title: The prostatic utricle is not a Müllerian duct remnant: immunohistochemical evidence for a distinct urogenital sinus origin.
abstract: OBJECTIVE
  The embryological origin of the utricle is thought to be a remnant of the fused caudal ends of the müllerian ducts (MDs). Others propose that the urogenital sinus (UGS) contributes either partially or totally to the development of this structure. Using immunohistochemical probes, we provide strong evidence that the utricle is of UGS origin only.
  
  
  METHODS
  Human fetal prostates, gestational ages 9 to 24 weeks, were serially cross-sectioned. Representative sections were stained with antibodies to p63 (basal cell marker), vimentin (mesoderm marker), uroplakins (marker for urothelium) Pax-2 (expressed in ductal and mesenchyme of urogenital system including the MDs and wolffian ducts) and Ki67 (proliferation). Apoptosis was detected with the TUNEL assay.
  
  
  RESULTS
  By 9 weeks there was weak expression of p63 in the basal layer of the UGS. At 11 weeks there was increased staining of p63 in the UGS and some p63 staining of the fused MDs, which expressed Pax-2 at this time. At 14 to 15 weeks as the MDs were undergoing apoptosis, there was an ingrowth of uroplakin-expressing UGS epithelium into the periurethral stroma, which formed a plate of p63 positive cells just beneath the UGS that was Ki67 positive. The remaining caudal MD epithelium was p63 negative and expressed vimentin and Pax-2. By 17 weeks the plate of p63 positive cells elongated forming the utricle that remained p63 positive but Pax-2 and vimentin negative.
  
  
  CONCLUSIONS
  We show that the utricle forms as an ingrowth of specialized cells from the dorsal wall of the UGS as the caudal MDs regress.
authors.affiliation: Department of Urology, New York University School of Medicine, New York, New York, USA. ellen.shapiro@med.nyu.edu
authors.forename: Ellen
authors.initials: E
authors.lastname: Shapiro
authors.forename: Hongying
authors.initials: H
authors.lastname: Huang
authors.forename: Deborah E
authors.initials: DE
authors.lastname: McFadden
authors.forename: Rachel J
authors.initials: RJ
authors.lastname: Masch
authors.forename: Eliza
authors.initials: E
authors.lastname: Ng
authors.forename: Herbert
authors.initials: H
authors.lastname: Lepor
authors.forename: Xue-Ru
authors.initials: XR
authors.lastname: Wu
mesh_terms: D004268:DNA-Binding Proteins; D016147:Genes, Tumor Suppressor; D005865:Gestational Age; D006801:Humans; D007150:Immunohistochemistry; D008297:Male; D009024:Morphogenesis; D009095:Mullerian Ducts / Q000033:anatomy & histology / Q000196:embryology* / Q000378:metabolism; D010750:Phosphoproteins / Q000096:biosynthesis; D011467:Prostate / Q000033:anatomy & histology / Q000196:embryology* / Q000378:metabolism; D015534:Trans-Activators / Q000096:biosynthesis; D014157:Transcription Factors; D025521:Tumor Suppressor Proteins
chemical_list: D004268:DNA-Binding Proteins; D010750:Phosphoproteins; C115051:TP63 protein, human; D015534:Trans-Activators; D014157:Transcription Factors; D025521:Tumor Suppressor Proteins