Two forms of genetic instability have been described in colorectal cancer: microsatellite instability and chromosomal instability. Microsatellite instability results from mutations in mismatch repair genes; chromosomal instability is the hallmark of many colorectal cancers, although it is not completely understood at the molecular level. As truncations of the Adenomatous Polyposis Coli (APC) gene are found in most colorectal tumours, we thought that mutations in APC might be responsible for chromosomal instability. To test this hypothesis, we examined mouse embryonic stem (ES) cells homozygous for Min (multiple intestinal neoplasia) or Apc1638T alleles. Here we show that Apc mutant ES cells display extensive chromosome and spindle aberrations, providing genetic evidence for a role of APC in chromosome segregation. Consistent with this, APC accumulates at the kinetochore during mitosis. Apc mutant cells form mitotic spindles with an abundance of microtubules that inefficiently connect with kinetochores. This phenotype is recapitulated by the induced expression of a 253-amino-acid carboxy-terminal fragment of APC in microsatellite unstable colorectal cancer cells. We conclude that loss of APC sequences that lie C-terminal to the beta-catenin regulatory domain contributes to chromosomal instability in colorectal cancer.

The Wnt signal-transduction pathway induces the nuclear translocation of membrane-bound beta-catenin (Catnb) and has a key role in cell-fate determination. Tight somatic regulation of this signal is essential, as uncontrolled nuclear accumulation of beta-catenin can cause developmental defects and tumorigenesis in the adult organism. The adenomatous polyposis coli gene (APC) is a major controller of the Wnt pathway and is essential to prevent tumorigenesis in a variety of tissues and organs. Here, we have investigated the effect of different mutations in Apc on the differentiation potential of mouse embryonic stem (ES) cells. We provide genetic and molecular evidence that the ability and sensitivity of ES cells to differentiate into the three germ layers is inhibited by increased doses of beta-catenin by specific Apc mutations. These range from a severe differentiation blockade in Apc alleles completely deficient in beta-catenin regulation to more specific neuroectodermal, dorsal mesodermal and endodermal defects in more hypomorphic alleles. Accordingly, a targeted oncogenic mutation in Catnb also affects the differentiation potential of ES cells. Expression profiling of wildtype and Apc-mutated teratomas supports the differentiation defects at the molecular level and pinpoints a large number of downstream structural and regulating genes. Chimeric experiments showed that this effect is cell-autonomous. Our results imply that constitutive activation of the Apc/beta-catenin signaling pathway results in differentiation defects in tissue homeostasis, and possibly underlies tumorigenesis in the colon and other self-renewing tissues.

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Autism spectrum disorder (ASD) and schizophrenia (SCZ) are two common neurodevelopmental syndromes that result from the combined effects of environmental and genetic factors. We set out to test the hypothesis that rare variants in many different genes, including de novo variants, could predispose to these conditions in a fraction of cases. In addition, for both disorders, males are either more significantly or more severely affected than females, which may be explained in part by X-linked genetic factors. Therefore, we directly sequenced 111 X-linked synaptic genes in individuals with ASD (n = 142; 122 males and 20 females) or SCZ (n = 143; 95 males and 48 females). We identified > 200 non-synonymous variants, with an excess of rare damaging variants, which suggest the presence of disease-causing mutations. Truncating mutations in genes encoding the calcium-related protein IL1RAPL1 (already described in Piton et al. Hum Mol Genet 2008) and the monoamine degradation enzyme monoamine oxidase B were found in ASD and SCZ, respectively. Moreover, several promising non-synonymous rare variants were identified in genes encoding proteins involved in regulation of neurite outgrowth and other various synaptic functions (MECP2, TM4SF2/TSPAN7, PPP1R3F, PSMD10, MCF2, SLITRK2, GPRASP2, and OPHN1).

No abstract

Diseases affecting motor neurons, such as amyotrophic lateral sclerosis (Lou Gerhig's disease), hereditary spastic paraplegia and spinal bulbar muscular atrophy (Kennedy's disease) are a heterogeneous group of chronic progressive diseases and are among the most puzzling yet untreatable illnesses. Over the last decade, identification of mutations in genes predisposing to these disorders has provided the means to better understand their pathogenesis. The discovery 13 years ago of SOD1 mutations linked to ALS, which account for less than 2% of total cases, had a major impact in the field. However, despite intensive research effort, the pathways leading to the specific motor neurons degeneration in the presence of SOD1 mutations have not been fully identified. This review provides an overview of the genetics of both familial and sporadic forms of ALS.

Tissue engineering of large bone defects is approached through implantation of autologous osteogenic cells, generally referred to as multipotent stromal cells or mesenchymal stem cells (MSCs). Animal-derived MSCs successfully bridge large bone defects, but models for ectopic bone formation as well as recent clinical trials demonstrate that bone formation by human MSCs (hMSCs) is inadequate. The expansion phase presents an attractive window to direct hMSCs by pharmacological manipulation, even though no profound effect on bone formation in vivo has been described so far using this approach. We report that activation of protein kinase A elicits an immediate response through induction of genes such as ID2 and FosB, followed by sustained secretion of bone-related cytokines such as BMP-2, IGF-1, and IL-11. As a consequence, PKA activation results in robust in vivo bone formation by hMSCs derived from orthopedic patients.bone tissue engineering ͉ osteogenesis ͉ PKA signaling

Restless legs syndrome (RLS) is a common neurological disorder characterized by an irresistible urge to move the legs at night, which is often accompanied by unpleasant sensations. A recent genomewide association study identified an association between RLS and intronic markers from the MEIS1 gene. Comparative genomic analysis indicates that MEIS1 is the only gene encompassed in this evolutionarily conserved chromosomal segment, i.e. a conservation synteny block, from mammals to fish. We carried out a series of experiments to delineate the role of MEIS1 in RLS pathogenesis and the underlying genetic mechanism. We sequenced all 13 MEIS1 exons and their splice junctions in 285 RLS probands with confirmed clinical diagnosis and did not identify any causative coding or exon-intron junction mutations. We found no evidence of structural variation or disease-associated haplotype differential splicing. However, sequencing of conserved regions of MEIS1 introns 8 and 9 identified a novel single nucleotide polymorphism (C13B_2) significantly associated with RLS (allelic association, P = 1.81E-07). We detected a significant decrease in MEIS1 mRNA expression by quantitative real-time polymerase chain reaction in lymphoblastoid cell lines (LCLs) and brain tissues from RLS patients homozygous for the intronic RLS risk haplotype, compared with those homozygous for the non-risk haplotype. Finally, we found significantly decreased MEIS1 protein levels in the same batch of LCLs and brain tissues from the homozygous carriers of the risk haplotype, compared with the homozygous non-carriers. Therefore, these data suggest that reduced expression of the MEIS1 gene, possibly through intronic cis-regulatory element(s), predisposes to RLS.