Identification of distinct epithelial factors in the developing mouse bladder and urethra (E14.5 and E18.5)

The lower urinary is derived from the endodermal precursor, the cloaca. Despite common embryological origins, the epithelial linings and surrounding mesenchyme of the bladder and urethra show divergence. The bladder forms from the anterior part of the urogenital sinus, a cloacal derivative formed after septation of the cloaca to give rise to the anorectal and urogenital tracts. The urethra elongates posteriorly and shows sex-specific differences as a result of hormonal action. The bladder is a target for regenerative therapies and tissue reconstruction strategies. A significant shortcoming of these strategies has been the inability to recapitulate all layers of bladder epithelial cells, most importantly the apical uroplakin positive layer that forms a tight, impermeable barrier against components in the urine. The urethral epithelium is contiguous with the bladder epithelium but has distinct cellular architecture and lacks a uroplakin expressing apical layer. We hypothesized that comparison of the developing urethra and bladder epithelium will identify early genes that are responsible for urethra and bladder-specific differentiation. In this study, we compared the epithelial compartments of the developing mouse bladder and urethra to identify genes that are differentially expressed in these two compartments. Our study identified transcription factor genes and other tissue-specific markers that are confined to either the urethra or bladder epithelium. Additionally, we describe sex-specific differences in the lower urinary tract epithelium which are more pronounced between the male and female urethral epithelium and less evident in the bladder epithelium between sexes. The objective of this study was to identify compartment specific gene expression in the developing bladder and urethra. We obtained timed-pregnant CD-1 female mice and collected embryos at embryonic day 14.5 and E18.5. The lower urinary tract, including bladder and pelvic urethra, were dissected from the embryos. The epithelial layer of the bladder and urethra were mechanically separated from the mesenchymal layer after enzymatic digest with trypsin. Tissues from female embryos from a litter were separately pooled. Each litter yielded 2 sample types: Female bladder epithelium and female urethral epithelium. A total of n=4 biological replicates for each sample type were obtained from 4 independent litters at E14.5. A total of n=3 biological replicates for each sample type were obtained from 3 independent litters at E18.5.