Identification and expression analysis of the human mu-protocadherin gene in fetal and adult kidneys

The microvillar protocadherin CDHR5 associates with EBP50 to promote brush border assembly

Transporting epithelial cells of the gut and kidney interact with their luminal environment through a densely packed collection of apical microvilli known as a brush border (BB). Proper brush border assembly depends on the intermicrovillar adhesion complex (IMAC), a protocadherin-based adhesion complex found at the distal tips of microvilli that mediates adhesion between neighboring protrusions to promote their organized packing. Loss of the IMAC adhesion molecule Cadherin-related family member 5 (CDHR5) results in significant brush border defects, though the functional properties of this protocadherin have not been thoroughly explored. Here, we show that the cytoplasmic tail of CDHR5 contributes to its correct apical targeting and functional properties in an isoform-specific manner. Library screening identified the Ezrin-associated scaffolds EBP50 and E3KARP as cytoplasmic binding partners for CDHR5. Consistent with this, loss of EBP50 disrupted proper brush border assembly with cells exhibiting markedly reduced apical IMAC levels. Together, our results shed light on the apical targeting determinants of CDHR5 and further define the interactome of the IMAC involved in brush border assembly.

Mesalazine initiates an anti-oncogenic β-catenin / MUCDHL negative feed-back loop in colon cancer cells by cell-specific mechanisms

Chronic inflammation associated with intestinal architecture and barrier disruption puts patients with inflammatory bowel disease (IBD) at increased risk of developing colorectal cancer (CRC). Widely used to reduce flares of intestinal inflammation, 5-aminosalicylic acid derivatives (5-ASAs) such as mesalazine appear to also exert more direct mucosal healing and chemopreventive activities against CRC. The mechanisms underlying these activities are poorly understood and may involve the up-regulation of the cadherin-related gene MUCDHL (CDHR5). This atypical cadherin is emerging as a new actor of intestinal homeostasis and opposes colon tumorigenesis. Here, we showed that mesalazine increase mRNA levels of MUCDHL and of other genes involved in the intestinal barrier function in most intestinal cell lines. In addition, using gain / loss of function experiments (agonists, plasmid or siRNAs transfections), luciferase reporter genes and chromatin immunoprecipitation, we thoroughly investigated the molecular mechanisms triggered by mesalazine that lead to the up-regulation of MUCDHL expression. We found that basal transcription of MUCDHL in different CRC cell lines is regulated positively by CDX2 and negatively by β-catenin through a negative feed-back loop. However, mesalazine-stimulation of MUCDHL transcription is controlled by cell-specific mechanisms, involving either enhanced activation of CDX2 and PPAR-γ or repression of the β-catenin inhibitory effect. This work highlights the importance of the cellular and molecular context in the activity of mesalazine and suggests that its efficacy against CRC depends on the genetic alterations of transformed cells.

Heterophilic and homophilic cadherin interactions in intestinal intermicrovillar links are species dependent

Enterocytes are specialized epithelial cells lining the luminal surface of the small intestine that build densely packed arrays of microvilli known as brush borders. These microvilli drive nutrient absorption and are arranged in a hexagonal pattern maintained by intermicrovillar links formed by 2 nonclassical members of the cadherin superfamily of calcium-dependent cell adhesion proteins: protocadherin-24 (PCDH24, also known as CDHR2) and the mucin-like protocadherin (CDHR5). The extracellular domains of these proteins are involved in heterophilic and homophilic interactions important for intermicrovillar function, yet the structural determinants of these interactions remain unresolved. Here, we present X-ray crystal structures of the PCDH24 and CDHR5 extracellular tips and analyze their species-specific features relevant for adhesive interactions. In parallel, we use binding assays to identify the PCDH24 and CDHR5 domains involved in both heterophilic and homophilic adhesion for human and mouse proteins. Our results suggest that homophilic and heterophilic interactions involving PCDH24 and CDHR5 are species dependent with unique and distinct minimal adhesive units.

The atypical cadherin MUCDHL antagonizes colon cancer formation and inhibits oncogenic signaling through multiple mechanisms

Cadherins form a large and pleiotropic superfamily of membranous proteins sharing Ca²⁺-binding repeats. While the importance of classic cadherins such as E- or N-cadherin for tumorigenesis is acknowledged, there is much less information about other cadherins that are merely considered as tissue-specific adhesion molecules. Here, we focused on the atypical cadherin MUCDHL that stood out for its unusual features and unique function in the gut. Analyses of transcriptomic data sets (n > 250) established that MUCDHL mRNA levels are down-regulated in colorectal tumors. Importantly, the decrease of MUCDHL expression is more pronounced in the worst-prognosis subset of tumors and is associated with decreased survival. Molecular characterization of the tumors indicated a negative correlation with proliferation-related processes (e.g., nucleic acid metabolism, DNA replication). Functional genomic studies showed that the loss of MUCDHL enhanced tumor incidence and burden in intestinal tumor-prone mice. Extensive structure/function analyses revealed that the mode of action of MUCDHL goes beyond membrane sequestration of ß-catenin and targets through its extracellular domain key oncogenic signaling pathways (e.g., EGFR, AKT). Beyond MUCDHL, this study illustrates how the loss of a gene critical for the morphological and functional features of mature cells contributes to tumorigenesis by dysregulating oncogenic pathways.

Up-regulation of CDHR5 expression promotes malignant phenotype of pancreatic ductal adenocarcinoma

CDHR5 has been reported to play key roles in carcinogenesis of various cancers, but its roles in pancreatic cancer have not been reported. The present study was designed to investigate its clinical value in pancreatic ductal adenocarcinoma (PDAC). Tissue microarray-based immunohistochemistry was performed to analyse the correlation between CDHR5 expression and clinical and pathological features of PDAC, as well as the CDHR5 expression during tumour progression. Cell function assays were performed to investigate CDHR5's effects on PDAC cells. Moreover, qRT-PCR was applied to investigate the expression of CDHR5 isoforms in PDAC cells. Expression of CDHR5 was higher on the membrane of PDAC cells. This high expression level was associated with shorter overall survival of PDAC patients and was identified as an independent prognostic factor for overall survival by multivariate Cox regression analysis. In addition, expression level of CDHR5 presented an increased trend in the occurrence and progression of PDAC. Cell experiment suggested that CDHR5 could notably promote invasion and migration of PDAC cells. Moreover, analysis of CDHR5 isoforms indicated CDHR5-L was the major isoform expressed in PDAC cell lines. CDHR5 appears to be a promising and novel prognostic factor for PDAC, and its promotion in PDAC metastasis might be ascribed to the isoform CDHR5-L.

Loss of cadherin related family member 5 (CDHR5) expression in clear cell renal cell carcinoma is a prognostic marker of disease progression

Reduced expression of Cadherin-Related Family Member 5 (CDHR5) was recently found implied in carcinogenesis of colon cancer, but its role in other tumors is unknown. We aimed to analyze the expression of CDHR5 in different subtypes of renal cell carcinoma. CDHR5 expression was immunohistochemically examined using tissue micro arrays (TMAs) covering 279 patients with primary renal cell carcinoma. Additionally, expression data from the TCGA (The Cancer Genome Atlas) of an independent cohort of 489 clear-cell RCC cases was evaluated. CDHR5 protein expression was found in 74.9% of cases, with higher levels seen in clear cell and papillary RCC. In the univariate analysis CDHR5 expression was significantly associated with a longer overall survival of RCC patients at the protein (p = 0.026, HR = 0.56) and transcript levels (TCGA-cohort: p = 0.0002, HR = 0.55). Importantly, differences in survival times were confirmed independently in multivariate analyses in a model with common clinicopathological variables at the transcript level (p = 0.0097, HR = 0.65). Investigation of the putative functional role of CDHR5 using TCGA data and Enrichment analysis for Gene Ontology and Pathways revealed associations with many metabolic and some tumor growth-associated processes and pathways. CDHR5 expression appears to be a promising and new independent prognostic biomarker in renal cell carcinoma.

Expression of μ-protocadherin is negatively regulated by the activation of the β-catenin signaling pathway in normal and cancer colorectal enterocytes

Mu-protocadherin (MUCDHL) is an adhesion molecule predominantly expressed by colorectal epithelial cells which is markedly downregulated upon malignant transformation. Notably, treatment of colorectal cancer (CRC) cells with mesalazine lead to increased expression of MUCDHL, and is associated with sequestration of β-catenin on the plasma membrane and inhibition of its transcriptional activity. To better characterize the causal relationship between β-catenin and MUCDHL expression, we performed various experiments in which CRC cell lines and normal colonic organoids were subjected to culture conditions inhibiting (FH535 treatment, transcription factor 7-like 2 siRNA inactivation, Wnt withdrawal) or stimulating (LiCl treatment) β-catenin activity. We show here that expression of MUCDHL is negatively regulated by functional activation of the β-catenin signaling pathway. This finding was observed in cell culture systems representing conditions of physiological stimulation and upon constitutive activation of β-catenin in CRC. The ability of MUCDHL to sequester and inhibit β-catenin appears to provide a positive feedback enforcing the effect of β-catenin inhibitors rather than serving as the primary mechanism responsible for β-catenin inhibition. Moreover, MUCDHL might have a role as biomarker in the development of CRC chemoprevention drugs endowed with β-catenin inhibitory activity.

Epigenetic silencing of the MUPCDH gene as a possible prognostic biomarker for cyst growth in ADPKD

Although autosomal dominant polycystic kidney disease (ADPKD) is a common genetic disease, and is characterized by the formation of multiple fluid-filled cysts, which results in renal failure, early diagnosis and treatment of ADPKD have yet to be defined. Herein, we observed that the promoter region of the gene encoding mucin-like protocadherin (MUPCDH) was hypermethylated in the renal tissue of patients with ADPKD compared to non-ADPKD controls. Inversely, MUPCDH was significantly repressed in ADPKD, especially in cyst-lining cells. Our results indicate that aberrant methylation of MUPCDH promoter CpG islands may be negatively correlated with reduced expression level of MUPCDH and that this contributes to abnormal cell proliferation in ADPKD. It suggests that methylation status of MUPCDH promoter can be used as a novel epigenetic biomarker and a therapeutic target in ADPKD.

Shaping the intestinal brush border

Epithelial cells from diverse tissues, including the enterocytes that line the intestinal tract, remodel their apical surface during differentiation to form a brush border: an array of actin-supported membrane protrusions known as microvilli that increases the functional capacity of the tissue. Although our understanding of how epithelial cells assemble, stabilize, and organize apical microvilli is still developing, investigations of the biochemical and physical underpinnings of these processes suggest that cells coordinate cytoskeletal remodeling, membrane-cytoskeleton cross-linking, and extracellular adhesion to shape the apical brush border domain.

New insights into the evolution of metazoan cadherins and catenins

E-Cadherin and β-catenin are the best studied representatives of the superfamilies of transmembrane cadherins and intracellular armadillo catenins, respectively. However, in over 600 million years of multicellular animal evolution, these two superfamilies have diversified remarkably both structurally and functionally. Although their basic building blocks, respectively, the cadherin repeat domain and the armadillo repeat domain, predate metazoans, the specific and complex domain compositions of the different family members and their functional roles in cell adhesion and signaling appear to be key features for the emergence of multicellular animal life. Basal animals such as placozoans and sponges have a limited number of distinct cadherins and catenins. The origin of vertebrates, in particular, coincided with a large increase in the number of cadherins and armadillo proteins, including modern "classical" cadherins, protocadherins, and plakophilins. Also, α-catenins increased. This chapter introduces the many different family members and describes the putative evolutionary relationships between them.

Cdx2 controls expression of the protocadherin Mucdhl, an inhibitor of growth and β-catenin activity in colon cancer cells

BACKGROUND & AIMS

The intestine-specific homeobox transcription factor Cdx2 is an important determinant of intestinal identity in the embryonic endoderm and regulates the balance between proliferation and differentiation in the adult intestinal epithelium. Human colon tumors often lose Cdx2 expression, and heterozygous inactivation of Cdx2 in mice increases colon tumorigenesis. We sought to identify Cdx2 target genes to determine how it contributes to intestinal homeostasis.

METHODS

We used expression profiling analysis to identify genes that are regulated by Cdx2 in colon cancer cells lines. Regulation and function of a potential target gene were further investigated using various cell assays.

RESULTS

In colon cancer cell lines, Cdx2 directly regulated the transcription of the gene that encodes the protocadherin Mucdhl. Mucdhl localized to the apex of differentiated cells in the intestinal epithelium, and its expression was reduced in most human colon tumors. Overexpression of Mucdhl inhibited low-density proliferation of colon cancer cells and reduced tumor formation in nude mice. One isoform of Mucdhl interacted with β-catenin and inhibited its transcriptional activity.

CONCLUSIONS

The transcription factor Cdx2 activates expression of the protocadherin Mucdhl, which interacts with β-catenin and regulates activities of intestinal cells. Loss of Cdx2 expression in colon cancer cells might reduce expression of Mucdhl and thereby lead to tumor formation.

Molecular heterogeneity in the choroid plexus epithelium: the 22-member γ-protocadherin family is differentially expressed, apically localized, and implicated in CSF regulation

The choroid plexus (CP) epithelium develops from the ependyma that lines the ventricular system, and plays a critical role in the development and function of the brain. In addition to being the primary site of CSF production, the CP maintains the blood-CSF barrier via apical tight junctions between epithelial cells. Here we show that the 22-member γ-protocadherin (γ-Pcdh) family of cell adhesion molecules, which we have implicated previously in synaptogenesis and neuronal survival, is highly expressed by both CP epithelial and ependymal cells, in which γ-Pcdh protein localization is, surprisingly, tightly restricted to the apical membrane. Multi-label immunostaining demonstrates that γ-Pcdhs are excluded from tight junctions, basolateral adherens junctions, and apical cilia tufts. RT-PCR analysis indicates that, as a whole, the CP expresses most members of the Pcdh-γ gene family. Immunostaining using novel monoclonal antibodies specific for single γ-Pcdh proteins shows that individual epithelial cells differ in their apically localized γ-Pcdh repertoire. Restricted mutation of the Pcdh-γ locus in the choroid plexus and ependyma leads to significant reductions in ventricular volume, without obvious disruptions of epithelial apical-basal polarity. Together, these results suggest an unsuspected role for the γ-Pcdhs in CSF production and demonstrate a surprising molecular heterogeneity in the CP epithelium.

Polymorphism at the mucin-like protocadherin gene influences susceptibility to gallstone disease

BACKGROUND

Gallstone disease (GSD) is a common disease that can be caused by environmental influences, common genetic factors and their interactions. Mucin glycoproteins may be one important factor for GSD. We conducted a case-control study to investigate the relationship between the mucin-like protocadherin (MUPCDH) gene polymorphisms and GSD.

METHODS

The study included 452 GSD cases and 491 healthy controls who had no evidence of gallstones by ultrasound examination. Two common tagging single nucleotide polymorphism (SNP) rs3758650 and rs7932167, and four non-synonymous SNPs rs34362213, rs2740375, rs7108757 and rs2740379 were genotyped. The genetic effects were evaluated using the multivariate regression model.

RESULTS

The genotypes of these SNPs were all in Hardy-Weinberg equilibrium. Three non-synonymous SNPs (rs34362213, rs7108757 and rs2740379) were monomorphic. The single SNP analysis showed two SNPs (rs7932167 and rs2740375) were not associated with GSD and only SNP rs3758650 had the association of the presence of GSD with an odds ratio (OR) of 1.59 (adjusted P=0.013) for the AG genotype and 5.82 (adjusted P=0.007) for the AA genotype when compared with the reference GG genotype. The haplotype analysis of the three polymorphic SNPs showed GCA was significant for GSD (adjusted p=0.001) with an odds ratio (OR) of 1.41 when compared to other haplotypes.

CONCLUSIONS

The MUPCDH genetic polymorphism rs3758650 was considered a genetic marker to predict symptomatic GSD subjects. It may be of importance for GSD patients with the risk SNPs to be frequently checked because they may develop symptomatic GSD.

Proteomic analysis of the enterocyte brush border

The brush border domain at the apex of intestinal epithelial cells is the primary site of nutrient absorption in the intestinal tract and the primary surface of interaction with microbes that reside in the lumen. Because the brush border is positioned at such a critical physiological interface, we set out to create a comprehensive list of the proteins that reside in this domain using shotgun mass spectrometry. The resulting proteome contains 646 proteins with diverse functions. In addition to the expected collection of nutrient processing and transport components, we also identified molecules expected to function in the regulation of actin dynamics, membrane bending, and extracellular adhesion. These results provide a foundation for future studies aimed at defining the molecular mechanisms underpinning brush border assembly and function.

Molecular evolution of the cadherin superfamily

This review deals with the large and pleiotropic superfamily of cadherins and its molecular evolution. We compiled literature data and an in-depth phylogenetic analysis of more than 350 members of this superfamily from about 30 species, covering several but not all representative branches within metazoan evolution. We analyzed the sequence homology between either ectodomains or cytoplasmic domains, and we reviewed protein structural data and genomic architecture. Cadherins and cadherin-related molecules are defined by having an ectodomain in which at least two consecutive calcium-binding cadherin repeats are present. There are usually 5 or 6 domains, but in some cases as many as 34. Additional protein modules in the ectodomains point at adaptive evolution. Despite the occurrence of several conserved motifs in subsets of cytoplasmic domains, these domains are even more diverse than ectodomains and most likely have evolved separately from the ectodomains. By fine tuning molecular classifications, we reduced the number of solitary superfamily members. We propose a cadherin major branch, subdivided in two families and 8 subfamilies, and a cadherin-related major branch, subdivided in four families and 11 subfamilies. Accordingly, we propose a more appropriate nomenclature. Although still fragmentary, our insight into the molecular evolution of these remarkable proteins is steadily growing. Consequently, we can start to propose testable hypotheses for structure-function relationships with impact on our models of molecular evolution. An emerging concept is that the ever evolving diversity of cadherin structures is serving dual and important functions: specific cell adhesion and intricate cell signaling.

In silico regulatory analysis for exploring human disease progression

Background

An important goal in bioinformatics is to unravel the network of transcription factors (TFs) and their targets. This is important in the human genome, where many TFs are involved in disease progression. Here, classification methods are applied to identify new targets for 152 transcriptional regulators using publicly-available targets as training examples. Three types of sequence information are used: composition, conservation, and overrepresentation.

Results

Starting with 8817 TF-target interactions we predict an additional 9333 targets for 152 TFs. Randomized classifiers make few predictions (~2/18660) indicating that our predictions for many TFs are significantly enriched for true targets. An enrichment score is calculated and used to filter new predictions.

Two case-studies for the TFs OCT4 and WT1 illustrate the usefulness of our predictions:

• Many predicted OCT4 targets fall into the Wnt-pathway. This is consistent with known biology as OCT4 is developmentally related and Wnt pathway plays a role in early development.

• Beginning with 15 known targets, 354 predictions are made for WT1. WT1 has a role in formation of Wilms' tumor. Chromosomal regions previously implicated in Wilms' tumor by cytological evidence are statistically enriched in predicted WT1 targets. These findings may shed light on Wilms' tumor progression, suggesting that the tumor progresses either by loss of WT1 or by loss of regions harbouring its targets.

• Targets of WT1 are statistically enriched for cancer related functions including metastasis and apoptosis. Among new targets are BAX and PDE4B, which may help mediate the established anti-apoptotic effects of WT1.

• Of the thirteen TFs found which co-regulate genes with WT1 (p ≤ 0.02), 8 have been previously implicated in cancer. The regulatory-network for WT1 targets in genomic regions relevant to Wilms' tumor is provided.

Conclusion

We have assembled a set of features for the targets of human TFs and used them to develop classifiers for the determination of new regulatory targets. Many predicted targets are consistent with the known biology of their regulators, and new targets for the Wilms' tumor regulator, WT1, are proposed. We speculate that Wilms' tumor development is mediated by chromosomal rearrangements in the location of WT1 targets.

Reviewers

This article was reviewed by Trey Ideker, Vladimir A. Kuznetsov(nominated by Frank Eisenhaber), and Tzachi Pilpel.

Alternatively spliced isoforms encoded by cadherin genes from C. elegansgenome

Cadherins are calcium-dependent, homophilic, cell-cell adhesion receptors that regulate morphogenesis, pattern formation and cell migration. The C. elegans Genome Sequencing Consortium has reported 12 genes from C. elegansgenome encoding members of the cadherin superfamily. Alternative splicing of eukaryotic pre-mRNAs is a mechanism for generating potentially many transcript isoforms from a single gene. Here, using a combination of various gene or exon finding programmes and several other bioinformatics tools followed by experimental validation using RT-PCR, we have studied alternative splicing pattern in the cadherin encoding genes from C. elegansgenome. We have predicted that 7 of the 12 genes encoding the cadherin superfamily undergo extensive alternative splicing and encode for 12 new unreported alternatively spliced transcripts. Most of the alternatively spliced exons were found to be present at the 5' end of genes. These new previously un-detected spliced variants in C. eleganscadherin superfamily of genes could play vital roles in explaining the way cadherins act to control the processes like cell adhesion and morphogenesis.

Protocadherin 12 (VE-cadherin 2) is expressed in endothelial, trophoblast, and mesangial cells

Protocadherin 12 protein (PCDH12, VE-cadherin 2) is a cell adhesion molecule that has been isolated from endothelial cells. Here, we have used Northern and Western blots, immunohistology, and flow cytometry to examine the distribution of PCDH12 in mouse tissues. It is an N-glycosylated protein of 150-kDa mass. In the endothelium, PCDH12 immunoreactivity was variable and dependent upon the vascular bed. In both the embryo and embryonic stem cell differentiation system, signals were localized in vasculogenic rather than angiogenic endothelium. In addition, the protein was strongly expressed in a subset of invasive cells of the placenta, which were identified as glycogen-rich trophoblasts. In adult mice, strong PCDH12 signals were observed in mesangial cells of kidney glomeruli whereas expression was not detected in other types of perivascular cells. As opposed to most protocadherins, PCDH12 is not expressed in early embryonic (day 12.5) and adult brains. As a first approach to obtain insight into PCDH12 function, we produced transgenic mice deficient in PCDH12, which were viable and fertile. They did not display any obvious histomorphological defects. We conclude that PCDH12 has a unique expression pattern and that its deficiency does not lead to conspicuous abnormalities. Moreover, PCDH12 is the first specific marker for both glycogen-rich trophoblasts and mesangial cells.

Alternatively spliced variants of protocadherin 8 exhibit distinct patterns of expression during mouse development

Protocadherins, a subgroup of the cadherin superfamily of calcium-dependent cell adhesion molecules, are considered to play important roles in the developing embryo particularly in the central nervous system. The Protocadherin 8 (Pcdh8) gene comprises three coding exons in both human and mouse, and the exon junctions are precisely conserved between these two species. Alternative splicing of Pcdh8 RNA leads to the formation of two isoforms that differ in the length of the cytoplasmic domains. We have investigated the expression of these short and long variants of Pcdh8 during early mouse development by RT/PCR and in situ hybridization. We found that both isoforms were predominantly expressed in the nervous system, and that their expression patterns appeared to be developmentally regulated. However, the short variant had a broader pattern of expression than the long variant and was found in some non-neuronal tissues, such as paraxial mesoderm, developing somites, and in limb interdigital mesenchyme where massive programmed cell death occurs. The differential expression of two alternative cytoplasmic domain variants suggests that Pcdh8 may regulate cell adhesion in a variety of developmental processes, and that this may involve different intracellular interactions.

Global analysis of genes differentially expressed in branching and non-branching regions of the mouse embryonic lung

During development, the proximal and distal regions of respiratory tract undergo distinct processes that ultimately give rise to conducting airways and alveoli. To gain insights into the genetic pathways differentially activated in these regions when branching morphogenesis is initiating, we characterized their transcriptional profiles in murine rudiments isolated at embryonic (E) day 11.5. By using oligonucleotide microarrays, we identified 83 and 128 genes preferentially expressed in branching and non-branching regions, respectively. The majority of these genes (85%) had not been previously described in the lung, or in other organs. We report restricted expression patterns of 22 of these genes were by in situ hybridization. Among them in the lung potential components of the Wnt, TGF beta, FGF and retinoid pathways identified in other systems, and uncharacterized genes, such as translocases, small GTPases and splicing factors. In addition, we provide a more detailed analysis of the expression pattern and regulation of a representative gene from the distal (transforming growth factor, beta induced) and proximal (WW domain-containing protein 2) regions. Our data suggest that these genes may regulate focal developmental events specific of each of these regions during respiratory tract formation.

Expression of a novel cadherin in the mouse and human intestine

Members of the cadherin superfamily mediate critical interactions in tissue differentiation and organogenesis, including differentiation and maintenance of the intestine. In this study, we report the identification and expression of a novel cadherin in the intestinal epithelium. We identified this cDNA by subtraction hybridization and obtained subsequent clones by screening a human cDNA library. Tissue distribution of the mRNA encoding the cadherin was assessed by RNA blot, reverse transcriptase PCR, and in situ hybridization. Protein expression was analyzed by protein blot and immunohistochemistry. The cDNA encodes an integral membrane protein with four consecutive cadherin binding domains followed by a series of mucin domains, a unique feature of this cadherin. Differences in the mucin domains account for four splice-forms. Multiple potential SH3-binding domains and a single potential PDZ-binding domain follow the transmembrane domain. Analysis revealed expression in the liver, kidney, and intestine. Three splice variants were found in the embryonic intestine as early as embryonic d 13 and in the adult intestine. The mRNA localizes to the mature enterocytes throughout the mouse small intestine and the protein, including several species from 90 to 100 kD, resides on the enterocyte basolateral membrane. We have identified intestinal expression of a novel cell cadherin with features suggesting the potential to transduce signals from neighboring cells to the cytoplasm.

Biallelic expression of HRAS and MUCDHL in human and mouse

At least eight genes clustered in 1 Mb of DNA on human chromosome (Chr) 11p15.5 are subject to parental imprinting, with monoallelic expression in one or more tissues. Orthologues of these genes show conserved linkage and imprinting on distal Chr 7 of mice. The extended imprinted region has a bipartite structure, with at least two differentially methylated DNA elements (DMRs) controlling the imprinting of two sub-domains. We previously described three biallelically expressed genes ( MRPL23, 2G7 and TNNT3) in 100 kb of DNA immediately downstream of the imprinted H19 gene, suggesting that H19 marks one border of the imprinted region. Here we extend this analysis to two additional downstream genes, HRAS and MUCDHL (mu-protocadherin). We find that these genes are biallelically expressed in multiple fetal and adult tissues, both in humans and in mice. The mouse orthologue of a third gene, DUSP8, located between H19 and MUCDHL, is also expressed biallelically. The DMR immediately upstream of H19 frequently shows a net gain of methylation in Wilms tumors, either via Chr 11p15.5 loss of heterozygosity (LOH) or loss of imprinting (LOI), but changes in methylation in CpG-rich sequences upstream and within the MUCDHL gene are rare in these tumors and do not correlate with LOH or LOI. These findings are further evidence for a border of the imprinted region immediately downstream of H19, and the data allow the construction of an imprinting map that includes more than 20 genes, distributed over 3 Mb of DNA on Chr 11p15.5.