Growth, Differentiation and Sexuality

10 Senescence and Longevity
H.D. Osiewacz 1 , A. Hamann 1
CONTENTS
I. Introduction ......................... 189
II. Senescence Syndrome in Podospora anserina 189
A. TheSenescencePhenotype ........... 189
B. MitochondrialDNAInstabilities ....... 190
C. Mitochondrial Functions
andmtDNAInstabilities ............. 191
D. TheRetrogradeResponse............. 192
III. Concluding Remarks ................... 196
References ........................... 197
I. Introduction
Most fungi, both unicellular yeasts as well as “multicellular”
filamentous fungi, appear to be immortal.
They propagate indefinitely either by single cell
divisionorby hyphal tip growth.Infact,individuals
ofthelattergroupmayformhugevegetationbodies
with diameters of over 0.5 km (Smith et al. 1992).
Remarkably, however, there are a few species which
are clearly characterized by limited growth. Each
individuum of these species ages and finally dies.
This holds true for the yeast Saccharomyces cerevisiae
butalsoforanumberoffilamentousfungi
(Jinks 1959; Handley and Caten 1973; Caten and
Handley 1978; Lazarus et al. 1980; de Vries et al.
1981, 1986; Lazarus and Küntzel 1981; Bertrand
et al. 1985, 1986; Böckelmann and Esser 1986; Almasan
and Mishra 1988; Court et al. 1991; Debets
et al. 1995; Navaraj et al. 2000; Fox and Kennell
2001).
In budding yeast, aging is characterized by the
limited ability of mother cells to divide and to produce
daughter cells, a process which is characterized
by the generation of bud scars on the surface
of the mother cell after the newly formed daughter
cell becomes separated from the mother. This
allows us to microscopically distinguish between
older and younger yeast cells. Today S. cerevisiae is
1 Institut für Molekulare Biowissenschaften, J.W. Goethe-
Universität, Marie-Curie-Str. 9, 60439 Frankfurt, Germany
one of a few models extensively studied in experimental
gerontology (for review, see Guarente 1997;
Guarente and Kenyon 2000; Jazwinski 2000, 2001,
2005; McMurray and Gottschling 2004).
Podospora anserina is a filamentous ascomycete
in which, in contrast to yeast, senescence
is visible at the macroscopic level. This and the
fact that P. anserina is an excellent system for
genetic analysis are the reasons why the aging of
this species has now been investigated for more
than 50 years. In this review we will focus on the
mechanisms involved in senescence and life span
control in P. anserina. Research performed on
this system has stimulated investigations in other
systems and clearly demonstrates that parts of
themechanismsinvolvedinlifespancontrolhave
been conserved during evolution. In this chapter,
we do not aim for a comprehensive description
of the work on aging in P. anserina but draw an
updated view about the current knowledge on
the mechanisms of aging in this aging model. For
more detailed description of earlier investigations,
the reader is referred to Esser and Tudzynski
(1980), Esser (1985), Griffiths (1992), Osiewacz
(1995, 2002a,b), Bertrand (2000), and Silar et al.
(2001).
II. Senescence Syndrome in Podospora
anserina
A. The Senescence Phenotype
In the early 1950s, G. Rizet reported for the first
time that all wild-type cultures of P. anserina do
not grow indefinitely but senesce after a strainspecific
period of time (Rizet 1953). After the germination
of ascospores, the mycelial culture grows
radially by hyphal tip growth. During aging, the
growth rate declines and the pigmentation of the
mycelium increases. In particular, the formation of
The Mycota I
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© Springer-Verlag Berlin Heidelberg 2006