Micrograph of the microtrabecular meshwork of a 3T3 cell. The microtrabecular meshwork of cytoplasmic matrix consists of mainly actin, which has been demembranated, extracted from tissue-culture cells that were quick frozen with liquid helium, deep etched, and rotary shadowed. The resulting micrographs viewed as negatives in stereo pairs have the three-dimensional quality of scanning electron micrographs and the high resolution of transmission electron microscopy. 3T3 cells are immortalized cells from the serial subcultivation using the smallest inoculum of mouse embryo fibroblasts. Unlike other immortalized cell lines, the 3T3 line did not give rise to tumors when injected into mice.