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At least 1,621 records · Page 90Linked to original sources
PubMed2002

Interallelic recombination is probably responsible for the occurrence of a new alpha(s1)-casein variant found in the goat species.

The alphas1-casein (alphas1-Cas) locus in the goat is characterized by a polymorphism, the main feature of which is to be qualitative as well as quantitative. A systematic analysis performed in an autochthon southern Italy breed identified a new rare allele (M), which was characterized at both the protein and genomic level. The M protein displays the slowest electrophoretic mobility of the alphas1-Cas variants described so far. MS and automated Edman degradation experiments showed that this behavior was due to the loss of two phosphate residues in the multiple phosphorylation site (64SP-SP-SP-SP-SP-E-70E) consecutively to a Ser-->Leu substitution at position 66 of the peptide chain (64S-SP-L-SP-SP-E-70E). This was confirmed by sequencing a genomic DNA fragment encompassing exon 9 where the 8th codon (TCG) was shown to be mutated to TTG. Sequencing of amplified genomic DNA segments spanning the 5' and 3' flanking regions of each exon allowed us to identify 23 single nucleotide polymorphisms and two insertion/deletion events in the coding as well as the noncoding regions. A comparison of specific haplotypes defined for each of the alphas1-CasF, A and M alleles indicates that the M allele probably arises from interallelic recombination between alleles A and B2, followed by a C-->T transition at nucleotide 23 of the ninth exon. The region encompassing the recombination break point was putatively located between nucleotide 86 upstream and nucleotide 40 downstream of exon 8. Interallelic recombination therefore appears to be a possible means of generating allelic diversity at the alphas1-Cas locus, at least in the goat. The previously proposed molecular phylogeny must now be revised, possibly starting from two ancestral allelic lineages.

Alleles↗
PubMed1996

Pinus banksiana has at least seven expressed alcohol dehydrogenase genes in two linked groups.

The alcohol dehydrogenase (Adh) gene family is much more complex in Pinus banksiana than in angio-sperms, with at least seven expressed genes organized as two tightly linked clusters. Intron number and position are highly conserved between P. banksiana and angiosperms. Unlike angiosperm Adh genes, numerous duplications, as large as 217 bp, were observed within the noncoding regions of P. banksiana Adh genes and may be a common feature of conifer genes. A high frequency of duplication over a wide range of scales may contribute to the large genome size of conifers.

Alcohol Dehydrogenase↗
PubMed2001

Control of Xist expression for imprinted and random X chromosome inactivation in mice.

Applying RNA fluorescence in situ hybridization to parthenogenetic embryos with two maternally derived X (X(M)) chromosomes and embryos with X chromosome aneuploidy such as X(P)0 (X(P), paternally derived X chromosome), X(M)X(M)X(P) and X(M)X(M)Y, we studied the control of Xist/Tsix expression for silencing the entire X chromosome in mice. The data show that the paternally derived Xist allele is highly expressed in every cell of the embryo from the 4-cell stage onward, irrespective of the number of X chromosomes in a diploid cell. The high level of Xist transcription is maintained in non-epiblast cells culminating in X(P)-inactivation, whereas in X(P)0 embryos it is terminated by the blastocyst stage, probably as a result of counting the number of X chromosomes in a cell occurring at the morula/blastocyst stage. Xist is also down-regulated in epiblast cells of X(M)X(P) and X(M)X(M)X(P) embryos to make X-inactivation random. In epiblast cells, Xist seems to be up-regulated after counting and random choice of the future inactive X chromosome(s). Although the maternal Xist allele is never activated in fertilized embryos before implantation, some parthenogenetic embryos show Xist up-regulation in a proportion of cells. These and other data reported earlier suggest that imprinted X-inactivation in non-epiblast tissues of rodents had been derived from the random X-inactivation system.

Animals↗
PubMed1995

A novel L23-related gene 40 kb downstream of the imprinted H19 gene is biallelically expressed in mid-fetal and adult human tissues.

The closely linked IGF2 and H19 genes on human chromosome 11p15.5 are monoallelically expressed as a result of genomic imprinting and show altered expression in Wilms' tumors (WTs). To map regional imprinting we have sought to isolate additional human genes close to IGF2/H19 and to characterize their allelic expression patterns. Here we report a novel gene, provisionally named L23MRP [L23 (mitochondrial)-related protein], which is oriented 'tail-to-tail' with H19 and is transcribed to within 40 kb of the last H19 exon. L23MRP is expressed biallelically in many mid-fetal and adult human tissues. This gene is also expressed at normal levels in WTs which have lost expression of H19 either via loss of the maternal chromosome 11p15.5 or via an epigenetic pathway involving site-specific DNA hypermethylation. These data indicate that, at least in post-embryonic stages, L23MRP is functionally insulated from the IGF2/H19 imprinted domain.

Adult↗
PubMed1996

Imprinting mutation in the Beckwith-Wiedemann syndrome leads to biallelic IGF2 expression through an H19-independent pathway.

The Beckwith-Wiedemann syndrome (BWS) is genetically linked to chromosome 11p15.5, and a variety of observations suggest that deregulation of imprinted genes in this region is causally involved in the pathogenesis of the disease. It has been shown that in some patients without cytogenetic abnormalities the otherwise repressed maternal copy of the insulin-like growth factor 2 (IGF2) gene is expressed, leading to biallelic expression of IGF2. In some of these cases, this is accompanied by repression and DNA methylation of the maternal (otherwise active) copy of the neighbouring H19 gene. Hence, it is attractive to think that mutations may interfere with some aspect of H19 imprinting, thus leading to an inactive maternal allele, and indirectly to activation of the maternal IGF2 allele as reported in mice with an H19 gene deletion. However, no mutations have been identified so far in these patients. The only known mutations associated with BWS are maternally transmitted translocations, which are clustered in two locations centrometric to IGF2. The first cluster is 200-400 kb from IGF2 and the second is several megabases away. Hence, genes located far from the translocation breakpoints are potentially deregulated by them. Here we provide the first evidence of alteration of imprinting in a translocation family, with biallelic expression of IGF2 and altered DNA replication patterns in the IGF2 region. Interestingly, H19 imprinting was normal, suggesting an H19-independent pathway to biallelic IGF2 transcription. DNA methylation in IGF2 remained monoallelic, suggesting that the mutation in this family had uncoupled allele-specific methylation from expression.

Alleles↗
PubMed1984

Structure and expression in Escherichia coli of a cloned rat interferon-alpha gene.

DNA synthesized by in vitro transcription on rat interferon (IFN) mRNA has been cloned and amplified as recombinant DNA. The nucleotide sequence of these rat IFN cDNA clones revealed i. the partial presence of the coding region of the gene and ii all cDNA clones were derived from the same subtype of rat IFN-alpha mRNA. Purified inserted fragments were used as a hybridisation probe against chromosomal "Southern blots" to show that at least twelve rat IFN-alpha-related sequences are present in the genome. A lambda-linked rat gene library was screened with the cDNA probes, resulting in an equivalent number of rat IFN-alpha-related hybrid phages. By use of a 3'-noncoding region as a probe, the chromosomal counterpart of the cDNA clones could be detected and the nucleotide sequence of its coding region has been determined. Expression of the coding region in E. coli yielded biologically active IFN, when tested for in vitro or in vivo antiviral activity.

Animals↗
PubMed2003

Effects of donor cell type and genotype on the efficiency of mouse somatic cell cloning.

Although it is widely assumed that the cell type and genotype of the donor cell affect the efficiency of somatic cell cloning, little systematic analysis has been done to verify this assumption. The present study was undertaken to examine whether donor cell type, donor genotype, or a combination thereof increased the efficiency of mouse cloning. Initially we assessed the developmental ability of embryos that were cloned from cumulus or immature Sertoli cells with six different genotypes (i.e., 2 x 6 factorial). Significantly better cleavage rates were obtained with cumulus cells than with Sertoli cells (P < 0.005, two-way ANOVA), which probably was due to the superior cell-cycle synchrony of cumulus cells at G0/G1. After embryo transfer, there was a significant effect of cell type on the birth rate, with Sertoli cells giving the better result (P < 0.005). Furthermore, there was a significant interaction (P < 0.05) between the cell type and genotype, which indicates that cloning efficiency is determined by a combination of these two factors. The highest mean birth rate (10.8 +/- 2.1%) was obtained with (B6 x 129)F1 Sertoli cells. In the second series of experiments, we examined whether the developmental ability of clones with the wild-type genotype (JF1) was improved when combined with the 129 genotype. Normal pups were cloned from cumulus and immature Sertoli cells of the (129 x JF1)F1 and (JF1 x 129)F1 genotypes, whereas no pups were born from cells with the (B6 x JF1)F1 genotype. The present study clearly demonstrates that the efficiency of somatic cell cloning, and in particular fetal survival after embryo transfer, may be improved significantly by choosing the appropriate combinations of cell type and genotype.

Animals↗
PubMed2004

An active murine transposon family pair: retrotransposition of "master" MusD copies and ETn trans-mobilization.

The ETn (Early Transposon) elements are among the most active murine mobile sequences, being responsible for a series of mutations by insertion in vivo. Yet they are noncoding, and it had long been suspected that ETn are mobilized in trans by coding-competent elements, most probably from the closely related MusD family of LTR-retrotransposons. A genome-wide in silico search for coding-competent MusD elements identified a total of nine such copies, which we cloned and marked to test their transpositional activity, using an ex vivo assay in heterologous cells. Three copies were found to be autonomous for transposition, with each gag, pro, and pol MusD gene absolutely required for mobility. These active MusD copies specifically trigger retrotransposition of marked ETn elements with high efficiency, by complementation in trans. Characterization of the structures of de novo transposed MusD and ETn marked elements, as well as of their integration sites, disclosed canonical retroviral-like retrotransposition, with 6-bp target site duplications common to both elements. These results highlight the parasitic molecular strategies that are used by the ETn elements for their mobility, and unambiguously identify their "master genes."

Animals↗
PubMed2004

Essentiality of the early transcript in the replication origin of the lactococcal prolate phage c2.

The genome of the prolate-headed lytic lactococcal bacteriophage c2 is organized into two divergently oriented blocks consisting of the early genes and the late genes. These blocks are separated by the noncoding origin of DNA replication. We examined the functional role of transcription of the origin in a plasmid model system. Deletion of the early promoter P(E)1 abolished origin function. Introduction of mutations into P(E)1 which did not eliminate promoter activity or replacement of P(E)1 with an unrelated but functional promoter did not abolish replication. The A-T-rich region upstream of P(E)1, which is conserved in prolate phages, was not required for plasmid replication. Replacement of the P(E)1 transcript template sequence with an unrelated sequence with a similar G+C content abolished replication, showing that the sequence encoding the transcript is essential for origin function. Truncated transcript and internal deletion constructs did not support replication except when the deletion was at the very 3' end of the DNA sequence coding for the transcript. The P(E)1 transcript could be detected for all replication-proficient constructs. Recloning in a plasmid vector allowed detection of P(E)1 transcripts from some fragments that did not support replication, indicating that stability of the transcript alone was not sufficient for replication. The data suggest that production of a transcript of a specific length and with a specific sequence or structure is essential for the function of the phage c2 origin in this model system.

Bacteriophages↗
PubMed1998

The absence of enhancer competition between Igf2 and H19 following transfer into differentiated cells.

H19 and Igf2 are reciprocally imprinted genes that lie 90 kb apart on mouse chromosome 7. The two genes are coexpressed during development, with the H19 gene expressed exclusively from the maternal chromosome and Igf2 from the paternal chromosome. It has been proposed that their reciprocal imprinting is governed by a competition between the genes for a common set of enhancers. The competition on the paternal chromosome is influenced by extensive allele-specific methylation of the H19 gene and its 5' flank, which acts to inhibit H19 transcription and thus indirectly leads to the activation of the Igf2 gene. In contrast, no allele-specific methylation has been detected on the maternal chromosome, and the basis for the preference for H19 transcription on that chromosome is unresolved. In this investigation, the mechanism controlling the silencing of the Igf2 gene on the maternal chromosome was explored by studying the transcriptional activity of a yeast artificial chromosome (YAC) containing Igf2 and H19 following transfer into differentiated tissue culture cells. Contrary to expectations, both H19 and Igf2 were expressed from a single integrated copy of the YAC. Furthermore, Igf2 expression appeared to be independent of the H19 locus, based on deletions of the H19 gene promoter and its enhancers. These results suggest that an active process is responsible for the transcriptional bias toward H19 on the maternal chromosome and that the hypomethylated state of this chromosome cannot be viewed as a "default" state. Moreover, the active process is not reproduced in a differentiated cell and may require passage through the female germ line.

Animals↗
PubMed2003

Functional characterization of a testis-specific DNA binding activity at the H19/Igf2 imprinting control region.

The DNA methylation state of the H19/Igf2 imprinting control region (ICR) is differentially set during gametogenesis. To identify factors responsible for the paternally specific DNA methylation of the ICR, germ line and somatic extracts were screened for proteins that bind to the ICR in a germ line-specific manner. A specific DNA binding activity that was restricted to the male germ line and enriched in neonatal testis was identified. Its three binding sites within the ICR are very similar to the consensus sequence for nuclear receptor extended half sites. To determine if these binding sites are required for establishment of the paternal epigenetic state, a mouse strain in which the three sites were mutated was generated. The mutated ICR was able to establish a male-specific epigenetic state in sperm that was indistinguishable from that established by the wild-type ICR, indicating that these sequences are either redundant or have no function. An analysis of the methylated state of the mutant ICR in the soma revealed no differences from the wild-type ICR but did uncover in both mutant and wild-type chromosomes a significant relaxation in the stringency of the methylated state of the paternal allele and the unmethylated state of the maternal allele in neonatal and adult tissues.

Animals↗
PubMed2004

Mutation of a single CTCF target site within the H19 imprinting control region leads to loss of Igf2 imprinting and complex patterns of de novo methylation upon maternal inheritance.

The differentially methylated imprinting control region (ICR) region upstream of the H19 gene regulates allelic Igf2 expression by means of a methylation-sensitive chromatin insulator function. We have previously shown that maternal inheritance of mutated (three of the four) target sites for the 11-zinc finger protein CTCF leads to loss of Igf2 imprinting. Here we show that a mutation in only CTCF site 4 also leads to robust activation of the maternal Igf2 allele despite a noticeably weaker interaction in vitro of site 4 DNA with CTCF compared to other ICR sites, sites 1 and 3. Moreover, maternally inherited sites 1 to 3 become de novo methylated in complex patterns in subpopulations of liver and heart cells with a mutated site 4, suggesting that the methylation privilege status of the maternal H19 ICR allele requires an interdependence between all four CTCF sites. In support of this conclusion, we show that CTCF molecules bind to each other both in vivo and in vitro, and we demonstrate strong interaction between two CTCF-DNA complexes, preassembled in vitro with sites 3 and 4. We propose that the CTCF sites may cooperate to jointly maintain both methylation-free status and insulator properties of the maternal H19 ICR allele. Considering many other CTCF targets, we propose that site-specific interactions between various DNA-bound CTCF molecules may provide general focal points in the organization of looped chromatin domains involved in gene regulation.

Animals↗
PubMed1998

Severe phenotype resulting from an active ring X chromosome in a female with a complex karyotype: characterisation and replication study.

We report on the characterisation of a complex chromosome rearrangement, 46,X,del(Xq)/47,X,del(Xq),+r(X), in a female newborn with multiple malformations. Cytogenetic and molecular methods showed that the del(Xq) contains the XIST locus and is non-randomly inactivated in all metaphases. The tiny r(X) chromosome gave a positive FISH signal with UBE1, ZXDA, and MSN cosmid probes, but not with a XIST cosmid probe. Moreover, it has an active status, as shown by a very short (three hour) terminal BrdU pulse followed by fluorescent anti-BrdU antibody staining. The normal X is of paternal origin and both rearranged chromosomes originate from the same maternal chromosome. We suggest that both abnormal chromosomes result from the three point breakage of a maternal isodicentric idic(X)(q21.1). Finally, the phenotype of our patient is compared to other published cases and, despite the absence of any 45,X clone, it appears very similar to those with a 45,X/46,X,r(X) karyotype where the tiny r(X) is active.

Abnormalities, Multiple↗
PubMed1997

The product of the imprinted H19 gene is an oncofetal RNA.

AIMS/BACKGROUND: The H19 gene is an imprinted, maternally expressed gene in humans. It is tightly linked and coregulated with the imprinted, paternally expressed gene of insulin-like growth factor 2. The H19 gene product is not translated into protein and functions as an RNA molecule. Although its role has been investigated for more than a decade, its biological function is still not understood fully. H19 is abundantly expressed in many tissues from early stages of embryogenesis through fetal life, and is down regulated postnatally. It is also expressed in certain childhood and adult tumours. This study was designed to screen the expression of H19 in human cancer and its relation to the expression of H19 in the fetus. METHODS: Using in situ hybridisation with a [35S] labelled probe, H19 mRNA was detected in paraffin wax sections of fetal tissues from the first and second trimesters of pregnancy and of a large array of human adult and childhood tumours arising from these tissues. RESULTS: The H19 gene is expressed in tumours arising from tissues which express this gene in fetal life. Its expression in the fetus and in cancer is closely linked with tissue differentiation. CONCLUSIONS: Based on these and previous data, H19 is neither a tumour suppressor gene nor an oncogene. Its product is an oncofetal RNA. The potential use of this RNA as a tumour marker should be evaluated.

Biomarkers, Tumor↗
PubMed2006

Running interference: prospects and obstacles to using small interfering RNAs as small molecule drugs.

RNA interference (RNAi) is a well-conserved, ubiquitous, endogenous mechanism that uses small noncoding RNAs to silence gene expression. The endogenous small RNAs, called microRNAs, are processed from hairpin precursors and regulate important genes involved in cell death, differentiation, and development. RNAi also protects the genome from invading genetic elements, encoded by transposons and viruses. When small double-stranded RNAs, called small interfering (si)RNAs, are introduced into cells, they bind to the endogenous RNAi machinery to disrupt the expression of mRNAs containing complementary sequences with high specificity. Any disease-causing gene and any cell type or tissue can potentially be targeted. This technique has been rapidly utilized for gene-function analysis and drug-target discovery and validation. Harnessing RNAi also holds great promise for therapy, although introducing siRNAs into cells in vivo remains an important obstacle. Pilot siRNA clinical studies began just three years after the discovery that RNAi works in mammalian cells. This review discusses recent progress and obstacles to using siRNAs as small molecule drugs.

Animals↗
PubMed2006

Frequent IGF2/H19 domain epigenetic alterations and elevated IGF2 expression in epithelial ovarian cancer.

Overexpression of the imprinted insulin-like growth factor-II (IGF2) is a prominent characteristic of gynecologic malignancies. The purpose of this study was to determine whether IGF2 loss of imprinting (LOI), aberrant H19 expression, and/or epigenetic deregulation of the IGF2/H19 imprinted domain contributes to elevated IGF2 expression in serous epithelial ovarian tumors. IGF2 LOI was observed in 5 of 23 informative serous epithelial ovarian cancers, but this did not correlate with elevated expression of IGF2 H19 RNA expression levels were also found not to correlate with IGF2 transcript levels. However, we identified positive correlations between elevated IGF2 expression and hypermethylation of CCCTC transcription factor binding sites 1 and 6 at the H19 proximal imprint center (P = 0.05 and 0.02, respectively). Hypermethylation of CCCTC transcription factor sites 1 and 6 was observed more frequently in cancer DNA compared with lymphocyte DNA obtained from women without malignancy (P < 0.0001 for both sites 1 and 6). Ovarian cancers were also more likely to exhibit maternal allele-specific hypomethylation upstream of the imprinted IGF2 promoters when compared with normal lymphocyte DNA (P = 0.004). This is the same region shown previously to be hypomethylated in colon cancers with IGF2 LOI, but this was not associated with LOI in ovarian cancers. Elevated IGF2 expression is a frequent event in serous ovarian cancer and this occurs in the absence of IGF2 LOI. These data indicate that the epigenetic changes observed in these cancers at the imprint center may contribute to IGF2 overexpression in a novel mechanistic manner.

Alleles↗
PubMed1995

Temporal and spatial regulation of H19 imprinting in normal and uniparental mouse embryos.

The mouse H19 gene is imprinted so that the paternal copy is both methylated and repressed during fetal development. However, the CpG-rich promoter region encompassing the transcription start is not methylated in sperm; this region must therefore become methylated postzygotically. We first examined the timing of DNA methylation of this region and the corresponding expression of H19. Both parental copies are initially undermethylated in blastocysts and the paternal copy then becomes fully methylated in the embryo around implantation; this methylation is more protracted in the extraembryonic lineages, especially in the trophoblast. By contrast to the lineage-dependent methylation, we observed exclusive expression of the maternal copy in preimplantation embryos and in all the lineages of early postimplantation embryos although variability may exist in cultured embryos. This indicates that methylation of the CpG-rich promoter is not a prerequisite for the paternal repression. We then examined whether methylation and expression occurs appropriately in the absence of a maternal or a paternal genome. Both H19 copies in androgenetic embryos are fully methylated while they are unmethylated in parthenogenetic embryos. This correlates with the lack of expression in androgenetic embryos but expression in parthenogenetic embryos. However, the androgenetic trophoblast was exceptional as it shows reduced methylation and expresses H19. These results suggest that promoter methylation is not the primary inactivation mechanism but is a stabilizing factor. Differential methylation in the more upstream region, which is established in the gametes, is a likely candidate for the gametic signal and may directly control H19 activity.

Animals↗