download report - Istituto Pasteur

P a r t i c i p a n t s :
Michele M. Bianchi, professor; Simona Loreti, Eugenia
Piccinni, post-doc fellows; Angela Alagia, Viviana
Casagrande, PhD students.
C o l l a b o r a t i o n s :
Laboratoire de Génomique CNRS et Ecole Normale Supérieure,
(Prof. Frédéric Devaux); Department of Genetics, Institute of
Biochemistry and Biophysics, Polish Academy of Sciences (Prof.
Anna Chelstowska); Dipartimento di Biologia Cellulare e dello
Sviluppo, Sapienza-Università di Roma (Prof. Laura Frontali,
Dr. Teresa Rinaldi, Prof. Gabriella Tocco).
Report of activity
The glioma-amplified sequence (GAS) 41 gene was
identified for the first time as an amplified sequence
in the human chromosome region 12q13-15, a locus
known to be involved in gene amplification in human
gliomas. Abnormalities like this are frequently found
in human tumors and are thought to be a manifestation
of the intrinsic genome instability of cancer
cells. In addition it is presumed that over-expression
of amplified genes confers a selective advantage to
cell clones. The goal of this scientific program is to
define the role of the presumptive transcription factor
Gas41 in chromatin organization and gene
expression. To this purpose we take advantage from
the extraordinary conservation of structure, and
very likely of function, of this protein across different
eukaryotic species. In particular the yeast
Saccharomyces cerevisiae Yaf9, that we have recently
characterized is highly homologous to Gas41 and
appears to share similar functions.
Yaf9 is structurally and functionally associated to
two chromatin modification complexes in S. cerevisiae:
the NuA4 histone acetyltransferase complex and
the SWR complex, involved in the substitution of
histone H2A with its isoform H2AZ. On the other
hand, Gas41 is involved in the Tip60 complex
Principal investigator: Rodolfo Negri
Professor of Molecular Biology
Dipartimento di Biologia Cellulare e dello Sviluppo
Tel: (+39) 06 44917790; Fax: (+39) 06 44917594
rodolfo.negri@uniroma1.it
63
Molecular genetics of eukaryotes - AREA 3
Role of the presumptive human transcription factor Gas41 and
of its S. cerevisiae homologue Yaf9 in chromatin organization
and gene expression
which appears to correspond to a near-perfect
fusion of the two yeast complexes NuA4 and SWR.
Since these complexes are involved in the formation
of a chromatin structure favourable to gene transcription,
it is very likely that Gas41 and Yaf9 transcription
functions are linked to the recruitment of
the complexes to regulated promoters in both yeast
and mammals.
The transcriptional role of Yaf9
in S. cerevisiae
Our group characterized yeast strains lacking Yaf9
(Del Vescovo et al., 2008; Casagrande et al., 2008).
These strains show genomic instability, a series of
growth phenotypes, including cesium chloride sensitivity,
as compared with its isogenic wild type, and
defined defects in cell morphology and spindle body
formation. These phenotypes are accompanied, and
possibly caused, by the transcriptional modulation of
several genes and by changes in the level of histone
acetylation and/or histone H2AZ variant occupancy
at genomic sites like regulated promoters and centromeres.
We analyzed the global transcriptional
response of S. cerevisiae cells exposed to different
concentrations of CsCl added in the growth medium
and at different times after addition. Early responsive
genes were mainly involved in cell wall structure and
biosynthesis. About half of the induced genes were
previously shown to respond to other alkali metal
cations in a fashion dependent on the HOG (High
Osmolarity and Glycerol) signaling pathway.
Western blot analysis confirmed that cesium concentrations
as low as 100 mM activate phosphorylation
of Hog1, the MAP kinase of the HOG pathway.
Another important fraction of the cesium-modulated
genes requires Yaf9 for full responsiveness, as shown
by the transcriptome of a yaf9∆ strain in the presence
of cesium. We showed that a cell wall-restructuring
process promptly occurs in response to
cesium addition, which is dependent on the presence
of both Hog1 and Yaf9 proteins. Moreover, the sen-