title: LIM homeobox transcription factors integrate signaling events that control three-dimensional limb patterning and growth.
abstract: Vertebrate limb development is controlled by three signaling centers that regulate limb patterning and growth along the proximodistal (PD), anteroposterior (AP) and dorsoventral (DV) limb axes. Coordination of limb development along these three axes is achieved by interactions and feedback loops involving the secreted signaling molecules that mediate the activities of these signaling centers. However, it is unknown how these signaling interactions are processed in the responding cells. We have found that distinct LIM homeodomain transcription factors, encoded by the LIM homeobox (LIM-HD) genes Lhx2, Lhx9 and Lmx1b integrate the signaling events that link limb patterning and outgrowth along all three axes. Simultaneous loss of Lhx2 and Lhx9 function resulted in patterning and growth defects along the AP and the PD limb axes. Similar, but more severe, phenotypes were observed when the activities of all three factors, Lmx1b, Lhx2 and Lhx9, were significantly reduced by removing their obligatory co-factor Ldb1. This reveals that the dorsal limb-specific factor Lmx1b can partially compensate for the function of Lhx2 and Lhx9 in regulating AP and PD limb patterning and outgrowth. We further showed that Lhx2 and Lhx9 can fully substitute for each other, and that Lmx1b is partially redundant, in controlling the production of output signals in mesenchymal cells in response to Fgf8 and Shh signaling. Our results indicate that several distinct LIM-HD transcription factors in conjunction with their Ldb1 co-factor serve as common central integrators of distinct signaling interactions and feedback loops to coordinate limb patterning and outgrowth along the PD, AP and DV axes after limb bud formation.
authors.affiliation: Section on Mammalian Molecular Genetics, Laboratory of Mammalian Genes and Development, Eunice Kennedy Shriver National Institute of Child Health and Human Development, Bethesda, MD 20892, USA.
authors.forename: Itai
authors.initials: I
authors.lastname: Tzchori
authors.forename: Timothy F
authors.initials: TF
authors.lastname: Day
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Carolan
authors.forename: Yangu
authors.initials: Y
authors.lastname: Zhao
authors.forename: Christopher A
authors.initials: CA
authors.lastname: Wassif
authors.forename: Liqi
authors.initials: L
authors.lastname: Li
authors.forename: Mark
authors.initials: M
authors.lastname: Lewandoski
authors.forename: Marat
authors.initials: M
authors.lastname: Gorivodsky
authors.forename: Paul E
authors.initials: PE
authors.lastname: Love
authors.forename: Forbes D
authors.initials: FD
authors.lastname: Porter
authors.forename: Heiner
authors.initials: H
authors.lastname: Westphal
authors.forename: Yingzi
authors.initials: Y
authors.lastname: Yang
mesh_terms: D000818:Animals; D019521:Body Patterning; D049109:Cell Proliferation; D005121:Extremities / Q000196:embryology*; D051526:Fibroblast Growth Factor 10 / Q000235:genetics / Q000378:metabolism; D018507:Gene Expression Regulation, Developmental; D053823:Hedgehog Proteins / Q000235:genetics / Q000378:metabolism; D018398:Homeodomain Proteins / Q000235:genetics / Q000378:metabolism*; D036341:Intercellular Signaling Peptides and Proteins / Q000235:genetics / Q000378:metabolism; D051379:Mice; D015398:Signal Transduction; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D016207:Cytokines
chemical_list: D051526:Fibroblast Growth Factor 10; D053823:Hedgehog Proteins; D018398:Homeodomain Proteins; D036341:Intercellular Signaling Peptides and Proteins; D014157:Transcription Factors; C496464:Fgf10 protein, mouse; C465570:Shh protein, mouse; C113178:Grem1 protein, mouse; D016207:Cytokines