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S Hennebicq

Publications and source records attributed to S Hennebicq.

12 recordsLinked to original sources
PubMed2006

[Epigenetics of the sperm cell].

In addition to genetic information, the spermatozoon carries another type of information, named epigenetic, which is not associated with variations of the DNA sequence. In somatic cells, it is now generally admitted that epigenetic information is not only regulated by DNA methylation but also involves modifications of the genome structure, or epigenome. During male germ cell maturation, the epigenome is globally re-organized, since most histones, which are associated to DNA in somatic cells, are removed and replaced by sperm specific nuclear proteins, the protamines, responsible for the tight compaction of the sperm DNA. However, a small proportion of histones, and probably other proteins, are retained within the sperm nucleus, and the structure of the sperm genome is actually heterogeneous. This heterogeneity of the sperm epigenome could support an epigenetic information, transmitted to the embryo, which could be crucial for its development. Although it is nowadays possible to appreciate the global structure of the sperm genome, the precise constitution of the sperm epigenome remains unknown. In particular, very recent data suggest that specific regions of the genome could be associated with particular proteins and define specific structures. This structural partitioning of the sperm genome could convey important epigenetic information, crucial for the embryo development.

DNA↗
PubMed2004

[Organizing the sperm nucleus].

Thanks to the success of new assisted reproductive technology, including sperm microinjection (i.c.s.i.), men with severe spermatogenesis impairments can now become biological fathers. Whether the germinal cell used for i.c.s.i. is conveying appropriate genetic and epigenetic information is an important concern. However, to date, there is a huge lack of data on which information is epigenetically conveyed to the offspring and how. The basic support for epigenetic marks is the nucleus structure. During spermatogenesis, a major re-organization of the male germ cells nucleus structure occurs, which includes a global condensation associated with a removal of most core somatic histones and their replacement by sperm-specific nuclear proteins. The available data on the molecular mechanisms involved in this process and how it could relate to the setting of male-specific epigenetic information is reviewed and discussed in light of our current knowledge about nuclear structure and functions.

Cell Nucleus↗
PubMed2002

Polyploidy in large-headed sperm: FISH study of three cases.

BACKGROUND: Macrocephalic or large headed sperm with multiflagella is a rare abnormality often associated with infertility. Sperm chromosomal abnormalities could be associated with this specific morphological abnormality. METHODS: The cytogenetic content of large-headed sperm was assessed by dual and three-colour fluorescence in-situ hybridization in three patients carrying this specific morphological abnormality. RESULTS: In all patients nearly all sperm contained at least one copy of each sex chromosome, and in more than half of them at least two copies of either chromosome 1 or 18 were identified. In some sperm a tetraploidy was found. CONCLUSIONS: These observations suggested that both meiotic I and II divisions were affected by incomplete partition of homologous chromosomes during meiosis I and of sister chromatids during meiosis II associated with a failure of nuclear cleavage. Furthermore, they provide evidence for a clear relationship between a specific morphological abnormality of the sperm and their abnormal cytogenetic content. The treatment of infertility using ICSI would probably be unsuccessful and have a high genetic risk in these cases.

Adult↗
PubMed2001

Risk of trisomy 21 in offspring of patients with Klinefelter's syndrome.

Intracytoplasmic sperm injection (ICSI) has given some patients with Klinefelter's syndrome (ie, men with an XXY sex-chromosome profile) the chance to become fathers, but the genetic makeup of the spermatozoa used for the injection is a concern. We studied the segregation of the sex chromosomes and chromosomes 1 and 21 by multicolour fluorescence in-situ hybridisation in a patient with non-mosaic Klinefelter's syndrome who was a candidate for ICSI. As other workers have found, we saw a higher rate of 24,XX and 24,XY spermatozoa in the patient than in controls. However, we also found a much higher frequency of disomy 21 in the spermatozoa of this patient than in controls (6.2 vs 0.4%). Any child conceived by ICSI using this man's sperm will thus have a proportionally higher risk of trisomy 21.

Chromosome Aberrations↗
PubMed1999

Capillary zone electrophoresis and MALDI-mass spectrometry for the monitoring of in vitro O-glycosylation of a threonine/serine-rich MUC5AC hexadecapeptide.

The in vitro N-acetylgalactosaminylation by human gastric UDP-GalNAc:polypeptide N-acetylgalactosaminyltransferases was assessed using the peptide motif GTTPSPVPTTSTTSAP, which is found naturally in the tandem repeat domains of the apomucin encoded by the gene MUC5AC. This peptide appeared to be an excellent tool for obtaining an insight into the extensive O-glycosylation processes of apomucins. Up to six N-acetylgalactosamines were added and the given glycopeptide species were well separated by capillary zone electrophoresis. Moreover, the degree of glycosylation (number of monosaccharide O-linked attachments) could be determined by MALDI-mass spectrometry without prior separation. Using different incubation times, we evidenced the accumulation of various glycopeptides, suggesting that the total glycosylation of an apomucin-peptide requires orderly N-acetylgalactosaminylation processing. This information was completed by experimental data showing that N-acetylgalactosaminylated octapeptides (the peptide backbones of which are part of GTTPSPVPTTSTTSAP) were able to selectively inhibit some N-acetylgalactosaminyltransferases. Our results suggest that this inhibition may influence the quality of the intermediate products appearing during the in vitro O-glycosylation process.

Amino Acid Sequence↗
PubMed1998

Improved capillary electrophoretic separation of glycosylated oligopeptides through addition of poly(vinyl alcohol), and analysis by electrospray mass spectrometry.

A method for the analysis of O-glycosylation of peptides has been developed, combining capillary electrophoretic (CE) separation and electrospray ionization mass spectrometry. Synthetic peptides with apomucin 'tandem repeat' sequences which present potential O-glycosylation sites on threonine and serine residues were used as model system. In vitro O-glycosylated peptide samples were obtained by incubation of the peptides with human gastric microsomal homogenates containing N-acetylgalactosamine transferase activity in the presence of uridyl diphosphate N-acetylgalactosamine (UDP-GalNAc). CE was carried out in the presence of the linear polymer poly(vinyl alcohol) in the electrophoresis solvent, resulting in a greatly improved separation of the up to five different glycoforms of peptides with lengths of 8, 16 or 23 amino acids, and the unglycosylated peptides. After separation and peak collection, the number of modifications with N-acetyl galactosamine (GalNAc) could be determined by electrospray ionization mass spectrometry. The glycosylation pattern was shown to depend on the amino acid sequence of the peptides.

Amino Acid Sequence↗
PubMed1998

Polypeptide:N-acetylgalactosaminyltransferase activities towards the mucin MUC5AC peptide motif using microsomal preparations of normal and tumoral digestive mucosa.

The selected-acceptor substrate peptide (TTSAPTTS), deduced from the human mucin gene MUC5AC (expressed essentially in the human gastric and tracheobronchial mucosa), was used to assay polypeptide:N-acetylgalactosaminyltransferases (GalNAc transferases) of different microsomal preparations, obtained from gastric and colonic mucosa in normal and tumoral situations. The O-glycosylated products, analyzed by capillary electrophoresis and electrospray mass spectrometry, showed a variable number of GalNAc O-linked to the different hydroxy amino acids of TTSAPTTS, depending on the tissue studied. Our observations were consistent with the existence of more than one form of GalNAc transferases which were expressed differentially in the gastrointestinal tract (stomach and/or colon). The levels of enzyme activities showed a tissue-specific pattern as they were high in normal colonic tissue and low in colon cancer. On the other hand, in the tumoral gastric tissue (displaying intestinal metaplasia) a high level of GalNAc transferase activities was obtained, similar to that found in the normal colon. Moreover, slight discrepancies (activities and number of O-linked GalNAc) were only detected between normal gastric and tumoral colonic preparations. Thus, the data indicated that the dedifferentiation of the gastric cancer tissue may induce GalNAc transferase activities similar to those in the normal colonic, tissue and that colonic and gastric tissues may contain families of glycosyltransferases involved specifically in reaction towards particular peptide or protein substrates. In addition, the analysis by capillary electrophoresis and electrospray mass spectrometry revealed, in tumoral gastric as well as in normal colonic tissues, a high dipeptidylaminotransferase activity inducing an elongation of TTSAPTTS by dithreonine. This activity was low in normal gastric and tumoral colonic tissues.

Animals↗
PubMed1998

Influence of the amino acid sequence on the MUC5AC motif peptide O-glycosylation by human gastric UDP-GalNAc:polypeptide N-acetylgalactosaminyltransferase(s).

The present work was carried out to study the role of the peptide moiety in the addition of O-linked N-acetylgalactosamineto human apomucin using human crude microsomal homogenates from gastric mucosa (as enzyme source) and a series of peptide acceptors representative of tandem repeat domains deduced from the MUC5AC mucin gene (expressed in the gastric mucosa). Being rich in threonine and serine placed in clusters, these peptides provided several potential sites for O-glycosylation. The glycosylated products were analysed by a combination of electrospray mass spectrometry and capillary electrophoresis in order to isolate the glycopeptides and to determine their sequence by Edman degradation. The O-glycosylation of our MUC5AC motif peptides gave information on the specificity and activity of the gastric microsomal UDP-N-acetylgalactosamine:polypeptide N-acetylgalactosaminyltransferase(s). The proline residues and the induced-conformations are of great importance for the recognition of MUC5AC peptides but they are not the only factors for the choice of the O-glycosylation sites. Moreover, for the di-glycosylated peptides, the flanking regions of the proline residues strongly influence the site of the second O-glycosylation.

Amino Acid Sequence↗
PubMed1998

Dipeptidyl aminotransferase activity and in vitro O-glycosylation of MUC5AC mucin motif peptides by human gastric microsomal preparations.

The in vitro O-glycosylation reaction of the MUC5AC mucin motif peptide, TTSAPTTS (in one-letter code), was achieved with human gastric microsomal homogenates. The analyses using capillary electrophoresis online coupled with electrospray mass spectrometry and further Edman degradation of the purified products (obtained by capillary electrophoresis at preparative scale) allowed us to distinguish two components at close masses: the addition of a mass of 202 corresponded to an N-terminal elongation of the peptide TTSAPTTS with the dipeptide (TT) and the addition of a mass of 203 corresponded to an N-acetylgalactosamine O-linkage. Using different peptidase inhibitors, a dipeptidyl peptidase/transferase activity was further characterized. A thiol dependence and an inhibition by H-Gly-PheCHN2 (specific to cathepsin C activity) were found. Moreover, besides TTSAPTTS, other MUC5AC motif peptides (GTTPSPVP, TSAPTTS) were also dipeptide donors (GT and TS, respectively) and our results suggested the involvement of a single dipeptidyl peptidase/transferase activity. Finally, this latter activity modified the in vitro GalNAc incorporation rates when using our selected MUC5AC motif peptides. Our study therefore shows that caution must be taken to prevent peptidic substrate elongation while performing in vitro O-glycosylation with microsomal preparations as the enzyme source. In fact, the results of the N-acetylgalactosamine incorporation rates and thus the microsomal N-acetylgalactosamine transferase affinity can be misinterpreted if dipeptidyl peptidase/transferase activity is not inhibited by the thiol inhibitor E-64 or the cathepsin C inhibitor H-Gly-PheCHN2.

Cathepsin C↗