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Retinoic acid signaling coordinates the behavior of multiple cell lineages during cardiac outflow morphogenesis

ABSTRACT: Retinoic acid (RA), the bioactive derivative of vitamin A, is essential for vertebrate heart development. Both excess and reduced RA signaling lead to cardiovascular malformations, particularly affecting the cardiac outflow tract (OFT). The cellular mechanisms underlying the effects of RA signaling during OFT morphogenesis are not fully understood. To address this question, we used transient maternal RA supplementation to rescue the early lethality resulting from inactivation of the murine retinaldehyde dehydrogenase 2 (Raldh2) gene. By embryonic day 13.5, Raldh2-/- hearts exhibited OFT septation defects. Although cardiac neural crest cells (cNCC) were present in OFT cushions of Raldh2-/- mutant embryos, we observed that cNCC were ectopically located in the peripheral region of the endocardial cushions, closer to the myocardium rather than immediately subjacent to the endocardium. Mislocated cNCC were aligned in parallel instead of perpendicular arrays to the endocardial surface within the proximal OFT. Supernumerary mesenchyme was generated both in and ex vivo within the cushions by Raldh2-/- mutant endocardium and found in place of the cNCC in a subendocardial, medial position. Although mislocated and misoriented, mutant cNCC resembled wildtype cells in their compaction density and individually elongated shape. Our data show that RA signaling acts on cNCC orientation relative to the septation plane and position within OFT cushions during septation process. Transcriptomic analysis and pathway-specific readout suggest that up-regulation of the Bmp pathway may be responsible for increased endothelial-to-mesenchymal transition, leading thereby to displacement of cNCC.

ORGANISM(S): Mus musculus

PROVIDER: GSE64556 | GEO | 2015/12/21

SECONDARY ACCESSION(S): PRJNA271297

REPOSITORIES: GEO

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Project description:Retinoic acid (RA), the bioactive derivative of vitamin A, is essential for vertebrate heart development. Both excess and reduced RA signaling lead to cardiovascular malformations, particularly affecting the cardiac outflow tract (OFT). The cellular mechanisms underlying the effects of RA signaling during OFT morphogenesis are not fully understood. To address this question, we used transient maternal RA supplementation to rescue the early lethality resulting from inactivation of the murine retinaldehyde dehydrogenase 2 (Raldh2) gene. By embryonic day 13.5, Raldh2-/- hearts exhibited OFT septation defects. Although cardiac neural crest cells (cNCC) were present in OFT cushions of Raldh2-/- mutant embryos, we observed that cNCC were ectopically located in the peripheral region of the endocardial cushions, closer to the myocardium rather than immediately subjacent to the endocardium. Mislocated cNCC were aligned in parallel instead of perpendicular arrays to the endocardial surface within the proximal OFT. Supernumerary mesenchyme was generated both in and ex vivo within the cushions by Raldh2-/- mutant endocardium and found in place of the cNCC in a subendocardial, medial position. Although mislocated and misoriented, mutant cNCC resembled wildtype cells in their compaction density and individually elongated shape. Our data show that RA signaling acts on cNCC orientation relative to the septation plane and position within OFT cushions during septation process. Transcriptomic analysis and pathway-specific readout suggest that up-regulation of the Bmp pathway may be responsible for increased endothelial-to-mesenchymal transition, leading thereby to displacement of cNCC. E10.5 stage embryonic mouse outflow tracts were microdissected. Four pools of four outflow tracts were established for wildtype (WT) and mutant (Raldh2-/-) embryos derived from dams whose food had been supplemented with all-trans-RA (Sigma) directly mixed into powdered food at 0.1 mg/g food and offered between E7.5 and E8.5. Total RNA was extracted using Macherey-Nagel NucleoSpinÂ® RNA columns without on-column DNase digestion.

Project description:Rationale: A critical step in heart development is the coordinated formation of nodal myocardium and cushion tissue from the atrioventricular canal (AVC). After its specification, the myocardium of the AVC aligns the chambers, forms the AV node, and induces the formation of the mesenchymal AV cushions, primordia of valves and septa, while it resists working myocardial differentiation. Objective: To assess what roles Tbx2 and Tbx3, two closely related T-box transcription factors expressed in the AVC, play in these processes. Methods and Results: We analyzed mice ectopically expressing Tbx3 in the atrial myocardium by genome-wide microarray and expression analysis. We found a prominent role for Tbx3 in defining the nodal phenotype by repressing working myocardial genes (sarcomeric, mitochondrial, fast conduction) and cell proliferation regulators, and in inducing node-associated genes. Moreover, there was a striking induction of genes associated with endocardial cushions and mesenchyme. Using gain-of-function models, we found that in the developing heart both Tbx2 and Tbx3 induce ectopic Bmp2 and Tgfb2 expression and endocardial cushion formation. Analysis of compound Tbx2/Tbx3 mutant embryos revealed that upon loss of more than two functional alleles, expansion of the AV myocardium does not occur and AV cushions fail to form. Conclusions: Tbx2 and Tbx3 locally stimulate development of the AVC myocardium, induce the AV nodal phenotype therein and trigger AV cushion formation from the overlying AV endocardium, providing a mechanism for the colocalization and coordination of these two important processes in heart development. Nppa-Cre4 (Cre4) mice were crossed with CT mice to obtain efficient activation of Tbx3 in atria of double transgenic Cre4-CT mice, as previously described (Hoogaars et al., 2007). To investigate the gene expression profile of atria of Cre4-CT mice, we performed whole genome microarray analysis using Sentrix Mouse-6 oligonucleotide beadchips. We compared the atrial gene expression profiles of six male double transgenic Cre4-CT mice and six male Cre4 control mice.

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Retinoic acid signaling coordinates the behavior of multiple cell lineages during cardiac outflow morphogenesis

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