download report - Istituto Pasteur

P a r t i c i p a n t s :
Cristina Mazzoni, researcher; Vanessa Palermo, post-doc fellow;
Mirko Torella, PhD student; Michele Saliola, technician.
C o l l a b o r a t i o n s :
Institute of Molecular Biosciences, University of Graz, Austria
(Prof. Frank Madeo); Dipartimento di Medicina e Patologia
Sperimentale, Sapienza-Università di Roma (Prof. Patrizia
Mancini).
Report of activity
The aim of the present project concerns the isolation
of anti-apoptotic genes and the study of their suppression
mechanisms.
Apoptosis is a form of programmed cell death
required for health, homeostasis and embryonic
development in metazoans. Apoptosis is required for
the removal of autoreactive immune cells, virusinfected
cells and cells with DNA damage which can
undergo transformation, playing an important role in
different diseases such as cancer, neurodegenerative
disorders, or stroke. A simple model system, such as
yeast, has been proved to be very useful to clarify the
regulatory network underlying this phenomenon.
In fact, during the past years, scientists were successful
in identifying new cell-death regulators of
humans, plants and fungi using the yeast
Saccharomyces cerevisiae. Moreover, yeast analogues of
some crucial components of the apoptotic cascade in
mammals have also been described, (i.e., caspase,
Omi, AIF and EndoG) suggesting that the basic
machinery of apoptosis is indeed present and functional
also in this unicellular organisms.
The biological significance of apoptosis in an unicellular
organism, like yeast, could be related to the possibility
in nature of discarding individual aged and
damaged cells from the whole population and allow
the survival of young and healthy cells.
Principal investigator: Claudio Falcone
Professor of Industrial Microbiology
Dipartimento di Biologia Cellulare e dello Sviluppo
Tel: (+39) 06 49912278; Fax: (+39) 06 49912256
claudio.falcone@uniroma1.it
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Molecular genetics of eukaryotes - AREA 3
New tools in deciphering aging and apoptotic pathways
Among the physiological conditions that can induce
programmed cell death in yeast there are the presence
of small quantities of the conjugation
pheromone (mating type pheromone), and aging.
In the first case, it has been demonstrated that only
those cells that are unable to mate will undergo apoptosis,
confirming that apoptosis acts as a selection for
the fitness.
Two different kinds of aging processes can be studied
in yeast: RLS (Replicative Life Span), that measures
the number of generation performed by a single
cell in the life, and CLS (Chronological Life Span),
which measures cell viability when cells stop dividing
(stationary phase). In both replicative and
chronological aging, the most aged cells die following
an apoptotic pathway.
In our laboratory, we constructed a viable S. cerevisiae
mutant with reduced longevity and showing all
markers of apoptosis. This mutant, namely Kllsm4∆1,
presents a delayed mRNA turnover in consequence of
defects in decapping, one of the first step in the
degradation of messenger RNAs.
This is a very upstream mutant for the onset of
apoptosis and we used it for the isolation of downstream
suppressors and the identification of different
apoptotic pathways.
One of the suppressors that we identified was HIR1,
the gene that encodes a transcriptional co-repressor
of histone genes.
We have shown that the over-expression of HIR1
reduced the transcription of histone genes, but also
of other genes, suggesting that the over-expression
of HIR1 would lead to the constitution of a
repressed chromatin. We postulated that the reduction
of transcription might compensate the
increased stability of mRNAs observed in the
Kllsm4∆1 mutant.
To better understand this relationship, we checked
during the cell cycle the expression of the histone
genes, in that their trascription is tightly regulated