title: Asymmetric activation of Dll4-Notch signaling by Foxn4 and proneural factors activates BMP/TGFβ signaling to specify V2b interneurons in the spinal cord.
abstract: During development of the ventral spinal cord, the V2 interneurons emerge from p2 progenitors and diversify into two major subtypes, V2a and V2b, that play key roles in locomotor coordination. Dll4-mediated Notch activation in a subset of p2 precursors constitutes the crucial first step towards generating neuronal diversity in this domain. The mechanism behind the asymmetric Notch activation and downstream signaling events are, however, unknown at present. We show here that the Ascl1 and Neurog basic helix-loop-helix (bHLH) proneural factors are expressed in a mosaic pattern in p2 progenitors and that Foxn4 is required for setting and maintaining this expression mosaic. By binding directly to a conserved Dll4 enhancer, Foxn4 and Ascl1 activate Dll4 expression, whereas Neurog proteins prevent this effect, thereby resulting in asymmetric activation of Dll4 expression in V2 precursors expressing different combinations of proneural and Foxn4 transcription factors. Lineage tracing using the Cre-LoxP system reveals selective expression of Dll4 in V2a precursors, whereas Dll4 expression is initially excluded from V2b precursors. We provide evidence that BMP/TGFβ signaling is activated in V2b precursors and that Dll4-mediated Notch signaling is responsible for this activation. Using a gain-of-function approach and by inhibiting BMP/TGFβ signal transduction with pathway antagonists and RNAi knockdown, we further demonstrate that BMP/TGFβ signaling is both necessary and sufficient for V2b fate specification. Our data together thus suggest that the mosaic expression of Foxn4 and proneural factors may serve as the trigger to initiate asymmetric Dll4-Notch and subsequent BMP/TGFβ signaling events required for neuronal diversity in the V2 domain.
authors.affiliation: Center for Advanced Biotechnology and Medicine and Department of Pediatrics, Rutgers University-Robert Wood Johnson Medical School, 679 Hoes Lane West, Piscataway, NJ 08854, USA.
authors.forename: Kamana
authors.initials: K
authors.lastname: Misra
authors.forename: Huijun
authors.initials: H
authors.lastname: Luo
authors.forename: Shengguo
authors.initials: S
authors.lastname: Li
authors.forename: Michael
authors.initials: M
authors.lastname: Matise
authors.forename: Mengqing
authors.initials: M
authors.lastname: Xiang
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D000818:Animals; D051792:Basic Helix-Loop-Helix Proteins / Q000096:biosynthesis / Q000378:metabolism; D019485:Bone Morphogenetic Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D002135:Calcium-Binding Proteins; D002454:Cell Differentiation; D019070:Cell Lineage; D002642:Chick Embryo; D005136:Eye Proteins / Q000378:metabolism*; D051858:Forkhead Transcription Factors / Q000378:metabolism*; D018507:Gene Expression Regulation, Developmental; D007395:Interneurons / Q000378:metabolism*; D047908:Intracellular Signaling Peptides and Proteins / Q000378:metabolism*; D008565:Membrane Proteins / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D009419:Nerve Tissue Proteins / Q000096:biosynthesis / Q000378:metabolism; D058953:Neural Stem Cells / Q000378:metabolism; D034622:RNA Interference; D034741:RNA, Small Interfering / Q000235:genetics; D051880:Receptors, Notch / Q000378:metabolism; D015398:Signal Transduction; D013116:Spinal Cord / Q000196:embryology*; D016212:Transforming Growth Factor beta / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D051792:Basic Helix-Loop-Helix Proteins; D019485:Bone Morphogenetic Proteins; D002135:Calcium-Binding Proteins; D005136:Eye Proteins; D051858:Forkhead Transcription Factors; D047908:Intracellular Signaling Peptides and Proteins; D008565:Membrane Proteins; D009419:Nerve Tissue Proteins; D034741:RNA, Small Interfering; D051880:Receptors, Notch; D016212:Transforming Growth Factor beta; C499317:Ascl1 protein, mouse; C519665:DLL4 protein, mouse; C438622:Foxn4 protein, mouse; C102938:Neurog2 protein, mouse; C486336:Neurog1 protein, mouse
keywords: Ascl1; BMP/TGFβ; Chick; Dll4-Notch; Foxn4; Mouse; Spinal cord; V2 interneuron; bHLH proneural factor