Imaging embryonic development in Caenorhabditis elegans.

Embryos are remarkable for their combination of pluripotency, three-dimensionality, and swiftness of subcellular and developmental rearrangements. Embryogenesis in the nematode Caenorhabditis elegans is uniquely suited among model systems to high-resolution dynamic imaging. Within a single high-magnification, high-numerical aperture (NA) microscope field, at submicrometer resolution, it is possible to observe several entire animals taking form. The full approximately 14-h course of embryonic cleavage and morphogenesis of this transparent, free-living worm is essentially invariant. Observing specific fluorescently labeled components during embryonic development promises to reveal the roles of organelles and molecules in an extremely diverse and reproducible set of contexts. The C. elegans community has created a growing collection of hundreds of transgenic strains expressing green fluorescent protein (GFP)-labeled versions of distinct endogenously expressed genes. The task of correlating the resulting expression and localization patterns in space and time is simultaneously alluring and technically demanding. This article describes the use of four-dimensional (4D) laser-scanning microscopy and subsequent data processing to record, portray, analyze, and compare the expression of fluorescently tagged gene products during development of the nematode embryo.