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Genetic dissection of differential signaling threshold requirements for the Wnt/beta-catenin pathway in vivo
Michael Buchert1, Dimitris Athineos, Helen E Abud
1Ludwig Institute for Cancer Research, Royal Melbourne Hospital, Parkville, Australia.
Abstract:
Contributions of null and hypomorphic alleles of Apc in mice produce both developmental and pathophysiological phenotypes. To ascribe the resulting genotype-to-phenotype relationship unambiguously to the Wnt/beta-catenin pathway, we challenged the allele combinations by genetically restricting intracellular beta-catenin expression in the corresponding compound mutant mice. Subsequent evaluation of the extent of resulting Tcf4-reporter activity in mouse embryo fibroblasts enabled genetic measurement of Wnt/beta-catenin signaling in the form of an allelic series of mouse mutants. Different permissive Wnt signaling thresholds appear to be required for the embryonic development of head structures, adult intestinal polyposis, hepatocellular carcinomas, liver zonation, and the development of natural killer cells. Furthermore, we identify a homozygous Apc allele combination with Wnt/beta-catenin signaling capacity similar to that in the germline of the Apc(min) mice, where somatic Apc loss-of-heterozygosity triggers intestinal polyposis, to distinguish whether co-morbidities in Apc(min) mice arise independently of intestinal tumorigenesis. Together, the present genotype-phenotype analysis suggests tissue-specific response levels for the Wnt/beta-catenin pathway that regulate both physiological and pathophysiological conditions.
Insights
Altered Apc gene alleles in mice impact development and disease by affecting the Wnt/beta-catenin pathway. Different Wnt signaling thresholds are crucial for various physiological and pathological processes, influencing tissue-specific responses.
Area of Science:
- Genetics
- Developmental Biology
- Cancer Biology
Background:
- The Adenomatous Polyposis Coli (Apc) gene plays a critical role in cellular processes.
- Mutations in Apc are linked to various developmental and pathophysiological conditions, primarily through the Wnt/beta-catenin signaling pathway.
Purpose of the Study:
- To precisely link Apc genotypes to specific phenotypes by modulating Wnt/beta-catenin signaling.
- To establish a quantitative measure of Wnt/beta-catenin signaling activity across a series of Apc mutant mice.
- To investigate the role of Wnt/beta-catenin signaling thresholds in diverse biological processes and diseases.
Main Methods:
- Generation of compound mutant mice with varying Apc allele combinations.
- Genetic restriction of intracellular beta-catenin expression.
- Measurement of Tcf4-reporter activity in mouse embryo fibroblasts to quantify Wnt/beta-catenin signaling.
- Comparative analysis of Apc mutant phenotypes with Wnt/beta-catenin signaling levels.
Main Results:
- Established an allelic series of mouse mutants for precise Wnt/beta-catenin signaling measurement.
- Identified distinct Wnt signaling thresholds required for embryonic head development, intestinal polyposis, hepatocellular carcinoma, liver zonation, and natural killer cell development.
- Characterized a homozygous Apc allele combination with signaling capacity mimicking Apc(min) mice to study co-morbidities.
Conclusions:
- Wnt/beta-catenin signaling operates at different thresholds to regulate diverse physiological and pathophysiological conditions.
- Genotype-phenotype relationships are tissue-specific and dependent on Wnt/beta-catenin pathway activity levels.
- This study provides a framework for understanding how Apc mutations contribute to disease through context-dependent Wnt signaling.
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