[
Genetics,
2022]
Light microscopes are the cell and developmental biologists' "best friend", providing a means to see structures and follow dynamics from the protein to the organism level. A huge advantage of C. elegans as a model organism is its transparency, which coupled with its small size means that nearly every biological process can be observed and measured with the appropriate probe and light microscope. Continuous improvement in microscope technologies along with novel genome editing techniques to create transgenic probes have facilitated the development and implementation of a dizzying array of methods for imaging worm embryos, larvae and adults. In this review we provide an overview of the molecular and cellular processes that can be visualized in living worms using light microscopy. A partial inventory of fluorescent probes and techniques successfully used in worms to image the dynamics of cells, organelles, DNA, and protein localization and activity is followed by a practical guide to choosing between various imaging modalities, including widefield, confocal, lightsheet, and structured illumination microscopy. Finally, we discuss the available tools and approaches, including machine learning, for quantitative image analysis tasks, such as colocalization, segmentation, object tracking, and lineage tracing. Hopefully, this review will inspire worm researchers who have not yet imaged their worms to begin, and push those who are imaging to go faster, finer, and longer.
[
WormBook,
2005]
The use of Wnt ligands for signaling between cells is a conserved feature of metazoan development. Activation of Wnt signal transduction pathways upon ligand binding can regulate diverse processes including cell proliferation, migration, polarity, differentiation and axon outgrowth. A ''canonical'' Wnt signaling pathway has been elucidated in vertebrate and invertebrate model systems. In the canonical pathway, Wnt binding leads to the stabilization of the transcription factor beta-catenin, which enters the nucleus to regulate Wnt pathway target genes. However, Wnt binding also acts through beta-catenin-independent, noncanonical pathways, such as the planar cell polarity (PCP) pathway and a pathway involving Ca 2+ signaling. This chapter examines our current understanding of Wnt signaling and Wnt-mediated processes in the nematode C. elegans. Like other species, the C. elegans genome encodes multiple genes for Wnt ligands (five) and Wnt receptors (four frizzleds, one Ryk/Derailed). Unlike vertebrates or Drosophila, the C. elegans genome encodes three beta-catenin genes, which appear to have distinct functions in Wnt signaling and cell adhesion. Canonical Wnt signaling clearly exists in C. elegans, utilizing the beta-catenin BAR-1 . However, a noncanonical pathway utilizing the beta-catenin WRM-1 also exists, and to date a similar pathway has not been described in other species. Evidence for beta-catenin independent noncanonical Wnt signaling is currently limited. The role of Wnt signaling in over a dozen C. elegans developmental processes, including the regulation of cell fate, polarity and migration, is described.