LAUSR

DNA methyltransferase 1 (DNMT1) is required for embryogenesis but roles in late forming organ systems including the prostate, which emerges from the urethral epithelium, have not been fully examined. We used a targeted genetic approach involving a Shhcre recombinase to demonstrate requirement of epithelial DNA methyltransferase-1 (Dnmt1) in mouse prostate morphogenesis. Dnmt1 mutant urethral cells exhibit DNA hypomethylation, DNA damage, p53 accumulation and undergo cell cycle arrest and apoptosis. Urethral epithelial cells are disorganized in Dnmt1 mutants, leading to impaired prostate growth and maturation and failed glandular development. We evaluated oriented cell division as a mechanism of bud elongation and widening by demonstrating that mitotic spindle axes typically form parallel or perpendicular to prostatic bud elongation axes. We then deployed a ShhcreERT allele to delete Dnmt1 from a subset of urethral epithelial cells, creating mosaic mutants with which to interrogate the requirement for cell division in specific prostatic bud epithelial populations. DNMT1- cell distribution within prostatic buds is not random as would be expected in a process where DNMT1 was not required. Instead, replication competent DNMT1 + cells primarily accumulate in prostatic bud margins and tips while replication impeded DNMT1- cells accumulate in prostatic bud cores. Together, these results highlight the role of DNMT1 in regulating epithelial bud formation by maintaining cell cycle progression and survival of rapidly dividing urethral epithelial cells, which can be extended to the study of other developing epithelial organs. In addition, our results show that prostatic buds consist of two epithelial cell populations with distinct molecular and functional characteristics that could potentially contribute to specialized lineages in the adult prostate.