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Published on: June 18, 2016
Characterization of the Roco protein family in Dictyostelium discoideum
Wouter N van Egmond1, Peter J M van Haastert
1Department of Cell Biochemistry, University of Groningen, Kerklaan 30, 9751 NN Haren, Netherlands.
Abstract:
The Roco family consists of multidomain Ras-GTPases that include LRRK2, a protein mutated in familial Parkinson's disease. The genome of the cellular slime mold Dictyostelium discoideum encodes 11 Roco proteins. To study the functions of these proteins, we systematically knocked out the roco genes. Previously described functions for GbpC, Pats1, and QkgA (Roco1 to Roco3) were confirmed, while novel developmental defects were identified in roco4- and roco11-null cells. Cells lacking Roco11 form larger fruiting bodies than wild-type cells, while roco4-null cells show strong developmental defects during the transition from mound to fruiting body; prestalk cells produce reduced levels of cellulose, leading to unstable stalks that are unable to properly lift the spore head. Detailed phylogenetic analysis of four slime mold species reveals that QkgA and Roco11 evolved relatively late by duplication of an ancestor roco4 gene (later than approximately 300 million years ago), contrary to the situation with other roco genes, which were already present before the split of the common ancestor of D. discoideum and Polysphondylium pallidum (before approximately 600 million years ago). Together, our data show that the Dictyostelium Roco proteins serve a surprisingly diverse set of functions and highlight Roco4 as a key protein for proper stalk cell formation.
Insights
Dictyostelium Roco proteins have diverse functions. Roco4 is crucial for stalk formation, while Roco11 affects fruiting body size, revealing new roles for these Ras-GTPases in development.
Area of Science:
- Cell Biology
- Developmental Biology
- Genetics
Background:
- The Roco family comprises multidomain Ras-GTPases, including LRRK2, implicated in Parkinson's disease.
- The Dictyostelium discoideum genome encodes eleven Roco proteins, suggesting diverse biological roles.
Purpose of the Study:
- To systematically investigate the functions of Dictyostelium Roco proteins through gene knockouts.
- To identify novel roles and developmental defects associated with specific Roco protein deficiencies.
Main Methods:
- Systematic gene knockout of eleven Roco genes in Dictyostelium discoideum.
- Phenotypic analysis of null mutants, focusing on developmental processes.
- Phylogenetic analysis of Roco gene evolution across related species.
Main Results:
- Confirmed known functions of Roco1-3 (GbpC, Pats1, QkgA).
- Identified novel developmental defects in roco4-null and roco11-null cells.
- Roco4-null cells exhibit defects in stalk formation due to reduced cellulose production; Roco11-null cells form larger fruiting bodies.
- Phylogenetic analysis indicates late evolution of QkgA and Roco11 via Roco4 duplication.
Conclusions:
- Dictyostelium Roco proteins exhibit a wide range of functions.
- Roco4 is essential for proper stalk cell development and structural integrity.
- Roco11 plays a role in regulating fruiting body size.
- The evolutionary history of Roco genes in slime molds is diverse, with some evolving more recently than others.
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