Aging mice have increased chromosome instability that is exacerbated by elevated Mdm2 expression

Detection of genomic structure variants associated with wrinkled skin in Xiang pig by next generation sequencing

Wrinkling is prominent manifestation of aging skin. A mutant phenotype characterized by systemic wrinkles and thickened skin was discovered in Xiang pig populations with incidence about 1-3%. The feature in histological structure was epidermal hyperplasia and thickening, collagen fibers disorder. To uncover genetic mechanisms for the mutant phenotype of Xiang pigs with systemic wrinkle (WXP), a genome-wide of structural variations (SVs) in WXP was described by next generation resequencing, taking Xiang pigs (XP) and European pigs (EUP) as compares. Total of 32,308 SVs were detected from three pig groups and 965 SVs were identified specifically from WXP, involving 481 protein-coding genes. These genes were mainly enriched in nuclear structure, ECM components and immunomodulatory pathways. According to gene function and enrichment analysis, we found that 65 candidate SVs in 59 protein genes were probably related with the systemic wrinkle of WXP. Of these, several genes are reported to be associate with aging, such as EIF4G2, NOLC1, XYLT1, FUT8, MDM2 and so on. The insertion/deletion and duplication variations of SVs in these genes resulted in the loss of stop-codon or frameshift mutation, and aberrant alternative splicing of transcripts. These genes are involved in cell lamin filament, intermediate filament cytoskeleton, supramolecular complex, cell differentiation and regulation of macromolecule metabolic process etc. Our study suggested that the loss of function or aberrant expression of these genes lead to structural disorder of nuclear and the extracellular matrix (ECM) in skin cells, which probably was the genetic mechanisms for the mutant phenotype of systemic skin wrinkle of Xiang pig.

Chromosomal Instability in Acute Myeloid Leukemia

Chromosomal instability (CIN), the increasing rate in which cells acquire new chromosomal alterations, is one of the hallmarks of cancer. Many studies highlighted CIN as an important mechanism in the origin, progression, and relapse of acute myeloid leukemia (AML). The ambivalent feature of CIN as a cancer-promoting or cancer-suppressing mechanism might explain the prognostic variability. The latter, however, is described in very few studies. This review highlights the important CIN mechanisms in AML, showing that CIN signatures can occur largely in all the three major AML types (de novo AML, secondary-AML, and therapy-related-AML). CIN features in AML could also be age-related and reflect the heterogeneity of the disease. Although most of these abnormalities show an adverse prognostic value, they also offer a strong new perspective on personalized therapy approaches, which goes beyond assessing CIN in vitro in patient tumor samples to predict prognosis. Current and emerging AML therapies are exploring CIN to improve AML treatment, which includes blocking CIN or increasing CIN beyond the limit threshold to induce cell death. We argue that the characterization of CIN features, not included yet in the routine diagnostic of AML patients, might provide a better stratification of patients and be extended to a more personalized therapeutic approach.

Distinct genomic profile in h. pylori-associated gastric cancer

Gastric cancer is one of the most common and deadly cancer types. Currently, four subtypes have been identified with unique molecular alterations: Epstein–Barr virus (EBV)‐positive, microsatellite instability (MSI), chromosomal instability (CIN), and genomic stable (GS) tumors. Notably, many gastric tumors are associated with the bacterium Helicobacter pylori but the genomic landscape of this subgroup of tumors remains largely unknown. Targeted sequencing covering 425 genes was performed retrospectively on 1703 gastric tumor tissues and matched normal blood samples. Nonsynonymous mutations, copy‐number variation (CNV), and MSI status were called from human DNA reads; nonhuman DNA reads were mapped to NCBI microbial reference genome using Kraken and significant species were identified. Overall, 37 (2.76%) from a total of 1703 samples were EBV‐positive, 200 (11.74%) samples were H. pylori‐positive, and 10 samples were positive for both. Among the rest, 59 (3.46%) samples were MSI, 380 (22.31%) were CIN, and 1017 (59.72%) were GS. Most of the 200 H. pylori‐positive samples tend to be genome stable (85.5%, p < 0.001) and microsatellite stable (95%, p = 0.04). Compared to 1017 GS tumors, mutations in AKT3, EPAS1, MLH1, and BKT and amplifications of NFE2L2, TERC, MCL1, and TOP1 were significantly enriched in H. pylori‐positive tumors. And compared to EBV‐positive tumors, mutations in PIK3CA, ARID1A, and PTEN were significantly depleted in H. pylori‐positive subtype while TP53 mutations were enriched. This study characterized the unique genomic landscape of H. pylori‐positive gastric tumors using targeted panel sequencing. The successful identification of DNA reads from infectious agents in tumor samples indicates that deep sequencing is a promising way to uncover characteristics of microbial environment in tumors.

Targeting Mouse Double Minute 2: Current Concepts in DNA Damage Repair and Therapeutic Approaches in Cancer

Defects in DNA damage repair may cause genome instability and cancer development. The tumor suppressor gene p53 regulates cell cycle arrest to allow time for DNA repair. The oncoprotein mouse double minute 2 (MDM2) promotes cell survival, proliferation, invasion, and therapeutic resistance in many types of cancer. The major role of MDM2 is to inhibit p53 activity and promote its degradation. In this review, we describe the influence of MDM2 on genomic instability, the role of MDM2 on releasing p53 and binding DNA repair proteins to inhibit repair, and the regulation network of MDM2 including its transcriptional modifications, protein stability, and localization following DNA damage in genome integrity maintenance and in MDM2-p53 axis control. We also discuss p53-dependent and p53 independent oncogenic function of MDM2 and the outcomes of clinical trials that have been used with clinical inhibitors targeting p53-MDM2 to treat certain cancers.

MAP9 Loss Triggers Chromosomal Instability, Initiates Colorectal Tumorigenesis, and Is Associated with Poor Survival of Patients with Colorectal Cancer

PURPOSE

Chromosomal instability (CIN) is a common phenomenon in colorectal cancer, but its role and underlying cause remain unknown. We have identified that mitotic regulator microtubule-associated protein 9 (MAP9) is a critical regulator of CIN in colorectal cancer. We thus studied the effect of MAP9 loss on colorectal cancer in Map9-knockout mice and in cell lines.

EXPERIMENTAL DESIGN

We generated colon epithelial-specific Map9-knockout mice and evaluated colorectal cancer development. Effect of Map9 knockout on colorectal cancer progression was determined in chemical or Apc^{Min /+} -induced colorectal cancer. Molecular mechanism of MAP9 was determined using spectral karyotyping, microtubule assays, and whole-genome sequencing (WGS). Clinical significance of MAP9 was examined in 141 patients with CRC.

RESULTS

Spontaneous colonic tumors (9.1%) were developed in colon epithelium-specific Map9-knockout mice at 17 months, but none was observed in wild-type littermates. Map9 deletion accelerated colorectal cancer formation both in Apc^{Min /+} mice and azoxymethane-treated mice, and reduced survival in Apc^{Min /+} mice. Mechanistically, MAP9 stabilized microtubules and mediated mitotic spindle assembly. MAP9 also maintained the spindle pole integrity and protected K-fiber from depolymerization at spindle poles. MAP9 loss induced severe mitosis failure, chromosome segregation errors, and aneuploidy, leading to transformation of normal colon epithelial cells. WGS confirmed enhanced CIN in intestinal tumors from Map9 knockout Apc^{Min /+} mice. In patients with colorectal cancer, MAP9 was frequently silenced and its downregulation was associated with poor survival.

CONCLUSIONS

MAP9 is a microtubule stabilizer that contributes to spindle stability and inhibits colorectal tumorigenesis, supporting the role of MAP9 as a tumor suppressor for preventing CIN in colorectal cancer.

Depletion of Limiting rDNA Structural Complexes Triggers Chromosomal Instability and Replicative Aging of Saccharomyces cerevisiae

Sir2 is a highly conserved NAD+-dependent histone deacetylase that functions in heterochromatin formation and promotes replicative life span (RLS) in the budding yeast, Saccharomyces cerevisiae Within the yeast rDNA locus, Sir2 is required for efficient cohesin recruitment and maintaining the stability of the tandem array. In addition to the previously reported depletion of Sir2 in replicatively aged cells, we discovered that subunits of the Sir2-containing complexes silent information regulator (SIR) and regulator of nucleolar silencing and telophase (RENT) were depleted. Several other rDNA structural protein complexes also exhibited age-related depletion, most notably the cohesin complex. We hypothesized that mitotic chromosome instability (CIN) due to cohesin depletion could be a driver of replicative aging. Chromatin immunoprecipitation assays of the residual cohesin (Mcd1-Myc) in moderately aged cells showed strong depletion from the rDNA and initial redistribution to the point centromeres, which was then lost in older cells. Despite the shift in cohesin distribution, sister chromatid cohesion was partially attenuated in aged cells and the frequency of chromosome loss was increased. This age-induced CIN was exacerbated in strains lacking Sir2 and its paralog, Hst1, but suppressed in strains that stabilize the rDNA array due to deletion of FOB1 or through caloric restriction. Furthermore, ectopic expression of MCD1 from a doxycycline-inducible promoter was sufficient to suppress rDNA instability in aged cells and to extend RLS. Taken together, we conclude that age-induced depletion of cohesin and multiple other nucleolar chromatin factors destabilize the rDNA locus, which then results in general CIN and aneuploidy that shortens RLS.

CIN and Aneuploidy: Different Concepts, Different Consequences

Chromosomal instability (CIN) and aneuploidy are similar concepts but not synonymous. CIN is the process that leads to chromosome copy number alterations, and aneuploidy is the result. While CIN and resulting aneuploidy often cause growth defects, they are also selected for in cancer cells. Although such contradicting fates may seem paradoxical at first, they can be better understood when CIN and aneuploidy are assessed separately, taking into account the in vitro or in vivo context, the rate of CIN, and severity of the aneuploid karyotype. As CIN can only be measured in living cells, which proves to be technically challenging in vivo, aneuploidy is more frequently quantified. However, CIN rates might be more predictive for tumor outcome than assessing aneuploidy rates alone. In reviewing the literature, we therefore conclude that there is an urgent need for new models in which we can monitor chromosome mis-segregation and its consequences in vivo. Also see the video abstract here: https://youtu.be/fL3LxZduchg.

Role of Mdm2 and Mdmx in DNA repair

Mdm2 and Mdmx are critical regulators of the p53 tumour suppressor and are overexpressed in many human malignancies. However, in recent years, their impact on genome instability was shown to be at least, in part, independent of p53. Both Mdm2 and Mdmx inhibit DNA break repair through their association with the Mre11/Rad50/Nbs1 DNA repair complex. Recent evidence indicates that harnessing Mdm2 and/or Mdmx-mediated inhibition of DNA break repair in cancer cells could provide a therapeutic opportunity, particularly for those malignancies that have lost functional p53.

Anatomy of Mdm2 and Mdm4 in evolution

Mouse double minute (Mdm) genes span an evolutionary timeframe from the ancient eukaryotic placozoa Trichoplax adhaerens to Homo sapiens, implying a significant and possibly conserved cellular role throughout history. Maintenance of DNA integrity and response to DNA damage involve many key regulatory pathways, including precise control over the tumour suppressor protein p53. In most vertebrates, degradation of p53 through proteasomal targeting is primarily mediated by heterodimers of Mdm2 and the Mdm2-related protein Mdm4 (also known as MdmX). Both Mdm2 and Mdm4 have p53-binding regions, acidic domains, zinc fingers, and C-terminal RING domains that are conserved throughout evolution. Vertebrates typically have both Mdm2 and Mdm4 genes, while analyses of sequenced genomes of invertebrate species have identified single Mdm genes, suggesting that a duplication event occurred prior to emergence of jawless vertebrates about 550–440 million years ago. The functional relationship between Mdm and p53 in T. adhaerens, an organism that has existed for 1 billion years, implies that these two proteins have evolved together to maintain a conserved and regulated function.

Modulation of the p53 family network by RNA-binding proteins

Since its discovery more than three decades ago, tumor suppressor p53 has been shown to play pivotal roles in both maintaining genomic integrity and tumor suppression. p53 functions as a transcription factor responding to a multitude of cellular stressors, regulating the transcription of many genes involved in cell-cycle arrest, senescence, autophagy, and apoptosis. Extensive work has revealed that p53 is one of the most commonly mutated tumor suppressor genes. The last three decades have demonstrated that p53 activity is controlled through transcriptional regulation and posttranslational modifications. However, evolving work is now uncovering that p53, and other p53 family members, are post-transcriptionally regulated by multiple RNA-binding proteins (RBPs). Understanding the regulation of p53 by RBPs may potentially open up the possibility for cancer therapeutic intervention. This review focuses on the posttranscriptional regulation of p53, and p53 family members, by RNA binding proteins and the reciprocal feedback pathways between several RNA-biding proteins modulating p53, and p53 family members.

Non-random aneuploidy specifies subgroups of pilocytic astrocytoma and correlates with older age

Pilocytic astrocytoma (PA) is the most common brain tumor in children but is rare in adults, and hence poorly studied in this age group. We investigated 222 PA and report increased aneuploidy in older patients. Aneuploid genomes were identified in 45% of adult compared with 17% of pediatric PA. Gains were non-random, favoring chromosomes 5, 7, 6 and 11 in order of frequency, and preferentially affecting non-cerebellar PA and tumors with BRAF V600E mutations and not with KIAA1549-BRAF fusions or FGFR1 mutations. Aneuploid PA differentially expressed genes involved in CNS development, the unfolded protein response, and regulators of genomic stability and the cell cycle (MDM2, PLK2),whose correlated programs were overexpressed specifically in aneuploid PA compared to other glial tumors. Thus, convergence of pathways affecting the cell cycle and genomic stability may favor aneuploidy in PA, possibly representing an additional molecular driver in older patients with this brain tumor.

Chromosomal instability: A common feature and a therapeutic target of cancer

Most cancer cells are aneuploid, containing abnormal numbers of chromosomes, mainly caused by elevated levels of chromosome missegregation, known as chromosomal instability (CIN). These well-recognized, but poorly understood, features of cancers have recently been studied extensively, unraveling causal relationships between CIN and cancer. Here we review recent findings regarding how CIN and aneuploidy occur, how they affect cellular functions, how cells respond to them, and their relevance to diseases, especially cancer. Aneuploid cells are under various kinds of stresses that result in reduced cellular fitness. Nevertheless, genetic heterogeneity derived from CIN allows the selection of cells better adapted to their environment, which supposedly facilitates generation and progression of cancer. We also discuss how we can exploit the properties of cancer cells exhibiting CIN for effective cancer therapy.

Genome Stability Requires p53

It is now clear that functional p53 is critical to protect the genome from alterations that lead to tumorigenesis. However, with the myriad of cellular stresses and pathways linked to p53 activation, much remains unknown about how p53 maintains genome stability and the proteins involved. The current understanding of the multiple ways p53 contributes to genome stability and how two of its negative regulators, Mdm2 and Mdmx, induce genome instability will be described.

Aneuploidy shortens replicative lifespan in Saccharomyces cerevisiae

Aneuploidy and aging are correlated; however, a causal link between these two phenomena has remained elusive. Here, we show that yeast disomic for a single native yeast chromosome generally have a decreased replicative lifespan. In addition, the extent of this lifespan deficit correlates with the size of the extra chromosome. We identified a mutation in BUL1 that rescues both the lifespan deficit and a protein trafficking defect in yeast disomic for chromosome 5. Bul1 is an E4 ubiquitin ligase adaptor involved in a protein quality control pathway that targets membrane proteins for endocytosis and destruction in the lysosomal vacuole, thereby maintaining protein homeostasis. Concurrent suppression of the aging and trafficking phenotypes suggests that disrupted membrane protein homeostasis in aneuploid yeast may contribute to their accelerated aging. The data reported here demonstrate that aneuploidy can impair protein homeostasis, shorten lifespan, and may contribute to age-associated phenotypes.

Mdm2 overexpression and p73 loss exacerbate genomic instability and dampen apoptosis, resulting in B-cell lymphoma

Many human tumors express high levels of the p53 inhibitor Mdm2, resulting from amplification of the Mdm2 locus or aberrant post-translational regulation of the Mdm2 protein. While the importance of Mdm2 in regulating p53 is clear, Mdm2 also has p53-independent roles. For example, overexpression of Mdm2 results in genomic instability in a p53-independent manner. In addition, Mdm2 has many additional binding partners; some such as the tumor suppressor p73 have also been implicated in genomic instability. In this study, cells and tumors with Mdm2 overexpression and p73 loss exhibit increased genomic instability as compared to either alteration alone and cooperate in development of B-cell lymphomagenesis. Cytogenetic analyses of mouse embryonic fibroblasts and pre-malignant B-cells demonstrate that loss of p73 exacerbates the chromosome breaks and fusions observed in Mdm2^Tg cells. B-cell lymphomas from Mdm2^Tg;p73+/− mice retain the remaining p73 allele, and exhibit elevated levels of the anti-apoptotic protein Bcl2 and thus dampen apoptosis. In summary, Mdm2 overexpression and p73 loss cooperate in genomic instability and tumor development, indicating that the oncogenic functions of Mdm2 are a combined effect of inhibiting p53 and p73 functions. Given that p73 is lost or silenced in human B-cell lymphomas [1–4], the Mdm2^Tg;p73+/− mouse serves as a model for human disease and may provide additional insight into the pathways that contribute to B-cell lymphomagenesis.

Aging and radiation: bad companions

Aging involves a deterioration of cell functions and changes that may predispose the cell to undergo an oncogenic transformation. The carcinogenic risks following radiation exposure rise with age among adults. Increasing inflammatory response, loss of oxidant/antioxidant equilibrium, ongoing telomere attrition, decline in the DNA damage response efficiency, and deleterious nuclear organization are age-related cellular changes that trigger a serious threat to genomic integrity. In this review, we discuss the mechanistic interplay between all these factors, providing an integrated view of how they contribute to the observed age-related increase in radiation sensitivity. As life expectancy increases and so it does the medical intervention, it is important to highlight the benefits of radiation protection in the elderly. Thus, a deep understanding of the mechanistic processes confining the threat of aging-related radiosensitivity is currently of foremost relevance.

Systems biology of cancer: entropy, disorder, and selection-driven evolution to independence, invasion and "swarm intelligence"

Our knowledge of the biology of solid cancer has greatly progressed during the last few years, and many excellent reviews dealing with the various aspects of this biology have appeared. In the present review, we attempt to bring together these subjects in a general systems biology narrative. It starts from the roles of what we term entropy of signaling and noise in the initial oncogenic events, to the first major transition of tumorigenesis: the independence of the tumor cell and the switch in its physiology, i.e., from subservience to the organism to its own independent Darwinian evolution. The development after independence involves a constant dynamic reprogramming of the cells and the emergence of a sort of collective intelligence leading to invasion and metastasis and seldom to the ultimate acquisition of immortality through inter-individual infection. At each step, the probability of success is minimal to infinitesimal, but the number of cells possibly involved and the time scale account for the relatively high occurrence of tumorigenesis and metastasis in multicellular organisms.

The Mdm network and its regulation of p53 activities: a rheostat of cancer risk

The potent transcriptional activity of p53 (Trp53, TP53) must be kept in check for normal cell growth and survival. Tumors, which drastically deviate from these parameters, have evolved multiple mechanisms to inactivate TP53, the most prevalent of which is the emergence of TP53 missense mutations, some of which have gain-of-function activities. Another important mechanism by which tumors bypass TP53 functions is via increased levels of two TP53 inhibitors, MDM2, and MDM4. Studies in humans and in mice reveal the complexity of TP53 regulation and the exquisite sensitivity of this pathway to small changes in regulation. Here, we summarize the factors that impinge on TP53 activity and thus cell death/arrest or tumor development.

MDM2 overexpression, activation of signaling networks, and cell proliferation

Frequent overexpression of MDM2 in human cancers suggests that the protein confers a survival advantage to cancer cells. However, overexpression of MDM2 in normal cells seems to restrict cell proliferation. This review discusses the cell growth regulatory functions of MDM2 in normal and genetically defective cells to assess how cancer cells evade the growth-restricting consequence of MDM2 overexpression. Similar to oncoproteins that induce a DNA damage response and oncogene induced senescence in non-transformed cells, MDM2 induces G1-arrest and intra-S phase checkpoint responses that control untimely DNA replication in the face of genetic challenges.

Increased expression of BubR1 protects against aneuploidy and cancer and extends healthy lifespan

The BubR1 gene encodes for a mitotic regulator that ensures accurate segregation of chromosomes through its role in the mitotic checkpoint and the establishment of proper microtubule-kinetochore attachments. Germline mutations that reduce BubR1 abundance cause aneuploidy, shorten lifespan, and induce premature aging phenotypes and cancer in both humans and mice. Reduced BubR1 expression is also a feature of chronological aging, but whether this age-related decline has biological consequences is unknown. Using a transgenic approach in mice, we show that sustained high expression of BubR1 preserves genomic integrity and reduces tumorigenesis, even in the presence of genetic alterations that strongly promote aneuplodization and cancer, such as oncogenic Ras. We find that BubR1 overabundance exerts its protective effect by correcting mitotic checkpoint impairment and microtubule-kinetochore attachment defects. Furthermore, sustained high expression of BubR1 extends lifespan and delays age-related deterioration and aneuploidy in several tissues. Collectively, these data uncover a generalized function for BubR1 in counteracting defects that cause whole chromosome instability and suggest that modulating BubR1 provides a unique opportunity to extend healthy lifespan.

Protecting the genome from mdm2 and mdmx

The contribution of Mdm2, and its recently identified family member Mdmx (Mdm4), to tumorigenesis has primarily focused on their negative regulation of the p53 tumor suppressor. Although Mdm2 and Mdmx clearly inhibit p53, which can lead to tumor development, both have also been shown to affect tumorigenesis independent of p53. Given that Mdm2 and/or Mdmx overexpression is common and likely underestimated in human cancers, understanding the functions of these proteins beyond p53 control is critical. In recent years, new functions of Mdm2 and Mdmx that lead to genome instability, a hallmark of malignancy, have emerged. Specifically, roles in the DNA damage response that are distinct from their regulation of p53 have been identified. Inhibition of p53 as well as other components of the DNA damage response by Mdm2 and Mdmx can result in delayed DNA repair and increased genome instability, making Mdm2 and Mdmx a danger to the genome when aberrantly expressed. However, the genome instability caused by altered levels of Mdm2 and Mdmx could be used therapeutically for the treatment of cancer. Specifically, drugs/small molecules that target the interaction between Mdm2 and p53 can stabilize Mdm2, resulting in negative consequences on the genome that could be exploited for cancer treatment, particularly malignancies lacking functional p53.

Splicing up mdm2 for cancer proteome diversity

Cancer cells often have high expression of Mdm2. However, in many cancers mdm2 is alternatively spliced, with more than 40 mRNA variants identified. Many of the alternative spliced mdm2 mRNAs have the potential to encode truncated Mdm2 isoforms. These putative Mdm2 isoforms can theoretically increase the diversity of the cancer proteome. The 3 best characterized are Mdm2-A, Mdm2-B, and Mdm2-C. As described in this review, the exogenous expression of these isoforms results in paradoxical phenotypes of transformation-associated growth as well as the inhibition of growth. Interestingly, these Mdm2 isoforms contribute tumor-promoting capacity in p53-null backgrounds. Herein we describe how alternative splicing of mdm2 may result in Mdm2 protein products that alter signal transduction to promote tumorigenesis. The tumor promoting capacity of Mdm2 isoforms is discussed in the context of functions that do not require the inhibition of p53. When N-terminal portions of Mdm2 are missing, the biochemical functions encoded by exon 12 are proposed to become more important. This may result in growth promoting functions when wild-type p53 is absent or compromised. The p53-independent tumor promoting activity of Mdm2 is proposed to result from C-terminal biochemical contributions of DNA binding, RNA binding, nucleolar localization, and nucleotide binding.

Decrease of p400 ATPase complex and loss of H2A.Z within the p21 promoter occur in senescent IMR-90 human fibroblasts

Replicative senescence in human diploid fibroblasts is characterised by an exhaustion of proliferative potential and permanent cell cycle arrest. During senescence, telomere shortening-generated DNA damage activates p53 pathway that upregulates cell cycle inhibitors, such as p21. Human p400 ATPase is a chromatin remodeller that plays a key role in the deposition of the histone variant, H2A.Z within the p21 promoter, repressing p21 gene expression. Decline of p400 ATPase in senescent IMR-90 cells prompted us to investigate structural changes in the chromatin of the p21 promoter during in vitro aging. Whereas doxorubicin treatment in early-passaged cells results in nucleosome density changes near the p53 binding sites of the p21 promoter, our studies show that senescent cells with a high p21 transcription activity had a comparable nucleosome distribution as unstressed young cells. However, H2A.Z that is highly enriched within the p21 promoter of young cells is depleted in senescent cells, suggesting that downregulation of p400 and loss of H2A.Z localisation play roles in relieving p21 gene repression in senescent IMR-90 cells. Taken together, our results indicate that age-dependent p400 downregulation and loss of H2A.Z localisation may contribute to the onset of replicative senescence through a sustained high rate of p21 transcription.

Engineering mouse models with myelodysplastic syndrome human candidate genes; how relevant are they?

Myelodysplastic syndromes represent particularly challenging hematologic malignancies that arise from a large spectrum of genetic events resulting in a disease characterized by a range of different presentations and outcomes. Despite efforts to classify and identify the key genetic events, little improvement has been made in therapies that will increase patient survival. Animal models represent powerful tools to model and study human diseases and are useful pre-clinical platforms. In addition to enforced expression of candidate oncogenes, gene inactivation has allowed the consequences of the genetic effects of human myelodysplastic syndrome to be studied in mice. This review aims to examine the animal models expressing myelodysplastic syndrome-associated genes that are currently available and to highlight the most appropriate model to phenocopy myelodysplastic syndrome disease and its risk of transformation to acute myelogenous leukemia.