8 research outputs found
Macroorchidism in FMR1 knockout mice is caused by increased Sertoli cell proliferation during testicular development
The fragile X syndrome is the most frequent hereditary form of mental
retardation. This X-linked disorder is, in most cases, caused by an
unstable and expanding trinucleotide CGG repeat located in the
5'-untranslated region of the gene involved, the fragile X mental
retardation 1 (FMR1) gene. Expansion of the CGG repeat to a length of more
than 200 trinucleotides results in silencing of the FMR1 gene promoter
and, thus, in an inactive gene. The clinical features of male fragile X
patients include mental retardat
Spatial learning, contextual fear conditioning and conditioned emotional response in Fmr1 knockout mice
Generalized glycogen storage and cardiomegaly in a knockout mouse model of Pompe disease
Glycogen storage disease type II (GSDII; Pompe disease), caused by
inherited deficiency of acid alpha-glucosidase, is a lysosomal disorder
affecting heart and skeletal muscles. A mouse model of this disease was
obtained by targeted disruption of the murine acid alpha-glucosidase gene
(Gaa) in embryonic stem cells. Homozygous knockout mice (Gaa -/-) lack Gaa
mRNA and have a virtually complete acid alpha-glucosidase deficiency.
Glycogen-containing lysosomes are detected soon after birth in liver,
heart and skeletal muscle cells. By 13 weeks of age, large focal deposits
of glycogen have formed. Vacuolar spaces stain positive for acid
phosphatase as a sign of lysosomal pathology. Both male and female
knockout mice are fertile and can be intercrossed to produce progeny. The
first born knockout mice are at present 9 months old. Overt clinical
symptoms are still absent, but the heart is typically enlarged and the
electrocardiogram is abnormal. The mouse model will help greatly to
understand the pathogenic mechanism of GSDII and is a valuable instrument
to explore the efficacy of different therapeutic interventions
Instability of a (CGG)98 repeat in the Fmr1 promoter
Fragile X syndrome is one of 14 trinucleotide repeat diseases. It arises
due to expansion of a CGG repeat which is present in the 5'-untranslated
region of the FMR1 gene, disruption of which leads to mental retardation.
The mechanisms involved in trinucleotide repeat expansion are poorly
understood and to date, transgenic mouse models containing transgenic
expanded CGG repeats have failed to reproduce the instability seen in
humans. As both cis-acting factors and the genomic context of the CGG
repeat are thought to play a role in expansion, we have now generated a
knock-in mouse Fmr1 gene in which the murine (CGG)8 repeat has been
exchanged with a human (CGG)98 repeat. Unlike other CGG transgenic models,
this model shows moderate CGG repeat instability upon both in maternal and
paternal transmission. This model will now enable us to study the timing
and the mechanism of repeat expansion in mice
The fragile X-related proteins FXR1P and FXR2P contain a functional nucleolar-targeting signal equivalent to the HIV-1 regulatory proteins
Fragile X syndrome is caused by the absence of the fragile X
mental-retardation protein (FMRP). FMRP and the fragile X-related proteins
1 and 2 (FXR1P and FXR2P) form a gene family with functional similarities,
such as RNA binding, polyribosomal association and nucleocytoplasmic
shuttling. In a previous study, we found that FMRP and FXR1P shuttle
between cytoplasm and nucleoplasm, while FXR2P shuttles between cytoplasm
and nucleolus. The nuclear and nucleolar-targeting properties of these
proteins were investigated further. Here, we show that FXR2P contains in
its C-terminal part, a stretch of basic amino acids 'RPQRRNRSRRRRFR' that
resemble the nucleolar-targeting signal (NoS) of the viral protein Rev.
This particular sequence is also present within exon 15 of the FXR1 gene.
This exon undergoes alternative splicing and is therefore only present in
some of the FXR1P isoforms. We investigated the intracellular distribution
of various FXR1P isoforms with (iso-e and iso-f) and without (iso-d) the
potential NoS in transfected COS cells treated with the nuclear export
inhibitor leptomycin-B. Both iso-e and iso-f showed a nucleolar
localization, as observed for FXR2P; iso-d was detected in the
nucleo-plasm outside the nucleoli. Further, when a labelled 16-residue
synthetic peptide corresponding to the NoS of FXR1P was added to human
fibroblast cultures a clear nucleolar signal was observed. Based on these
data we argue that the intranuclear distribution of FXR2P and FXR1P
isoforms is very likely to be mediated by a similar NoS localized in their
C-terminal region. This domain is absent in some FXR1P isoforms as well as
in all FMRP isoforms, suggesting functional differences for this family of
proteins, possibly related to RNA metabolism in different tissues
Different targets for the fragile X-related proteins revealed by their distinct nuclear localizations
Fragile X syndrome is caused by the absence of the fragile X mental
retardation protein (FMRP). FMRP and its structural homologues FXR1P and
FXR2P form a family of RNA-binding proteins (FXR proteins). The three
proteins associate with polyribosomes as cytoplasmic mRNP particles. Here
we show that small amounts of FMRP, FXR1P and FXR2P shuttle between
cytoplasm and nucleus. Mutant FMRP of a severely affected fragile X
patient (FMRPI304N) does not associate with polyribosomes and shuttles
more frequently than normal FMRP, indicating that the association with
polyribosomes regulates the shuttling process. Using leptomycin B we
demonstrate that transport of the FXR proteins out of the nucleus is
mediated by the export receptor exportin1. Finally, inactivation of the
nuclear export signal in two FXR proteins shows that FMRP shuttles between
cytoplasm and nucleoplasm, while FXR2P shuttles between cytoplasm and
nucleolus. Therefore, molecular dissection of the shuttling routes used by
the FXR proteins suggests that they transport different RNAs
Characterization and localization of the FMR-1 gene product associated with fragile X syndrome
THE fragile X syndrome is the most frequent form of inherited mental retardation after Down's syndrome, having an incidence of one in 1,250 males1,2. The fragile X syndrome results from amplification of the CGG repeat found in the FMR-1 gene3–6. This CGG repeat shows length variation in normal individuals and is increased significantly in both carriers and patients3–6; it is located 250 base pairs distal to a CpG island6 which is hypermethylated in fragile X patients4–7. The methylation probably results in downregulation of FMR-1 gene expression8. No information can be deduced about the function of the FMR-1 protein from its predicted sequence. Here we investigate the nature and function of the protein encoded by the FMR-1 gene using polyclonal antibodies raised against the predicted amino-acid sequences. Four different protein products, possibly resulting from alternative splicing, have been identified by immunoblotting in lymphoblastoid cell lines of healthy individuals. All these proteins were missing in cell lines from patients not expressing FMR-1 messenger RNA. The intracellular localization of the FMR-1 gene products was investigated by transient expression in COS-1 cells and found to be cytoplasmic. Localization was also predominantly cytoplasmic in the epithelium of the oesophagus, but in some cells was obviously nuclear
Knockout mouse model for Fxr2: a model for mental retardation
Fragile X syndrome is a common form of mental retardation caused by the
absence of the FMR1 protein, FMRP. Fmr1 knockout mice exhibit a phenotype
with some similarities to humans, such as macro-orchidism and behavioral
abnormalities. Two homologs of FMRP have been identified, FXR1P and FXR2P.
These proteins show high sequence similarity, including all functional
domains identified in FMRP, such as RNA binding domains. They have an
overlap in tissue distribution to that of FMRP. Interactions between the
three FXR proteins have also been described. FXR2P shows high expression
in brain and testis, like FMRP. To study the function of FXR2P, we
generated an Fxr2 knockout mouse model. No pathological differences
between knockout and wild-type mice were found in brain or testis. Given
the behavioral phenotype in fragile X patients and the phenotype
previously reported for the Fmr1 knockout mouse, we performed a thorough
evaluation of the Fxr2 knockout phenotype using a behavioral test battery.
Fxr2 knockout mice were hyperactive (i.e. traveled a greater distance,
spent more time moving and moved faster) in the open-field test, impaired
on the rotarod test, had reduced levels of prepulse inhibition, displayed
less contextual conditioned fear, impaired at locating the hidden platform
in the Morris water task and were less sensitive to a heat stimulus.
Interestingly, there are some behavioral phenotypes in Fxr2 knockout mice
which are similar to those observed in Fmr1 knockout mice, but there are
also some different behavioral abnormalities that are only observed in the
Fxr2 mutant mice. The findings implicate a role for Fxr2 in central
nervous system function