Changing Patterns of Keratin Expression could be Associated with Functional Maturation of the Developing Human Bladder

PURPOSE: We investigate the keratin phenotype of human transitional epithelium at various gestational ages and whether keratin composition of transitional epithelium is related to bladder function and morphology. MATERIALS AND METHODS: Consecutive sections from formalin fixed paraffin embedded blocks of autopsy bladder tissue from 21 male and 5 female fetuses, gestational age 12 to 40 weeks and 7 infants 2 days to 19 months old were cut and stained with antibodies recognizing basal cell keratins 5, 14 and 17, intermediate squamous cell keratin 13 and columnar cell keratins 7, 8, 18 and 20. RESULTS: With gestational age there were distinct changes in expression of keratins recognizing columnar cells, consisting of focal loss of keratin 7 in transitional epithelium, restriction of keratin 20 expression to umbrella cells and expression of keratin 18 throughout the full thickness of transitional epithelium. Basal cell keratin 5 was found above the basal cell layer while keratins 14 and 17 were not found. Squamous cell keratin 13 was found throughout the full thickness of the urothelium. CONCLUSIONS: The changes with gestational age in expression of some keratins may be related to the development of the reservoir function of the bladder. The impermeability of transitional epithelium, particularly during early fetal development, is possibly a function of umbrella and intermediate transitional cells.