Stochastic phenotypes in RAS-dependent developmental diseases

Area of Science:

• Developmental Biology
• Genetics
• Molecular Biology

Background:

• Germline mutations affecting RAS signaling pathways are linked to developmental disorders.
• Phenotypic variability, even in genetically identical individuals, is a hallmark of these conditions.

Purpose of the Study:

• To investigate the origins of unexplained phenotypic variations in RAS-related developmental disorders.
• To dissect the impact of subtle increases in RAS pathway signaling on development.

Main Methods:

• Utilized gene-edited Drosophila melanogaster with activating MEK variants (a RAS pathway enzyme).
• Quantified signaling output in vivo and assessed cell fate errors in larval trachea.
• Employed a stochastic signaling model to interpret results.

Main Results:

• Activating MEK variants caused a small but consistent increase in RAS signaling output.
• A reduced fraction of mutation carriers reached adulthood, but most survivors displayed normal RAS-dependent structures.
• Cell fate errors were observed in a subset of animals, consistent with stochastic variation.

Conclusions:

• Subtle increases in RAS signaling can shift phenotypic distributions, leading to variable outcomes due to stochastic effects.
• This provides a framework for understanding phenotypic heterogeneity in RAS-related developmental disorders.
• The findings offer insights into the impact of other pathogenic alleles and mild mutations.