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Biomedical subjects

B Hendrich

Publications and source records attributed to B Hendrich.

14 recordsLinked to original sources
PubMed2001

Human diseases with underlying defects in chromatin structure and modification.

Chromatin structure is important for regulating gene expression and for the proper condensation and segregation of chromosomes during cell division. Several human genetic diseases have been found to be due to mutations in genes producing proteins known or suspected to be involved in maintaining or modifying chromatin structure. Here we describe these 'chromatin diseases' and review what is known about the associated chromatin proteins in light of recent advances in the understanding of chromatin components, modification and function.

Chromatin↗
PubMed2001

The p120 catenin partner Kaiso is a DNA methylation-dependent transcriptional repressor.

We describe a novel mammalian DNA binding activity that requires at least two symmetrically methylated CpG dinucleotides in its recognition sequence, preferably within the sequence 5'CGCG. A key component of the activity is Kaiso, a protein with POZ and zinc-finger domains that is known to associate with p120 catenin. We find that Kaiso behaves as a methylation-dependent transcriptional repressor in transient transfection assays. Kaiso is a constituent of one of two methyl-CpG binding complexes originally designated as MeCP1. The data suggest that zinc-finger motifs are responsible for DNA binding, and may therefore target repression to specific methylated regions of the genome. As Kaiso associates with p120 catenin, Kaiso may link events at the cell surface with DNA methylation-dependent gene silencing.

Animals↗
PubMed2001

Closely related proteins MBD2 and MBD3 play distinctive but interacting roles in mouse development.

MBD2 and MBD3 are closely related proteins with consensus methyl-CpG binding domains. MBD2 is a transcriptional repressor that specifically binds to methylated DNA and is a component of the MeCP1 protein complex. In contrast, MBD3 fails to bind methylated DNA in murine cells, and is a component of the Mi-2/NuRD corepressor complex. We show by gene targeting that the two proteins are not functionally redundant in mice, as Mbd3-/- mice die during early embryogenesis, whereas Mbd2-/- mice are viable and fertile. Maternal behavior of Mbd2-/- mice is however defective and, at the molecular level, Mbd2-/- mice lack a component of MeCP1. Mbd2-mutant cells fail to fully silence transcription from exogenous methylated templates, but inappropriate activation of endogenous imprinted genes or retroviral sequences was not detected. Despite their differences, Mbd3 and Mbd2 interact genetically suggesting a functional relationship. Genetic and biochemical data together favor the view that MBD3 is a key component of the Mi-2/NuRD corepressor complex, whereas MBD2 may be one of several factors that can recruit this complex to DNA.

Age Factors↗
PubMed2001

A mouse Mecp2-null mutation causes neurological symptoms that mimic Rett syndrome.

Rett syndrome (RTT) is an inherited neurodevelopmental disorder of females that occurs once in 10,000-15,000 births. Affected females develop normally for 6-18 months, but then lose voluntary movements, including speech and hand skills. Most RTT patients are heterozygous for mutations in the X-linked gene MECP2 (refs. 3-12), encoding a protein that binds to methylated sites in genomic DNA and facilitates gene silencing. Previous work with Mecp2-null embryonic stem cells indicated that MeCP2 is essential for mouse embryogenesis. Here we generate mice lacking Mecp2 using Cre-loxP technology. Both Mecp2-null mice and mice in which Mecp2 was deleted in brain showed severe neurological symptoms at approximately six weeks of age. Compensation for absence of MeCP2 in other tissues by MeCP1 (refs. 19,20) was not apparent in genetic or biochemical tests. After several months, heterozygous female mice also showed behavioral symptoms. The overlapping delay before symptom onset in humans and mice, despite their profoundly different rates of development, raises the possibility that stability of brain function, not brain development per se, is compromised by the absence of MeCP2.

Animals↗
PubMed2000

Methylation moves into medicine.

Two human genetic diseases have recently been shown to be due to mutations in genes encoding proteins involved in DNA methylation. The phenotypes of these two diseases are surprisingly distinct from each other and provide insights into the functions of DNA methylation in mammals.

DNA Methylation↗
PubMed2000

Our own experience with CT angiography in early diagnosis of cerebral vascular malformations.

Computed tomography (CT) and intraarterial cerebral angiography are essential methods in early diagnosis of cerebral vascular malformations. In recent years however non-invasive or minimally invasive methods like MR angiography and CT angiography (CTA), which could potentially replace angiography, have been developed. The aim of presented study is to demonstrate our own experience in application of CTA in early diagnosis of cerebral vascular malformations. The material consists of 86 CTA examinations performed shortly after non-traumatic intracranial haemorrhage. Angiographic correlation has been available in 23 patients and surgical one--in 31 cases. CTA studies began with serio-CT to select the optimal time between contrast injection and CT scanning. After that 100-120 ml of non-ionic contrast medium was injected intravenously (5 ml per sec.) and spiral CT acqusition was performed with the delay calculated on the basis of the serio-CT. The obtained images were postprocessed on the workstation using always MIP and in many cases also SSD and VRT reconstructions. Vascular malformations have been diagnosed in 44 of 86 CTA studies including 38 patients with aneurysms (total number 51) and 6 patients with AVMs. In 17 cases the diameter of the aneurysm did not exceed 5 mm. In all surgical cases the CTA diagnosis of the aneurysm has been confirmed. There was however one false-negative case. On the other hand in 7 patients CTA revealed the small aneurysm, despite unclear angiographic appearance. In 2 of 6 patients with CTA suspicion of AVM this diagnosis has been excluded either by angiography or surgery. Comparison of CTA and angiography in 22 aneurysms showed in 17 cases superiority of CTA in evaluation of aneurysmal neck and the relationship between aneurysm and adjacent vessels (especially with VRT and SSD reconstructions). In patients with AVMs however the evaluation of supplying and draining vessels was better with angiography. On the base of our material we can conclude that CTA is very efficient in detecting and evaluating the aneurysms. We believe that CTA can replace angiography if it reveals aneurysm in a site corresponding with location of haemorrhage on CT. In patients with suspicion of AVM value of CTA is doubtful and angiography remains the method of choice.

Cerebral Angiography↗
PubMed1999

Somatic frameshift mutations in the MBD4 gene of sporadic colon cancers with mismatch repair deficiency.

Defects of mismatch repair are thought to be responsible for carcinogenesis in hereditary non-polyposis colorectal cancer and about 15% of sporadic colon cancers. The phenotype is seen as microsatellite instability and is known to be caused either by mutations in mismatch repair genes or by aberrant methylation of these genes stabilizing their downregulation. Lack of repair of microsatellite sequence errors, created during replication, leads to a mutation-prone phenotype. Where mutations occur within mononucleotide tracts within exons they cause translation frameshifts, premature cessation of translation and abnormal protein expression. Such mutations have been observed in the TGFbetaRII, BAX, IGFIIR, MSH3 and MSH6 genes in colon and other cancers. We describe here frameshift mutations affecting the gene for the methyl-CpG binding thymine glycosylase, MBD4, in over 40% of microsatellite unstable sporadic colon cancers. The mutations all appear heterozygous but their location would ensure truncation of the protein between the methyl-CpG binding and glycosylase domains, thus potentially generating a dominant negative effect. It is thus possible that such mutations enhance mutation frequency at other sites in these tumours. A suggestion has been made that MBD4 (MED1) mutations may lead to an increased rate of microsatellite instability but this mechanism appears unlikely due to the nature of mutations we have found.

Base Pair Mismatch↗
PubMed1999

The thymine glycosylase MBD4 can bind to the product of deamination at methylated CpG sites.

In addition to its well-documented effects on gene silencing, cytosine methylation is a prominent cause of mutations. In humans, the mutation rate from 5-methylcytosine (m5C) to thymine (T) is 10-50-fold higher than other transitions and the methylated sequence CpG is consequently under-represented. Over one-third of germline point mutations associated with human genetic disease and many somatic mutations leading to cancer involve loss of CpG. The primary cause of mutability appears to be hydrolytic deamination. Cytosine deamination produces mismatched uracil (U), which can be removed by uracil glycosylase, whereas m5C deamination generates a G x T mispair that cannot be processed by this enzyme. Correction of m5CpG x TpG mismatches may instead be initiated by the thymine DNA glycosylase, TDG. Here we show that MBD4, an unrelated mammalian protein that contains a methyl-CpG binding domain, can also efficiently remove thymine or uracil from a mismatches CpG site in vitro. Furthermore, the methyl-CpG binding domain of MBD4 binds preferentially to m5CpG x TpG mismatches-the primary product of deamination at methyl-CpG. The combined specificities of binding and catalysis indicate that this enzyme may function to minimize mutation at methyl-CpG.

Amino Acid Sequence↗
PubMed1999

Genomic structure and chromosomal mapping of the murine and human Mbd1, Mbd2, Mbd3, and Mbd4 genes.

DNA methylation is essential for murine development and is implicated in the control of gene expression. MeCP2, MBD1, MBD2, MBD3, and MBD4 comprise a family of mammalian, nuclear proteins related by the presence in each of an amino acid motif called the methyl-CpG binding domain (MBD). Each of these proteins, with the exception of MBD3, is capable of binding specifically to methylated DNA. MeCP2, MBD1 and MBD2 can also repress transcription. We describe the genomic structure and chromosomal localization of the human and murine Mbd1, Mbd2, Mbd3, and Mbd4 genes. We find that the highly similar MBD2 and MBD3 proteins are encoded by genes that map to different chromosomes in humans and mice but show a similar genomic structure. The Mbd1 and Mbd2 genes, in contrast, map together to murine and human Chromosomes (Chrs)18. The Mbd3 and Mbd4 genes map to murine Chrs 10 and 6, respectively, while the human MBD3 and MBD4 genes map to Chrs 19 and 3, respectively.

Animals↗
PubMed1999

MBD2 is a transcriptional repressor belonging to the MeCP1 histone deacetylase complex.

Mammalian DNA is methylated at many CpG dinucleotides. The biological consequences of methylation are mediated by a family of methyl-CpG binding proteins. The best characterized family member is MeCP2, a transcriptional repressor that recruits histone deacetylases. Our report concerns MBD2, which can bind methylated DNA in vivo and in vitro and has been reported to actively demethylate DNA (ref. 8). As DNA methylation causes gene silencing, the MBD2 demethylase is a candidate transcriptional activator. Using specific antibodies, however, we find here that MBD2 in HeLa cells is associated with histone deacetylase (HDAC) in the MeCP1 repressor complex. An affinity-purified HDAC1 corepressor complex also contains MBD2, suggesting that MeCP1 corresponds to a fraction of this complex. Exogenous MBD2 represses transcription in a transient assay, and repression can be relieved by the deacetylase inhibitor trichostatin A (TSA; ref. 12). In our hands, MBD2 does not demethylate DNA. Our data suggest that HeLa cells, which lack the known methylation-dependent repressor MeCP2, use an alternative pathway involving MBD2 to silence methylated genes.

Amino Acid Sequence↗
PubMed1998

Identification and characterization of a family of mammalian methyl-CpG binding proteins.

Methylation at the DNA sequence 5'-CpG is required for mouse development. MeCP2 and MBD1 (formerly PCM1) are two known proteins that bind specifically to methylated DNA via a related amino acid motif and that can repress transcription. We describe here three novel human and mouse proteins (MBD2, MBD3, and MBD4) that contain the methyl-CpG binding domain. MBD2 and MBD4 bind specifically to methylated DNA in vitro. Expression of MBD2 and MBD4 tagged with green fluorescent protein in mouse cells shows that both proteins colocalize with foci of heavily methylated satellite DNA. Localization is disrupted in cells that have greatly reduced levels of CpG methylation. MBD3 does not bind methylated DNA in vivo or in vitro. MBD1, MBD2, MBD3, and MBD4 are expressed in somatic tissues, but MBD1 and MBD2 expression is reduced or absent in embryonic stem cells which are known to be deficient in MeCP1 activity. The data demonstrate that MBD2 and MBD4 bind specifically to methyl-CpG in vitro and in vivo and are therefore likely to be mediators of the biological consequences of the methylation signal.

Amino Acid Sequence↗