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G Vassart

Publications and source records attributed to G Vassart.

At least 271 records · Page 15Linked to original sources
PubMed1987

Structural organization of the 5' region of the thyroglobulin gene. Evidence for intron loss and "exonization" during evolution.

More than one third of thyroglobulin (1190 residues out of 2750) is made of one peptide motif repeated ten times in tandem. Segments unrelated to the motif interrupt this structure at various places. The corresponding gene region, which extends over 40 x 10(3) bases, was studied in detail. All exon borders and exon/intron junctions were localized precisely and sequenced, and their positions were correlated with the repetitive organization of the protein. When intron positions were compiled on a consensus sequence of all repeats, three categories of introns were observed. Except between repeats numbers 5 and 6, an intron was invariably found within the Cys codon making the limit of each motif. This category of intron most probably reflects the serial duplication events responsible for the evolution of this region of the gene. All other introns, except no. 2, are found at positions were the repetitive structure is disrupted by "inserted" peptides. We present the hypothesis that this second category of introns was already present in the original unit before the first duplication. Thereafter, they would have experienced either complete loss (some units do not contain any intron) or partial or total exonization, resulting in the slipping of intronic material into coding sequence. Intron no. 2, finally, separates motif no. 1 at a position on the boundary between two segments presenting sequence homology. This last type of intron probably reflects an initial duplication event at the origin of a primordial thyroglobulin gene motif. With all these characteristics, the thyroglobulin gene is presented as a paradigm for the analysis of the fate of introns in gene evolution.

Amino Acid Sequence↗
PubMed1987

Polymorphic DNA marker on X chromosome and manic depression.

Heredity is an important factor in vulnerability to manic depression. A genetic linkage has been demonstrated between manic depression and coagulation factor IX at Xq27 with a TaqI polymorphism at the F9 locus in DNA samples from peripheral leucocytes of manic depressive probands and relatives in 10 informative families. Statistical analysis of the pedigrees gave a maximum lod score of 3.10 at a recombination fraction of 0.11, demonstrating a linkage between a manic depressive locus and the F9 locus in the Xq27 region.

Bipolar Disorder↗
PubMed1987

Structural organization of the bovine thyroglobulin gene and of its 5'-flanking region.

The structural organization of the bovine thyroglobulin gene has been investigated by a combination of Southern genomic blotting and direct analysis of cloned gene fragments isolated from a chromosomal DNA library. The entire locus is spread over more than 200,000 base pairs which makes it one of the largest eukaryotic genes studies to date. The coding information is scattered into at least 42 exons, 34 of which have been precisely identified. A different evolutionary origin of the 5' and 3' regions of the gene is supported by the highly different proportion of exonic material they contain (12% and 3%, respectively) and by the existence of sequence homology between the 3' region of thyroglobulin and acetylcholinesterase. Detailed sequence analysis of the 5' region of the gene and its flanking segment demonstrated that a significant homology exists between bovine and human thyroglobulin sequences, except for the presence within the ruminant promoter region of a 220-base-pair sequence belonging to the bovine monomer repeated family.

Animals↗
PubMed1987

A sequence in M13 phage detects hypervariable minisatellites in human and animal DNA.

The term "DNA fingerprint" has been used to describe the extensive restriction fragment length polymorphism associated with hypervariable minisatellites present in the human genome. Until now, it was necessary to hybridize Southern blots to specific probes cloned from human genomic DNA in order to obtain individual-specific restriction patterns. The present study describes the surprising finding that the insert-free, wild-type M13 bacteriophage detects hypervariable minisatellites in human and in animal DNA, provided no competitor DNA is used during hybridization. The effective sequence in M13 was traced to two clusters of 15-base pair repeats within the protein III gene of the bacteriophage. This unexpected use of M13 renders the DNA fingerprinting technology more readily available to molecular biology laboratories.

Animals↗
PubMed1987

Preparation of single-stranded deoxyribonucleic acid probes using an immobilized template.

A new method for the easy preparation of specific single-stranded DNA fragments is presented. Recombinant M13 DNA containing the strand complementary to the sequence of interest is made partially double-stranded by elongating a conventional M13 sequencing primer. Following linearization by enzymatic digestion downstream from the insert (relative to priming site), this DNA is coupled to diazotized paper through its single-stranded (vector) portion. Subsequent denaturation of the double-stranded region generates an immobilized template strand. Successive runs of primed syntheses of the (desired) complementary strand can be realized using the same template. The copies are easily isolated by release upon denaturation. DNA probes prepared by this method have proven to be valuable tools for gene analysis.

DNA, Recombinant↗
PubMed1987

A nonsense mutation causes hereditary goitre in the Afrikander cattle and unmasks alternative splicing of thyroglobulin transcripts.

The hereditary goitre of Afrikander cattle is an autosomal recessive disease characterized in homozygotes by the production of abnormal thyroglobulin (Tg) and the coexistence in the thyroid of normal-sized 8.4-kilobase (kb) Tg mRNA with a misspliced 7.3-kb message having lost exon 9. We have cloned and sequenced the cDNA segment corresponding to the abnormal exon 8-exon 10 junction and the relevant genomic DNA region. The mutation responsible for the disease is a cytosine to thymine transition creating a stop codon at position 697 in exon 9. The original reading frame is maintained in the 7.3-kb mRNA, which, as it lacks the mutated exon, is translatable into a potentially functional protein. This puzzling phenotype in which a mutated exon is apparently removed selectively from transcripts by alternative splicing leads us to suggest that the 7.3-kb transcript could be present in normal animals. Using a sensitive oligonucleotide hybridization assay, we have demonstrated that a 7.3-kb mRNA lacking exon 9 does exist in normal thyroids as a minor mRNA species. As it is fully translatable, the 7.3-kb mRNA is expected to be more stable than the normal-sized 8.4-kb message. This probably accounts for the higher proportion of 7.3-kb transcript found in the goitre.

Amino Acid Sequence↗
PubMed1987

Genetic variation of the bovine thyroglobulin gene studied at the DNA level.

The bovine thyroglobulin gene has been analysed for variation using restriction endonucleases. Six independent restriction fragment length polymorphisms have been identified. One of these results most probably from a 2.5-kb deletion, the others being compatible with point mutations. We determined that an individual taken at random within the Belgian White and Blue breed is, on average, heterozygous for one out of 1700 nucleotides within the thyroglobulin gene.

Animals↗
PubMed1987

Normal and defective expression of the thyroglobulin gene.

Molecular studies of the thyroglobulin (Tg) gene have progressed significantly in recent years. Cloning and sequencing the complete bovine Tg cDNA led to the knowledge of the primary structure of the Tg subunit. This large polypeptidic chain displays a repetitive structure, especially in its amino-terminal half, and bears a striking homology with the acetylcholinesterase molecule of Torpedo californica in its carboxy-terminal portion. The four specific domains known to be involved in the formation of the thyroid hormones have been assigned to both terminal parts of the polypeptide, a location which could play a role in the process leading to hormone release. The very large (greater than 250 kb) Tg gene has been localized on the long arm of chromosome 8 in man, in close linkage with the c-myc oncogene. The study of its structure allowed the characterization of the molecular defect responsible for a congenital flaw in Tg gene expression in a herd of South-African cattle. This work led to the unexpected finding that the Tg pre-mRNA undergoes alternative splicing in normal animals, too. A DNA segment involved in the transcriptional control of Tg gene expression by cAMP has been identified by transfecting primary cultured thyrocytes with recombinant genes.

Animals↗
PubMed1987

Control of thyroglobulin gene transcription by TSH and cAMP.

The availability of the sequence of Tg promoter from three different species enabled a fruitful comparison to be made from which a general picture of the organization of the Tg gene promoter region emerged. Chromatin structure studies identified tissue-specific modifications at the level of DNA protein interactions. A DNA element has been shown to be involved in transcription control by cAMP. This sequence includes a highly conserved region of the Tg gene promoter, overlaps a domain of the promoter which becomes hypersensitive to DNase I when the gene is expressed and displays specific protein-DNA interaction. These observations are consistent with the possibility that this sequence is a target element for trans-acting factor(s) which control(s) the transcriptional activity of the gene.

Animals↗
PubMed1986

Analysis of sequence and structure homologies between thyroglobulin and acetylcholinesterase: possible functional and clinical significance.

The homology between thyroglobulin and acetylcholinesterase (1) has been analyzed in detail. It contains 28.3% identical amino acids and extends over 544 residues, involving more than 90% of the acetylcholinesterase molecule and the C-terminal portion of thyroglobulin. The hydropathy profiles of the homologous regions have been determined and compared. Their striking resemblance suggests that both proteins adopt a similar three dimensional structure and militates for some common property. As thyroglobulin and acetylcholinesterase are known to interact with cell membranes, we suggest that the acetylcholinesterase-like domain of thyroglobulin is involved in the binding. These observations demonstrate that thyroglobulin has evolved from the condensation of a duplicated copy of the acetylcholinesterase gene with an archaic thyroglobulin gene encoding the major hormonogenic domain. The extensive homology in hydropathy profiles suggests that the two proteins may share antigenic determinants. If this were the case, it would provide a rationale for the demonstration of immunoreactive thyroglobulin in neurons (2) and the pathogenesis of Grave's ophthalmopathy.

Acetylcholinesterase↗
PubMed1986

Methylation and expression of the human thyroglobulin gene.

The DNA methylation pattern at the 5'end of the human thyroglobulin gene has been determined in different tissues. Out of the four HpaII/MspI sites (5'-CCGG-3') present in this region, three were found to be non-methylated in thyroid DNA, while full methylation was observed in liver, salivary gland and sperm DNA. This demethylation therefore correlates with expression of the thyroglobulin gene. However, all four sites were found to be non-methylated in placental DNA, regardless of the activity of the gene.

Base Sequence↗
PubMed1986

Integrity of the thyroglobulin locus in tricho-rhino-phalangeal syndrome II.

The thyroglobulin gene has been mapped to chromosome band 8q24 by several investigators. This is the band implicated in the causation of Langer-Giedion syndrome (tricho-rhino-phalangeal syndrome II). We have examined a restriction fragment length polymorphism at the thyroglobulin locus in a patient with Langer-Giedion syndrome and 8q deletion in order to: (1) localize the Langer-Giedion deletion more precisely, (2) define the relative map positions of the thyroglobulin gene and the Langer-Giedion locus. The results indicate that the locus of the thyroglobulin gene is intact in the patient with an interstitial deletion of proximal band 8q24.1 which confirms its more distal localization reported earlier by Bergé-Lefranc et al. (1985). It also assigns the critical region for the causation of Langer-Giedion syndrome to the proximal part of band 8q24, viz. 8q24.11----q24.13.

Child↗