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Formation of asymmetric unit membrane during urothelial differentiation (1996)

Sun, Tung-Tien ; Zhao, Haiping ; Provet, John ; [et al.]

Springer

Molecular biology reports 23 (1996), S. 3-11

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ISSN: 1573-4978

Keywords: asymmetric unit membrane ; bladder epithelium ; differentiation ; uroplakins ; urothelium

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Abstract Mammalian urothelium undergoes unique membrane specialization during terminal differentiation making numerous rigid-looking membrane plaques (0.3–0.5 μm diameter) that cover the apical cell surface. The outer leaflet of these membrane plaques is almost twice as thick as the inner leaflet hence the name asymmetric unit membrane (AUM). Ultrastructural studies established that the outer leaflet of AUM is composed of 16 nm particles forming two dimensional crystals, and that each particle forms a ‘twisted ribbon’ structure. We showed recently that highly purified bovine AUMs contain four major integral membrane proteins: uroplakins Ia (27 kD), Ib (28 kD), II (15 kD) and III (47 kD). Studies of the protease sensitivity of the different subdomains of uroplakins and other considerations suggest that UPIa and UPIb have 4 transmembrane domains, while UPII and UPIII have only one transmembrane domain. Chemical Crosslinking studies showed that UPIa and UPIb, which share 39% amino acid sequence, are topologically adjacent to UPII and UPIII, respectively, thus raising the possibility that there exist two biochemically distinct AUM particles, i.e., those containing UPIa/UPII vs. UPIb/UPIII. Bovine urothelial cells grown in the presence of 3T3 feeder cells undergo clonal growth forming stratified colonies capable of synthesizing and processing all known uroplakins. Transgenic mouse studies showed that a 3.6 kb 5′-flanking sequence of mouse uroplakin II gene can drive the expression of bacterial LacZ gene to express in the urothelium. Further studies on the biosynthesis, assembly and targeting of uroplakins will offer unique opportunities for better understanding the structure and function of AUM as well as the biology of mammalian urothelium.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00357068

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Chromosomal localization of uroplakin genes of cattle and mice (1993)

Ryan, Anne M. ; Womack, James E. ; Yu, Jun ; [et al.]

Springer

Mammalian genome 4 (1993), S. 656-661

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ISSN: 1432-1777

Source: Springer Online Journal Archives 1860-2000

Topics: Biology , Medicine

Notes: Abstract The asymmetric unit membrane (AUM) of the apical surface of mammalian urinary bladder epithelium contains several major integral membrane proteins, including uroplakins IA and IB (both 27 kDa), II (15 kDa), and III (47 kDa). These proteins are synthesized only in terminally differentiated bladder epithelial cells. They are encoded by separate genes and, except for uroplakins IA and IB, appear to be unrelated in their amino acid sequences. The genes encoding these uroplakins were mapped to chromosomes of cattle through their segregation in a panel of bovine x rodent somatic cell hybrids. Genes for uroplakins IA, IB, and II were mapped to bovine (BTA) Chromosomes (Chrs) 18 (UPK1A), 1 (UPK1B), and 15 (UPK2), respectively. Two bovine genomic DNA sequences reactive with a uroplakin III cDNA probe were identified and mapped to BTA 6 (UPK3A) and 5 (UPK3B). We have also mapped genes for uroplakins 1A and II in mice, to the proximal regions of mouse Chr 7 (Upk1a) and 9 (Upk2), respectively, by analyzing the inheritance of restriction fragment length variants in recombinant inbred mouse strains. These assignments are consistent with linkage relationships known to be conserved between cattle and mice. The mouse genes for uroplakins IB and III were not mapped because the mouse genomic DNA fragments reactive with each probe were invariant among the inbred strains tested. Although the stoichiometry of AUM proteins is nearly constant, the fact that the uroplakin genes are unlinked indicates that their expression must be independently regulated. Our results also suggest likely positions for two human uroplakin genes and should facilitate further analysis of their possible involvement in disease.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00360903

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