Cloning, characterization, and mRNA expression analysis of novel human fetal cochlear cDNAs.

To identify novel genes that are expressed specifically or preferentially in the cochlea, we constructed a cDNA library enriched for human cochlear cDNAs using a suppression subtractive hybridization technique. We analyzed 2640 clones by sequencing and BLAST similarity searches. One hundred and fifty-five different cDNA fragments mapped in nonsyndromic hearing impairment loci for which the causative gene has not been cloned yet. Approximately 30% of the clones show no similarity to any known human gene or expressed sequence tag (EST). Clones mapping in nonsyndromic deafness loci and a selection of clones that represent novel ESTs were analyzed by reverse transcriptase-polymerase chain reaction (RT-PCR) of RNA derived from 12 human fetal tissues. Our data suggest that a quarter of the novel genes in our library are preferentially expressed in fetal cochlea. These may play a physiologically important role in the hearing process and represent candidate genes for hereditary hearing impairment.

A locus on chromosome 15q for a dominantly inherited nemaline myopathy with core-like lesions.

Nemaline myopathy is a congenital neuromuscular disorder characterized by muscle weakness and the presence of nemaline rods. Five genes have now been associated with nemaline myopathy: alpha-tropomyosin-3 (TPM3), alpha-actin (ACTA1), nebulin (NEB), beta-tropomysin (TPM2) and troponin T (TNNT1). In addition, mutations in the ryanodine receptor gene (RYR1) have been associated with core-rod myopathy. Here we report linkage in two unrelated families, with a variant of nemaline myopathy, with associated core-like lesions. The clinical phenotype consists of muscle weakness in addition to a peculiar kind of muscle slowness. A genome-wide scan revealed a locus for nemaline myopathy with core-like lesions on chromosome 15q21-q23 for both families. Combining the two families gave a two-point LOD score of 10.65 for D15S993. The alpha-tropomyosin-1 gene (TPM1) located within this region is the strongest candidate gene. However, no mutations were found in the protein-coding region of TPM1, although small deletions or mutations in an intron cannot be excluded. The critical region contains few other candidate genes coding for muscle proteins and several genes of unknown function, and has not yet been sequenced completely. The novel phenotype of nemaline myopathy in the two presented families corresponds to an also novel, as yet uncharacterized, genotype.

Rhesus macaque and chimpanzee DC-SIGN act as HIV/SIV gp120 trans-receptors, similar to human DC-SIGN.

Dendritic cells (DC) have been implicated in the pathogenesis of both human and simian immunodeficiency viruses (HIV and SIV, respectively). The DC-specific HIV-1 trans-receptor DC-SIGN is thought to be essential for viral dissemination by DC. Abundant expression in lymphoid tissues also implies a function for DC-SIGN in chronic HIV-1 infections, in facilitating persistent infection of T cells. We have therefore isolated the rhesus macaque and chimpanzee homologues of DC-SIGN to investigate their function in a primate model. Both rhesus macaque and chimpanzee DC-SIGN are highly similar to the human homologue. Three monoclonal antibodies against human DC-SIGN, AZN-D1, -D2 and -D3, cross-react with rhesus macaque DC-SIGN, whereas AZN-D2 does not cross-react with chimpanzee DC-SIGN. The primate homologues are abundantly expressed in lymphoid tissues such as lymph nodes, as well as in mucosal tissues involved in sexual transmission of HIV-1, and are functionally similar to human DC-SIGN. They have a high affinity for the immunological ligands of DC-SIGN: ICAM-2 and -3. Moreover, both homologues bind the HIV-1 envelope glycoprotein gp120 and therefore can act as a HIV-1 trans-receptor in the same way as human DC-SIGN. These data demonstrate that primate models are suitable to further dissect the role of DC-SIGN in the transmission and pathogenesis of infection with immunodeficiency viruses.

DC-SIGN, a dentritic cell-specific HIV-1 receptor present in placenta that infects T cells in trans-a review.

Dendritic cells (DC) capture micro-organisms that enter peripheral mucosal tissues and then migrate to secondary lymphoid organs, where they present in antigenic form to resting T cells and thus initiate adaptive immune responses. Here we describe the properties of a DC-specific C-type lectin, DC-SIGN, that is highly expressed on DC present in mucosal tissues and binds to the HIV-1 envelope glycoprotein gp120. DC-SIGN does not function as a receptor for viral entry into DC, but instead promotes efficient infection in trans of cells that express CD4 and chemokine receptors. The interaction of DC-SIGN with HIV gp120 may be an important target for therapeutic intervention and vaccine development.

A dendritic cell-specific intercellular adhesion molecule 3-grabbing nonintegrin (DC-SIGN)-related protein is highly expressed on human liver sinusoidal endothelial cells and promotes HIV-1 infection.

The discovery of dendritic cell (DC)-specific intercellular adhesion molecule (ICAM)-3-grabbing nonintegrin (DC-SIGN) as a DC-specific ICAM-3 binding receptor that enhances HIV-1 infection of T cells in trans has indicated a potentially important role for adhesion molecules in AIDS pathogenesis. A related molecule called DC-SIGNR exhibits 77% amino acid sequence identity with DC-SIGN. The DC-SIGN and DC-SIGNR genes map within a 30-kb region on chromosome 19p13.2-3. Their strong homology and close physical location indicate a recent duplication of the original gene. Messenger RNA and protein expression patterns demonstrate that the DC-SIGN-related molecule is highly expressed on liver sinusoidal cells and in the lymph node but not on DCs, in contrast to DC-SIGN. Therefore, we suggest that a more appropriate name for the DC-SIGN-related molecule is L-SIGN, liver/lymph node-specific ICAM-3-grabbing nonintegrin. We show that in the liver, L-SIGN is expressed by sinusoidal endothelial cells. Functional studies indicate that L-SIGN behaves similarly to DC-SIGN in that it has a high affinity for ICAM-3, captures HIV-1 through gp120 binding, and enhances HIV-1 infection of T cells in trans. We propose that L-SIGN may play an important role in the interaction between liver sinusoidal endothelium and trafficking lymphocytes, as well as function in the pathogenesis of HIV-1.

A single amino acid in the cytoplasmic domain of the beta 2 integrin lymphocyte function-associated antigen-1 regulates avidity-dependent inside-out signaling.

The leukocyte-specific beta(2) integrin lymphocyte function-associated antigen-1 (LFA-1) (alpha(L)/beta(2)) mediates activation-dependent adhesion to intercellular adhesion molecule (ICAM)-1. In leukocytes, LFA-1 requires activation by intracellular messengers to bind ICAM-1. We observed malfunctioning of LFA-1 activation in leukemic T cells and K562-transfected cells. This defective inside-out integrin activation is only restricted to beta(2) integrins, since beta(1) integrins expressed in K562 readily respond to activation signals, such as phorbol 12-myristate 13-acetate. To unravel these differences in inside-out signaling between beta(1) and beta(2) integrins, we searched for amino acids in the beta(2) cytoplasmic domain that are critical in the activation of LFA-1. We provide evidence that substitution of a single amino acid (L732R) in the beta(2) cytoplasmic DLRE motif, creating the DRRE motif, is sufficient to completely restore PMA responsiveness of LFA-1 expressed in K562. In addition, an intact TTT motif in the C-terminal domain is necessary for the acquired PMA responsiveness. We observed that restoration of the PMA response altered neither LFA-1 affinity nor the phosphorylation status of LFA-1. In contrast, strong differences were observed in the capacity of LFA-1 to form clusters, which indicates that inside-out activation of LFA-1 strongly depends on cytoskeletal induced receptor reorganization that was induced by activation of the Ca(2+)-dependent protease calpain.

Non-syndromic autosomal dominant progressive non-specific mid-frequency sensorineural hearing impairment with childhood to late adolescence onset (DFNA21).

An autosomal dominant trait of progressive, non-syndromic, non-specific mid-frequency sensorineural hearing impairment was identified in a Dutch family. Many affected family members (n = 21) were identified, among whom seven out of nine relatives aged < 30 years do not show pure mid-frequency hearing impairment, which suggests variable expression. Regression analysis was used to evaluate the age-related hearing threshold data in a cross-sectional analysis in 24 affected patients and in a longitudinal analysis in five of these. At all frequencies, progression in hearing impairment (i.e. the regression coefficient) was significant and fairly similar: the pooled value was about 1.0 dB/y. There was no significant (i.e. not =0 dB) offset threshold (i.e. Y intercept at age 0) found at any frequency. The regression lines could be pooled for the low frequencies (0.25-0.5 kHz) and the mid/high frequencies (1-8 kHz) and this produced apparent onset ages of about 3 and 4 years and annual threshold increases of 0.75 and 1.1 dB/y, respectively. In most patients there is a relatively late onset age (maximum in the range of at least 25-45 years). However, based on the longitudinal analysis of a patient from the age of 4 years onwards in some patients sensorineural hearing impairment might be congenital/prelingual. Oculo-vestibular function was found to be normal. Results from linkage studies tentatively position the underlying gene defect telomeric to the repositioned DFNA13 locus at chromosome 6p21-22.

Identification of DC-SIGN, a novel dendritic cell-specific ICAM-3 receptor that supports primary immune responses.

Contact between dendritic cells (DC) and resting T cells is essential to initiate a primary immune response. Here, we demonstrate that ICAM-3 expressed by resting T cells is important in this first contact with DC. We discovered that instead of the common ICAM-3 receptors LFA-1 and alphaDbeta2, a novel DC-specific C-type lectin, DC-SIGN, binds ICAM-3 with high affinity. DC-SIGN, which is abundantly expressed by DC both in vitro and in vivo, mediates transient adhesion with T cells. Since antibodies against DC-SIGN inhibit DC-induced proliferation of resting T cells, our findings predict that DC-SIGN enables T cell receptor engagement by stabilization of the DC-T cell contact zone.

DC-SIGN, a dendritic cell-specific HIV-1-binding protein that enhances trans-infection of T cells.

Dendritic cells (DC) capture microorganisms that enter peripheral mucosal tissues and then migrate to secondary lymphoid organs, where they present these in antigenic form to resting T cells and thus initiate adaptive immune responses. Here, we describe the properties of a DC-specific C-type lectin, DC-SIGN, that is highly expressed on DC present in mucosal tissues and binds to the HIV-1 envelope glycoprotein gp120. DC-SIGN does not function as a receptor for viral entry into DC but instead promotes efficient infection in trans of cells that express CD4 and chemokine receptors. We propose that DC-SIGN efficiently captures HIV-1 in the periphery and facilitates its transport to secondary lymphoid organs rich in T cells, to enhance infection in trans of these target cells.

DC-SIGN-ICAM-2 interaction mediates dendritic cell trafficking.

Dendritic cells (DCs) are recruited from blood into tissues to patrol for foreign antigens. After antigen uptake and processing, DCs migrate to the secondary lymphoid organs to initiate immune responses. We now show that DC-SIGN, a DC-specific C-type lectin, supports tethering and rolling of DC-SIGN-positive cells on the vascular ligand ICAM-2 under shear flow, a prerequisite for emigration from blood. The DC-SIGN-ICAM-2 interaction regulates chemokine-induced transmigration of DCs across both resting and activated endothelium. Thus, DC-SIGN is central to the unusual trafficking capacity of DCs, further supported by the expression of DC-SIGN on precursors in blood and on immature and mature DCs in both peripheral and lymphoid tissues.

A novel ribosomal S6-kinase (RSK4; RPS6KA6) is commonly deleted in patients with complex X-linked mental retardation.

Large deletions in Xq21 often are associated with contiguous gene syndromes consisting of X-linked deafness type 3 (DFN3), mental retardation (MRX), and choroideremia (CHM). The identification of deletions associated with classic CHM or DFN3 facilitated the positional cloning of the underlying genes, REP-1 and POU3F4, respectively, and enabled the positioning of the MRX gene in between these genes. Here, we report the cloning and characterization of a novel gene, ribosomal S6-kinase 4 (RSK4; HGMW-approved symbol RPS6KA6), which maps in the MRX critical region. RSK4 is completely deleted in eight patients with the contiguous gene syndrome including MRX, partially deleted in a patient with DFN3 and present in patients with an Xq21 deletion and normal intellectual abilities. RSK4 is most abundantly expressed in brain and kidney. The predicted protein of 746 amino acids shows a high level of homology to three previously isolated members of the human RSK family. RSK2 is involved in Coffin-Lowry syndrome and nonspecific MRX. The localization of RSK4 in the interval that is commonly deleted in mentally retarded males together with the high degree of amino acid identity with RSK2 suggests that RSK4 plays a role in normal neuronal development. Further mutation analyses in males with X-linked mental retardation must prove that RSK4 is indeed a novel MRX gene.

Intrafamilial variability of the ocular phenotype in a Polish family with a missense mutation (A63D) in the Norrie disease gene.

PURPOSE: To describe the phenotypic variability in a Polish Norrie disease (ND) family associated with the missense mutation A63D. METHODS: A patient with spared vision from a Polish ND family underwent detailed ophthalmological examinations including slit-lamp biomicroscopy, ultrasound (USG), angiography, Goldmann kinetic visual field, and electroretinography (ERG). Mutation screening was carried out using the single-strand conformation polymorphism (SSCP) technique and subsequent DNA sequencing of the coding part of the ND gene. RESULTS: A mutation was detected (exon 3, A63D) in a large Polish family with 12 affected males, all but one presenting with classical ND symptoms. In one male, partially preserved vision was observed up to 40 years of age (distance acuity of the right eye 1/50 and left eye 2/50). Slit-lamp examination revealed remnants of a persistent primary vitreous and hyaloid artery. Upon angiography, the retina was vascularized within the posterior pole but not in the periphery. The ERG revealed pathological changes characteristic for chorioretinal degenerations. CONCLUSION: Within one family, individuals with identical sequence alterations in the ND gene can show remarkable phenotypic variability of the ocular symptoms. These findings indicate the involvement of additional factors (epigenetic or genetic) in ocular pathogenesis of ND.

Positional cloning of the gene for X-linked retinitis pigmentosa 2.

X-linked retinitis pigmentosa (XLRP) results from mutations in at least two different loci, designated RP2 and RP3, located at Xp11.3 and Xp21.1, respectively. The RP3 gene was recently isolated by positional cloning, whereas the RP2 locus was mapped genetically to a 5-cM interval. We have screened this region for genomic rearrangements by the YAC representation hybridization (YRH) technique and detected a LINE1 (L1) insertion in one XLRP patient. The L1 retrotransposition occurred in an intron of a novel gene that consisted of five exons and encoded a polypeptide of 350 amino acids. Subsequently, nonsense, missense and frameshift mutations, as well as two small deletions, were identified in six additional patients. The predicted gene product shows homology with human cofactor C, a protein involved in the ultimate step of beta-tubulin folding. Our data provide evidence that mutations in this gene, designated RP2, are responsible for progressive retinal degeneration.

Positional cloning of the gene for X-linked retinitis pigmentosa 3: homology with the guanine-nucleotide-exchange factor RCC1.

The gene for retinitis pigmentosa 3 (RP3), the most frequent form of X-linked RP (XLRP), has been mapped previously to a chromosome interval of less than 1000 kbp between the DXS1110 marker and the OTC locus at Xp21.1-p11.4. Employing a novel technique, YAC Representation Hybridization (YRH)', we have recently identified a small XLRP associated microdeletion in this interval, as well as several putative exons including the 3' end of a gene that was truncated by the deletion. cDNA library screening and sequencing of a cosmid centromeric to the deletion has now enabled us to identify numerous additional exons and to detect several point mutations in patients with XLRP. The predicted gene product shows homology to RCC1, the guanine-nucleotide-exchange factor (GEF) of the Ras-like GTPase Ran. Our findings suggest that we have cloned the long-sought RP3 gene, and that it may encode the GEF of a retina-specific GTP-binding protein.

Identification of a gene disrupted by a microdeletion in a patient with X-linked retinitis pigmentosa (XLRP).

The gene for the most frequent from of X-linked retinitis pigmentosa (XLRP), RP3, has been assigned by genetic and physical mapping to a segment of less than 1000 kbp, which is flanked by the marker DXS1110 and the ornithine transcarbamylase (OTC) gene. In search of microdeletions, we have screened the DNA of 30 unrelated patients with XLRP by employing a representative set of YAC-derived DNA fragments that were generated by restriction enzyme digestion and PCR amplification. In one of these patients, a 6.4 kbp microdeletion was detected which was not present in the DNA of 444 male controls. A cosmid contig spanning the deletion was constructed and used to isolate cDNAs from retina-specific libraries. Exons corresponding to these expressed sequences as well as other putative exons were identified by sequencing more than 30 kbp of the critical region. So far, no point mutations in these putative exon sequences have been identified.

Linkage analysis in a Dutch family with X-linked recessive congenital stationary night blindness (XL-CSNB).

Linkage analysis has been performed in a large Dutch pedigree with X-linked recessive congenital stationary night blindness (CSNB) by utilizing 16 DNA markers from the proximal short arm of the human X chromosome (Xp21.1-11.2). Thirteen polymorphic markers are at least partially informative and have enabled pairwise and multipoint linkage analysis. For three loci, i.e. DXS228, the monoamine oxidase B gene and the Norrie disease gene (NDG), multipoint linkage studies have yielded maximum lod scores of > 3.0 at a recombination fraction of zero. Analysis of recombination events has enabled us to rule out the possibility that the underlying defect in this family is allelic to RP3; the gene defect could also be excluded from the proximal part of the region known to carry RP2. Linkage data are consistent with a possible involvement of the NDG but mutations in the open reading frame of this gene have not been found.

Continuous beta-galactosidase production in insect cells with a p10 gene based baculovirus vector in a two-stage bioreactor system.

Continuous production of polyhedra or baculovirus-expressed proteins in insect cell cultures is limited to about 4 weeks. The decrease in production has been ascribed to the interference of defective deletion mutants with wild-type baculoviruses. The deleted genome sequences include the polyhedrin gene (or the heterologous gene of interest); in the remaining part, the major late p10 gene is always maintained. In the present study, the productivity of a recombinant baculovirus with the lacZ gene from Escherichia coli cloned downstream of the p10 promoter at the p10 locus was investigated. It was hypothesized that this p10 promoter driven gene is preserved over a longer period of time in a continuously operated two-stage bioreactor system than foreign genes behind the polyhedrin promoter at the polyhedrin locus. In two separate runs, beta-galactosidase production with the p10-lacZ recombinant reached quasi-steady-state levels of 30 and 60 units/cm3. Polyhedron production was about 3 x 10(6) and 6 x 10(6) polyhedra/cm3, respectively. However, both polyhedron and beta-galactosidase production decreased after about 30 days of relatively constant production. In the infection reactor, deletion mutants of the virus, which contained both the polyhedrin and lacZ gene, were predominant. Therefore, the presence of the polyhedrin or p10 gene alone in deletion mutants is not sufficient for prolonged expression; other genes involved in major late gene expression and not present in the deleted virus are probably necessary.