THE DISTINCT STEPS OF CELL DETACHMENT DURING DEVELOPMENT OF MOUSE UROEPITHELIAL CELLS IN THE BLADDER

In developing mouse urinary bladder the urothelial cells respond to ur ine accumulation by cell detachment, i.e. desquamation. To elucidate t he steps of urothelial cell detachment during embryonic development an d first urine accumulation in bladder lumen, superficial and intermedi ate cell layers were investigated. Different electron microscopic and cytochemical methods have been used. It was possible to distinguish be tween an early and late events on the basis of morphology. At the begi nning cell detachment involves interruption of tight junctions between neighbouring superficial cells and the formation of numerous endocyto tic vesicles. Endocytotic and cup-shaped vesicles then fuse and form l arge parallel rows of vacuoles and multivesicular bodies in desquamati ng superficial cells and in the neighbouring superficial and intermedi ate cells. These observations clearly demonstrate the existence of spe cific steps during the detachment of embryonic uroepithelial cells. Ap optosis accompanies cell desquamation. Only predetermined superficial bridge cells die in an apoptotic manner. (C) 1997 Academic Press Limit ed.