Long-Term High-Resolution Imaging of Developing C. elegans Larvae with Microfluidics

Integration of EGFR and LIN-12/Notch Signaling by LIN-1/Elk1, the Cdk8 Kinase Module, and SUR-2/Med23 in Vulval Precursor Cell Fate Patterning in Caenorhabditis elegans

Six initially equivalent, multipotential Vulval Precursor Cells (VPCs) in Caenorhabditis elegans adopt distinct cell fates in a precise spatial pattern, with each fate associated with transcription of different target genes. The pattern is centered on a cell that adopts the "1°" fate through Epidermal Growth Factor Receptor (EGFR) activity, and produces a lateral signal composed of ligands that activate LIN-12/Notch in the two flanking VPCs to cause them to adopt "2°" fate. Here, we investigate orthologs of a transcription complex that acts in mammalian EGFR signaling-lin-1/Elk1, sur-2/Med23, and the Cdk8 Kinase module (CKM)-previously implicated in aspects of 1° fate in C. elegans and show they act in different combinations for different processes for 2° fate. When EGFR is inactive, the CKM, but not SUR-2, helps to set a threshold for LIN-12/Notch activity in all VPCs. When EGFR is active, all three factors act to resist LIN-12/Notch, as revealed by the reduced ability of ectopically-activated LIN-12/Notch to activate target gene reporters. We show that overcoming this resistance in the 1° VPC leads to repression of lateral signal gene reporters, suggesting that resistance to LIN-12/Notch helps ensure that P6.p becomes a robust source of the lateral signal. In addition, we show that sur-2/Med23 and lin-1/Elk1, and not the CKM, are required to promote endocytic downregulation of LIN-12-GFP in the 1° VPC. Finally, our analysis using cell fate reporters reveals that both EGFR and LIN-12/Notch signal transduction pathways are active in all VPCs in lin-1/Elk1 mutants, and that lin-1/Elk1 is important for integrating EGFR and lin-12/Notch signaling inputs in the VPCs so that the proper gene complement is transcribed.

Live-cell confocal microscopy and quantitative 4D image analysis of anchor-cell invasion through the basement membrane in Caenorhabditis elegans

Cell invasion through basement membrane (BM) barriers is crucial in development, leukocyte trafficking and the spread of cancer. The mechanisms that direct invasion, despite their importance in normal and disease states, are poorly understood, largely because of the inability to visualize dynamic cell-BM interactions in vivo. This protocol describes multichannel time-lapse confocal imaging of anchor-cell invasion in live Caenorhabditis elegans. Methods presented include outline-slide preparation and worm growth synchronization (15 min), mounting (20 min), image acquisition (20-180 min), image processing (20 min) and quantitative analysis (variable timing). The acquired images enable direct measurement of invasive dynamics including formation of invadopodia and cell-membrane protrusions, and removal of BM. This protocol can be combined with genetic analysis, molecular-activity probes and optogenetic approaches to uncover the molecular mechanisms underlying cell invasion. These methods can also be readily adapted by any worm laboratory for real-time analysis of cell migration, BM turnover and cell-membrane dynamics.