0-TESTO COMPLETO.pdf - Fondazione Santa Lucia

Sezione III: Attività per progetti
region revealed by probe p13E-11 consists of identical KpnI units, each 3.3
kb in size, [hereafter referred to as D4Z4 repeats], tandemly arrayed so that
the variation in the size of EcoRI fragments is due to variability in the number
of D4Z4 repeats [Wijmenga et al. 1993]. The number of D4Z4 repeats
varies from 11 to 150 in the general population, whereas less than 11
repeats are present in sporadic and familial FSHD patients [van Deutekom
et al. 1993].
The lack of candidate genes in the 4q35 region led to the hypothesis that
deletion of D4Z4 repeats might modify the chromatin organization of the 4q
subtelomeric region and alter gene expression [Hewitt et al. 1994; Winokur et
al. 1994]. Indeed we observed that the adenine nucleotide translocator gene
(ANT1), the FSHD Region Gene 1 (FRG1) [van Deutekom et al. 1996], and the
FSHD Region Gene 2 (FRG2) [Rijkers et al. 2004] were abnormally up-regulated
in FSHD affected muscles.
Investigating the possibility that deletion of D4Z4 repeats initiates transcriptional
misregulation at 4q35, we identified a transcriptional repressor
complex that binds D4Z4 repetitive elements in vitro and in vivo and mediates
transcriptional repression of 4q35 genes. Based upon these results we proposed
that deletion of D4Z4 leads to the inappropriate transcriptional derepression
of 4q35 genes resulting in disease [Gabellini et al. 2002; Tupler,
Gabellini 2004].
The model we proposed to explain FSHD pathogenesis has been controversial
[Winokur et al. 2003, Jang et al. 2003, Rijkers et al. 2004]. At present,
there is a general agreement in the research community that the underlying
molecular mechanism of FSHD is altered gene expression [Tupler, Gabellini
2004; Masny et al. 2004; Tam et al. 2004] and FSHD has being included in a
NIH PA to study: Nuclear Structure-Function Defects in the Pathogenesis of
Muscular Dystrophy (http://grants.nih.gov/grants/guide/rfa-files/RFA-NS-07-
001.html).
We also generated transgenic mice independently over-expressing ANT1,
FRG1 and FRG2, the three genes we found up-regulated in FSHD affected
muscle. We found that FRG1 transgenic mice develop a muscular dystrophy
with features characteristic of the human disease. Moreover, we observed that
in muscle of FRG1 transgenic mice and FSHD patients, specific pre-mRNAs
undergo aberrant alternative splicing. Collectively, our observations suggest
that FSHD results from inappropriate over-expression of FRG1 in skeletal
muscle, which leads to abnormal alternative splicing of specific pre-mRNAs
[Gabellini et al. 2006].
However, despite the significant breakthroughs made, FSHD pathophysiology
remains elusive and no specific therapy exists to treat this disorder. Several
questions must be addressed.
Are the diagnostic criteria previously established for FSHD still valid?
In 1991, diagnostic criteria for FSHD were established in order to support
selection of FSHD families for linkage studies. However, recent publications
reported FSHD patients showing atypical phenotypes. By studying the large
cohort of patients we collected, we will re-evaluate those criteria in view of the
results of genotype-phenotype correlation.
764 2009