Cytosolic Ras supports eye development in Drosophila

Area of Science:

• Molecular Biology
• Developmental Biology
• Cell Biology

Background:

• Ras proteins require posttranslational modifications, including prenylation of their CAAX sequence, for membrane association and biological activity.
• Ras1 is crucial for proper eye development in the fruit fly, Drosophila melanogaster.

Purpose of the Study:

• To investigate the role of membrane association in Drosophila Ras1 function during eye development.
• To determine if prenylation efficiency impacts Ras1's ability to rescue Ras1-null phenotypes.

Main Methods:

• Mosaic analysis with a repressible cell marker (MARCM) in Drosophila.
• Assessing the rescue of Ras1-null eye disc cell phenotypes using various Ras1 transgenes.
• Evaluating the impact of mutations affecting CAAX sequence modification and membrane targeting.

Main Results:

• Drosophila Ras1 exhibits inefficient prenylation due to a lysine at the A(1) position, leading to a significant soluble pool.
• Ras1 transgenes with enhanced membrane targeting failed to rescue the Ras1-null phenotype.
• Ras1 with a mutated CAAX cysteine, preventing membrane targeting, fully rescued eye development.
• Constitutively active Ras1(12V,C186S) lacking membrane targeting induced a hypermorphic phenotype and stimulated MAPK signaling.

Conclusions:

• Membrane association of Drosophila Ras1 is not required for its function in eye development.
• Soluble, non-membrane-associated Ras1 can be biologically active and sufficient for rescuing Ras1-null phenotypes.
• These findings challenge the conventional understanding of Ras protein localization and function.