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Hutchinson–Gilford progeria syndrome (HGPS) is a lethal premature and accelerated aging disease caused by a de novo point mutation in LMNA encoding A‐type lamins. Progerin, a truncated and toxic prelamin A issued from aberrant splicing, accumulates in HGPS cells' nuclei and is a hallmark of the disease. Small amounts of progerin are also produced during normal aging. We show that progerin is sequestered into abnormally shaped promyelocytic nuclear bodies, identified as novel biomarkers in late passage HGPS cell lines. We found that the proteasome inhibitor MG132 induces progerin degradation through macroautophagy and strongly reduces progerin production through downregulation of SRSF‐1 and SRSF‐5 accumulation, controlling prelamin A mRNA aberrant splicing. MG132 treatment improves cellular HGPS phenotypes. MG132 injection in skeletal muscle of Lmna G609G/G609G mice locally reduces SRSF‐1 expression and progerin levels. Altogether, we demonstrate progerin reduction based on MG132 dual action and shed light on a promising class of molecules toward a potential therapy for children with HGPS. Synopsis Progerin is a toxic protein that accumulates in the nuclei of Progeria patients' cells, sequestered in abnormal PML‐NBs. The proteasome inhibitor MG132 is shown to degrade progerin by activating autophagy and transcriptional inhibition through SRSF‐1 and SRSF‐5 splicing regulation. Ubiquitinylated progerin is sequestered into abnormal ProMyelocytic Leukemia Nuclear Bodies (PML‐NBs). Progerin reduction is based on MG132 dual action: autophagy activation and splicing regulation. MG132 in vitro treatment rescues most of the biological hallmarks of progeria. MG132 local treatment efficiently reduces progerin levels in vivo , in the Lmna G609G/G609G mouse model. The powerful and dual activities of MG132 make it a promising drug towards a future and safe therapeutic development for Progeria and related Prelamin‐A processing defective diseases. Graphical Abstract Progerin is a toxic protein that accumulates in the nuclei of Progeria patients' cells, sequestered in abnormal PML‐NBs. The proteasome inhibitor MG132 is shown to degrade progerin by activating autophagy and transcriptional inhibition through SRSF‐1 and SRSF‐5 splicing regulation.

Rapid growth of the embryonic heart occurs by addition of progenitor cells of the second heart field to the poles of the elongating heart tube. Failure or perturbation of this process leads to congenital heart defects. In order to provide further insight into second heart field development we characterized the insertion site of a transgene expressed in the second heart field and outflow tract as the result of an integration site position effect. Here we show that the integration site of the A17-Myf5-nlacZ-T55 transgene lies upstream of Hes1, encoding a basic helix-loop-helix containing transcriptional repressor required for the maintenance of diverse progenitor cell populations during embryonic development. Transgene expression in a subset of Hes1 expression sites, including the CNS, pharyngeal epithelia, pericardium, limb bud and lung endoderm suggests that Hes1 is the endogenous target of regulatory elements trapped by the transgene. Hes1 is expressed in pharyngeal endoderm and mesoderm including the second heart field. Analysis of Hes1 mutant hearts at embryonic day 15.5 reveals outflow tract alignment defects including ventricular septal defects and overriding aorta. At earlier developmental stages, Hes1 mutant embryos display defects in second heart field proliferation, a reduction in cardiac neural crest cells and failure to completely extend the outflow tract. Hes1 is expressed in cardiac progenitor cells in the early embryo and is required for development of the arterial pole of the heart.

Unbalanced translocations, that involve the proximal chromosome 15 long arm and the telomeric region of a partner chromosome, result in a karyotype of 45 chromosomes with monosomy of the proximal 15q imprinted region. Here, we present our analysis of eight such unbalanced translocations that, depending on the parental origin of the rearranged chromosome, were associated with either Prader–Willi or Angelman syndrome. First, using FISH with specific BAC clones, we characterized the chromosome 15 breakpoint of each translocation and demonstrate that four of them are clustered in a small 460 kb interval located in the proximal 15q14 band. Second, analyzing the sequence of this region, we demonstrate the proximity of a low-copy repeat 15 (LCR15)-duplicon element that is known to facilitate recombination events at meiosis and to promote rearrangements. The presence, in this region, of both a cluster of translocation breakpoints and a LCR15-duplicon element defines a new breakpoint cluster (BP6), which, to our knowledge, is the most distal breakpoint cluster described in proximal 15q. Third, we demonstrate that the breakpoints for other rearrangements including large inv dup (15) chromosomes do not map to BP6, suggesting that it is specific to translocations. Finally, the translocation breakpoints located within BP6 result in very large proximal 15q deletions providing new informative genotype–phenotype correlations.

The Chudley–Lowry syndrome (ChLS, MIM 309490) is an X-linked recessive condition characterized by moderate to severe mental retardation, short stature, mild obesity, hypogonadism, and distinctive facial features characterized by depressed nasal bridge, anteverted nares, inverted-V-shaped upper lip, and macrostomia. The original Chudley–Lowry family consists of three affected males in two generations. Linkage analysis had localized the gene to a large interval, Xp21–Xq26 and an obligate carrier was demonstrated to have highly skewed X inactivation. The combination of the clinical phenotype, consistent with that of the patients with ATR-X syndrome, the skewed X-inactivation pattern in a carrier female, as well as the mapping interval including band Xq13.3, prompted us to consider the XNP/ATR-X gene being involved in this syndrome. Using RT-PCR analysis, we screened the entire XNP/ATR-X gene and found a mutation in exon 2 (c.109C>T) giving rise to a stop codon at position 37 (p.R37X). Western blot and immunocytochemical analyses using a specific monoclonal antibody directed against XNP/ATR-X showed the protein to be present in lymphoblastoid cells from one affected male, despite the premature stop codon. To explain these discordant results, we further analyzed the 5′ region of the XNP/ATR-X gene and found three alternative transcripts, which differ in the presence or absence of exon 2, and the length of exon 1. Our data suggest that ChLS is allelic to the ATR-X syndrome with its less severe phenotype being due to the presence of some XNP/ATR-X protein.

By systematic analysis of a human testis library, we have isolated the hH-Rev107-3 cDNA, identical to hH-Rev107-1 cDNA, which was previously described as a class II tumor suppressor gene. In this study, two transcripts (1 and 0.8 kb) were detected by Northern blot in all human tissues, excepted in thymus. The strongest expression was found in testis, skeletal muscle and heart. These two mRNA are probably transcribed from only one gene that we mapped to the q12-q13 region of the chromosome 11. In human testis, hH-Rev107 gene expression was localized, by in situ hybridization, within the round spermatids. To investigate a possible role for hH-Rev107 protein in testicular malignant growth, we examined the expression of this gene in germ cell tumors. A strong hH-Rev107 gene expression was observed in normal testis as well as in samples with preinvasive carcinoma in situ but was completely absent in overt tumors, both seminomas and non-seminomas. By in situ hybridization, CIS was found hH-Rev107 positive and tumor negative. A semi-quantitative assessment of hH-Rev107 mRNA level in testicular germ cell tumors, by RT-PCR, exhibited a ninefold decrease in the gene expression. No gross structural aberrations of hH-Rev107 gene were detected in these human primary tumors. The results suggest that down-regulation of hH-Rev107 may be associated with invasive progression of testicular germ cell tumors.

The I mmunodeficiency, C entromeric instability, and F acial (ICF) syndrome is a rare autosomal recessive disorder that results from mutations in the DNMT3B gene, encoding a DNA-methyltransferase that acts on GC-rich satellite DNAs. This syndrome is characterized by immunodeficiency, facial dysmorphy, mental retardation of variable severity and chromosomal abnormalities that essentially involve juxtacentromeric heterochromatin of chromosomes 1 and 16. These abnormalities demonstrate that hypomethylation of satellite DNA can induce alterations in the structure of heterochromatin. In order to investigate the effect of DNA hypomethylation on heterochromatin organization, we analyzed the in vivo distribution of HP1 proteins, essential components of heterochromatin, in three ICF patients. We observed that, in a large proportion of ICF G2 nuclei, all HP1 isoforms show an aberrant signal concentrated into a prominent bright focus that co-localizes with the undercondensed 1qh or 16qh heterochromatin. We found that SP100, SUMO-1 and other proteins from the promyelocytic leukemia nuclear bodies (NBs) form a large body that co-localizes with the HP1 signal. This is the first description of altered nuclear distribution of HP1 proteins in the constitutional ICF syndrome. Our results show that satellite DNA hypomethylation does not prevent HP1 proteins from associating with heterochromatin. They suggest that, at G2 phase, HP1 proteins are involved in the heterochromatin condensation and may therefore remain concentrated at these sites until the condensation is complete. They also indicate that proteins from the NB could play a role in this process. Finally, satellite DNA length polymorphism could affect the efficiency of heterochromatin condensation and thus contribute to the variability of the ICF phenotype.

Identifying the genes responsible for isolated deafness in man is an important challenge. Nearly one in every 1000 children is affected by hearing impairment at birth or before 2 years of age, that is, in the prelingual period. Of these cases, approximately 65% are genetically determined, and the vast majority of these (80%) are inherited in an autosomal recessive mode (DFNB forms). To date, 22 DFNB loci have been identified. With the exception of the DFNB1 form, which accounts for about half of the cases of prelingual deafness (Denoyelle et al. 1997; Estivill et al. 1998), most of the other deafness loci are represented with only one or few affected families. As a result, most of the localization intervals are too large to undertake the identification of the corresponding genes by a positional cloning strategy. To circumvent these difficulties, we recently developed a candidate gene approach based on the isolation of genes specifically expressed in the cochlea. The products of these genes are indeed likely to play a crucial role in the development and/or the function of the inner ear, and could underlie deafness (Petit 1996). We therefore undertook the construction of a mouse cochlea subtracted cDNA library, following the representational difference analysis method (Hubank and Schatz 1994). By this approach, we first identified a gene encoding a protein related to mucin, which we named otogelin (Otgn), which is specifically expressed in the inner ear. Immunofluorescence studies demonstrated that this protein is a component of all the acellular membranes of the inner ear (Cohen-Salmon et al. 1997). The acellular membranes of the inner ear, that is, the tectorial membrane in the cochlea, the otoconial membrane in the utricule, the saccule, and the cupula of the semicircular canal in the vestibule, are acellular gelatinous structures covering the neuroepithelia. Their displacement relative to the neuroepithelia, induced either by the sound in the cochlea or by movements of the head or gravity in the vestibule, leads to the deflection of the sensory hair cell stereocilia bundle, which in turn opens the mechanotransduction canal (Hudspeth and Corey 1977; Denk and Holt 1995). These membranes have been reported to be composed of collagenase-sensitive (collagens type II, V, IX), and -insensitive proteins (Richardson et al. 1987; Thalmann et al. 1987). Belonging to this last category, three proteins specific to the inner ear have been identified up to now in mouse, the alpha - and beta -tectorins (Legan et al. 1997) and otogelin (Cohen-Salmon et al. 1997). Recently, mutations in the human alpha -tectorin gene TECTA have been shown to cause an autosomal dominant form of nonsyndromic deafness, DFNA12 (Verhoeven et al. 1998). In order to investigate whether otogelin could be involved in hearing impairment in mouse and/or human, we mapped the corresponding genes on mouse and human chromosomes. Localization on the mouse chromosomes was performed by fluorescence in situ hybridization on 50 metaphase spreads prepared from a WNP male mouse, in which all the autosomes except Chr 19 were in the form of metacentric Robertsonian translocations (Bonhomme and Guenet 1989). A 4.2-kb Otgn cDNA fragment (position 3174 to 7467) was used as probe. Specific labeling of the two Chr 7, in the 7B4-7C region, was observed in 44 metaphases (Fig. 1). So far, no deafness locus has been mapped to this chromosomal region (Steel 1995).

Sliding between adjacent microtubules within the axonema gives rise to the motility of cilia and flagella. The driving force is produced by dynein complexes which are mainly composed of the axonemal dynein heavy chains. We used cells of human respiratory epithelium after in vitro ciliogenesis to clone cDNA fragments of nine dynein heavy chain genes, one of which had never been identified before. Dynein heavy chains are highly conserved from protozoa to human and the evolutionary ancestry of these dynein heavy chain cDNA fragments was deduced by phylogenetic analysis. These dynein heavy chain cDNAs are highly transcribed in human tissues containing axonema such as trachea, testis and brain, but not in adult heart or placenta. PAC clones containing dynein heavy chains were obtained and used to determine by FISH their chromosomal position in the human genome. They were mapped to 2p12-p11, 2q33, 3p21.2-p21.1, 13q14, 16p12 and 17p12. The chromosomal assignment of these dynein heavy chain genes which was confirmed by GeneBridge 4 radiation hybrid screening, will be extremely useful for linkage analysis efforts in patients with primary ciliary dyskinesia (PCD).

Marfan syndrome (MFS), one of the most common genetic disorders of connective tissue, is characterized by skeletal, cardiovascular and ocular abnormalities. The incidence of the disease is about 1 in 20,000, with life expectancy severely reduced because of cardiovascular complications. As the underlying defect is unknown, MFS diagnosis is based solely on clinical criteria. Certain phenotypic features of MFS are also shared by other conditions, which may be genetically distinct entities although part of a clinical continuum. Immunohistochemical studies have implicated fibrillin, a major component of elastin-associated microfibrils, in MFS aetiology. Genetic linkage analysis with random probes has independently localized the MFS locus to chromosome 15. Here we report that these two experimental approaches converge with the cloning and mapping of the fibrillin gene to chromosome 15q15-21, and with the establishment of linkage to MFS. We also isolated a second fibrillin gene and mapped it to chromosome 5q23-31. We linked this novel gene to a condition, congenital contractural arachnodactyly, that shares some of the features of MFS. Thus, the cosegregation of two related genes with two related syndromes implies that fibrillin mutations are likely to be responsible for different MFS phenotypes.

TSPY, a candidate gene for a factor that promotes gonadoblastoma formation (GBY), is a testis-specific multicopy gene family in the male-specific region of the human Y (MSY) chromosome. Although it was originally proposed that male-specific genes on the Y originated from a transposed copy of an autosomal gene (Lahn & Page 1999b), at least two male-specific genes (RBMY and SRY) descended from a formerly recombining X-Y identical gene pair. Here we show that a TSPY homologue with similar gene structure lies in conserved positions, close to SMCX, on the X chromosome in human (TSPX ) and mouse (Tspx). TSPX is widely expressed and subject to X inactivation. TSPX and TSPY therefore evolved from an identical gene pair on the original mammalian sex chromosomes. This supports the hypothesis that even male-specific genes on the Y chromosome may have their origin in ubiquitously expressed genes on the X. It also strengthens the case for TSPY as a candidate for GBY, since independent functional studies link TSPX to cell cycle regulation.