title: A novel TGFβ modulator that uncouples R-Smad/I-Smad-mediated negative feedback from R-Smad/ligand-driven positive feedback.
abstract: As some of the most widely utilised intercellular signalling molecules, transforming growth factor β (TGFβ) superfamily members play critical roles in normal development and become disrupted in human disease. Establishing appropriate levels of TGFβ signalling involves positive and negative feedback, which are coupled and driven by the same signal transduction components (R-Smad transcription factor complexes), but whether and how the regulation of the two can be distinguished are unknown. Genome-wide comparison of published ChIP-seq datasets suggests that LIM domain binding proteins (Ldbs) co-localise with R-Smads at a substantial subset of R-Smad target genes including the locus of inhibitory Smad7 (I-Smad7), which mediates negative feedback for TGFβ signalling. We present evidence suggesting that zebrafish Ldb2a binds and directly activates the I-Smad7 gene, whereas it binds and represses the ligand gene, Squint (Sqt), which drives positive feedback. Thus, the fine tuning of TGFβ signalling derives from positive and negative control by Ldb2a. Expression of ldb2a is itself activated by TGFβ signals, suggesting potential feed-forward loops that might delay the negative input of Ldb2a to the positive feedback, as well as the positive input of Ldb2a to the negative feedback. In this way, precise gene expression control by Ldb2a enables an initial build-up of signalling via a fully active positive feedback in the absence of buffering by the negative feedback. In Ldb2a-deficient zebrafish embryos, homeostasis of TGFβ signalling is perturbed and signalling is stably enhanced, giving rise to excess mesoderm and endoderm, an effect that can be rescued by reducing signalling by the TGFβ family members, Nodal and BMP. Thus, Ldb2a is critical to the homeostatic control of TGFβ signalling and thereby embryonic patterning.
authors: Weatherall Institute of Molecular Medicine, University of Oxford, John Radcliffe Hospital, Oxford, United Kingdom.
authors: Wenchao
authors: W
authors: Gu
authors: Weatherall Institute of Molecular Medicine, University of Oxford, John Radcliffe Hospital, Oxford, United Kingdom; BHF Centre of Research Excellence, Oxford, United Kingdom.
authors: Rui
authors: R
authors: Monteiro
authors: Weatherall Institute of Molecular Medicine, University of Oxford, John Radcliffe Hospital, Oxford, United Kingdom.
authors: Jie
authors: J
authors: Zuo
authors: Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, United Kingdom.
authors: Filipa Costa
authors: FC
authors: Simões
authors: Department of Cell Biology, Erasmus Medical Centre, Rotterdam, The Netherlands.
authors: Andrea
authors: A
authors: Martella
authors: INSERM U872, Université René Descartes Sorbonne Paris Cité, Team 17, Centre de Recherche des Cordeliers, Paris, France.
authors: Charlotte
authors: C
authors: Andrieu-Soler
authors: Department of Cell Biology, Erasmus Medical Centre, Rotterdam, The Netherlands.
authors: Frank
authors: F
authors: Grosveld
authors: Weatherall Institute of Molecular Medicine, University of Oxford, John Radcliffe Hospital, Oxford, United Kingdom.
authors: Tatjana
authors: T
authors: Sauka-Spengler
authors: Weatherall Institute of Molecular Medicine, University of Oxford, John Radcliffe Hospital, Oxford, United Kingdom; BHF Centre of Research Excellence, Oxford, United Kingdom.
authors: Roger
authors: R
authors: Patient
mesh_terms: D000818:Animals; D001483:Base Sequence; D019521:Body Patterning / Q000235:genetics*; D004625:Embryo, Nonmammalian; D004707:Endoderm / Q000166:cytology / Q000196:embryology / Q000378:metabolism; D025461:Feedback, Physiological; D018507:Gene Expression Regulation, Developmental; D006801:Humans; D060588:LIM Domain Proteins / Q000037:antagonists & inhibitors / Q000172:deficiency / Q000235:genetics*; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism; D008648:Mesoderm / Q000166:cytology / Q000196:embryology / Q000378:metabolism; D051379:Mice; D008845:Microinjections; D008969:Molecular Sequence Data; D060172:Morpholinos / Q000235:genetics / Q000378:metabolism; D055456:Nodal Signaling Ligands / Q000235:genetics / Q000378:metabolism*; D016415:Sequence Alignment; D015398:Signal Transduction; D051906:Smad7 Protein / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic; D016212:Transforming Growth Factor beta / Q000235:genetics / Q000378:metabolism*; D015027:Zebrafish; D029961:Zebrafish Proteins / Q000037:antagonists & inhibitors / Q000172:deficiency / Q000235:genetics* / Q000378:metabolism*
chemical_list: D060588:LIM Domain Proteins; D008565:Membrane Proteins; D060172:Morpholinos; D055456:Nodal Signaling Ligands; D051906:Smad7 Protein; D016212:Transforming Growth Factor beta; D029961:Zebrafish Proteins; C112437:ldb2a protein, zebrafish; C485171:ndr1 protein, zebrafish; C501108:nomo protein, zebrafish; C497810:smad7 protein, zebrafish