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Updated: Jul 19, 2026
Visualizing Neuroblast Cytokinesis During C. elegans Embryogenesis
Published on: March 12, 2014
The Caenorhabditis elegans P21-activated kinases are differentially required for UNC-6/netrin-mediated commissural
Mark Lucanic1, Maureen Kiley, Neville Ashcroft
1Center for Neuroscience, and Cell and Developmental Biology Graduate Group, University of California, Davis, CA 95616, USA.
Abstract:
P21 activated kinases (PAKs) are major downstream effectors of rac-related small GTPases that regulate various cellular processes. We have identified the new PAK gene max-2 in a screen for mutants disrupted in UNC-6/netrin-mediated commissural axon guidance. There are three Caenorhabditis elegans PAKs. We find that each C. elegans PAK represents a distinct group previously identified in other species. Here we examine their roles in the postembryonic migration of the P cell neuroblasts and the axon guidance of the ventral cord commissural motoneurons (VCCMNs). We find that the two PAKs, max-2 and pak-1, are redundantly required for P cell migration and function with UNC-73/Trio and the rac GTPases (CED-10 and MIG-2). During axon guidance of the VCCMNs, PAK-1 also acts with the rac GTPases, CED-10 and MIG-2, and is completely redundant with MAX-2. Interestingly, we find that unlike MAX-2 activity during P cell migration, for motoneuron axon guidance max-2 is also required in parallel to this PAK-1 pathway, independent of rac GTPase signaling. Finally, we provide evidence that MAX-2 functions downstream of the UNC-6/netrin receptor UNC-5 during axon repulsion and is an integral part of its signaling.
Insights
The study identifies MAX-2, a p21-activated kinase (PAK), crucial for Caenorhabditis elegans development. MAX-2 and PAK-1 redundantly regulate cell migration and axon guidance, with MAX-2 having distinct roles in neuronal development.
Area of Science:
- Cell Biology
- Neuroscience
- Genetics
Background:
- P21-activated kinases (PAKs) are key regulators of cellular processes, downstream of rac GTPases.
- UNC-6/netrin signaling mediates commissural axon guidance, a critical process in neural development.
Purpose of the Study:
- To investigate the roles of Caenorhabditis elegans PAKs, specifically MAX-2 and PAK-1, in P cell neuroblast migration and ventral cord commissural motoneuron (VCCMN) axon guidance.
- To elucidate the functional relationship between MAX-2, PAK-1, rac GTPases, and UNC-6/netrin signaling pathways.
Main Methods:
- Genetic screening to identify mutants in UNC-6/netrin-mediated axon guidance.
- Analysis of gene function in postembryonic P cell migration and VCCMN axon guidance using C. elegans models.
- Investigating the interplay between PAKs, rac GTPases (CED-10, MIG-2), and UNC-73/Trio.
Main Results:
- MAX-2 and PAK-1 are redundantly required for P cell migration, functioning with UNC-73/Trio and rac GTPases (CED-10, MIG-2).
- For VCCMN axon guidance, PAK-1 acts with CED-10 and MIG-2 and is redundant with MAX-2.
- MAX-2 also functions independently of rac GTPases in VCCMN axon guidance, and downstream of the UNC-5 receptor in axon repulsion signaling.
Conclusions:
- MAX-2 and PAK-1 exhibit both redundant and distinct roles in C. elegans neurodevelopment.
- MAX-2 is a novel component of the UNC-6/netrin signaling pathway, particularly in axon repulsion mediated by UNC-5.
- This study expands our understanding of PAK signaling in regulating cell migration and axon guidance.
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