Growth, Differentiation and Sexuality

196 H.D. Osiewacz and A. Hamann
III. Concluding Remarks
As discussed above, the dynamics of “healthy”
mitochondria – mitochondria which efficiently
produce ATP but only low amounts of ROS –
appears to be of high relevance for every organism.
A shift of the population from “healthy” to
damaged mitochondria leads to degeneration and
senescence. Various processes, including different
types of remodelling, are important pathways.
The most prominent hallmark of senescence in P.
anserina is the quantitative rearrangement of the
mtDNAduringaging.Assumingthattheproteinsof
the respiration chain become damaged, mitochondrial
function can be guaranteed only by successive
Fig. 10.5. Molecular networks controlling cellular metal
homeostasis. All proteins underlined in the diagram have
been studied in P. anserina in some detail (the COX subunits
COX1 and COX2, the copper transporter CTR3 and
CTR2, GRISEA, SOD1 and SOD2, the metallothionein MT1,
COX17 and AOX) or have been deduced from the available
genomic sequence with significant homology to proteins
of yeast or Arabidopsis (the copper chaperones ATX1
and CCS1, the multi-copper oxidase FET3, the Cu(I) AT-
Pase CCC2, and the COX assembly factors SCO1, COX11
replacement of defective molecules. Thus, remodelling
of the mitochondria via the insertion of newly
synthesized proteins (nuclear- and mitochondrialencoded
subunits) represents an important step in
maintaining mitochondrial function.
Since mitochondria are important organelles
involved in a key physiological process central in
all eukaryotes – the process of energy transduction
– many aspects of the biogenesis and metabolism
of mitochondria are important for aging not only
in P. anserina but also in more complex organisms,
including humans. Here, also the complex molecular
networks involved in cellular metal homeostasis
are significant (Fig. 10.5). In P. anserina, various
components of the network of regulatory circuits
and COX23). Others are assumed to be present but have
yet not been identified in the Podospora sequence, presumably
due to low conservation at the protein level (the
iron permease FTR1, and the COX assembly factor COX19).
The low-affinity copper transporter X and the iron transporter
Y are speculative. In particular, the pathways delivering
copper into the matrix of mitochondria and back
into the intermembrane space for incorporation into COX
are speculative and supported only by circumstantial evidence