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Fig. 3 Metastatic cells following single-cell malignant transformation. (A) A zebrafish larva, in which a single cell in the brain was photoinduced (at 1 day post-fertilization [dpf]) to express the oncogene KRASG12V by the blue fluorescence of the expression marker (H2b-mTFP) as in Figure 2, shows that the progeny of the cell of origin of cancer give rise to a tumor mass in the brain (white arrowhead), as well as to migrating metastatic-like cells that disseminate in the whole organism (white arrowhead), some localizing in proximity of arterial branchial arches (indicated by ? and white arrowhead), trunk, and tail fin. (B) H2b-mTFP positive cells can migrate far from the site of induction (brain) and colonize ectopic tissues located in the heart and (C) the bottom of otic vesicle (in proximity of the primary head sinus, designated by ?), the digestive tract (designated by ? and ?), a feature characteristic of metastatic cancer cells. Note that no anesthetics (e.g. tricaine) or mounting media (low melting point agarose or methylcellulose) were used to block live zebrafish, during both monitoring and imaging performed on live zebrafish. An asterisk (*) indicates the eye and a white arrow the otic vesicle. Scale bars and body axes (a: anterior; p: posterior; d: dorsal; v: ventral) are indicated.