Caenorhabditis elegansis a well-established model system particularly suited for studying cell–cell fusion because of its highly predictable and rapid development and its known cell lineage. This chapter focuses on understanding the ultrastructural components of cell fusion through the use of transmission electron microscopy (TEM). Published TEM studies have described the initial demonstration of syncytial cells in the worm, the vesiculation of the bilayers between cells during widening of the normal fusion aperture, and the appearance of microfusion intermediates in the membranes of cells with fusion-defective mutations. Capturing events observed in embryos on the light microscope and preserving the integrity of cellular membranes for examination by TEM require some special considerations that differ from many ultrastructural studies of cells. The principles of different techniques for TEM and details of protocols that have been used to investigate cell fusion in the nematode are discussed in this chapter.
