title: The short stature homeobox 2 (Shox2)-bone morphogenetic protein (BMP) pathway regulates dorsal mesenchymal protrusion development and its temporary function as a pacemaker during cardiogenesis.
abstract: The atrioventricular (AV) junction plays a critical role in chamber septation and transmission of cardiac conduction pulses. It consists of structures that develop from embryonic dorsal mesenchymal protrusion (DMP) and the embryonic AV canal. Despite extensive studies on AV junction development, the genetic regulation of DMP development remains poorly understood. In this study we present evidence that Shox2 is expressed in the developing DMP. Intriguingly, this Shox2-expressing domain possesses a pacemaker-specific genetic profile including Hcn4 and Tbx3. This genetic profile leads to nodal-like electrophysiological properties, which is gradually silenced as the AV node becomes matured. Phenotypic analyses of Shox2(-/-) mice revealed a hypoplastic and defectively differentiated DMP, likely attributed to increased apoptosis, accompanied by dramatically reduced expression of Bmp4 and Hcn4, ectopic activation of Cx40, and an aberrant pattern of action potentials. Interestingly, conditional deletion of Bmp4 or inhibition of BMP signaling by overexpression of Noggin using a Shox2-Cre allele led to a similar DMP hypoplasia and down-regulation of Hcn4, whereas activation of a transgenic Bmp4 allele in Shox2(-/-) background attenuated DMP defects. Moreover, the lack of Hcn4 expression in the DMP of mice carrying Smad4 conditional deletion and direct binding of pSmad1/5/8 to the Hcn4 regulatory region further confirm the Shox2-BMP genetic cascade in the regulation of DMP development. Our results reveal that Shox2 regulates DMP fate and development by controlling BMP signaling through the Smad-dependent pathway to drive tissue growth and to induce Hcn4 expression and suggest a temporal pacemaking function for the DMP during early cardiogenesis.
authors.affiliation: From the Department of Cell and Molecular Biology, Tulane University, New Orleans, Louisiana 70118.
authors.forename: Cheng
authors.initials: C
authors.lastname: Sun
authors.affiliation: From the Department of Cell and Molecular Biology, Tulane University, New Orleans, Louisiana 70118.
authors.forename: Diankun
authors.initials: D
authors.lastname: Yu
authors.affiliation: From the Department of Cell and Molecular Biology, Tulane University, New Orleans, Louisiana 70118.
authors.forename: Wenduo
authors.initials: W
authors.lastname: Ye
authors.affiliation: From the Department of Cell and Molecular Biology, Tulane University, New Orleans, Louisiana 70118.
authors.forename: Chao
authors.initials: C
authors.lastname: Liu
authors.affiliation: From the Department of Cell and Molecular Biology, Tulane University, New Orleans, Louisiana 70118.
authors.forename: Shuping
authors.initials: S
authors.lastname: Gu
authors.affiliation: From the Department of Cell and Molecular Biology, Tulane University, New Orleans, Louisiana 70118.
authors.forename: Nathan R
authors.initials: NR
authors.lastname: Sinsheimer
authors.affiliation: From the Department of Cell and Molecular Biology, Tulane University, New Orleans, Louisiana 70118.
authors.forename: Zhongchen
authors.initials: Z
authors.lastname: Song
authors.affiliation: From the Department of Cell and Molecular Biology, Tulane University, New Orleans, Louisiana 70118.
authors.forename: Xihai
authors.initials: X
authors.lastname: Li
authors.affiliation: From the Department of Cell and Molecular Biology, Tulane University, New Orleans, Louisiana 70118.
authors.forename: Chun
authors.initials: C
authors.lastname: Chen
authors.affiliation: From the Department of Cell and Molecular Biology, Tulane University, New Orleans, Louisiana 70118.
authors.forename: Yingnan
authors.initials: Y
authors.lastname: Song
authors.affiliation: From the Department of Cell and Molecular Biology, Tulane University, New Orleans, Louisiana 70118.
authors.forename: Shusheng
authors.initials: S
authors.lastname: Wang
authors.affiliation: From the Department of Cell and Molecular Biology, Tulane University, New Orleans, Louisiana 70118.
authors.forename: Laura
authors.initials: L
authors.lastname: Schrader
authors.affiliation: From the Department of Cell and Molecular Biology, Tulane University, New Orleans, Louisiana 70118 ychen@tulane.edu.
authors.forename: YiPing
authors.initials: Y
authors.lastname: Chen
mesh_terms: D000200:Action Potentials; D000483:Alleles; D000818:Animals; D017209:Apoptosis; D001683:Biological Clocks; D055415:Bone Morphogenetic Protein 4 / Q000235:genetics; D019485:Bone Morphogenetic Proteins / Q000378:metabolism*; D002454:Cell Differentiation; D004594:Electrophysiology; D005260:Female; D018507:Gene Expression Regulation, Developmental; D006321:Heart / Q000196:embryology*; D006346:Heart Septum / Q000196:embryology; D018398:Homeodomain Proteins / Q000235:genetics / Q000378:metabolism*; D064428:Hyperpolarization-Activated Cyclic Nucleotide-Gated Channels / Q000235:genetics / Q000378:metabolism; D008648:Mesoderm / Q000378:metabolism; D051379:Mice; D008822:Mice, Transgenic; D010641:Phenotype; D015398:Signal Transduction
chemical_list: C525810:Bmp4 protein, mouse; D055415:Bone Morphogenetic Protein 4; D019485:Bone Morphogenetic Proteins; C578706:Hcn4 protein, mouse; D018398:Homeodomain Proteins; D064428:Hyperpolarization-Activated Cyclic Nucleotide-Gated Channels; C484663:Shox2 protein, mouse
keywords: Bone Morphogenetic Protein (BMP); Dorsal Mesenchymal Protrusion; Gene Regulation; Heart Development; SMAD Transcription Factor; Shox2; Signal Transduction; Smad4-dependent