Chromosomal localization of uroplakin genes of cattle and mice

Cloning and molecular dissection of the 8.8 kb pig uroplakin II promoter using transgenic mice and RT4 cells

Uroplakin II (UPII) gene expression is highly tissue and cell specific, with mRNA present in the suprabasal cell layers of the bladder and urethra. Previous reports described the mouse UPII (mUPII) promoter as primarily urothelium selective. However, ectopic expression of a transgene under the 3.6 kb mUPII promoter was also detected in brain, kidney, and testis in some transgenic mouse lines. Here, we have cloned an 8.8 kb pig UPII (pUPII) promoter region and investigated which cells within the bladder and urethra express a transgene consisting of the pUPII promoter fused to human erythropoietin (hEPO) or a luciferase gene. pUPII-luciferase expression vectors with various deletions of the promoter region were introduced into mouse fibroblast (NIH3T3), Chinese hamster ovary (CHO), and human bladder transitional carcinoma (RT4). A 2.1 kb pUPII promoter fragment displayed high levels of luciferase activity in transiently transfected RT4 cells, whereas the 8.8 kb pUPII promoter region displayed only low levels of activity. The pUPII-hEPO expression vector was injected into the pronucleus of zygotes to make transgenic mice. To elucidate the in vivo molecular mechanisms controlling the tissue- and cell-specific expression of the pUPII promoter gene, transgenic mice containing 2.1 and 8.8 kb pUPII promoter fragments linked to the genomic hEPO gene were generated. An erythropoietin (EPO) assay showed that all nine transgenic lines carrying the 8.8 kb construct expressed recombinant human erythropoietin (rhEPO) only in their urethra and bladder, whereas two transgenic lines carrying the 2.1 kb pUPII promoter displayed hEPO expression in several organs including bladder, kidney, spleen, heart, and brain. These studies demonstrate that the 2.1 kb promoter contains the DNA elements necessary for high levels of expression, but lacks critical sequences necessary for tissue-specific expression. We compared binding sites in the 2.1 and 8.8 kb promoter sequences and found five peroxisome proliferator responsive elements (PPREs) in the 8.8 kb promoter. Our data demonstrated that proliferator-activated receptor (PPAR)-gamma activator treatment in RT4 cells induced the elevated expression of hEPO mRNA under the control of the 8.8 kb pUPII promoter, but not the 2.1 kb promoter. Collectively, our data suggested that all the major trans-regulatory elements required for bladder- and urethra-specific transcription are located in the 8.8 kb upstream region and that it may enhance tissue-specific protein production and be of interest to clinicians who are searching for therapeutic modalities with high efficacy and low toxicity.

Lack of major involvement of human uroplakin genes in vesicoureteral reflux: implications for disease heterogeneity

BACKGROUND

Primary vesicoureteral reflux (VUR) is a hereditary disorder characterized by the retrograde flow of urine into the ureters and kidneys. It affects about 1% of the young children and is thus one of the most common hereditary diseases. Its associated nephropathy is an important cause of end-stage renal failure in children and adults. Recent studies indicate that genetic ablation of mouse uroplakin (UP) III gene, which encodes a 47 kD urothelial-specific integral membrane protein forming urothelial plaques, causes VUR and hydronephrosis.

METHODS

To begin to determine whether mutations in UP genes might play a role in human VUR, we genotyped all four UP genes in 76 patients with radiologically proven primary VUR by polymerase chain reaction (PCR) amplification and sequencing of all their exons plus 50 to 150 bp of flanking intronic sequences.

RESULTS

Eighteen single nucleotide polymorphisms (SNPs) were identified, seven of which were missense, with no truncation or frame shift mutations. Since healthy relatives of the VUR probands are not reliable negative controls for VUR, we used a population of 90 race-matched, healthy individuals, unrelated to the VUR patients, as controls to perform an association study. Most of the SNPs were not found to be significantly associated with VUR. However, SNP1 of UP Ia gene affecting a C to T conversion and an Ala7Val change, and SNP7 of UP III affecting a C to G conversion and a Pro154Ala change, were marginally associated with VUR (both P= 0.08). Studies of additional cases yielded a second set of data that, in combination with the first set, confirmed a weak association of UP III SNP7 in VUR (P= 0.036 adjusted for both subsets of cases vs. controls).

CONCLUSION

Such a weak association and the lack of families with simple dominant Mendelian inheritance suggest that missense changes of uroplakin genes cannot play a dominant role in causing VUR in humans, although they may be weak risk factors contributing to a complex polygenic disease. The fact that no truncation or frame shift mutations have been found in any of the VUR patients, coupled with our recent finding that some breeding pairs of UP III knockout mice yield litters that show not only VUR, but also severe hydronephrosis and neonatal death, raises the possibility that major uroplakin mutations could be embryonically or postnatally lethal in humans.

Chromosomal localization of the human urothelial "tetraspan" gene, UPK1B, to 3q13.3-q21 and detection of a TaqI polymorphism

The TI1/UPK1b gene codes for a protein of the "tetraspan" family and is expressed as a differentiation product of the mammalian urothelium. A partial genomic clone of the human homologue of the TI1/UPK1b gene was isolated and used as probe to localize the human gene to chromosome 3q13.3-q21 by in situ hybridization. Using the same probe, a TaqI restriction fragment length polymorphism, with 29% heterozygosity, was identified by Southern analysis.

Regeneration of bladder urothelium, smooth muscle, blood vessels and nerves into an acellular tissue matrix

PURPOSE

To study the cellular events occurring during bladder development and regeneration we developed an in vivo model of bladder augmentation with an acellular tissue graft. We propose that the extracellular matrix orchestrates the regenerative capacity of host bladder cells (urothelium, smooth muscle, blood vessels and nerve cells) after bladder augmentation with acellular tissue matrix.

MATERIALS AND METHODS

A total of 40 adult rats underwent partial cystectomy and augmentation with a patch of extracellular matrix representing the full thickness of rat gastric or bladder tissue. Sections were examined histologically to assess urothelial, smooth muscle and neuronal invasion of the graft.

RESULTS

A total of 32 rats was evaluated 1 day to 26 weeks after grafting. Epithelialization occurred by day 4, accompanied by granulocytic infiltration. Smooth muscle regenerated 2 weeks after grafting in juxtaposition to epithelial surfaces and it matured into normal sized bundles by 26 weeks. Neovascularity was noted 2 weeks postoperatively. Neural elements formed around developing smooth muscle bundles as early as 4 weeks after grafting.

CONCLUSIONS

We demonstrated the regeneration of urothelium, smooth muscle, blood vessels and nerves within a full thickness grafted acellular tissue matrix scaffold in the rat. The spatial orientation of these elements suggests that mesenchymal-epithelial interactions occur during phenotypic regeneration of the bladder. Urothelium appears to regulate the early forming smooth muscle. This in vivo model provides a suitable method to study cellular events during regeneration.

A tissue-specific promoter that can drive a foreign gene to express in the suprabasal urothelial cells of transgenic mice

Uroplakins are a group of integral membrane proteins that are synthesized as the major differentiation products of urothelium. The luminal portions of these proteins form 12-nm protein particles arranged in a two-dimensional crystalline array. The expression of uroplakin genes is bladder specific and differentiation dependent; little is known, however, about their molecular regulation. Here we describe the cloning of mouse uroplakin II gene and demonstrate, in transgenic mouse experiments, that a 3.6-kb 5'-flanking sequence of this gene can drive a bacterial lacZ (reporter) gene to express in the suprabasal cell layers of the urothelium. The transgene was not expressed in any tested (nonurothelial) epithelial and other tissues (except hypothalamus). These results suggest that most of the cis elements that confer the bladder-specific and differentiation-dependent expression of mouse uroplakin II gene must reside in the 3.6-kb sequence. The availability of a promoter capable of delivering a foreign molecule to the differentiated cell layers of bladder epithelium opens avenues for studying normal and pathological urothelial differentiation in transgenic mice.

Uroplakins Ia and Ib, two major differentiation products of bladder epithelium, belong to a family of four transmembrane domain (4TM) proteins

The mammalian bladder epithelium elaborates, as a terminal differentiation product, a specialized plasma membrane called asymmetric unit membrane (AUM) which is believed to play a role in strengthening and stabilizing the urothelial apical surface through its interactions with an underlying cytoskeleton. Previous studies indicate that the outer leaflet of AUM is composed of crystalline patches of 12-nm protein particles, and that bovine AUMs contain three major proteins: the 27- to 28-kD uroplakin I, the 15-kD uroplakin II and the 47-kD uroplakin III. As a step towards elucidating the AUM structure and function, we have cloned the cDNAs of bovine uroplakin I (UPI). Our results established the existence of two isoforms of bovine uroplakin I: a 27-kD uroplakin Ia and a 28-kD uroplakin Ib. These two glycoproteins are closely related with 39% identity in their amino acid sequences. Hydropathy plot revealed that both have four potential transmembrane domains (TMDs) with connecting loops of similar length. Proteolytic digestion of UPIa inserted in vitro into microsomal vesicles suggested that its two main hydrophilic loops are exposed to the luminal space, possibly involved in interacting with the luminal domains of other uroplakins to form the 12-nm protein particles. The larger loop connecting TMD3 and TMD4 of both UPIa and UPIb contains six highly conserved cysteine residues; at least one centrally located cysteine doublet in UPIa is involved in forming intramolecular disulfide bridges. The sequences of UPIa and UPIb (the latter is almost identical to a hypothetical, TGF beta-inducible, TI-1 protein of mink lung epithelial cells) are homologous to members of a recently described family all possessing four transmembrane domains (the "4TM family"); members of this family include many important leukocyte differentiation markers such as CD9, CD37, CD53, and CD63. The tissue-specific and differentiation-dependent expression as well as the naturally occurring crystalline state of uroplakin I molecules make them uniquely suitable, as prototype members of the 4TM family, for studying the structure and function of these integral membrane proteins.