Polyploidy and differentiation in the transitional epithelium of mouse urinary bladder

Abstract

1. There is a wide range in the size of nuclei from transitional epithelium of mouse urinary bladder, with the largest nuclei being nearest the lumen. These characteristics are present at birth and do not change significantly thereafter. 2. Microspectrophotometric measurements of nuclear DNA fall into several classes, indicating the presence of polyploidy. All surface cells and some deep cells are polyploid. 3. Neither the amount of DNA per nucleus nor the distribution of nuclear diameters is significantly altered in pituitary dwarf mice. 4. The counting of chromosomes in squash preparations of transitional epithelium showed the presence of polyploid chromosome groups in the mouse embryo from day 16 2/3 to birth. 5. The appearance of polyploidy in embryonic transitional epithelium was paralleled by the appearance of many binucleate cells, the nuclei of which were seen to enter division synchronously. The widespread presence of two prophases in a single cell and the lack of such duality in the later stages of division was taken as evidence of polyploid formation through fusion at late prophase and subsequent normal division into two polyploid nuclei. 6. The manner in which polyploidy was involved in the histogenesis of transitional epithelium led to the hypothesis that one characteristic of cytoplasmic differentiation in surface cells was brought about, at least in part, by nuclear differentiation.