Stochastic phenotypic switching arises in response to directional selection in experimentally evolved multicellular...

Area of Science:

• Evolutionary biology
• Cell biology
• Genetics

Background:

• Phenotypic diversity in genetically identical populations can be adaptive.
• Evolutionary transitions like multicellularity may stem from pre-existing phenotypic heterogeneity.
• Understanding the origins of diversity is crucial for evolutionary studies.

Purpose of the Study:

• To characterize phenotypic diversity in experimentally evolved multicellular yeast (Saccharomyces cerevisiae).
• To investigate the mechanisms maintaining phenotypic heterogeneity in isogenic populations.
• To explore the role of stochastic phenotypic switching in nascent multicellularity.

Main Methods:

• Experimental evolution of Saccharomyces cerevisiae.
• Characterization of distinct morphotypes using microscopy and growth assays.
• Genetic analysis to identify mutations.
• Gene expression profiling.
• Mathematical modeling of phenotypic switching.

Main Results:

• A bistable system with two distinct morphotypes (large multicellular clusters and small single-cell clusters) was identified.
• The bistable system results from a loss-of-function mutation in the ACE2 gene.
• Small clusters arise from phenotypic switching of multicellular individuals.
• Significant gene expression differences exist between morphotypes, indicating distinct growth states.

Conclusions:

• Stochastic phenotypic switching, driven by an ACE2 mutation, maintains diversity in multicellular yeast.
• This diversity can be adaptive during the evolution of multicellularity.
• The study provides insights into the mechanisms of biological diversity generation in evolving populations.