poorly understood. Here, we show that the Lhx3-LIM domains are essential for recruiting transcriptional coactivators to the Isl1-Lhx3 complex. Using a yeast genetic screening system, we identify Lhx3 point mutants that bind to NLI but not Isl1. Accordingly, these mutants fail to assemble the Isl1-Lhx3 complex. However, their interaction with coactivators is relatively intact, and they are fully functional in the Lhx3 complex and V2 interneuron specification. Interestingly, when these Lhx3 mutants are directly fused to Isl1, their transcriptional activity in the Isl1-Lhx3 complex is restored. We further show that this restoration reflects an unexpected role of the Lhx3-LIM domains, likely together with Isl1, to form an interaction interface for coactivators. Our results suggest that the Lhx3-LIM domains play critical roles in transactivation of the Isl1-Lhx3 complex by not only directing the assembly of the Isl1-Lhx3 complex but also recruiting coactivators to the complex.
authors.affiliation: College of Pharmacy and Research Institute of Pharmaceutical Sciences, Seoul National University, Seoul, South Korea.
authors.forename: So Yeon
authors.initials: SY
authors.lastname: Seo
authors.affiliation: Neuroscience Section, Papé Family Pediatric Research Institute, Department of Pediatrics, and Department of Cell, Developmental & Cancer Biology, Oregon Health and Science University, Portland, Oregon, USA.
authors.forename: Bora
authors.initials: B
authors.lastname: Lee
authors.affiliation: College of Pharmacy and Research Institute of Pharmaceutical Sciences, Seoul National University, Seoul, South Korea leeseung@snu.ac.kr.
authors.forename: Seunghee
authors.initials: S
authors.lastname: Lee
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002642:Chick Embryo; D002645:Chickens; D057809:HEK293 Cells; D006801:Humans; D060850:LIM-Homeodomain Proteins / Q000737:chemistry / Q000502:physiology*; D051379:Mice; D008969:Molecular Sequence Data; D009046:Motor Neurons / Q000378:metabolism; D054730:Protein Interaction Domains and Motifs; D055503:Protein Multimerization; D021381:Protein Transport; D051381:Rats; D013116:Spinal Cord / Q000166:cytology / Q000196:embryology / Q000378:metabolism; D014157:Transcription Factors / Q000737:chemistry / Q000502:physiology*
chemical_list: D060850:LIM-Homeodomain Proteins; C094898:Lhx3 protein; D014157:Transcription Factors; C063843:insulin gene enhancer binding protein Isl-1