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A novel, putative MEK kinase controls developmental timing and spatial patterning in Dictyostelium and is regulated
1Department of Biology, Center for Molecular Genetics, University of California, San Diego, La Jolla, California 92093-0634 USA.
Abstract:
We have identified a developmentally regulated, putative MEK kinase (MEKKalpha) that contains an F-box and WD40 repeats and plays a complex role in regulating cell-type differentiation and spatial patterning. Cells deficient in MEKKalpha develop precociously and exhibit abnormal cell-type patterning with an increase in one of the prestalk compartments (pstO), a concomitant reduction in the prespore domain, and a loss of the sharp compartment boundaries, resulting in overlapping prestalk and prespore domains. Overexpression of MEKKalpha or MEKKalpha lacking the WD40 repeats results in very delayed development and a severe loss of compartment boundaries. Prespore and prestalk cells are interspersed throughout the slug. Analysis of chimeric organisms suggests that MEKKalpha function is required for the proper induction and maintenance of prespore cell differentiation. We show that the WD40 repeats target MEKKalpha to the cortical region of the cell, whereas the F-box/WD40 repeats direct ubiquitin-mediated MEKKalpha degradation. We identify a UBC and a UBP (ubiquitin hydrolase) that interact with the F-box/WD40 repeats. Our findings indicate that cells lacking the ubiquitin hydrolase have phenotypes similar to those of MEKKalpha null (mekkalpha-) cells, further supporting a direct genetic and biochemical interaction between MEKKalpha, the UBC, and the UBP. We demonstrate that UBC and UBP differentially control MEKKalpha ubiquitination/deubiquitination and degradation through the F-box/WD40 repeats in a cell-type-specific and temporally regulated manner. Our results represent a novel mechanism that includes targeted protein degradation by which MAP kinase cascade components can be controlled. More importantly, our findings suggest a new paradigm of spatial and temporal control of the kinase activity controlling spatial patterning during multicellular development, which parallels the temporally regulated degradation of proteins required for cell-cycle progression.
Insights
MEKKalpha regulates cell differentiation and spatial patterning during development. Its degradation, controlled by ubiquitin pathways, is crucial for proper cell-type specification and developmental timing.
Area of Science:
- Developmental Biology
- Cell Signaling
- Molecular Biology
Background:
- Cell-type differentiation and spatial patterning are critical for multicellular development.
- Mitogen-activated protein kinase (MAPK) pathways regulate diverse cellular processes, including development.
- The precise regulation of kinase activity is essential for controlling developmental timing and spatial organization.
Purpose of the Study:
- To identify and characterize a novel MEK kinase (MEKKalpha) involved in developmental regulation.
- To elucidate the role of MEKKalpha in cell-type differentiation and spatial patterning.
- To investigate the molecular mechanisms controlling MEKKalpha activity, including its degradation pathway.
Main Methods:
- Genetic analysis of MEKKalpha-deficient and overexpressing cells.
- Chimeric organism analysis to assess cell-cell interactions and differentiation.
- Biochemical assays to identify interacting proteins and pathways (UBC, UBP).
- Analysis of ubiquitination and deubiquitination processes.
Main Results:
- MEKKalpha deficiency leads to precocious development and abnormal cell patterning, with altered prestalk/prespore domains.
- MEKKalpha overexpression causes delayed development and severe loss of compartment boundaries.
- WD40 repeats target MEKKalpha to the cell cortex, while F-box/WD40 repeats mediate its ubiquitination-dependent degradation.
- UBC and UBP (ubiquitin hydrolase) interact with MEKKalpha and differentially regulate its degradation in a cell-type and temporally specific manner.
Conclusions:
- MEKKalpha plays a crucial role in regulating cell-type differentiation and spatial patterning during development.
- Targeted protein degradation via the ubiquitin-proteasome system is a novel mechanism for controlling MAPK cascade components.
- This study reveals a new paradigm for spatial and temporal control of kinase activity in multicellular development, paralleling cell-cycle regulation.