Rac1 Signaling Is Required for Anterior Second Heart Field Cellular Organization and Cardiac Outflow Tract Development

J Am Heart Assoc. 2015 Dec 31;5(1):e002508. doi: 10.1161/JAHA.115.002508.


Background: The small GTPase Rac1 regulates diverse cellular functions, including both apicobasal and planar cell polarity pathways; however, its role in cardiac outflow tract (OFT) development remains unknown. In the present study, we aimed to examine the role of Rac1 in the anterior second heart field (SHF) splanchnic mesoderm and subsequent OFT development during heart morphogenesis.

Methods and results: Using the Cre/loxP system, mice with an anterior SHF-specific deletion of Rac1 (Rac1(SHF)) were generated. Embryos were collected at various developmental time points for immunostaining and histological analysis. Intrauterine echocardiography was also performed to assess aortic valve blood flow in embryos at embryonic day 18.5. The Rac1(SHF) splanchnic mesoderm exhibited disruptions in SHF progenitor cellular organization and proliferation. Consequently, this led to a spectrum of OFT defects along with aortic valve defects in Rac1(SHF) embryos. Mechanistically, it was found that the ability of the Rac1(SHF) OFT myocardial cells to migrate into the proximal OFT cushion was severely reduced. In addition, expression of the neural crest chemoattractant semaphorin 3c was decreased. Lineage tracing showed that anterior SHF contribution to the OFT myocardium and aortic valves was deficient in Rac1(SHF) hearts. Furthermore, functional analysis with intrauterine echocardiography at embryonic day 18.5 showed aortic valve regurgitation in Rac1(SHF) hearts, which was not seen in control hearts.

Conclusions: Disruptions of Rac1 signaling in the anterior SHF results in aberrant progenitor cellular organization and defects in OFT development. Our data show Rac1 signaling to be a critical regulator of cardiac OFT formation during embryonic heart development.

Keywords: Rac1; cellular organization; congenital heart defect; outflow tract development.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Aortic Valve / abnormalities
  • Aortic Valve / enzymology*
  • Aortic Valve Insufficiency / diagnosis
  • Aortic Valve Insufficiency / enzymology*
  • Aortic Valve Insufficiency / genetics
  • Cell Lineage
  • Cell Movement
  • Gene Expression Regulation, Developmental
  • Genetic Predisposition to Disease
  • Gestational Age
  • Heart Defects, Congenital / diagnosis
  • Heart Defects, Congenital / enzymology*
  • Heart Defects, Congenital / genetics
  • Mice, Knockout
  • Morphogenesis
  • Myocardium / enzymology*
  • Myocardium / pathology
  • Neural Crest / abnormalities
  • Neural Crest / enzymology
  • Neuropeptides / deficiency
  • Neuropeptides / genetics
  • Neuropeptides / metabolism*
  • Phenotype
  • Semaphorins / genetics
  • Semaphorins / metabolism
  • Signal Transduction
  • rac1 GTP-Binding Protein / deficiency
  • rac1 GTP-Binding Protein / genetics
  • rac1 GTP-Binding Protein / metabolism*


  • Neuropeptides
  • Rac1 protein, mouse
  • Semaphorins
  • semaphorin 3C protein, mouse
  • rac1 GTP-Binding Protein