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Defects in heart and lung development in compound heterozygotes for two different targeted mutations at the N-myc
C B Moens1, B R Stanton, L F Parada
1Division of Molecular and Developmental Biology, Samuel Lunenfeld Research Institute, Toronto, Ontario, Canada.
Abstract:
Two types of mutant allele, one leaky and one null, have been generated by gene targeting at the N-myc locus in embryonic stem cells and the phenotypes of mice homozygous for these mutations have been described. These mutations have shown that N-myc has a number of functions during development, including a role in branching morphogenesis in the lung, which manifests itself at birth in mice homozygous for the leaky allele, and roles in the development of the mesonephric tubules, the neuroepithelium, the sensory ganglia, the gut and the heart, which become evident at midgestation in embryos homozygous for the null allele. In an attempt to define roles for N-myc at other stages of development, we have combined the two types of N-myc mutant allele in a compound heterozygote that as a result contains approximately 15% of normal levels of N-Myc protein. Compound heterozygotes died during gestation at a time intermediate to the times of death of embryos homozygous for either mutation individually, and their death appeared to result from cardiac failure stemming from hypoplasia of the compact subepicardial layer of the myocardium. Investigation of the expression pattern of N-myc and various markers of differentiation in wild-type and compound heterozygote mutant hearts has suggested that N-myc may function in maintaining the proliferation and/or preventing the differentiation of compact layer myocytes. This study illustrates the importance of generating different mutations at a given locus to elucidate fully the function of a particular gene during development.
Insights
Investigating N-myc gene function, this study generated compound heterozygote mice with reduced N-myc protein. These mice exhibited embryonic lethality due to cardiac failure, highlighting N-myc
Area of Science:
- Developmental biology
- Molecular genetics
- Genetics
Background:
- The N-myc gene plays crucial roles in embryonic development.
- Previous studies generated leaky and null N-myc mutant alleles in mice.
Purpose of the Study:
- To investigate the function of N-myc at different developmental stages.
- To characterize the phenotype of compound heterozygotes with reduced N-myc levels.
Main Methods:
- Gene targeting in embryonic stem cells to create N-myc mutant alleles.
- Generation of compound heterozygote mice with combined leaky and null alleles.
- Phenotypic analysis of mutant embryos, including cardiac development.
Main Results:
- Compound heterozygotes with ~15% N-myc protein died during gestation.
- Embryonic lethality resulted from cardiac failure due to hypoplasia of the compact myocardium.
- N-myc appears to maintain proliferation and/or prevent differentiation of compact layer myocytes.
Conclusions:
- Different mutations at a single locus are essential for fully understanding gene function.
- N-myc is critical for cardiac development, specifically for the proliferation and differentiation of compact layer myocytes.