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Updated: Jun 13, 2026
Imaging Cleared Embryonic and Postnatal Hearts at Single-cell Resolution
Published on: October 7, 2016
Dkk1 and Dkk2 regulate epicardial specification during mouse heart development
Matthew D Phillips1, Mahua Mukhopadhyay, Cristina Poscablo
1Laboratory of Mammalian Genes and Development, Program in the Genomics of Development, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, HHS, Bethesda, MD 20892, USA.
Background:
Dkk1 and Dkk2 interact with LRP5 and LRP6 to modulate canonical Wnt signaling during development, and are known to be expressed in the developing heart. However, a loss-of-function mutation in either gene by itself produces no discernable heart phenotype.
Methods:
Using standard husbandry techniques, Dkk1 null and Dkk2 null mouse lines were crossed to create double null embryos, which we examined using histological and immunohistochemical methods.
Results:
Double null embryos die perinatally, with a gross head phenotype reminiscent of Dkk1 null embryos. Upon examination of late stage hearts, we observe myocardial defects including ventricular septal defects. At earlier stages, double mutant hearts show myocardial and epicardial hyperplasia. Myocardial hypertrophy is associated with a moderate increase in cell proliferation, but epicardial hypercellularity is not. Rather, the field of proepicardial precursor cells near the liver shows a broadening of expression for the cardiac-specific gap junction protein Connexin 43.
Conclusions:
Dkk1 and Dkk2 both inhibit Wnt signaling to regulate early myocardial proliferation and each can compensate for the loss of the other in that role. Wnt signaling regulates myocardial proliferation in both heart fields at early stages. Additionally, Wnt signaling is sufficient to increase proepicardial specification as measured by Connexin 43 expression, resulting in a hypercellular epicardium and perhaps contributing to later defects.
Insights
Dickkopf-1 (Dkk1) and Dickkopf-2 (Dkk2) proteins are crucial for heart development. Their combined absence leads to perinatal death and significant cardiac defects, revealing their compensatory roles in regulating Wnt signaling and myocardial proliferation.
Area of Science:
- Developmental Biology
- Molecular Biology
- Cardiovascular Research
Background:
- Dkk1 and Dkk2 are Wnt signaling inhibitors crucial for development.
- They interact with LRP5/LRP6 receptors to modulate canonical Wnt pathways.
- Individual loss-of-function mutations in Dkk1 or Dkk2 do not cause observable heart defects.
Purpose of the Study:
- To investigate the combined role of Dkk1 and Dkk2 in embryonic heart development.
- To elucidate the function of Dkk1 and Dkk2 in regulating Wnt signaling during cardiac morphogenesis.
Main Methods:
- Generation of Dkk1 null and Dkk2 null double mutant mouse embryos.
- Histological and immunohistochemical analysis of embryonic hearts at various developmental stages.
Main Results:
- Double null embryos exhibit perinatal lethality and severe head malformations.
- Myocardial defects, including ventricular septal defects, are observed in late-stage hearts.
- Early stages show myocardial and epicardial hyperplasia, with altered Connexin 43 expression in proepicardial cells.
Conclusions:
- Dkk1 and Dkk2 redundantly inhibit Wnt signaling, regulating early myocardial proliferation.
- Wnt signaling is essential for myocardial proliferation in both early heart fields.
- Wnt signaling influences proepicardial cell specification, potentially contributing to later cardiac defects.
