Transcriptional Derepression Uncovers Cryptic Higher-Order Genetic Interactions

Area of Science:

• Genetics
• Molecular Biology
• Yeast Genetics

Background:

• Cryptic genetic variants usually have no phenotypic effect.
• Phenotypic capacitance describes the unmasking of these variants.
• Understanding phenotypic capacitance is crucial for trait variation and disease risk.

Purpose of the Study:

• To investigate the genetic and molecular mechanisms of phenotypic capacitance.
• To explore how mutations reveal cryptic genetic variants.
• To understand the role of genetic interactions in trait expression.

Main Methods:

• Utilizing a yeast cross with a segregating cryptic colony morphology trait.
• Analyzing the effects of mutations in the IRA2 gene, a negative regulator of the Ras pathway.
• Investigating the impact of SFL1 gene deletion, a downstream repressor in the Ras pathway.

Main Results:

• The colony morphology trait is expressed when IRA2 mutations co-occur with specific cryptic variants in six genes.
• Four of these genes are transcription factors downstream of the Ras pathway, indicating complex transcriptional regulation.
• The IRA2 mutation reveals cryptic variants by disrupting transcriptional silencing, a mechanism supported by SFL1 deletion.

Conclusions:

• Higher-order genetic interactions between mutations and cryptic variants drive phenotypic capacitance.
• These interactions can lead to complex gene expression changes normally suppressed by negative regulation.
• Phenotypic capacitance highlights the importance of genetic background in trait manifestation and disease susceptibility.