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Updated: Aug 6, 2026
En Face Endocardial Cushion Preparation for Planar Morphogenesis Analysis in Mouse Embryos
Published on: July 27, 2022
MEKK4 regulates developmental EMT in the embryonic heart
Mark V Stevens1, Patti Parker, Richard R Vaillancourt
1Department of Pharmacology and Toxicology, College of Pharmacy, The University of Arizona, Tucson, Arizona, USA.
Insights
Mitogen-activated protein kinase kinase kinase 4 (MEKK4) is crucial for heart development. Its kinase activity is essential, but not sufficient, for the mesenchymal transition required for forming heart valves and septa.
Area of Science:
- Developmental biology
- Molecular signaling
- Cardiovascular science
Background:
- Congenital heart malformations are common birth defects, highlighting gaps in understanding heart development.
- Molecular mechanisms regulating cardiogenesis are not fully defined, hindering repair strategies.
- The role of MEKK4 (MAP kinase kinase kinase 4) in embryonic development and heart formation is largely unknown.
Purpose of the Study:
- To investigate the function of MEKK4 in cardiovascular development and cardiogenesis.
- To determine MEKK4's role in epithelial to mesenchymal transformation (EMT) during heart development.
Main Methods:
- Detected MEKK4 transcripts in developing heart tissues, including myocardium, endocardium, and cardiac cushion cells undergoing EMT.
- Utilized an in vitro assay with a kinase-inactive MEKK4 (MEKK4(KI)) to assess its effect on EMT.
- Employed ventricular explants with constitutively active MEKK4 to evaluate its sufficiency in inducing mesenchymal cell outgrowth.
Main Results:
- MEKK4 transcripts are present in key cell populations during early heart development.
- Kinase-inactive MEKK4 (MEKK4(KI)) inhibited mesenchyme production in an in vitro EMT assay.
- Active MEKK4 alone could not induce mesenchymal cell outgrowth in ventricular explants lacking normal EMT.
Conclusions:
- MEKK4 plays a critical role in cardiovascular development.
- MEKK4's kinase activity is necessary but not sufficient for developmental EMT.
- Understanding MEKK4's function provides insights into signaling pathways controlling heart formation and defects.
Abstract:
Congenital heart malformations occur at a rate of one per one hundred births and are considered the most frequent birth defects. This high incidence of cardiac defects underscores the complex developmental processes required to form the first functioning organ in mammals. The molecular cues which govern heart development are poorly defined and require an improved understanding in order to advance repair strategies for heart defects. The cytoplasmic MAP kinase kinase kinase, MEKK4, is a critical effector in cellular stress responses; however, the function of MEKK4 during embryonic development and cardiogenesis is not well understood. We have identified MEKK4 as a critical signaling molecule during cardiovascular development. We report the detection of MEKK4 transcripts to early myocardium, endocardium and to cardiac cushion cells that have executed epithelial to mesenchymal transformation (EMT). These observations suggest that MEKK4 may function during production of the cushion mesenchyme as required to create valves and the septated heart. We used a kinase inactive form of MEKK4(MEKK4(KI)) in an in vitro assay that recapitulates in vivo EMT, and show that MEKK4(KI) attenuates mesenchyme production. However, addition of a constitutively active MEKK4 into ventricular explants, a system that does not normally undergo EMT, is not able to cause mesenchymal cell outgrowth. Thus, the kinase activity of MEKK4 is essential, but not sufficient, to support developmental EMT. This knowledge provides a basis to understand how MEKK4 may integrate signaling cascades controlling heart development.
