Genomic structure and chromosomal mapping of the mouse N-cadherin gene

The Usher syndrome 1C protein harmonin regulates canonical Wnt signaling

Human Usher syndrome (USH) is the most common form of hereditary combined deaf-blindness. USH is a complex genetic disorder, and the pathomechanisms underlying the disease are far from being understood, especially in the eye and retina. The USH1C gene encodes the scaffold protein harmonin which organizes protein networks due to binary interactions with other proteins, such as all USH proteins. Interestingly, only the retina and inner ear show a disease-related phenotype, although USH1C/harmonin is almost ubiquitously expressed in the human body and upregulated in colorectal cancer. We show that harmonin binds to β-catenin, the key effector of the canonical Wnt (cWnt) signaling pathway. We also demonstrate the interaction of the scaffold protein USH1C/harmonin with the stabilized acetylated β-catenin, especially in nuclei. In HEK293T cells, overexpression of USH1C/harmonin significantly reduced cWnt signaling, but a USH1C-R31* mutated form did not. Concordantly, we observed an increase in cWnt signaling in dermal fibroblasts derived from an USH1C ^{R31*/R80Pfs*69} patient compared with healthy donor cells. RNAseq analysis reveals that both the expression of genes related to the cWnt signaling pathway and cWnt target genes were significantly altered in USH1C patient-derived fibroblasts compared to healthy donor cells. Finally, we show that the altered cWnt signaling was reverted in USH1C patient fibroblast cells by the application of Ataluren, a small molecule suitable to induce translational read-through of nonsense mutations, hereby restoring some USH1C expression. Our results demonstrate a cWnt signaling phenotype in USH establishing USH1C/harmonin as a suppressor of the cWnt/β-catenin pathway.

Promoter, alternative splice forms, and genomic structure of protocadherin 15

We originally showed that the protocadherin 15 gene (Pcdh15) is necessary for hearing and balance functions; mutations in Pcdh15 affect hair cell development in Ames waltzer (av) mice. Here we extend that study to understand better how Pcdh15 operates in a cell. The original report identified 33 exons in Pcdh15, with exon 1 being noncoding; additional exons of Pcdh15 have since been reported. The 33 exons of Pcdh15 described originally are embedded in 409 kb of mouse genomic sequence, while the corresponding exons of human PCDH15 are spread over 980 kb of genomic DNA; the exons in Pcdh15/PCDH15 range in size from 9 to approximately 2000 bp. The genomic organization of Pcdh15/PCDH15 bears similarity to that of cadherin 23, but differs significantly from other protocadherin genes, such as Pcdhalpha, beta, or gamma. A CpG island is located approximately 2900 bp upstream of the PCDH15 transcriptional start site. The Pcdh15/PCDH15 promoter lacks TATAA or CAAT sequences within 100 bases upstream of the transcription start site; deletion mapping showed that Pcdh15 harbors suppressor and enhancer elements. Preliminary searches for alternatively spliced transcripts of Pcdh15 identified novel splice variants not reported previously. Results from our study show that both mouse and human protocadherin 15 genes have complex genomic structures and transcription control mechanisms.

Multiple N-cadherin enhancers identified by systematic functional screening indicate its Group B1 SOX-dependent regulation in neural and placodal development

Neural plate and sensory placodes share the expression of N-cadherin and Group B1 Sox genes, represented by Sox2. A 219-kb region of the chicken genome centered by the N-cadherin gene was scanned for neural and placodal enhancers. Random subfragments of 4.5 kb average length were prepared and inserted into tkEGFP reporter vector to construct a library with threefold coverage of the region. Each clone was then transfected into N-cadherin-positive (lens, retina and forebrain) or -negative embryonic cells, or electroporated into early chicken embryos to examine enhancer activity. Enhancers 1-4 active in the CNS/placode derivatives and non-specific Enhancer 5 were identified by transfection, while electroporation of early embryos confirmed enhancers 2-4 as having activity in the early CNS and/or sensory placodes but with unique spatiotemporal specificities. Enhancers 2-4 are dependent on SOX-binding sites, and misexpression of Group B1 Sox genes in the head ectoderm caused ectopic development of placodes expressing N-cadherin, indicating the involvement of Group B1 Sox functions in N-cadherin regulation. Enhancers 1, 2 and 4 correspond to sequence blocks conserved between the chicken and mammalian genomes, but enhancers 3 and 5 are unique to the chicken.

N-cadherin is not essential for limb mesenchymal chondrogenesis

The cell adhesion molecule N-cadherin is implicated in many morphogenetic processes, including mesenchyme condensation during limb development. To further understand N-cadherin function, we characterized a new N-cadherin allele containing the lacZ reporter gene under the regulation of the mouse N-cadherin promoter. The reporter gene recapitulates the expression pattern of the N-cadherin gene, including expression in heart, neural tube, and somites. In addition, strong expression was observed in areas of active cellular condensation, a prerequisite for chondrogenic differentiation, including the developing mandible, vertebrae, and limbs. Previous studies from our laboratory have shown that limb buds can form in N-cadherin-null embryos expressing a cardiac-specific cadherin transgene, however, these partially rescued embryos do not survive long enough to observe limb development. To overcome the embryonic lethality, we used an organ culture system to examine limb development ex vivo. We demonstrate that N-cadherin-deficient limb buds were capable of mesenchymal condensation and chondrogenesis, resulting in skeletal structures. In contrast to previous studies in chicken using N-cadherin-perturbing antibodies, our organ culture studies with mouse tissue demonstrate that N-cadherin is not essential for limb mesenchymal chondrogenesis. We postulate that another cell adhesion molecule, possibly cadherin-11, is responsible for chondrogenesis in the N-cadherin-deficient limb.

GATA-4 regulates cardiac morphogenesis through transactivation of the N-cadherin gene

Cardia bifida is known to occur in animal models lacking the cardiogenic transcriptional factor GATA-4. The downstream target genes responsible for this cardiac deformity remain unknown, however. Treatment with small interfering RNAs (siRNA) specifically targeting GATA-4 into cardiac mesodermal cells led to the development of cardia bifida in chick embryos. RT-PCR using mRNAs extracted from cardiac tubes revealed that the GATA-4-specific siRNA selectively suppresses expression of N-cadherin mRNA, one of the genes essential for the single heart formation, without affecting other cardiac marker mRNAs. Analysis of the N-cadherin gene promoter activity using a luciferase reporter gene system and electrophoretic mobility shift assays revealed that GATA-4 binds directly to the N-cadherin gene promoter region, thereby transactivating its expression. We therefore concluded that the cardia bifida observed in the GATA-4-deleted model is caused by the transcriptional down-regulation of N-cadherin expression.

Adhesion-independent mechanism for suppression of tumor cell invasion by E-cadherin

Loss of E-cadherin expression or function in tumors leads to a more invasive phenotype. In this study, we investigated whether the invasion suppressor activity of E-cadherin is mediated directly by tighter physical cell adhesion, indirectly by sequestering beta-catenin and thus antagonizing beta-catenin/T cell factor (TCF) signaling, or by other signaling pathways. To distinguish mechanisms, we expressed wild-type E-cadherin and various E-cadherin mutants in invasive E-cadherin-negative human breast (MDA-MB-231) and prostate (TSU-Pr1) epithelial carcinoma cell lines using a tetracycline-inducible system. Our data confirm that E-cadherin inhibits human mammary and prostate tumor cell invasion. We find that adhesion is neither necessary nor sufficient for suppressing cancer invasion. Rather, the invasion suppressor signal is mediated through the beta-catenin-binding domain of the E-cadherin cytoplasmic tail but not through the p120ctn-binding domain. beta-catenin depletion also results in invasion suppression. However, alteration in the beta-catenin/TCF transcriptional regulation of target genes is not required for the invasion suppressor activity of E-cadherin, suggesting the involvement of other beta-catenin-binding proteins.

Identification and characterization of three members of a novel subclass of protocadherins

Protocadherins are members of a nonclassic subfamily of calcium-dependent cell-cell adhesion molecules in the cadherin superfamily. Although the extracellular domains have several common structural features, there is no extensive homology between the cytoplasmic domains of protocadherin subfamily members. We have identified a new subclass of protocadherins based on a shared and highly conserved 17-amino-acid cytoplasmic motif. The subclass currently consists of 18 protocadherin members. Two of these, PCDH18 and PCDH19, are novel protocadherins and a third is the human orthologue of mouse Pcdh10. All three genes encode six ectodomain repeats with cadherin-like attributes and, consistent with the structural characteristics of protocadherins, a large first exon encodes the extracellular domain of each gene.

Cadherins in the central nervous system

The central nervous system (CNS) is divided into diverse embryological and functional compartments. The early embryonic CNS consists of a series of transverse subdivisions (neuromeres) and longitudinal domains. These embryonic subdivisions represent histogenetic fields in which neurons are born and aggregate in distinct cell groups (brain nuclei and layers). Different subsets of these aggregates become selectively connected by nerve fiber tracts and, finally, by synapses, thus forming the neural circuits of the functional systems in the CNS. Recent work has shown that 30 or more members of the cadherin family of morphoregulatory molecules are differentially expressed in the developing and mature brain at almost all stages of development. In a regionally specific fashion, most cadherins studied to date are expressed by the embryonic subdivisions of the early embryonic brain, by developing brain nuclei, cortical layers and regions, and by fiber tracts, neural circuits and synapses. Each cadherin shows a unique expression pattern that is distinct from that of other cadherins. Experimental evidence suggests that cadherins contribute to CNS regionalization, morphogenesis and fiber tract formation, possibly by conferring preferentially homotypic adhesiveness (or other types of interactions) between the diverse structural elements of the CNS. Cadherin-mediated adhesive specificity may thus provide a molecular code for early embryonic CNS regionalization as well as for the development and maintenance of functional structures in the CNS, from embryonic subdivisions to brain nuclei, cortical layers and neural circuits, down to the level of individual synapses.

Paternal exposure to cyclophosphamide alters cell-cell contacts and activation of embryonic transcription in the preimplantation rat embryo

Paternal exposure to chronic low doses of cyclophosphamide, an anticancer agent, results in aberrant embryonic development of the progeny. We hypothesized that paternal exposure to cyclophosphamide disturbs zygotic gene activity regulating proper progression through preimplantation development and that this disturbance results in improper cell-cell interactions. To test this hypothesis, we analyzed cell-cell interactions and the expression of cytoskeletal elements in preimplantation embryos sired by male rats gavaged with saline or 6 mg kg(-1) day(-1) cyclophosphamide for 5 wk. Embryos from control litters had 4-12 cells on Day 2 of gestation; cell-cell contacts were observed consistently. Embryos from litters sired by cyclophosphamide-treated males were frequently abnormal and had lower cell numbers and decreased cell-cell contacts. Steady state concentrations of the mRNAs for cell adhesion molecules (cadherins and connexin 43) and structural proteins (beta-actin, collagen, and vimentin) were low in two- and four-cell control embryos; expression increased dramatically by the eight-cell stage. In contrast, embryos sired by cyclophosphamide-treated males displayed the highest expression of most trancripts at the two-cell stage. In parallel with the mRNA profiles, E-cadherin immmunoreactivity was nearly absent in two-cell control embryos and was strong by the eight-cell stage; immunoreactivity in embryos sired by drug-treated fathers was strong at the two-cell stage but absent at later stages. Thus, drug exposure of the paternal genome led to dysregulated expression of structural elements and decreased cell interactions during preimplantation embryonic development.

Construction of a long-range YAC physical map spanning the 10-cM region between the markers D18Mit109 and D18Mit68 on mouse proximal chromosome 18

Four yeast artificial chromosome (YAC) contigs, physically approximately 8 Mb, have been constructed spanning a 10-cM region on mouse proximal chromosome 18 and include the sites of 21 known genes, including those near the twirler (Tw) locus and the recently isolated Niemann-Pick type C1 (npc1) gene, formerly designated as the spm locus. This physical map consists of 49 YAC clones that cover roughly 15% of the chromosome. The physical order of 38 microsatellite sequence-tagged sites (STSs) could be assembled and confirmed based on their presence or absence in individual YACs, from proximal D18Mit109 through distal D18Mit68. These YACs provide an important resource for the further characterization and identification of known and unknown genes. The physical map has been integrated with our previously published genetic linkage map and showed an average genetic to physical distance of cM/Mb > 1.1.

Large exons encoding multiple ectodomains are a characteristic feature of protocadherin genes

Recent studies revealed a striking difference in the genomic organization of classic cadherin genes and one family of "nonclassic cadherin" genes designated protocadherins. Specifically, the DNA sequences encoding the ectodomain repeats of classic cadherins are interrupted by multiple introns. By contrast, all of the encoded ectodomains of each member of the protocadherin gene clusters are present in one large exon. To determine whether large ectodomain exons are a general feature of protocadherin genes we have investigated the genomic organization of several additional human protocadherin genes by using DNA sequence information in GenBank. These genes include protocadherin 12 (Pcdh12), an ortholog of the mouse vascular endothelial cadherin-2 gene; hFmi1 and hFmi2, homologs of the Drosophila planar cell polarity gene, flamingo; hFat2, a homolog of the Drosophila tumor suppressor gene fat; and the Drosophila DN-cadherin and DE-cadherin genes. Each of these genes was found to be a member of the protocadherin subfamily, based on amino acid sequence comparisons of their ectodomains. Remarkably, all of these protocadherin genes share a common feature: most of the genomic DNA sequences encoding their ectodomains are not interrupted by an intron. We conclude that the presence of unusually large exons is a characteristic feature of protocadherin genes.

Large exons encoding multiple ectodomains are a characteristic feature of protocadherin genes

Recent studies revealed a striking difference in the genomic organization of classic cadherin genes and one family of "nonclassic cadherin" genes designated protocadherins. Specifically, the DNA sequences encoding the ectodomain repeats of classic cadherins are interrupted by multiple introns. By contrast, all of the encoded ectodomains of each member of the protocadherin gene clusters are present in one large exon. To determine whether large ectodomain exons are a general feature of protocadherin genes we have investigated the genomic organization of several additional human protocadherin genes by using DNA sequence information in GenBank. These genes include protocadherin 12 (Pcdh12), an ortholog of the mouse vascular endothelial cadherin-2 gene; hFmi1 and hFmi2, homologs of the Drosophila planar cell polarity gene, flamingo; hFat2, a homolog of the Drosophila tumor suppressor gene fat; and the Drosophila DN-cadherin and DE-cadherin genes. Each of these genes was found to be a member of the protocadherin subfamily, based on amino acid sequence comparisons of their ectodomains. Remarkably, all of these protocadherin genes share a common feature: most of the genomic DNA sequences encoding their ectodomains are not interrupted by an intron. We conclude that the presence of unusually large exons is a characteristic feature of protocadherin genes.

Cloning and expression of mouse Cadherin-7, a type-II cadherin isolated from the developing eye

We report the molecular cloning of Cadherin-7 from the embryonic mouse eye. The deduced amino acid sequence shows it to be a type-II cadherin similar to Xenopus F-cadherin and chick Cadherin-7. The mouse Cadherin-7 gene maps to chromosome 1, outside the conserved linkage group of cadherin genes on chromosome 8. Cadherin-7 is expressed throughout the entire period of neural development and mRNA levels are developmentally regulated in both the embryonic and the postnatal central nervous system (CNS). In adult mice, Cadherin-7 expression is restricted to the CNS, with highest levels in the retina. In the developing eye, Cadherin-7 mRNA is found only in the neural retina. It is expressed by all retinal neuroblasts from E11 onward, but becomes progressively restricted to neurons in the inner neuroblast and developing ganglion cell layers (GCL). In the adult retina it is confined to subpopulations of cells in the GCL and to amacrine cells in the inner part of the inner nuclear layer. This expression pattern suggests a role for Cadherin-7 in mouse retinal development, particularly in the formation and maintenance of the GCL.

Expression and function of the splice variant of the human cadherin-11 gene in subordination to intact cadherin-11

Cadherin-11, a member of the type II classic cadherin subfamily, differs from type I family molecules such as P-, E-, and N-cadherins. An isoform of the human cadherin-11 gene, termed the variant form, encodes a truncated protein with a different cytoplasmic domain. The resulting protein does not possess any part of the cytoplasmic domain common to other cadherins. In the present study, analysis of the genomic organization of the cadherin-11 gene revealed that an insertion of 179 bp in an intron generates an alternatively spliced form. The mRNA expression of the variant form of cadherin-11 was examined in normal tissues by reverse transcription-polymerase chain reaction and/or Northern blot analyses. The variant form was expressed in the heart, brain, placenta, lung, and bone, but not in the kidney, skeletal muscle, pancreas, and liver. Western blot analyses revealed that the variant form is expressed as an 85 kDa protein, and that an additional secreted form also exists as an 80 kDa protein originated from cleavage of the intact form. Gene transfer of the variant form into L cells demonstrated that it lacked the adhesion properties characteristic of the intact form of cadherin-11 but enhanced the activity of Ca2+-dependent adhesion of the intact form of cadherin-11. The variant was expressed on the surface together with the intact form and stabilized the interaction between the intact form and beta-catenin. These findings suggest that expression of the variant form of human cadherin-11 may regulate the intact cadherin-11-mediated adhesion and alter the morphogenetic processes during mesenchymal cell differentiation including osteoblasts.

Multiple cadherin mRNA expression and developmental regulation of a novel cadherin in the developing mouse eye

Cadherins form a large family of transmembrane glycoproteins whose members include the classical cadherins, the desmosomal cadherins, and the protocadherins. The classical cadherins mediate homophilic cell-cell adhesion and are key regulators of many morphogenetic processes. More than a dozen classical cadherins are expressed in both the developing and the mature central nervous system. Although individual cadherins have been identified in the retina of various species, we wished to determine the range of cadherins expressed at distinct developmental stages in the mouse retina. Using a PCR-based cloning strategy, we detected 10 different classical cadherin mRNAs of both type I and type II subtypes. The most abundant cDNA was that encoding the type II cadherin, Cadherin-11. The other type II cadherins detected were VE- and T2-cadherin and Cadherin-6 and -12. Four type I cadherins, N-, R-, P-, and E-cadherin, were also present. One cadherin cDNA encoded a novel cadherin, called EY-cadherin for cloned from eye. EY-cadherin is most closely related to human Cadherin-14 (93% identical). EY-cadherin mRNA was detected in the adult mouse eye, brain, and testis with a 20-fold increase in expression levels in the embryonic head from E11 to E19 and a 50-fold increase in expression levels in the postnatal eye from PN1 to PN16. Multiple cadherin gene expression is consistent with the hypothesis that different cadherins regulate morphogenetic processes, such as neuronal migration and lamination, and determine the specific interneuronal connections found in the mature retina.

Characterization of the regulatory regions in the human desmoglein genes encoding the pemphigus foliaceous and pemphigus vulgaris antigens

The adhesive proteins in the desmosome type of cell junction consist of two members of the cadherin superfamily, the desmogleins and desmocollins. Both desmogleins and desmocollins occur as at least three different isoforms with various patterns of expression. The molecular mechanisms controlling the differential expression of the desmosomal cadherin isoforms are not yet known. We have begun an investigation of desmoglein gene expression by cloning and analysing the promoters of the human genes coding for the type 1 and type 3 desmogleins (DSG1 and DSG3). The type 1 isoform is restricted to the suprabasal layers of the epidermis and is the autoantigen in the autoimmune blistering skin disease pemphigus foliaceous. The type 3 desmoglein isoform is also expressed in the epidermis, but in lower layers than the type 1 isoform, and is the autoantigen in pemphigus vulgaris. Phage lambda genomic clones were obtained containing 4.2 kb upstream of the translation start site of DSG1 and 517 bp upstream of the DSG3 start site. Sequencing of 660 bp upstream of DSG1 and 517 bp upstream of DSG3 revealed that there was no obvious TATA box, but a possible CAAT box was present at -238 in DSG1 and at -193 in DSG3 relative to the translation start site. Primer extension analysis and RNase protection experiments revealed four putative transcription initiation sites for DSG1 at positions -163, -151, -148 and -141, and seven closely linked sites for DSG3, the longest being at -140 relative to the translation start site. The sequences at these possible sites at -166 to -159 in DSG1 (TTCAGTCC) and at -124 to -117 in DSG3 (CTTAGACT) have some similarity to the initiator sequence (CTCANTCT) described for a TATA-less promoter often from -3 to +5, and the true transcription initiator site might therefore be the A residue in these sequences. There were two regions of similarity between the DSG1 and DSG3 promoters just upstream of the transcription initiation sites, of 20 and 13 bp, separated by 41 bp in DSG1 and 36 bp in DSG3. The significance of these regions of similarity remains to be elucidated, but the results suggest that they represent a point at which these two desmoglein genes are co-ordinately regulated. Analysis of the upstream sequences revealed GC-rich regions and consensus binding sites for transcription factors including AP-1 and AP-2. Exon boundaries were conserved compared with the classical cadherin E-cadherin, but the equivalent of the second cadherin intron was lacking. A 4.2 kb region of the human DSG1 promoter sequence was linked to the lacZ gene reporter gene in such a way that there was only one translation start site, and this construct was used to generate transgenic mice. We present the first transgenic analysis of a promoter region taken from a desmosomal cadherin gene. Our results suggest that the 4.2 kb upstream region of DSG1 does not contain all the regulatory elements necessary for correct expression of this gene but might have elements that regulate activity during hair growth.

Exon-intron organization of the human type 2 desmocollin gene (DSC2): desmocollin gene structure is closer to "classical" cadherins than to desmogleins

The cadherins are a superfamily of calcium-dependent glycoproteins that are cell adhesion molecules. Two families of cadherins, the desmocollins (Dsc) and desmogleins (Dsg), are found only in the desmosome type of cell-cell junction. They are each present in at least three different isoforms with differing spatial and temporal distributions and are specified by two clusters of closely linked genes on human chromosome 18q12.1. The human DSC2 gene, coding for the most widely distributed form of the desmocollins, has been found to consist of more than 32 kb of DNA. By using PCR we have determined the exon-intron organization. The gene is arranged into 17 exons ranging in size from 46 to 258 bp; exon 16 is alternatively spliced, giving rise to the a and b forms of the protein. This has revealed a remarkable degree of conservation of intron position with other cadherins. The desmocollin exon-intron organization is more similar to the so-called classical cadherins than to the desmogleins, especially in the cytoplasmic domain. Intron 1 is the largest in DSC2, as it is in the desmogleins, in contrast to the classical cadherins, where intron 2 is extremely large; this latter intron is missing from the desmogleins.

Analysis of the E-cadherin and P-cadherin promoters in murine keratinocyte cell lines from different stages of mouse skin carcinogenesis

We previously isolated the 5' upstream sequences of the mouse P-cadherin gene, in which putative binding sites for several transcription factors were identified between nt-101 and +30. In the study reported here, the promoter activity of the postulated 5' cis-acting sequences of the P-cadherin promoter, and the activity of the proximal E-cadherin promoter were investigated in several murine keratinocyte cell lines showing different levels of P- and E-cadherin expression as well as different morphology and tumorigenic behavior. Cell-type specificity and optimal activity of P-cadherin expression in murine keratinocytes was conferred by 5' sequences located between nt -200 and +30, and the GC-rich region (nt -101 to +80) and a CCAAT box element (nt -65) had a major regulatory role. The cell-type specificity of the E-cadherin promoter, on the other hand, was mediated by a combination of positive regulatory elements, a GC-rich region (nt -58 to -24), and a CCAAT box (nt -65) and repressor elements inside the E-pal sequence. Interestingly, the maximum repressor effect of the E-pal element was observed in non-expressing undifferentiated spindle cells. In vitro binding studies indicated that the GC-rich region of the P-cadherin promoter was mainly recognized by Sp1-related nuclear factors, whereas both AP2- and Sp1-related factors were involved in the interaction of the GC-rich region of the E-cadherin promoter. Common factors (probably related to the CP1 family) seemed also to be involved in the recognition of the CCAAT-box element of both the E- and P-cadherin promoters, but additional specific factors participated in the interaction with the CCAAT box of the E-cadherin promoter. Our studies also support the hypothesis that loss or modification of some of the regulatory factors occurs during mouse skin tumor progression.

The Sycp1 loci of the mouse genome: successive retropositions of a meiotic gene during the recent evolution of the genus

The murine Sycp1 gene is expressed at the early stages of meiosis. We show that it is composed of a number of small exons and localized on mouse chromosome 3. In the laboratory strains, two retrogenes were also identified. The first one (Sycp1-ps1), on chromosome 7, has accumulated point mutations and deletions and is not transcribed. A second retrogene (Sycp1-ps2), on chromosome 8, is inserted within the continuity of a moderately repeated element, in an intron of another gene (Cad11). The two retroposition events can be dated to distinct periods in the evolution of the Muridae. Sycp1-ps2 has kept features indicative of a relatively recent origin, namely a nearly intact coding region, a poly(A) tail, and 14-bp terminal repeats. Its recent origin was confirmed by the fact that it is found in all the laboratory strains of mice, but neither in a recent isolate from Mus musculus domesticus wild stocks nor in the closely related subspecies M. musculus musculus, M. m. molossinus, M. m. castaneus, and M. m. bactrianus. Appearance of the more ancient Sycp1-ps1 retrogene is concomitant with the radiation of the genus. It is present in various Mus species (M. spretus, M. spicilegus, M. macedonicus, and M. cookii), but neither in the rat nor in the more closely related Pyromis genus. Transposition of retrotranscripts during meiosis and their hereditary establishment thus appear to occur relatively frequently. They may, therefore, play a significant role in the evolutionary process.

The gene of the neural cell recognition molecule F11: conserved exon-intron arrangement in genes of neural members of the immunoglobulin superfamily

The chicken neural glycoprotein F11 is a cell recognition molecule implicated in neurohistogenesis, in particular in the context of neurite outgrowth and fasciculation. F11 is a glycosyl-phosphatidylinositol-linked member of the immunoglobulin superfamily that is also termed contactin or F3 in humans and rodents, respectively. In this study, we report the complete structure of the F11 gene. It is composed of 23 exons distributed over more than 100 kb of genomic DNA and each of the ten domains of the F11 protein is encoded by two exons. The sizes of the introns vary by two orders of magnitude ranging from 150 bp to more than 15 kb. All interdomain introns are in phase one, i.e. are inserted after the first nucleotide of a codon, being consistent with assembly of a F11 progenitor gene via exon shuffling. The intradomain introns are localized at variable sites within the domains and have different intron phases. This study reveals a remarkable similarity of the F11 gene with the gene of axonin-1, a related neural immunoglobulin superfamily member which is also implicated in neurite outgrowth and fasciculation. The intron positions with respect to the protein domain organization are found to be identical, strongly suggesting that both genes are derived from a common ancestor that already had this exon-intron structure.

Isolation of a Xenopus laevis genomic clone representing a novel N-cadherin related gene

We have isolated a Xenopus laevis genomic sequence distinct from, but sharing high sequence similarity with N-cadherin. We present evidence that the gene represented by this sequence, named XNcad3, resides at a separate locus to the two previously isolated N-cadherin clones from this species. Extensive analysis could detect no expression of XNcad3 in embryonic or adult tissues. It seems likely that XNcad3 represents a non-expressed pseudogene, or perhaps a novel cadherin with a restricted expression pattern.

Molecular characterization of Br-cadherin, a developmentally regulated, brain-specific cadherin

Cadherins are a family of transmembrane proteins that play a crucial role in cell adhesion and in morphogenesis. Several of the cadherins are expressed in the nervous system, but none is neuron-specific. We characterize a new member of the cadherin family, Br-cadherin, which is present exclusively in the central nervous system. Although the Br-cadherin protein is confined to the central nervous system, its mRNA is present in several additional tissues, suggesting that there is posttranscriptional control of this gene's expression. Within the central nervous system, Br-cadherin appears to be expressed specifically by neurons. In the mouse, its expression becomes detectable during the first postnatal week, which corresponds temporally to the onset of synaptogenesis and dendrite outgrowth in the brain. This pattern of expression is consistent with a role for Br-cadherin in neuronal development, perhaps specifically with synaptogenesis.

Protocadherins and diversity of the cadherin superfamily

Recent cadherin studies have revealed that many cadherins and cadherin-related proteins are expressed in various tissues of different multicellular organisms. These proteins are characterized by the multiple repeats of the cadherin motif in their extracellular domains. The members of the cadherin superfamily are divided into two groups: classical cadherin type and protocadherin type. The current cadherins appear to have evolved from a protocadherin type. Recent studies have proved the cell adhesion role of classical cadherins in embryogenesis. In contrast, the biological role of protocadherins is elusive. Circumstantial evidence, however, suggests that protocadherins are involved in a variety of cell-cell interactions. Since protocadherins, and many other new cadherins as well, have unique properties, studies of these cadherins may provide insight into the structure and biological role of the cadherin superfamily.

Cloning of the gene for human pemphigus vulgaris antigen (desmoglein 3), a desmosomal cadherin. Characterization of the promoter region and identification of a keratinocyte-specific cis-element

Pemphigus vulgaris antigen is a cadherin-like desmosomal cell adhesion molecule expressed primarily in suprabasal keratinocytes within the epidermis. Previously characterized structural features have defined this molecule as a desmoglein, DSG3. In this study, we have cloned the human DSG3 gene and examined the transcriptional regulation of its expression. The total gene consisted of 15 exons and was estimated to span >23 kilobases. Comparison of exon-intron organization of DSG3 with bovine DSG1 and several classical cadherin genes revealed striking conservation of the structure. Up to 2.8 kilobases of the upstream genomic sequences were sequenced and found to contain several putative cis-regulatory elements. The promoter region was GC-rich and TATA-less, similar to previously characterized mammalian cadherin promoters. The putative promoter region was subcloned into a vector containing chloramphenicol acetyl transferase reporter gene. Transient transfections with a series of deletion clones indicated that the DSG3 promoter demonstrated keratinocyte-specific expression, as compared with dermal fibroblasts examined in parallel, and fine mapping identified a 30-base pair segment at -200 to -170 capable of conferring epidermal specific expression. The results provide evidence for the transcriptional regulation of the pemphigus vulgaris antigen gene, potentially critical for development of the epidermis and physiologic terminal differentiation of keratinocytes.

Lanceolate hair (lah): a recessive mouse mutation with alopecia and abnormal hair

A new autosomal recessive mutation of the house mouse developed generalized alopecia associated with breakage of abnormal hair shafts. This mutation, named 'lanceolate hair' (symbol: lah), arose in a mutagenesis experiment using ethylnitrosourea. Hair shafts were short with a focal degeneration at the breakpoint characterized by a pronounced enlargement at the apex, resembling a lance head. Plucked hair fibers were 2.0 to 3.5 mm in length with a normal base, suggesting that there was a synchronized developmental defect. Histologic examination of anagen follicles revealed abnormal cornification of the matrix region with degeneration resulting in the focal hair shaft deformity. Catagen follicles showed pronounced follicular dystrophy but telogen follicles were almost normal. There was a marked, persistent thickening of the epidermis associated with a non-scarring, relatively non-inflammatory ichthyosiform dermatitis. These features are found in the Netherton's syndrome of the human, for which this mouse mutation may represent a model. The lah mutation has been localized to the centromeric end of mouse Chromosome 18.

Structural and functional diversity of cadherin superfamily: are new members of cadherin superfamily involved in signal transduction pathway?

A large number of cadherins and cadherin-related proteins are expressed in different tissues of a variety of multicellular organisms. These proteins share one property: their extracellular domains consist of multiple repeats of a cadherin-specific motif. A recent structure study has shown that the cadherin repeats roughly corresponding to the folding unit of the extracellular domains. The members of the cadherin superfamily are roughly classified into two groups, classical type cadherins proteins and protocadherin type according to their structural properties. These proteins appear to be derived from a common ancestor that might have cadherin repeats similar to those of the current protocadherins, and to have common functional properties. Among various cadherins, E-cadherin was the first to be identified as a Ca(2+)-dependent homophilic adhesion protein. Recent knockout mice experiments have proven its biological role, but there are still several puzzling unsolved properties of the cell adhesion activity. Other members of cadherin superfamily show divergent properties and many lack some of the expected properties of cell adhesion protein. Since recent studies of various adhesion proteins reveal that they are involved in different signal transduction pathways, the idea that the new members of cadherin superfamily may participate in more general cell-cell interaction processes including signal transduction is an intriguing hypothesis. The cadherin superfamily is structurally divergent and possibly functionally divergent as well.

Location of the 9257 and ataxia mutations on mouse chromosome 18

The location of three mutations on proximal Chromosome (Chr) 18 was determined by analysis of the offspring of several backcrosses. The results demonstrate that ataxia and the insertional mutation TgN9257Mm are separated by less than 1 cM and are located approximately 3 cM from the centromere, while the balding locus is 7 cM more distal. Previous data demonstrated that the twirler locus also maps within 1 cM of ataxia. The corrected locations will contribute to identification of appropriate candidate genes for these mutations. Two polymorphic microsatellite markers for proximal Chr 18 are described, D18Umi1 and D18Umi2. The Lama3 locus encoding the alpha 3 subunit of nicein was mapped distal to ataxia and did not recombine with Tg9257.

Protocadherin Pcdh2 shows properties similar to, but distinct from, those of classical cadherins

Cell adhesion and several other properties of a recently identified cadherin-related protein, protocadherin Pcdh2, were characterized. A chimeric Pcdh2 in which the original cytoplasmic domain was replaced with the cytoplasmic domain of E-cadherin was expressed in mouse L cells. The expressed protein had a molecular mass of about 150 kDa and was localized predominantly at the cell periphery, as was the wild-type Pcdh2. In a conventional cell aggregation assay, the transfectants showed cell aggregation activity comparable to that of classical cadherins. This activity was Ca(2+)-dependent and was inhibited by the addition of anti-Pcdh2 antibody, indicating that the chimeric Pcdh2, and probably the wild-type Pcdh2, has Ca(2+)-dependent cell aggregation activity. Mixed cell aggregation assay using L cells and different types of transfectants showed that the activity of Pcdh2 was homophilic and molecular type specific and that Pcdh2 was transfectants did not aggregate with other types of transfectants or with L cells. In immunoprecipitation, the chimeric Pcdh2 co-precipitated with a 105 kDa and a 95 kDa protein, whereas wild-type Pcdh2 co-precipitated with no major protein. Pcdh2 was easily solubilized with non-ionic detergent, in contrast to the case of classical cadherins. On immunofluorescence microscopy, the somas of Purkinje cells were diffusely stained with anti-human Pcdh2 antibody. Mouse Pcdh1 and Pcdh2 were mapped to a small segment of chromosome 18, suggesting that various protocadherins form a gene cluster at this region. The present results suggest that Pcdh2, and possibly other protocadherins as well as protocadherin-related proteins such as Drosophila fat, mediate Ca(2+)-dependent and specific homophilic cell-cell interaction in vivo and play an important role in cell adhesion, cell recognition, and/or some other basic cell processes.

Cloning and characterization of the human invasion suppressor gene E-cadherin (CDH1)

E-cadherin is a Ca(2+)-dependent epithelial cell-cell adhesion molecule. Downregulation of E-cadherin expression often correlates with strong invasive potential and poor prognosis of human carcinomas. By using recombinant lambda phage, cosmid, and P1 phage clones, we isolated the full-length human E-cadherin gene (CDH1). The gene spans a region of approximately 100 kb, and its location on chromosome 16q22.1 was confirmed by FISH analysis. Detailed restriction mapping and partial sequence analysis of the gene allowed us to identify 16 exons and a 65-kb-long intron 2. The intron-exon boundaries are highly conserved in comparison with other "classical cadherins." In intron 1 we identified a 5' high-density CpG island that may be implicated in transcription regulation during embryogenesis and malignancy.

Identification of Evi-3, a novel common site of retroviral integration in mouse AKXD B-cell lymphomas

We have identified a novel common site of ecotropic viral integration called ecotropic viral integration site 3 (Evi-3) in B-cell lineage lymphomas of the AKXD recombinant inbred strains of mice. A number of virally induced pre-B-, B-, myeloid, and T-cell lymphomas were screened for viral rearrangements at Evi-3; rearrangements were found in pre-B- and B-cell lymphomas but not in other hematopoietic tumors. Genetic mapping studies localized Evi-3 to mouse chromosome 18, distinct from proto-oncogene and common viral integration loci identified previously in the mouse. Each proviral integration at Evi-3 is contained within a 200-bp region that lies inside a CpG island. All but one of the proviruses have integrated in the same 5'-to-3' transcriptional orientation. Transcripts from Evi-3 are expressed in a developmentally regulated manner in B cells. Taken together, these data suggest that Evi-3 represents a novel proto-oncogene involved in mouse B-cell lymphomas.

Cell binding specificity of mouse R-cadherin and chromosomal mapping of the gene

R-cadherin was originally identified as a chicken cadherin expressed by the retina. Here, we describe the identification of a mouse homologue of R-cadherin. We isolated mouse cDNAs encoding a cadherin with 94% identity in amino acid sequence to the chicken R-cadherin, and defined this molecule as mouse R-cadherin. L cells transfected with the mouse R-cadherin cDNA acquired a cadherin-mediated cell-cell adhesiveness as found for other cadherins. To examine the binding specificity of mouse R-cadherin, L cells expressing this cadherin (mRL) were mixed with L cells expressing chicken R-cadherin (cRL), mouse N-cadherin (mNL), mouse E-cadherin (mEL) and mouse P-cadherin (mPL). While mRL cells randomly intermixed with cRL cells, those cells aggregated separately from mEL or mPL cells. Mixing of mRL with mNL cells gave an intermediate result; that is, they formed both separate and chimeric aggregates, suggesting that R- and N-cadherin can interact with each other although each has a preference to bind to its own type. Similar properties were previously found for chicken R-cadherin. Thus, the cell binding specificity of R-cadherin is entirely conserved between the two species, suggesting a conserved role for this protein in morphogenesis. We also located the mouse R-cadherin gene to chromosome 2.

Molecular biology of cadherins in the nervous system

Cadherins are cell-cell adhesion molecules belonging to the Ca(2+)-dependent cadherin superfamily. In the last few years the number of cadherins identified in the nervous system has increased considerably. Cadherins are integral membrane glycoproteins. They are structurally closely related and interspecies homologies are high. The function is mediated through a homophilic binding mechanism, and intracellular proteins, directly or indirectly connected to the cadherins and the cytoskeleton, are necessary for cadherin activity. Cadherins have been implicated in segregation and aggregation of tissues at early developmental stages and in growth and guidance of axons during nervous system development. These functions are modified by changes in type(s) and amount of cadherins expressed at different developmental stages. The regulatory elements guiding cadherin expression are currently being elucidated.