Biomedical subjects

F Lyko

Publications and source records attributed to F Lyko.

4 recordsLinked to original sources

PubMed1998

Identification of a silencing element in the human 15q11-q13 imprinting center by using transgenic Drosophila.

Prader-Willi syndrome (PWS) and Angelman syndrome are neurogenetic disorders caused by the lack of a paternal or a maternal contribution from human chromosome 15q11-q13, respectively. Deletions in the transcription unit of the imprinted SNRPN gene have been found in patients who have PWS or Angelman syndrome because of a parental imprint switch failure in this chromosomal domain. It has been suggested that the SNRPN exon 1 region, which is deleted in the PWS patients, contains an imprint switch element from which the maternal and paternal epigenotypes of the 15q11-q13 domain originate. Using the model organism Drosophila, we show here that a fragment from this region can function as a silencer in transgenic flies. Repression was detected specifically from this element and could not be observed with control human sequences. Additional experiments allowed the delineation of the silencer to a fragment of 215 bp containing the SNRPN promoter region. These results provide an additional link between genomic imprinting and an evolutionary conserved silencing mechanism. We suggest that the identified element participates in the long range regulation of the imprinted 15q11-q13 domain or locally represses SNRPN expression from the maternal allele.

Alleles↗

PubMed1998

Imprinting and gene silencing in mice and Drosophila.

H19 and Igf2 are located within a large imprinting domain that confers monoallelic silencing of parental alleles. The silent paternal allele of H19 is hypermethylated and relatively resistant to nucleases. Using a 130 kb yeast artificial chromosome clone, appropriate imprinting of both H19 and Igf2 was observed at single insert loci in transgenic mice. Imprinting was also observed for H19-lacZ transgenes containing 4 kb of upstream sequence, but only at multicopy loci. The H19 RNA is therefore not essential for imprinting. When the H19-lacZ transgene was introduced into Drosophila, a 1.2 kb region was identified within the 4 kb upstream flank that functioned as a bi-directional silencer. This cis element is located within a region that is apparently necessary for imprinting in mice. These studies suggest an evolutionarily conserved mechanism for gene silencing in Drosophila and imprinting in mice. We propose a new model for imprinting of H19 and Igf2 in mice in which silencing of H19 is the default state, and activation of the maternal allele requires a specific activator element.

Animals↗

PubMed1997

An imprinting element from the mouse H19 locus functions as a silencer in Drosophila.

Genomic imprinting as originally described in Sciara is displayed by many organisms. In mammals, X-inactivation and the parent-of-origin-specific silencing of imprinted genes are examples of this phenomenon. A heritable chromatin structural modification may be the critical mechanism in such instances of chromosome condensation and preferential gene inactivation. H19 is an imprinted gene in which the repressed paternal allele is hypermethylated and the compacted chromatin is relatively resistant to digestion by nucleases. In order to uncover underlying conserved epigenetic mechanisms we have introduced a mouse H19 transgene into Drosophila. We show here that a 1.2-kb H19 upstream sequence functions in cis as a parent-of-origin independent silencing element in Drosophila. Strikingly, this cis-acting element is located within an upstream region that is necessary for H19 imprinting in mice. These results suggest involvement of an evolutionary conserved mechanism in both genes silencing in Drosophila and imprinting in mice.

Animals↗

PubMed1995

Signal sequence processing in rough microsomes.

Secretory proteins are synthesized with a signal sequence that is usually cleaved from the nascent protein during the translocation of the polypeptide chain into the lumen of the endoplasmic reticulum. To determine the fate of a cleaved signal sequence, we used a synchronized in vitro translocation system. We found that the cleaved signal peptide of preprolactin is further processed close to its COOH terminus. The resulting fragment accumulated in the microsomal fraction and with time was released into the cytosol. Signal sequence cleavage and processing could be reproduced with reconstituted vesicles containing Sec61, signal recognition particle receptor, and signal peptidase complex.

Amino Acid Sequence↗