During the tumor progression, micrometastases at their earliest stages have been difficult to analyze qualitatively or quantitatively because of lacking suitable sensitive markers to discriminate small numbers of tumor cells from cell populations
of
normal tissue. To identify the distribution of micrometastases and tracing of F9 teratocarcinoma stem cell in vivo, we used chick embryos and the polymerase china reaction(PCR) as simple, sensitive, and quantitative assay system. Hence, F9 cells
which
metastasized in the liver of chick embryo were detected by PCR using specific primers for mouse β-globin gene.
In addition, another assay method was developed for detecting micrometastases of F9 cells with Ecoli lacZ gene as a genetical and histochemical marker. After the subsequent transfection of the lacZ gene into F9 cells, an intensely blue-staining
clone
harboring lacZ gene was isolated by using chromogenic substrate, 5-bromo-4-chloro-3-indoly-β-D-galacto-pyranoside (X-Gal). The lacZ-bearing F9 cells at primary tumor sites as well as at secondary organs can be stained intensely blue spots and
easily
distinguished from the host tissue cells after hours, days, or weeks postinjection.
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