X-Message-Number: 26279
Date: Fri, 3 Jun 2005 20:27:37 -0700 (PDT)
From: Doug Skrecky <>
Subject: first success at engineered negligible senescence

[Quote from reference #2: "A single culture of mutant ex1 has
been growing in the laboratory on cornmeal agar plates for over
12 years without signs of senescence." Note that the maximum
lifespan of wild type podospora is 50 days, and this can be
extended to 130 days by the addition to the medium of 30 micromole
of the copper chelator bathocuproinedisulfonic acid.]

Reference #1:
Biogerontology. 2002;3(3):143-53
Respiration, copper availability and SOD activity in P. anserina
strains with different lifespan.
    P. anserina mutants with impairments in complex IV (COX) of
the respiratory chain are characterized by an increase in lifespan.
Examples are the nuclear grisea mutant with a moderate lifespan
extension (60%) and the immortal extranuclear ex1 mutant. Here we
report data demonstrating that in mutant ex1 the level of the
alternative oxidase (PaAOX) is significantly higher than in mutant
grisea. PaAOX levels appear to be reversely dependent on COX
activity. The activity profile of superoxide dismutases in the ex1
mutant resembles the profile in senescent wild-type cultures with
a high cytoplasmic copper/zinc superoxide dismutase (PaSOD1) and a
low mitochondrial manganese superoxide dismutase (PaSOD2) activity.
In the grisea mutant, PaSOD1 activity is only detectable in
cultures grown in copper-supplemented medium. The two
copper-regulated genes PaCtr3 (coding for a high affinity copper
transporter) and PaSod2 are not expressed in the two mutants grown
in standard medium. The repression of these genes as well as the
activity of PaSOD1 is dependent on the availability of cellular
copper, which appears to be high in COX-deficient strains such as
mutant ex1 and in the senescent wild-type strain. In the wild-type,
changes in the cellular localization of copper and in the delivery
of this metal to different proteins appear to occur during
senescence. Collectively, the data explain the characteristic
lifespan of the investigated strains as the result of differences
in energy transduction and in the machinery protecting against
oxidative stress.

Reference #2:
Mol Cell Biol. 2001 Jan;21(2):390-9.
Copper-modulated gene expression and senescence in the filamentous
fungus Podospora anserina.
    We have previously shown that the control of cellular copper
homeostasis by the copper-modulated transcription factor GRISEA
has an important impact on the phenotype and lifespan of Podospora
anserina. Here we demonstrate that copper depletion leads to the
induction of an alternative respiratory pathway and to an increase
in lifespan. This response compensates mitochondrial dysfunctions
via the expression of PaAox, a nuclear gene coding for an
alternative oxidase. It resembles the retrograde response in
Saccharomyces cerevisiae. In P. anserina, this pathway appears to
be induced by specific impairments of the copper-dependent
cytochrome c oxidase. It is not induced as the result of a general
decline of mitochondrial functions during senescence. We cloned
and characterized PaAox. Transcript levels are decreased when
cellular copper, superoxide, and hydrogen peroxide levels are
raised. Copper also controls transcript levels of PaSod2, the gene
encoding the mitochondrial manganese superoxide dismutase (PaSOD2).
PaSod2 is a target of transcription factor GRISEA. During the
senescence of wild-type strain s, the activity of PaSOD2 decreases,
whereas the activity of the cytoplasmic copper/zinc superoxide
dismutase (PaSOD1) increases. Collectively, the data explain the
postponed senescence of mutant grisea as a defined consequence of
copper depletion, ultimately leading to a reduction of oxidative
stress. Moreover, they suggest that during senescence of the
wild-type strain, copper is released from mitochondria. The involved
mechanism is unknown. However, it is striking that the permeability
of mitochondrial membranes in animal systems changes during apoptosis
and that mitochondrial proteins with an important impact on this
type of cellular death are released.

Free full text for reference #2:


http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pubmed&pubmedid=11134328

Reference #3
Mech Ageing Dev. 1992 Sep;65(2-3):277-88  Oxidative stress and
ageing in the fungus Podospora anserina.
    The ageing phenomenon exhibited by the ascomycetous fungus
Podospora anserina can be either delayed or induced by either
different carbon sources or effectors. As these effects seem to have
analogy to catabolite-repression of respiratory genes, experiments
concerning respiratory functions have been carried out. Ageing is
parallelled by switching from cytochrome c-oxidase-mediated
respiration to alternative, cyanide-resistant respiration for reasons
still unknown. The latter is always accompanied by appearance of the
phenol oxidizing enzyme laccase (EC 1.10.3.2), which seems to act as
an alternative oxidase. The existence of a second,
non-mitochondrially encoded respiratory pathway relieves the
selective pressure on mitochondria leading to disintegrated,
non-functional mtDNA and thereby whole mitochondria which accumulate
in the hyphal cells. Mutants lacking cytochrome c-oxidase aa3 or
laccase have stable mitochondrial populations and live eternally.

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