UZH-Logo

Maintenance Infos

Polyglutamine-mediated and heavy metal-induced transcription from Yeast to Humans


Atanesyan, L. Polyglutamine-mediated and heavy metal-induced transcription from Yeast to Humans. 2011, University of Zurich, Faculty of Science.

Abstract

Project I: Many proteins, especially regulatory proteins of gene expression, contain homopolymeric repeats of single amino acids, such as glutamine, asparagine, serine, glycine, proline and alanine. Especially polyamino acid tracts that are encoded by repeats of a same codon are genetically unstable, due to polymerase slippage and out-of-register recombination, and thus subject to expansion and shrinkage. No less than 18 diseases are known to date to be caused by polyglutamine or polyalanine expansions. Since polyamino acid tracts are found from yeast to humans and even in bacteria the question arose whether they might also exert some positive effects, i.e., whether they might confer
some kind of selective advantage. In our lab it had been shown before that a polyglutamine tract in a synthetic transcription factor can contribute to transcriptional activation, and it was postulated that expansion and shrinkage are useful to reversibly alter the activity of transcription factors in short-term evolution [Gerber HP et al, Science 1994, 263:808-11]. I have confirmed and extended these results by showing a clear, positive correlation between the length of a polyglutamine stretch and the transcriptional activation by the factor Gal4DBD-polyQ-VP16AD (Gal4DBD = DNA binding domain of the yeast Gal4 transcription factor, polyQ = polyglutamine stretch, VP16AD = activation domain of the viral protein VP16) in widely divergent species, namely, human cells, transgenic flies, and baker’s yeast. I also wished to test the hypothesis that homopolymeric codons are genetically less stable than a mixture of codons for a homopolymeric amino acid tract, but the number of generations was probably too small to observe differences. Project II. It is now widely recognized that a major challenge for any cell is to keep the right balance of essential trace metals and at the same time minimize the effect of nonessential ones such as cadmium, mercury, lead and silver. This is achieved by a variety of mechanisms, notably metal-specific import or export, binding to specific chaperones, storage, and detoxification by scavenging and export. Even essential metals such as copper and iron can have adverse effects if in excess, by interfering with metabolic functions via misincorporation into proteins, or by generation of reactive oxygen species due to redox cycling. Metallothioneins are small, cysteine-rich proteins which avidly bind a number of essential and non-essential heavy metals. Here I characterize metallothionein E (MtnE), the fifth and apparently ultimate member of the Drosophila metallothionein family. It is strongly expressed in the intestinal tract, notably in the socalled copper cells and in the iron cells of the midgut. I was also involved in the
characterization of two related, small Drosophila proteins named Dumpy-30L1 and Dumpy-30L2. Dumpy-30L1 binds to, and thereby downregulates, the activity of MTF-1 (metal-responsive transcription factor-1). Accordingly, overexpression of Dumpy-30L1 rendered flies more sensitive to an excess of dietary copper or zinc. Targeted disruption
of the gene for Dumpy-30L2 revealed a different phenotype in that male fertility was compromised. Furthermore, I was involved in a study led by D. Steiger on the characterization of Ctr1C, a copper importer which is strongly expressed in male gonads and contributes, together with the importer Ctr1B, to male fertility [Steiger et al, JBC 2010, 285(22):17089-97]. All these studies have led to a deeper understanding of various aspects of cellular metal homeostasis.

Project I: Many proteins, especially regulatory proteins of gene expression, contain homopolymeric repeats of single amino acids, such as glutamine, asparagine, serine, glycine, proline and alanine. Especially polyamino acid tracts that are encoded by repeats of a same codon are genetically unstable, due to polymerase slippage and out-of-register recombination, and thus subject to expansion and shrinkage. No less than 18 diseases are known to date to be caused by polyglutamine or polyalanine expansions. Since polyamino acid tracts are found from yeast to humans and even in bacteria the question arose whether they might also exert some positive effects, i.e., whether they might confer
some kind of selective advantage. In our lab it had been shown before that a polyglutamine tract in a synthetic transcription factor can contribute to transcriptional activation, and it was postulated that expansion and shrinkage are useful to reversibly alter the activity of transcription factors in short-term evolution [Gerber HP et al, Science 1994, 263:808-11]. I have confirmed and extended these results by showing a clear, positive correlation between the length of a polyglutamine stretch and the transcriptional activation by the factor Gal4DBD-polyQ-VP16AD (Gal4DBD = DNA binding domain of the yeast Gal4 transcription factor, polyQ = polyglutamine stretch, VP16AD = activation domain of the viral protein VP16) in widely divergent species, namely, human cells, transgenic flies, and baker’s yeast. I also wished to test the hypothesis that homopolymeric codons are genetically less stable than a mixture of codons for a homopolymeric amino acid tract, but the number of generations was probably too small to observe differences. Project II. It is now widely recognized that a major challenge for any cell is to keep the right balance of essential trace metals and at the same time minimize the effect of nonessential ones such as cadmium, mercury, lead and silver. This is achieved by a variety of mechanisms, notably metal-specific import or export, binding to specific chaperones, storage, and detoxification by scavenging and export. Even essential metals such as copper and iron can have adverse effects if in excess, by interfering with metabolic functions via misincorporation into proteins, or by generation of reactive oxygen species due to redox cycling. Metallothioneins are small, cysteine-rich proteins which avidly bind a number of essential and non-essential heavy metals. Here I characterize metallothionein E (MtnE), the fifth and apparently ultimate member of the Drosophila metallothionein family. It is strongly expressed in the intestinal tract, notably in the socalled copper cells and in the iron cells of the midgut. I was also involved in the
characterization of two related, small Drosophila proteins named Dumpy-30L1 and Dumpy-30L2. Dumpy-30L1 binds to, and thereby downregulates, the activity of MTF-1 (metal-responsive transcription factor-1). Accordingly, overexpression of Dumpy-30L1 rendered flies more sensitive to an excess of dietary copper or zinc. Targeted disruption
of the gene for Dumpy-30L2 revealed a different phenotype in that male fertility was compromised. Furthermore, I was involved in a study led by D. Steiger on the characterization of Ctr1C, a copper importer which is strongly expressed in male gonads and contributes, together with the importer Ctr1B, to male fertility [Steiger et al, JBC 2010, 285(22):17089-97]. All these studies have led to a deeper understanding of various aspects of cellular metal homeostasis.

Downloads

284 downloads since deposited on 12 Mar 2012
33 downloads since 12 months
Detailed statistics

Additional indexing

Item Type:Dissertation
Referees:Schaffner W, Basler K
Communities & Collections:07 Faculty of Science > Institute of Molecular Life Sciences
Dewey Decimal Classification:570 Life sciences; biology
Language:English
Date:17 January 2011
Deposited On:12 Mar 2012 13:39
Last Modified:05 Apr 2016 15:36
Related URLs:http://opac.nebis.ch/F/?local_base=NEBIS&CON_LNG=GER&func=find-b&find_code=SYS&request=006436808
Permanent URL: http://doi.org/10.5167/uzh-58895

Download

[img]
Preview
Filetype: PDF
Size: 14MB

TrendTerms

TrendTerms displays relevant terms of the abstract of this publication and related documents on a map. The terms and their relations were extracted from ZORA using word statistics. Their timelines are taken from ZORA as well. The bubble size of a term is proportional to the number of documents where the term occurs. Red, orange, yellow and green colors are used for terms that occur in the current document; red indicates high interlinkedness of a term with other terms, orange, yellow and green decreasing interlinkedness. Blue is used for terms that have a relation with the terms in this document, but occur in other documents.
You can navigate and zoom the map. Mouse-hovering a term displays its timeline, clicking it yields the associated documents.

Author Collaborations