Candidate gene acting as a suppressor of the RH locus in most cases of Rh-deficiency.

The Rh antigen is a multi-subunit complex composed of Rh polypeptides and associated glycoproteins (Rh50, CD47, LW and glycophorin B); these interact in the red cell membrane and are lacking or severely reduced in Rhnull cells. As a result, individuals with Rhnull suffer chronic haemolytic anaemia known as the Rh-deficiency syndrome. Most frequently, Rhnull phenotypes are caused by homozygosity of an autosomal suppressor gene unlinked to the RH locus (Rhnull regulator or Rhmod types). We have analysed the genes and transcripts encoding Rh, CD47 and Rh50 proteins in five such unrelated Rhnull cases. In all patients, we identified alteration of Rh50--frameshift, nucleotide mutations, or failure of amplification--which correlated with Rhnull phenotype. We propose that mutant alleles of Rh50, which map to chromosome 6p11-21.1, are likely candidates for suppressors of the RH locus accounting for most cases of Rh-deficiency.

The human necdin gene, NDN, is maternally imprinted and located in the Prader-Willi syndrome chromosomal region.

Prader-Willi syndrome (PWS) is a neurogenetic disorder that results from the absence of a normal paternal contribution to the 15q11-13 region. The clinical manifestations of PWS are a transient severe hypotonia in the newborn period, with mental retardation, hypogonadism and obesity observed later in development. Five transcripts with exclusive expression from the paternal allele have been isolated, but none of these has been shown to be involved in PWS. In this study, we report the isolation and characterization of NDN, a new human imprinted gene. NDN is exclusively expressed from the paternal allele in the tissues analysed and is located in the PWS region. It encodes a putative protein homologous to the mouse brain-specific NECDIN protein, NDN; as in mouse, expression in brain is restricted to post-mitotic neurons. NDN displays several characteristics of an imprinted locus, including allelic DNA methylation and asynchronous DNA replication. A complete lack of NDN expression in PWS brain and fibroblasts indicates that the gene is expressed exclusively from the paternal allele in these tissues and suggests a possible role of this new gene in PWS.

A mouse model for hereditary thyroid dysgenesis and cleft palate.

Alteration of thyroid gland morphogenesis (thyroid dysgenesis) is a frequent human malformation. Among the one in three to four thousand newborns in which congenital hypothyroidism is detected, 80% have either an ectopic, small and sublingual thyroid, or have no thyroid tissue. Most of these cases appear sporadically, although a few cases of recurring familial thyroid dysgenesis have been described. The lack of evidence for hereditary thyroid dysgenesis may be due to the severity of the hypothyroid phenotype. Neonatal screening and early thyroid hormone therapy have eliminated most of the clinical consequences of hypothyroidism such that the heritability of this condition may become apparent in the near future. We have recently cloned cDNA encoding a forkhead domain-containing transcription factor, TTF-2, and have located the position of the gene, designated Titf2, to mouse chromosome 4 (ref. 3). Titf2 is expressed in the developing thyroid, in most of the foregut endoderm and in craniopharyngeal ectoderm, including Rathke's pouch. Expression of Titf2 in thyroid cell precursors is down-regulated as they cease migration, suggesting that this factor is involved in the process of thyroid gland morphogenesis. Here we show that Titf2-null mutant mice exhibit cleft palate and either a sublingual or completely absent thyroid gland. Thus, mutation of Titf2-/- results in neonatal hypothyroidism that shows similarity to thyroid dysgenesis in humans.

Insensitivity to anti-müllerian hormone due to a mutation in the human anti-müllerian hormone receptor.

Anti-Müllerian hormone (AMH) and its receptor are involved in the regression of Müllerian ducts in male fetuses. We have now cloned and mapped the human AMH receptor gene and provide genetic proof that it is required for AMH signalling, by identifying a mutation in the AMH receptor in a patient with persistent Müllerian duct syndrome. The mutation destroys the invariant dinucleotide at the 5' end of the second intron, generating two abnormal mRNAs, one missing the second exon, required for ligand binding, and the other incorporating the first 12 bases of the second intron. The similar phenotypes observed in AMH-deficient and AMH receptor-deficient individuals indicate that the AMH signalling machinery is remarkably simple, consisting of one ligand and one type II receptor.

The mouse neuronal cell surface protein F3: a phosphatidylinositol-anchored member of the immunoglobulin superfamily related to chicken contactin.

Several members of the Ig superfamily are expressed on neural cells where they participate in surface interactions between cell bodies and processes. Their Ig domains are more closely related to each other than to Ig variable and constant domains and have been grouped into the C2 set. Here, we report the cloning and characterization of another member of this group, the mouse neuronal cell surface antigen F3. The F3 cDNA sequence contains an open reading frame that could encode a 1,020-amino acid protein consisting of a signal sequence, six Ig-like domains of the C2 type, a long premembrane region containing two segments that exhibit sequence similarity to fibronectin type III repeats and a moderately hydrophobic COOH-terminal sequence. The protein does not contain a typical transmembrane segment but appears to be attached to the membrane by a phosphatidylinositol anchor. Antibodies against the F3 protein recognize a prominent 135-kD protein in mouse brain. In fetal brain cultures, they stain the neuronal cell surface and, in cultures maintained in chemically defined medium, most prominently neurites and neurite bundles. The mouse f3 gene maps to band F of chromosome 15. The gene transcripts detected in the brain by F3 cDNA probes are developmentally regulated, the highest amounts being expressed between 1 and 2 wk after birth. The F3 nucleotide and deduced amino acid sequence show striking similarity to the recently published sequence of the chicken neuronal cell surface protein contactin. However, there are important differences between the two molecules. In contrast to F3, contactin has a transmembrane and a cytoplasmic domain. Whereas contactin is insoluble in nonionic detergent and is tightly associated with the cytoskeleton, about equal amounts of F3 distribute between buffer-soluble, nonionic detergent-soluble, and detergent-insoluble fractions. Among other neural cell surface proteins, F3 most resembles the neuronal cell adhesion protein L1, with 25% amino acid identity between their extracellular domains. Based on its structural similarity with known cell adhesion proteins of nervous tissue and with L1 in particular, we propose that F3 mediates cell surface interactions during nervous system development.

A new member of the Rho family, Rnd1, promotes disassembly of actin filament structures and loss of cell adhesion.

Members of the Rho GTPase family regulate the organization of the actin cytoskeleton in response to extracellular growth factors. We have identified three proteins that form a distinct branch of the Rho family: Rnd1, expressed mostly in brain and liver; Rnd2, highly expressed in testis; and Rnd3/RhoE, showing a ubiquitous low expression. At the subcellular level, Rnd1 is concentrated at adherens junctions both in confluent fibroblasts and in epithelial cells. Rnd1 has a low affinity for GDP and spontaneously exchanges nucleotide rapidly in a physiological buffer. Furthermore, Rnd1 lacks intrinsic GTPase activity suggesting that in vivo, it might be constitutively in a GTP-bound form. Expression of Rnd1 or Rnd3/RhoE in fibroblasts inhibits the formation of actin stress fibers, membrane ruffles, and integrin-based focal adhesions and induces loss of cell-substrate adhesion leading to cell rounding (hence Rnd for "round"). We suggest that these proteins control rearrangements of the actin cytoskeleton and changes in cell adhesion.

Localization of the human NCAM gene to band q23 of chromosome 11: the third gene coding for a cell interaction molecule mapped to the distal portion of the long arm of chromosome 11.

cDNA clones containing sequences coding for the murine neural cell adhesion molecule (N-CAM) were used in Southern hybridizations on human genomic DNA and demonstrated approximately 90% homology between human and murine NCAM genes. In situ hybridization with one of these clones was performed on human metaphase chromosomes and allowed the localization of the human NCAM gene to band q23 of chromosome 11. The genes for two other cell surface molecules believed to be involved in cell-cell interactions, Thy-1 and the delta chain of the T3-T cell receptor complex, have recently been localized to the same region of chromosome 11 in man. Moreover, this region of the human chromosome 11 appears to be syntenic to a region of murine chromosome 9 that also contains the staggerer locus: staggerer mice show abnormal neurological features which may be related to abnormalities in the conversion of the embryonic to the adult forms of the N-CAM molecule.

Regional expression of the homeobox gene Nkx-2.2 in the developing mammalian forebrain.

A novel mouse homeobox-containing gene, Nkx-2.2, has been isolated. Nkx-2.2 is a member of a family of genes whose homeodomains are homologous to that of the Drosophila NK-2 gene. Nkx-2.2 transcripts are found in localized domains of the brain during mouse embryogenesis. Nkx-2.2 expression in the brain abuts and partially overlaps with the expression domains of two other related homeobox-containing genes, TTF-1 and Dlx. The expression domains of the three genes in the developing prosencephalon coincide with anatomical boundaries, particularly apparent in the diencephalon. This result raises the possibility that these genes may specify regional differentiation of the developing diencephalon into its anatomically and functionally defined subregions. Nkx-2.2 may be involved in specifying diencephalic neuromeric boundaries.

TFEC, a basic helix-loop-helix protein, forms heterodimers with TFE3 and inhibits TFE3-dependent transcription activation.

We have identified a new basic helix-loop-helix (BHLH) DNA-binding protein, designated TFEC, which is closely related to TFE3 and TFEB. The basic domain of TFEC is identical to the basic DNA-binding domain of TFE3 and TFEB, whereas the helix-loop-helix motif of TFEC shows 88 and 85% identity with the same domains in TFE3 and TFEB, respectively. Like the other two proteins, TFEC contains a leucine zipper motif, which has a lower degree of sequence identity with homologous domains in TFE3 and TFEB than does the BHLH segment. Little sequence identity exists outside these motifs. Unlike the two other proteins, TFEC does not contain an acidic domain, which for TFE3 mediates the ability to activate transcription. Like the in vitro translation product of TFE3, the in vitro-translated TFEC binds to the mu E3 DNA sequence of the immunoglobulin heavy-chain gene enhancer. In addition, the product of cotranslation of TFEC RNA and TFE3 RNA forms a heteromeric protein-DNA complex with mu E3 DNA. In contrast to TFE3, TFEC is unable to transactivate a reporter gene linked to a promoter containing tandem copies of the immunoglobulin mu E3 enhancer motif. Cotransfection of TFEC DNA and TFE3 DNA strongly inhibits the transactivation caused by TFE3. TFEC RNA is found in many tissues of adult rats, but the relative concentrations of TFEC and TFE3 RNAs vary considerably in these different tissues. No TFEC RNA was detectable in several cell lines, including fibroblasts, myoblasts, chondrosarcoma cells, and myeloma cells, indicating that TFEC is not ubiquitously expressed.

Structure, mapping, and expression of erp, a growth factor-inducible gene encoding a nontransmembrane protein tyrosine phosphatase, and effect of ERP on cell growth.

We have characterized a growth factor-inducible gene, erp, and demonstrated that it encodes a 367-amino-acid nontransmembrane tyrosine phosphatase protein with significant similarity to the vaccinia virus H1 protein. Immunoprecipitation analyses show that the erp protein, ERP, is rapidly induced following serum stimulation of quiescent fibroblasts. ERP has been expressed as a fusion protein with glutathione S-transferase and shown to have tyrosine as well as serine protein phosphatase activity. The enzymatic activity of ERP depends on the presence of reducing agents such as dithiothreitol, and its tyrosine phosphatase activity is inhibited by sodium vanadate, a potent inhibitor of protein tyrosine phosphatases. The number of stable NIH 3T3 clones obtained after transfection with a vector expressing the complete ERP protein is reduced more than 90% compared with that after transfection with a vector expressing a mutated inactive ERP protein. The remaining ERP-expressing clones present a significant increase in the proportion of bi- and multinucleated cells and a decrease in proliferation rate. Studies on the genomic structure reveal that the erp transcription unit is 2.8 kbp long and split into four exons. The erp gene maps to the 17A2-17C region of the murine genome. Our results demonstrate that the protein product of the immediate-early gene erp has a negative effect on cell proliferation.

Structure, chromosome location, and expression of the mouse zinc finger gene Krox-20: multiple gene products and coregulation with the proto-oncogene c-fos.

We have analyzed the structure and the regulation of Krox-20, a mouse zinc finger-encoding gene which is transiently activated following serum stimulation of quiescent fibroblast cells in culture. The gene is localized on chromosome 10, band B5, in the mouse, and the homologous human gene also maps to chromosome 10 (region q21.1 to q22.1). Alternative splicing of the 5'-most intron of the Krox-20 gene gives rise to mRNAs encoding putative zinc finger proteins with different N termini. The first exon contains a sequence element with strong similarity to the c-fos proto-oncogene serum response element (SRE). This element can functionally substitute for the c-fos SRE, and it binds the same nuclear protein. It is probably responsible for the serum induction of Krox-20, possibly in combination with a weaker SRE located in the 5'-flanking region of the gene. Our findings suggest that c-fos, Krox-20, and a number of immediate-early serum response genes are coregulated and that the SRE and its cognate protein are essential components of this regulatory pathway.

Characterization of Spi-B, a transcription factor related to the putative oncoprotein Spi-1/PU.1.

We have cloned a human cDNA from a new gene, spi-B, on the basis of its homology with the DNA-binding domain of the Spi-1/PU.1 putative oncogene product. spi-B codes for a protein of 262 amino acids presenting 43% overall identity with Spi-1. Its highly basic carboxy-terminal region exhibits 34% sequence identity with the DNA-binding domain of the Ets-1 protein. We showed that the Spi-B protein is able to bind the purine-rich sequence (PU box) recognized by Spi-1/PU.1 and to activate transcription of a reporter plasmid containing PU boxes. Chromosome in situ hybridization allowed us to map spi-B to the 19q13.3-19q13.4 region of the human genome. spi-B, like spi-1, was found to be expressed in various murine and human hematopoietic cell lines except T lymphoid cell lines.

Definition of a T-cell receptor beta gene core enhancer of V(D)J recombination by transgenic mapping.

V(D)J recombination in differentiating lymphocytes is a highly regulated process in terms of both cell lineage and the stage of cell development. Transgenic and knockout mouse studies have demonstrated that transcriptional enhancers from antigen receptor genes play an important role in this regulation by activating cis-recombination events. A striking example is the T-cell receptor beta-chain (TCRbeta) gene enhancer (Ebeta), which in the mouse consists of at least seven nuclear factor binding motifs (betaE1 to betaE7). Here, using a well-characterized transgenic recombination substrate approach, we define the sequences within Ebeta required for recombination enhancer activity. The Ebeta core is comprised of a limited set of motifs (betaE3 and betaE4) and an additional previously uncharacterized 20-bp sequence 3' of the betaE4 motif. This core element confers cell lineage- and stage-specific recombination within the transgenic substrates, although it cannot bypass the suppressive effects resulting from transgene integration in heterochromatic centromeres. Strikingly, the core enhancer is heavily occupied by nuclear factors in immature thymocytes, as shown by in vivo footprinting analyses. A larger enhancer fragment including the betaE1 through betaE4 motifs but not the 3' sequences, although active in inducing germ line transcription within the transgenic array, did not retain the Ebeta recombinational activity. Our results emphasize the multifunctionality of the TCRbeta enhancer and shed some light on the molecular mechanisms by which transcriptional enhancers and associated nuclear factors may impact on cis recombination, gene expression, and lymphoid cell differentiation.

Isolation and characterization of Suv39h2, a second histone H3 methyltransferase gene that displays testis-specific expression.

Higher-order chromatin has been implicated in epigenetic gene control and in the functional organization of chromosomes. We have recently discovered mouse (Suv39h1) and human (SUV39H1) histone H3 lysine 9-selective methyltransferases (Suv39h HMTases) and shown that they modulate chromatin dynamics in somatic cells. We describe here the isolation, chromosomal assignment, and characterization of a second murine gene, Suv39h2. Like Suv39h1, Suv39h2 encodes an H3 HMTase that shares 59% identity with Suv39h1 but which differs by the presence of a highly basic N terminus. Using fluorescent in situ hybridization and haplotype analysis, the Suv39h2 locus was mapped to the subcentromeric region of mouse chromosome 2, whereas the Suv39h1 locus resides at the tip of the mouse X chromosome. Notably, although both Suv39h loci display overlapping expression profiles during mouse embryogenesis, Suv39h2 transcripts remain specifically expressed in adult testes. Immunolocalization of Suv39h2 protein during spermatogenesis indicates enriched distribution at the heterochromatin from the leptotene to the round spermatid stage. Moreover, Suv39h2 specifically accumulates with chromatin of the sex chromosomes (XY body) which undergo transcriptional silencing during the first meiotic prophase. These data are consistent with redundant enzymatic roles for Suv39h1 and Suv39h2 during mouse development and suggest an additional function of the Suv39h2 HMTase in organizing meiotic heterochromatin that may even impart an epigenetic imprint to the male germ line.

SOX7 transcription factor: sequence, chromosomal localisation, expression, transactivation and interference with Wnt signalling.

The Sox gene family consists of several genes related by encoding a 79 amino acid DNA-binding domain known as the HMG box. This box shares strong sequence similarity to that of the testis determining protein SRY. SOX proteins are transcription factors having critical roles in the regulation of diverse developmental processes in the animal kingdom. We have characterised the human SOX7 gene and compared it to its mouse orthologue. Chromosomal mapping analyses localised mouse Sox7 on band D of mouse chromosome 14, and assigned human SOX7 in a region of shared synteny on human chromosome 8 (8p22). A detailed expression analysis was performed in both species. Sox7 mRNA was detected during embryonic development in many tissues, most abundantly in brain, heart, lung, kidney, prostate, colon and spleen, suggesting a role in their respective differentiation and development. In addition, mouse Sox7 expression was shown to parallel mouse Sox18 mRNA localisation in diverse situations. Our studies also demonstrate the presence of a functional transactivation domain in SOX7 protein C-terminus, as well as the ability of SOX7 protein to significantly reduce Wnt/beta-catenin-stimulated transcription. In view of these and other findings, we suggest different modes of action for SOX7 inside the cell including repression of Wnt signalling.

A screening method to identify genes commonly overexpressed in carcinomas and the identification of a novel complementary DNA sequence.

We describe a differential screening method for cDNA libraries which used a combination of subtracted and PCR-amplified cDNA probes, and which can be applied to the selection of genes expressed in multiple tissues. This technique was used to identify genes commonly overexpressed in breast and basal cell carcinomas. These represent stromally dependent, invasive tumors with and without metastatic capacity. Thus, this screening sought to identify genes involved in the early stages of tumor progression. We identified a total of 16 genes, including c-erbB-2 and tissue inhibitor of metalloproteinases 3 whose products have been implicated in tumorigenesis or invasion. We also identified a novel sequence (D52) showing little homology with others described in any species, which maps to the human chromosomal band 8q21. In situ RNA hybridizations of breast carcinoma sections indicated that the D52 gene was expressed in cancer cells, whereas other genes identified in the differential screening were expressed in fibroblastic or inflammatory cells within the tumor stroma. Thus, the procedure developed in this study selected genes expressed in a diversity of cell types, indicating its potential usefulness in other systems.

Identification of a new interferon-alpha-inducible gene (p27) on human chromosome 14q32 and its expression in breast carcinoma.

A new complementary DNA, p27, has been cloned and sequenced from estradiol-treated MCF7 human breast carcinoma cells. It encodes a putative highly hydrophobic protein of 122 amino acids which has a 33% overall sequence similarity to the product of the 6-16 gene (R. L. Friedman, S. P. Manly, M. McMahon, I. M. Kerr, and G. R. Stark, Cell, 38: 745-755, 1984), which is transcriptionally induced by interferons of the alpha/beta type. We demonstrate here that the p27 gene, which is located in band q32 of human chromosome 14, is also induced by interferon-alpha in human cell lines of different origin and that expression is independent of the presence of estradiol receptor in the cells. High levels of p27 RNA were found in vivo in approximately 50% of primary human breast carcinomas (21 were tested by Northern blotting). In situ hybridization to some of the p27-overexpressing tumors showed that the p27 RNA is localized in cancer cells and sometimes also in fibroblastic cells of tumor stroma. p27 RNA levels in the tumors did not correlate with the presence of estrogen receptor or with the expression of the estrogen-induced pS2 gene. Further studies are now necessary to elucidate the cause of p27 gene overexpression in breast carcinoma and in particular to determine whether it corresponds to chromosomal rearrangements in the 14q32 region and/or to induction by interferons of the alpha/beta type.

A novel putative receptor protein tyrosine kinase of the met family.

By successive screenings of cDNA libraries prepared from human tumours and from human foreskin keratinocytes, we have isolated overlapping cDNAs coding for a novel protein which we call Ron, with sequence characteristics of a receptor protein tyrosine kinase. Ron is a 1400 amino acid protein structurally similar to the 1408 amino acid product of the C-MET proto-oncogene, the receptor for hepatocyte growth factor and scatter factor. The two proteins have 63% overall sequence identity in their intracellular regions. We have localised the RON gene to human chromosome region 3p21, a region frequently deleted in small cell carcinoma of the lung and in renal cell carcinoma, and which is believed to harbour unidentified tumour suppressor genes. Interestingly, normal lung tissue contains transcripts of the RON gene.

The putative oncogene Spi-1: murine chromosomal localization and transcriptional activation in murine acute erythroleukemias.

We have shown previously that spleen focus forming virus integration near the Spi-1 putative oncogene is observed in 95% of erythroid Friend tumors (Moreau-Gachelin et al., 1988). Here we describe how the proviral insertion in the Spi-1 domain is associated with the enhanced transcription of a 1.4 kb mRNA normally expressed at a low level in normal cells. The gene is localized on murine chromosome 2, band E3. The structure of the Spi-1 gene was determined by sequencing genomic and cDNA clones. The gene has an open reading frame encoding a protein of 218 amino acids, extending over five exons. Proviruses always integrate outside, upstream and in the opposite orientation of the protein-encoding domain. This suggests that SFFV integration activates the expression of Spi-2 gene that may contribute to the erythroleukemic process.