Is the genetic basis of DiGeorge syndrome in HAND?
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Adaptor Proteins, Vesicular Transport↗
Biomedical subjects
A Baldini
Publications and source records attributed to A Baldini.
Identification of a gene that reverses the immortal phenotype of a subset of cells and is a member of a novel family of transcription factor-like genes.
Based on the dominance of cellular senescence over immortality, immortal human cell lines have been assigned to four complementation groups for indefinite division. Human chromosomes carrying senescence genes have been identified, including chromosome 4. We report the cloning and identification of a gene, mortality factor 4 (MORF 4), which induces a senescent-like phenotype in immortal cell lines assigned to complementation group B with concomitant changes in two markers for senescence. MORF 4 is a member of a novel family of genes with transcription factor-like motifs. We present here the sequences of the seven family members, their chromosomal locations, and a partial characterization of the three members that are expressed. Elucidation of the mechanism of action of these genes should enhance our understanding of growth regulation and cellular aging.
Amino Acid Sequence↗
Coronary artery constriction in rats: necrotic and apoptotic myocyte death.
The purpose of this study was to determine whether coronary artery narrowing was associated with the activation of necrotic and apoptotic myocyte cell death in the myocardium and whether these 2 forms of cell death were restricted to the left ventricle, or involved the other portions of the heart. Coronary artery narrowing was surgically induced in rats, and the animals were killed from 45 minutes to 12 days after surgery. Myocyte apoptosis was detected by the terminal deoxynucleotidyl transferase assay, confocal microscopy, and deoxyribonucleic acid (DNA) agarose gel electrophoresis. Myocyte necrosis was identified by myosin monoclonal antibody labeling of the cytoplasm. A separate group of animals was treated with trimetazidine in an attempt to interfere with tissue injury. Coronary artery narrowing was characterized by myocyte apoptosis in the left ventricle and interventricular septum, which progressively increased from 45 minutes to 6 days. However, apoptosis was not observed at 12 days. Conversely, myocyte necrosis reached its maximum value at 1 day and was still present at 12 days. This form of cell death affected not only the left ventricular free wall and interventricular septum, but also the right ventricle. Cell necrosis markedly exceeded apoptosis at all intervals. At the peak of cell death, myocyte necrosis was 52-fold and 33-fold higher than apoptosis in the left ventricle and septum. In conclusion, necrotic myocyte cell death is the prevailing form of damage produced by coronary artery narrowing, but apoptotic cell death contributes to the loss of myocytes in the ischemic heart. Trimetazidine treatment attenuated the extent of myocardial damage produced by global ischemia.
Animals↗
Characterization and physical mapping in human and mouse of a novel RING finger gene in Xp22.
Microphthalmia with linear skin defects (MLS) is an X-linked dominant male-lethal syndrome caused by different deletions of chromosome Xp22. Through the screening of cDNA libraries with the cross-species conserved marker 61B3-R (DXS1141), we identified a new gene at the telomeric breakpoint of the MLS critical region, which encodes a transcript containing a RING finger domain. This novel gene was independently cloned by another group and found to be mutated in Opitz syndrome. In this study we characterized the expression pattern of this gene, identified various splice variants, delineated its exon-intron boundaries, and determined that it is not mutated in either Aicardi or Goltz syndrome, two X-linked dominant conditions with phenotypes that overlap with that of MLS syndrome. This novel RING finger gene is expressed throughout mouse embryonic development, with the highest levels of expression in E7-E11. FISH and hybridization to mouse YACs confirmed human and mouse synteny in the order of this gene and other genes in the MLS critical region; however, this gene spans the boundary of the pseudoautosomal region in mouse but not in humans.
Abnormalities, Multiple↗
DOC-2, a candidate tumor suppressor gene in human epithelial ovarian cancer.
Using RNA fingerprinting (RAP) strategy and Northern blot analysis, we identified a differentially expressed sequence DOC-2 which is detectable in all normal human ovarian surface epithelial (HOSE) cell cultures but not in ovarian cancer cell lines and tissues. Subsequent cloning of DOC-2 from a cDNA library generated from the HOSE cells was carried out using the 3' and 5' RACE approach. A 3268 base pair full length cDNA of DOC-2 was isolated and sequenced. The predicted protein has a length of 770 amino acids. Homology search of all NCBI sequences indicated that the amino acid sequence of DOC-2 shares 93% homology with the mouse p96/mDab2 phosphoprotein and has a phosphotyrosine interacting domain (PID) and multiple SH3 binding motifs. Chromosomal localization by FISH showed that the DOC-2 gene is located on 5p13. Western blot analysis showed that the 105 kDa DOC-2 protein was down-regulated in all the carcinoma cell lines. In-situ immunohistochemistry performed on normal ovaries, and benign, borderline and invasive ovarian tumor tissues showed down regulation of DOC-2 protein particularly in serous ovarian tumor tissues. When DOC-2 was transfected into the ovarian carcinoma cell line SKOV3, the stable transfectants showed significantly reduced growth rate and ability to form tumors in nude mice. These data suggest that down-regulation of DOC-2 may play an important role in ovarian carcinogenesis.
Adaptor Proteins, Signal Transducing↗
Structure and expression of the human ubiquitin fusion-degradation gene (UFD1L).
We report the genomic organization, RNA and protein expression patterns of the gene encoding for the human homolog of the yeast ubiquitin fusion-degradation protein-1 (UFD1L). This enzyme is involved in a ubiquitin-dependent proteolytic pathway (UFD), firstly described in yeast. The human UFD1L gene is organized into 12 exons ranging in size from 33 to 161 bp. Sequence analysis of the 5'-flanking region of the gene revealed a high GC content, multiple CCAAT-binding motifs, CREB, CFT, and AP-2 sites. RNA transcripts were detected in all tissues and cell lines examined, including thymus, thymocytes, T- and B-cells, fibroblasts, chorionic villi, and amniocytes. In Western blot, the UFD1L antibody demonstrated the presence of multiple protein isoforms in all the tested tissues. Expression profile and promoter characteristics suggest UFD1L is a housekeeping gene with implications in the pathogenesis of DiGeorge/velo-cardio-facial syndrome, due to 22q11.2 deletions.
Adaptor Proteins, Vesicular Transport↗
Congenital heart defects and 22q11 deletions: which genes count?
Hemizygous deletions on the long arm of chromosome 22 (del22q11) are a relatively common cause of congenital heart disease. For some specific heart defects such as interrupted aortic arch type B and tetralogy of Fallot with absent pulmonary valve, del22q11 is probably the most frequent genetic cause. Although extensive gene searches have been successful in discovering many novel genes in the deleted segment, standard positional cloning has so far failed to demonstrate a role for any of these genes in the disease. We show how the use of experimental animal models is beginning to provide an insight into the developmental role of some of these genes, while novel genome manipulation technologies promise to dissect the genetic aspects of this complex syndrome.
Animals↗
Mutations in LMX1B cause abnormal skeletal patterning and renal dysplasia in nail patella syndrome.
The LIM-homeodomain protein Lmx1b plays a central role in dorso-ventral patterning of the vertebrate limb. Targeted disruption of Lmx1b results in skeletal defects including hypoplastic nails, absent patellae and a unique form of renal dysplasia (see accompanying manuscript by H. Chen et al.; ref. 2). These features are reminiscent of the dominantly inherited skeletal malformation nail patella syndrome (NPS). We show that LMX1B maps to the NPS locus and that three independent NPS patients carry de novo heterozygous mutations in this gene. Functional studies show that one of these mutations disrupts sequence-specific DNA binding, while the other two mutations result in premature termination of translation. These data demonstrate a unique role for LMX1B in renal development and in patterning of the skeletal system, and suggest that alteration of Lmx1b/LMX1B function in mice and humans results in similar phenotypes. Furthermore, we provide evidence for the first described mutations in a LIM-homeodomain protein which account for an inherited form of abnormal skeletal patterning and renal failure.
Amino Acid Sequence↗
Functional analysis of Gscl in the pathogenesis of the DiGeorge and velocardiofacial syndromes.
Gscl encodes a Goosecoid-related homeodomain protein that is expressed during mouse embryogenesis. In situ hybridization and immunohistochemistry studies show that Gscl is expressed in the pons region of the developing central nervous system and primordial germ cells. Gscl expression is also detected in a subset of adult tissues, including brain, eye, thymus, thyroid region, stomach, bladder and testis. Gscl is located within a region of the mouse genome that is syntenic with the region commonly deleted in DiGeorge and velocardiofacial syndrome (DGS/VCFS) patients. DGS/VCFS patients have craniofacial abnormalities, cardiac outflow defects and hypoplasia of the parathyroid gland and thymus due to haploinsufficiency of a gene or genes located within the deleted region. Thus, the genomic location of Gscl and its expression in a subset of the tissues affected in DGS/VCFS patients suggest that Gscl may contribute to the pathogenesis of DGS/VCFS. To determine the role of Gscl during mouse embryogenesis and in DGS/VCFS, we have deleted Gscl by gene targeting in mouse embryonic stem cells. Both Gscl heterozygous and Gscl null mice were normal and fertile, suggesting that Gscl is not a major factor in DGS/VCFS. Interestingly, expression of the adjacent Es2 gene in the pons region of Gscl null fetuses was absent, suggesting that mutations within the DGS/VCFS region can influence expression of adjacent genes. In addition, embryos that lacked both Gscl and the related Gsc gene appeared normal. These studies represent the first functional analysis of a DGS/VCFS candidate gene in vivo. These Gscl null mice will be an important genetic resource for crosses with other mouse models of the DGS/VCFS.
Abnormalities, Multiple↗
ES2, a gene deleted in DiGeorge syndrome, encodes a nuclear protein and is expressed during early mouse development, where it shares an expression domain with a Goosecoid-like gene.
ES2 is a gene deleted in DiGeorge syndrome (DGS) and velocardiofacial syndrome (VCFS) which has homologs in species as distant as Caenorhabditis elegans and Drosophila . The function of ES2 is unknown, and the predicted protein sequence does not contain motifs which suggest a particular role in the developmental defects present in DGS and VCFS. Here we show that the mouse homolog, Es2 , is transcribed in two forms resulting from the use of alternative polyadenylation signals. Structural analysis programs predict that the Es2 -encoded peptide has a coiled-coil domain, and transfection experiments with an Es2 -green fluorescent protein (GFP) fusion construct show that the peptide is recruited into the nucleus. Es2 is highly expressed during mouse embryogenesis from E7 onwards. In situ hybridization with an RNA probe revealed that the gene is widely expressed; however, relatively higher expression was detected in the nervous system, with a particularly high area of expression in a sub-region of the pons. The Es2 expression domain in the pons is shared with a Goosecoid-like gene ( Gscl) which is located upstream of Es2 , and raises the possibility that the two genes share regulatory elements and/or interact in this region of the developing brain. This finding suggests that different genes in the deleted region may be functionally related and might explain the occurrence of the characteristic phenotype in patients with non-overlapping genetic lesions.
Amino Acid Sequence↗
Localization of BRRN1, the human homologue of Drosophila barr, to 2q11.2.
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Blotting, Southern↗
DiGeorge anomaly and chromosome 10p deletions: one or two loci?
We report on a patient with DiGeorge syndrome (DGS) phenotype or anomaly and an unbalanced translocation [45,XY,-10,-22,+der(10),t(10;22)(p13;q11)] resulting in monosomy of 10p13-pter and 22q11-pter. Because both regions involved in this rearrangement have been implicated in DGS, we performed a molecular cytogenetic analysis of both loci in this patient. Results indicate that the chromosome 22 DGS locus is intact but that the terminal deletion of the short arm of chromosome 10 is adjacent to or partially overlapping with the recently defined consensus deleted region observed in DGS patients with 10p deletions. We conclude that the DGS anomaly in our patient is likely to be due to haploinsufficiency of genes located on chromosome 10p. Most, if not all, of the region included in the previously described 10p smallest region of deletion overlap is not deleted in our patient. Therefore, this deletion breakpoint either narrows the previously proposed 10p region or defines a second region within 10p critical for the DGS anomaly.
Adult↗
Deletion of chromosome 22q11 and pseudohypoparathyroidism.
A newborn boy with complex congenital heart disease, unilateral renal agenesis, and hypocalcemia was found to have a submicroscopic deletion of 22q11.2 (DiGeorge anomaly). In evaluating the pathogenesis of the hypocalcemia, repeatedly elevated or normal levels of parathyroid hormone were found, consistent with a diagnosis of pseudohypoparathyroidism. Pseudohypoparathyroidism can be due to mutation of a GTP binding protein (Gs-alpha protein) located on chromosome 20. Since there is another G protein locus (Gz alpha) adjacent to the DiGeorge critical region of chromosome 22, we hypothesized that a more extensive deletion may lead to pseudohypoparathyroidism. Fluorescence in situ hybridization was performed using a probe containing the Gz alpha gene, but no deletion was detected. This patient emphasizes the importance of determining the pathogenesis of the hypocalcemia in cases of DiGeorge anomaly.
Chromosome Deletion↗
The human transaldolase gene (TALDO1) is located on chromosome 11 at p15.4-p15.5.
Transaldolase (TAL) is a key enzyme of the pentose phosphate pathway, which is responsible for generation of reducing equivalents to protect cellular integrity from reactive oxygen intermediates. While exons 2 and 3 are highly repetitive, the complete TAL-H gene is mapped to a single genomic locus (TALDO1(2)) by several independent approaches. Southern blot hybridization of a 827-bp 3' EcoRI fragment of the TAL-H cDNA to human-mouse somatic cell hybrid DNA localized TALDO1 to the p13-->pter region of chromosome 11. Fluorescence in situ hybridization with a 15-kb genomic fragment harboring exons 1 and 2 mapped TALDO1 to 11p15.4-p15.5. A truncated and mutated segment of TAL-H exon 5 terminating with a poly(A) tail was identified in a pseudogene locus (TALDOP1) on chromosome 1. Reverse transcriptase-PCR studies of human-mouse somatic cell hybrids revealed the presence of the functional TAL-H gene on chromosome 11 and its absence on human chromosome 1. Mapping of radiation hybrids placed TALDO1 between markers WI-1421 and D11S922 on 11p15.
Base Sequence↗
A genetic etiology for interruption of the aortic arch type B.
Interrupted aortic arch (IAA) type B is a congenital heart defect believed to be caused by an anomaly of bronchial arch mesenchymal development. IAA type B has been associated with DiGeorge syndrome (DGS), which includes conotruncal heart defects, T-cell immunodeficiency, hypocalcemia, and facial abnormalities. The great majority of DGS cases are associated with hemizygous deletions at the chromosome 22q11 locus. The present study was designed to establish the involvement of the 22q11 locus in the etiology of IAA type B, independently from the typical DGS phenotype. An evaluation was performed on 73 patients with conotruncal heart defects using fluorescence in situ hybridization (FISH) analysis with probes from the 22q11 DGS locus. From this group, 7 patients were deleted (including 4 of the 11 patients with IAA type B). FISH analysis was extended to a total of 22 patients with IAA type B and 11 of these (50%) were deleted. FISH and Southern blot analyses using additional markers within the DiGeorge chromosomal region were performed on patients found not to be deleted in the initial FISH screening. No small deletions or rearrangements were detected. In our patient population, a single, specific genetic defect is the basis for one half of the IAA type B cases. These data suggest that IAA type B is one of the most etiologically homogeneous congenital heart defects. A 22q11 deletion in IAA type B may or may not be associated with the typical DGS phenotype. Therefore, IAA type B, per se, should be an indication for 22q11 deletion testing.
Aorta, Thoracic↗
Human acetyl-CoA carboxylase 2. Molecular cloning, characterization, chromosomal mapping, and evidence for two isoforms.
cDNA encoding the 280-kDa acetyl-CoA carboxylase 2 (ACC2) isoform was isolated from human liver using the polymerase chain reaction. Sequencing the cDNA revealed an open reading frame of 7,449 base pairs (bp) that encode 2,483 amino acids (Mr 279,380). Using 5-kilobase pair cDNA clones as probes, we localized the gene encoding the 280-kDa human carboxylase to chromosome 12q23. When the cDNA of ACC2 was compared with that of ACC1, the nucleotide sequences and the predicted amino acid sequences had about 60 and 80% identity, respectively. Ser77 and Ser79, which were found to be critical for the phosphorylation and subsequent inactivation of rat ACC1 (Ser78 and Ser80 of human ACC1), are conserved in ACC2 and are represented as Ser219 and Ser221, respectively. On the other hand, Ser1200, which is also a phosphorylation site in rat ACC1 (Ser1201 of human ACC1), is not conserved in ACC2. The homology between the amino acid sequences of the two human carboxylases, however, is primarily found downstream of residues Ser78 and Ser81 in human ACC1 and their equivalents, that is Ser219 and Ser221 in ACC2, suggesting that the sequence of the first 218 amino acids at the N terminus of ACC2 represents a unique peptide that accounts, in part, for the variance between the two carboxylases. Using a cDNA probe (400 bp) that encodes the N-terminal amino acid residues of ACC2 in Northern blot analyses of different human and mouse tissues showed that ACC2 is predominantly expressed in liver, heart, and the skeletal muscles. Polyclonal antibodies raised against the N-terminal peptide (amino acid residues 1-220) reacted specifically and equally with human and rat ACC2 carboxylases, confirming the uniqueness of this N-terminal peptide and its conservation in animal ACC2. In addition, we present evidence for the presence of an isoform of ACC2 (Mr 270,000) in human liver that differs from the 280-kDa ACC2 by the absence of 303 nucleotides that encode 101 amino acids in the region between Arg1114 and Asp1215. The regulation and physiological significance of the two ACC2 isoforms remain to be determined.
Acetyl-CoA Carboxylase↗
Delineation of a duplication map of chromosome 3q: a new case confirms the exclusion of 3q25-q26.2 from the duplication 3q syndrome critical region.
We report on the clinical, cytogenetic, and molecular characterization of a propositus and his mother with a duplication of 3q25-q26, minor anomalies, and mental retardation. The duplication, detected by cytogenetic analysis, was confirmed and delineated by comparative genomic hybridization and fluorescence in situ hybridization using probes previously mapped to the region. Comparison of the mapping data obtained in these patients and those obtained in patients that present with a typical dup(3q) syndrome phenotype shows that the segment duplicated in these patients lies proximally to the reported dup(3q) syndrome critical region, thus explaining the absence in our patients of the characteristic phenotype of dup(3q) syndrome patients. Accumulation of mapping data in patients with segmental duplications of 3q will eventually allow us to build a duplication map of the region and a genotype-phenotype correlation.
Adolescent↗
Comparative mapping of the DiGeorge syndrome region in mouse shows inconsistent gene order and differential degree of gene conservation.
We have constructed a comparative map in mouse of the critical region of human 22q11 deleted in DiGeorge (DGS) and Velocardiofacial (VCFS) syndromes. The map includes 11 genes potentially haploinsufficient in these deletion syndromes. We have localized all the conserved genes to mouse Chromosome (Chr) 16, bands B1-B3. The determination of gene order shows the presence of two regions (distal and proximal), containing two groups of conserved genes. The gene order in the two regions is not completely conserved; only in the proximal group is the gene order identical to human. In the distal group the gene order is inverted. These two regions are separated by a DNA segment containing at least one gene which, in the human DGS region, is the most proximal of the known deleted genes. In addition, the gene order within the distal group of genes is inverted relative to the human gene order. Furthermore, a clathrin heavy chain-like gene was not found in the mouse genome by DNA hybridization, indicating that there is an inconsistent level of gene conservation in the region. These and other independent data obtained in our laboratory clearly show a complex evolutionary history of the DGS-VCFS region. Our data provide a framework for the development of a mouse model for the 22q11 deletion with chromosome engineering technologies.
Animals↗