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Endocytosis-mediated downregulation of LIN-12/Notch upon Ras activation in Caenorhabditis elegans
Daniel D Shaye1, Iva Greenwald
1Department of Genetics and Development, and Howard Hughes Medical Institute, Columbia University, College of Physicians and Surgeons, New York, New York 10032, USA.
Abstract:
The coordination of signals from different pathways is important for cell fate specification during animal development. Here, we define a novel mode of crosstalk between the epidermal growth factor receptor/Ras/mitogen-activated protein kinase cascade and the LIN-12/Notch pathway during Caenorhabditis elegans vulval development. Six vulval precursor cells (VPCs) are initially equivalent but adopt different fates as a result of an inductive signal mediated by the Ras pathway and a lateral signal mediated by the LIN-12/Notch pathway. One consequence of activating Ras is a reduction of LIN-12 protein in P6.p (ref. 2), the VPC believed to be the source of the lateral signal. Here we identify a 'downregulation targeting signal' (DTS) in the LIN-12 intracellular domain, which encompasses a di-leucine-containing endocytic sorting motif. The DTS seems to be required for internalization of LIN-12, and on Ras activation it might mediate altered endocytic routing of LIN-12, leading to downregulation. We also show that if LIN-12 is stabilized in P6.p, lateral signalling is compromised, indicating that LIN-12 downregulation is important in the appropriate specification of cell fates in vivo.
Insights
Researchers discovered a new mechanism in C. elegans development where Ras pathway activation reduces LIN-12/Notch protein levels. This downregulation, mediated by a specific signal, is crucial for correct cell fate specification.
Area of Science:
- Developmental Biology
- Cell Signaling
- Molecular Biology
Background:
- Cell fate specification in animal development relies on integrating signals from multiple pathways.
- In Caenorhabditis elegans vulval development, epidermal growth factor receptor/Ras/mitogen-activated protein kinase (MAPK) and LIN-12/Notch pathways interact.
- Vulval precursor cells (VPCs) achieve distinct fates through Ras-mediated inductive signals and LIN-12/Notch-mediated lateral signals.
Purpose of the Study:
- To define a novel crosstalk mechanism between the Ras/MAPK and LIN-12/Notch pathways.
- To investigate the role of LIN-12 protein downregulation in Caenorhabditis elegans vulval development.
Main Methods:
- Identification of a 'downregulation targeting signal' (DTS) within the LIN-12 intracellular domain.
- Analysis of the DTS's role in LIN-12 protein internalization and endocytic routing.
- Experimental manipulation to stabilize LIN-12 protein in specific cells (P6.p) to assess the impact on lateral signaling.
Main Results:
- A novel 'downregulation targeting signal' (DTS) was identified in the LIN-12 intracellular domain, containing a di-leucine-containing endocytic sorting motif.
- The DTS is essential for LIN-12 internalization, and Ras activation appears to alter its endocytic routing, leading to protein downregulation.
- Stabilization of LIN-12 protein in the P6.p cell compromised lateral signaling, highlighting the importance of its downregulation.
Conclusions:
- LIN-12/Notch pathway downregulation, mediated by the DTS and Ras activation, is a critical component of cell fate specification during C. elegans vulval development.
- This study reveals a novel mode of crosstalk between the Ras/MAPK and LIN-12/Notch pathways, impacting cell-cell communication and developmental outcomes.
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