The chromosomes of giant trophoblast cells of the mouse

Treatment of mouse trophoblast cells with actinomycin D causes the nuclear contents to condense into discrete bodies. A similar effect is observed when the antibiotic is applied to diploid or tetraploid blastocyst cells and in these cases the number of condensed bodies produced correlates closely to the known chromosome number. It is therefore argued that these bodies represent chromosomes. In the highly DNA-enriched trophoblast nuclei the number of these chromosomes generally does not exceed 40, the diploid number for mouse, indicating a considerable degree of polyteny in these cell nuclei.