EMFIBSEMFIG 2: FIB/SEM imaging of a C. elegans embryo.

Wild type C. elegans embryo at the cell proliferation stage is viewed by focused ion beam milling and SEM. Tissues are not yet formed, but early blastomeres are viewed at different cell cycle stages. Most of these will later give rise to multiple cell types. Gastrulation has begun, and some cells are now internalized. A few cells extend pseudopodia, either to facilitate local cell movements, or perhaps as early steps in morphogenesis. Substantial extracellular space separates the embryonic cells from the eggshell, while a distinct lipid layer encloses all of the cells more tightly. Fluid beneath the lipid layer is destined to become the early basis for the blastocoel. Specimen was processed by Ken Nguyen using high pressure freezing, freeze substitution, and an OTO protocol, before infiltration into plastic resin. Blockface imaging by SEM was conducted by Dr. William Rice using the FEI Helios FIB/SEM at New York Structural Biology Center.

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