Abnormal centrosome-centriole cycle in chronic myeloid leukaemia?

Extra centrosomes delay DNA damage-driven tumorigenesis

Deregulated centrosome numbers are frequently found in human cancer and can promote malignancies in model organisms. Current research aims to clarify if extra centrosomes are cause or consequence of malignant transformation, and if their biogenesis can be targeted for therapy. Here, we show that oncogene-driven blood cancer is inert to genetic manipulation of centrosome numbers, whereas the formation of DNA damage-induced malignancies is delayed. We provide first evidence that this unexpected phenomenon is connected to extra centrosomes eliciting a pro-death signal engaging the apoptotic machinery. Apoptosis induction requires the PIDDosome multi-protein complex, as it can be abrogated by loss of any of its three components, Caspase-2, Raidd/Cradd, or Pidd1. BCL2 overexpression equally blocks cell death, documenting for the first time induction of mitochondrial apoptosis downstream of extra centrosomes. Our findings demonstrate context-dependent effects of centrosome amplification during transformation and ask to adjust current belief that extra centrosomes are intrinsically pro-tumorigenic.

Combination Effects of Integrin-linked Kinase and Abelson Kinase Inhibition on Aberrant Mitosis and Cell Death in Glioblastoma Cells

In cancer cells, inhibition of integrin-linked kinase (ILK) increases centrosome declustering causing mitotic arrest and cell death. Yet, not all cancer cells are susceptible to anti-ILK treatment alone. We investigate a combination drug strategy targeting ILK and another oncogenic kinase, Abelson kinase (ABL). Drug-concentration viability assays (i.e., MTT assays) indicate that ILK and ABL inhibitors in combination decreased the viability of glioblastoma cells over the ILK drug QLT-0267 alone. Combination strategies also increased aberrant mitoses and cell death over QLT-0267 alone. This was evident from an increase in mitotic arrest, apoptosis and a sub-G1 peak following FAC analysis. In vitro, ILK and ABL localized to the centrosome and the putative ILK kinase domain was important for this localization. Increased levels of cytosolic ABL are associated with its transformative abilities. ILK inhibitor effects on survival correlated with its ability to decrease cytosolic ABL levels and inhibit ABL's localization to mitotic centrosomes in glioblastoma cells. ILK inhibitor effects on ABL's centrosomal localization were reversed by the proteasomal inhibitor MG132 (a drug that inhibits ABL degradation). These results indicate that ILK regulates ABL at mitotic centrosomes and that combination treatments targeting ILK and ABL are more effective then QLT-0267 alone at decreasing the survival of dividing glioblastoma cells.

Tools used to assay genomic instability in cancers and cancer meiomitosis

Genomic instability is a defining characteristic of cancer and the analysis of DNA damage at the chromosome level is a crucial part of the study of carcinogenesis and genotoxicity. Chromosomal instability (CIN), the most common level of genomic instability in cancers, is defined as the rate of loss or gain of chromosomes through successive divisions. As such, DNA in cancer cells is highly unstable. However, the underlying mechanisms remain elusive. There is a debate as to whether instability succeeds transformation, or if it is a by-product of cancer, and therefore, studying potential molecular and cellular contributors of genomic instability is of high importance. Recent work has suggested an important role for ectopic expression of meiosis genes in driving genomic instability via a process called meiomitosis. Improving understanding of these mechanisms can contribute to the development of targeted therapies that exploit DNA damage and repair mechanisms. Here, we discuss a workflow of novel and established techniques used to assess chromosomal instability as well as the nature of genomic instability such as double strand breaks, micronuclei, and chromatin bridges. For each technique, we discuss their advantages and limitations in a lab setting. Lastly, we provide detailed protocols for the discussed techniques.

Haploinsufficiency of cohesin protease, Separase, promotes regeneration of hematopoietic stem cells in mice

Cohesin recently emerged as a new regulator of hematopoiesis and leukemia. In addition to cohesin, whether proteins that regulate cohesin's function have any direct role in hematopoiesis and hematologic diseases have not been fully examined. Separase, encoded by the ESPL1 gene, is an important regulator of cohesin's function. Canonically, protease activity of Separase resolves sister chromatid cohesion by cleaving cohesin subunit-Rad21 at the onset of anaphase. Using a Separase haploinsufficient mouse model, we have uncovered a novel role of Separase in hematopoiesis. We report that partial disruption of Separase distinctly alters the functional characteristics of hematopoietic stem/progenitor cells (HSPCs). Although analyses of peripheral blood and bone marrow of Espl1+/Hyp mice broadly displayed unperturbed hematopoietic parameters during normal hematopoiesis, further probing of the composition of early hematopoietic cells in Espl1+/Hyp bone marrow revealed a mild reduction in the frequencies of the Lin- Sca1+ Kit- (LSK) or LSK CD48+ CD150- multipotent hematopoietic progenitors population without a significant change in either long-term or short-term hematopoietic stem cells (HSCs) subsets at steady state. Surprisingly, however, we found that Separase haploinsufficiency promotes regeneration activity of HSCs in serial in vivo repopulation assays. In vitro colony formation assays also revealed an enhanced serial replating capacity of hematopoietic progenitors isolated from Espl1+/Hyp mice. Microarray analysis of differentially expressed genes showed that Separase haploinsufficiency in HSCs (SP-KSL) leads to enrichment of gene signatures that are upregulated in HSCs compared to committed progenitors and mature cells. Taken together, our findings demonstrate a key role of Separase in promoting hematopoietic regeneration of HSCs.

Increased separase activity and occurrence of centrosome aberrations concur with transformation of MDS

ESPL1/separase, a cysteine endopeptidase, is a key player in centrosome duplication and mitotic sister chromatid separation. Aberrant expression and/or altered separase proteolytic activity are associated with centrosome amplification, aneuploidy, tumorigenesis and disease progression. Since centrosome alterations are a common and early detectable feature in patients with myelodysplastic syndrome (MDS) and cytogenetic aberrations play an important role in disease risk stratification, we examined separase activity on single cell level in 67 bone marrow samples obtained from patients with MDS, secondary acute myeloid leukemia (sAML), de novo acute myeloid leukemia (AML) and healthy controls by a flow cytometric separase activity assay. The separase activity distribution (SAD) value, a calculated measure for the occurrence of cells with prominent separase activity within the analyzed sample, was tested for correlation with the centrosome, karyotype and gene mutation status. We found higher SAD values in bone marrow cells of sAML patients than in corresponding cells of MDS patients. This concurred with an increased incidence of aberrant centrosome phenotypes in sAML vs. MDS samples. No correlation was found between SAD values and the karyotype/gene mutation status. During follow-up of four MDS patients we observed increasing SAD values after transformation to sAML, in two patients SAD values decreased during azacitidine therapy. Cell culture experiments employing MDS-L cells as an in vitro model of MDS revealed that treatment with rigosertib, a PLK1 inhibitor and therapeutic drug known to induce G2/M arrest, results in decreased SAD values. In conclusion, the appearance of cells with unusual high separase activity levels, as indicated by increased SAD values, concurs with the transformation of MDS to sAML and may reflect separase dysregulation potentially contributing to clonal evolution during MDS progression. Separase activity measurement may therefore be useful as a novel additional molecular marker for disease monitoring.

Separase is a marker for prognosis and mitotic activity in breast cancer

Background:

Cancer cell proliferation is a critical feature in classifying and predicting the outcome of breast carcinoma. Separase has a central role in cell cycle progression in unleashing sister-chromatids at anaphase onset. Abnormally functioning separase is known to lead to chromosomal instability.

Methods:

The study comprises 349 breast carcinoma patients treated in Central Hospital of Central Finland. The prognostic value, role as a proliferation marker and regulatory interactions of separase are evaluated by immunohistochemical and double- and triple-immunofluorescence (IF) detections based on complete clinical data and >22-year follow-up of the patient material.

Results:

In our material, abnormal separase expression predicted doubled risk of breast cancer death (P<0.001). Up to 11.3-year survival difference was observed when comparing patients with and without separase expressing cancer cell mitoses. Particularly, abnormal separase expression predicted impaired survival for luminal breast carcinoma (P<0.001, respectively). In multivariate analyses, abnormal separase expression showed independent prognostic value. The complex inhibitory interactions involving securin and cyclin B1 were investigated in double- and triple-IFs and revealed patient subgroups with aberrant regulation and expression patterns of separase.

Conclusions:

In our experience, separase is a promising and clinically applicable proliferation marker. Separase expression shows strong and independent prognostic value and could be developed into a biomarker for treatment decisions in breast carcinoma, particularly defining prognostic subgroups among luminal carcinomas.

c-MYB is a transcriptional regulator of ESPL1/Separase in BCR-ABL-positive chronic myeloid leukemia

Background

Genomic instability and clonal evolution are hallmarks of progressing chronic myeloid leukemia (CML). Recently, we have shown that clonal evolution and blast crisis correlate with altered expression and activity of Separase, a cysteine endopeptidase that is a mitotic key player in chromosomal segregation and centriole duplication. Hyperactivation of Separase in human hematopoietic cells has been linked to a feedback mechanism that posttranslationally stimulates Separase proteolytic activity after imatinib therapy-induced reduction of Separase protein levels.

Methods and Results

In search for potential therapy-responsive transcriptional mechanisms we have investigated the role of the transcription factor c-MYB for Separase expression in CML cell lines (LAMA-84, K562, BV-173) and in clinical samples. Quantitative RT-PCR and Western blot immunostaining experiments revealed that c-MYB expression levels are decreased in an imatinib-dependent manner and positively correlate with Separase expression levels in cell lines and in clinical CML samples. RNA silencing of c-MYB expression in CML cell lines resulted in reduced Separase protein levels. Gelshift and ChIP assays confirmed that c-MYB binds to a putative c-MYB binding sequence located within the ESPL1 promoter.

Conclusions

Our data suggest that ESPL1/Separase is a regulatory target of c-MYB. Therefore, c-MYB, known to be required for BCR-ABL-dependent transformation of hematopoietic progenitors and leukemogenesis, may also control the Separase-dependent fidelity of mitotic chromosomal segregation and centriole duplication essential for maintenance of genomic stability.

Clonal Evolution and Blast Crisis Correlate with Enhanced Proteolytic Activity of Separase in BCR-ABL b3a2 Fusion Type CML under Imatinib Therapy

Unbalanced (major route) additional cytogenetic aberrations (ACA) at diagnosis of chronic myeloid leukemia (CML) indicate an increased risk of progression and shorter survival. Moreover, newly arising ACA under imatinib treatment and clonal evolution are considered features of acceleration and define failure of therapy according to the European LeukemiaNet (ELN) recommendations. On the basis of 1151 Philadelphia chromosome positive chronic phase patients of the randomized CML-study IV, we examined the incidence of newly arising ACA under imatinib treatment with regard to the p210BCR-ABL breakpoint variants b2a2 and b3a2. We found a preferential acquisition of unbalanced ACA in patients with b3a2 vs. b2a2 fusion type (ratio: 6.3 vs. 1.6, p = 0.0246) concurring with a faster progress to blast crisis for b3a2 patients (p = 0.0124). ESPL1/Separase, a cysteine endopeptidase, is a key player in chromosomal segregation during mitosis. Separase overexpression and/or hyperactivity has been reported from a wide range of cancers and cause defective mitotic spindles, chromosome missegregation and aneuploidy. We investigated the influence of p210BCR-ABL breakpoint variants and imatinib treatment on expression and proteolytic activity of Separase as measured with a specific fluorogenic assay on CML cell lines (b2a2: KCL-22, BV-173; b3a2: K562, LAMA-84). Despite a drop in Separase protein levels an up to 5.4-fold increase of Separase activity under imatinib treatment was observed exclusively in b3a2 but not in b2a2 cell lines. Mimicking the influence of imatinib on BV-173 and LAMA-84 cells by ESPL1 silencing stimulated Separase proteolytic activity in both b3a2 and b2a2 cell lines. Our data suggest the existence of a fusion type-related feedback mechanism that posttranslationally stimulates Separase proteolytic activity after therapy-induced decreases in Separase protein levels. This could render b3a2 CML cells more prone to aneuploidy and clonal evolution than b2a2 progenitors and may therefore explain the cytogenetic results of CML patients.

Growth factor dependent regulation of centrosome function and genomic instability by HuR

The mRNA binding protein HuR is over expressed in cancer cells and contributes to disease progression through post-transcriptional regulation of mRNA. The regulation of HuR and how this relates to glioma is the focus of this report. SRC and c-Abl kinases regulate HuR sub-cellular trafficking and influence accumulation in the pericentriolar matrix (PCM) via a growth factor dependent signaling mechanism. Growth factor stimulation of glioma cell lines results in the associate of HuR with the PCM and amplification of centrosome number. This process is regulated by tyrosine phosphorylation of HuR and is abolished by mutating tyrosine residues. HuR is overexpressed in tumor samples from patients with glioblastoma and associated with a reduced survival. These findings suggest HuR plays a significant role in centrosome amplification and genomic instability, which contributes to a worse disease outcome.

Morgana acts as an oncosuppressor in chronic myeloid leukemia

We recently described morgana as an essential protein able to regulate centrosome duplication and genomic stability, by inhibiting ROCK. Here we show that morgana (+/-) mice spontaneously develop a lethal myeloproliferative disease resembling human atypical chronic myeloid leukemia (aCML), preceded by ROCK hyperactivation, centrosome amplification, and cytogenetic abnormalities in the bone marrow (BM). Moreover, we found that morgana is underexpressed in the BM of patients affected by atypical CML, a disorder of poorly understood molecular basis, characterized by nonrecurrent cytogenetic abnormalities. Morgana is also underexpressed in the BM of a portion of patients affected by Philadelphia-positive CML (Ph(+) CML) caused by the BCR-ABL oncogene, and in this condition, morgana underexpression predicts a worse response to imatinib, the standard treatment for Ph(+) CML. Thus, morgana acts as an oncosuppressor with different modalities: (1) Morgana underexpression induces centrosome amplification and cytogenetic abnormalities, and (2) in Ph(+) CML, it synergizes with BCR-ABL signaling, reducing the efficacy of imatinib treatment. Importantly, ROCK inhibition in the BM of patients underexpressing morgana restored the efficacy of imatinib to induce apoptosis, suggesting that ROCK inhibitors, combined with imatinib treatment, can overcome suboptimal responses in patients in which morgana is underexpressed.

Genetic events other than BCR-ABL1

The BCR-ABL1 oncoprotein is the cause of chronic myeloid leukemia and occurs as a consequence of the translocation t(9;22), a well-defined genetic event that results in the formation of the Philadelphia chromosome. While this genomic aberration is recognized to be the main culprit of the chronic phase of chronic myeloid leukemia, the natural clonal evolution of this myeloproliferative neoplasm involves the accumulation of secondary alterations through genomic instability. Thus, efforts to dissect the frequency and nature of the genomic events at diagnosis and at later stages are producing valuable insights into understanding the mechanisms of blastic transformation and development of resistance in chronic myeloid leukemia. The identification of alternative BCR-ABL1-dependent and BCR-ABL1-independent targets that sustain the survival of leukemic blasts and/or leukemia-initiating cells will facilitate the development of novel viable therapeutic options for patients who become resistant or intolerant to the currently available therapeutic options based on tyrosine kinase inhibitors.

Potential mechanisms of disease progression and management of advanced-phase chronic myeloid leukemia

Despite vast improvements in the treatment of Philadelphia chromosome-positive chronic myeloid leukemia (CML) in chronic phase (CP), advanced stages of CML, accelerated phase or blast crisis, remain notoriously difficult to treat. Treatments that are highly effective against CML-CP produce disappointing results against advanced disease. Therefore, a primary goal of therapy should be to maintain patients in CP for as long as possible, by (1) striving for deep, early molecular response to treatment; (2) using tyrosine kinase inhibitors that lower risk of disease progression; and (3) more closely observing patients who demonstrate cytogenetic risk factors at diagnosis or during treatment.

Centrosome aberrations in bone marrow cells from patients with myelodysplastic syndromes correlate with chromosomal instability

Centrosomes play important roles in the maintenance of genetic stability and centrosomal aberrations are a hallmark of cancer. Deregulation of centriole duplication leads to supernumerary centrosomes, sister chromatid missegregation and could result in chromosomal instability (CIN) and aneuploidy. CIN is a common feature in at least 45% of patients with myelodysplastic syndromes (MDS). Therefore, we sought to investigate the centrosomal status and its role for development of CIN in bone marrow (BM) cells of MDS patients. BM cells of 34 MDS patients were examined cytogenetically. Furthermore, cells were immunostained with a centrosome-specific antibody to pericentrin to analyze the centrosomal status. Umbilical cord blood specimens and BM cells of healthy persons (n = 11 and n = 4) served as controls. In addition, the protein expression of the protease separase responsible for genetic stability was examined by western blot analysis. Centrosome abnormalities were detected in 10% (range, 4-17%) of cells of MDS samples, but in only 2% (range, 0-4%) of cells of healthy controls. Normal karyotypes were found in control cells and in BM cells of 16/34 MDS patients. The incidence of centrosomal alterations was higher in BM cells of patients with cytogenetic alterations (mean, 12%) compared to BM cells of patients without cytogenetic changes (mean, 7%). Our results indicate that centrosome alterations are a common and early detectable feature in MDS patients and may contribute to the acquisition of chromosomal aberrations. We assume that centrosome defects could be involved in disease progression and may serve as a future prognostic marker.

Nuclear segmentation, condensation and bilateral symmetry in polymorphonuclear leukocytes reflect genomic order and favor immunologic function

Segmentation, condensation and bilateral symmetry of the nuclei of polymorphonuclear leukocytes seem related to their function. Segmentation of the nuclei into two or more lobes and their condensation facilitate their passage (diapedesis) through the endothelial layer of blood vessels to the extravasal space and subsequent locomotion through the interstitial compartment of different tissues. Bilateral symmetry of these nuclei along with their association to the cytoskeletal fibers contribute to their efficiency in locomotion by alignment of the axis of nuclear symmetry to the axis of cellular polarity, which orients towards the direction of locomotion in response to cytokines and other stimuli. Observations of the cytogenetic facets of intranuclear order support these assumptions.

Higher-order orchestration of hematopoiesis: is cohesin a new player?

Hematopoiesis-the process that generates distinct lineage-committed blood cells from a single multipotent hematopoietic stem cell-is a complex process of cellular differentiation regulated by a set of dynamic transcriptional programs. Cytokines and growth factors, transcription factors, chromatin remodeling, and modifying enzymes have been suggested to enact critical roles during hematopoiesis, leading to the development of myeloid, lymphoid, erythroid and platelet precursors. How is such a complex process orchestrated? Is there a higher order of hematopoiesis regulation? These are some of the unresolved questions in the field of hematopoiesis. Here, we suggest that cohesin, which is known to mediate chromosomal cohesion between sister chromatids, may have a central role in the orchestration of hematopoiesis and serve as a master transcriptional regulator.

Protein segregation between dividing hematopoietic progenitor cells in the determination of the symmetry/asymmetry of cell division

In the present study, we investigated how the symmetry/asymmetry of cell division in mitotic CD34(+) cells can be evaluated by determining the plane of cell division and the potential distribution of proteins between daughter cells. The orientation of the mitotic spindle is dependent upon the positioning of the centrosomes, which determine the plane of cell division and the sharing of proteins. If the functions of unequally shared proteins are relevant to the kinetics of cell division, they could determine whether the daughter cells undergo self-renewal or differentiation. The kinetic function of the proteins of interest was investigated using a colony-replating assay and carboxyfluorescein succinimidyl ester (CFSE) staining. We used Notch/Numb as a model system, since they have a role in balancing symmetric/asymmetric divisions. Mitotic cells were examined microscopically and centrosomal markers γ-tubulin/pericentrin were used with activated Notch-1 and Numb. We monitored the first crucial divisions by CFSE staining and found an inverse relationship between activated Notch and Numb expression, suggesting a reciprocal regulation. We suggest that the subpopulations expressing activated Notch or Numb have different cell fates. To determine the influence of Notch signaling on progenitor cell self-renewal, we used the γ-secretase inhibitor N-[N-(3,5-Difluorophenacetyl-L-alanyl)]-S-phenylglycine t-Butyl ester (DAPT). DAPT influences self-renewal/differentiation outcome by affecting the frequency of symmetric renewal divisions without affecting the rate of divisions. Overall, the purpose of this study was to establish a cellular system for predicting the symmetry/asymmetry of hematopoietic progenitor divisions at the level of centrosomes and protein distribution and to investigate the influence of these proteins on progenitor cell kinetics.

The proteolytic activity of separase in BCR-ABL-positive cells is increased by imatinib

Separase, an endopeptidase required for the separation of sister-chromatides in mitotic anaphase, triggers centriole disengagement during centrosome duplication. In cancer, separase is frequently overexpressed, pointing to a functional role as an aneuploidy promoter associated with centrosomal amplification and genomic instability. Recently, we have shown that centrosomal amplification and subsequent chromosomal aberrations are a hallmark of chronic myeloid leukemia (CML), increasing from chronic phase (CP) toward blast crisis (BC). Moreover, a functional linkage of p210BCR-ABL tyrosine kinase activity with centrosomal amplification and clonal evolution has been established in long-term cell culture experiments. Unexpectedly, therapeutic doses of imatinib (IM) did not counteract; instead induced similar centrosomal alterations in vitro. We investigated the influence of IM and p210BCR-ABL on Separase as a potential driver of centrosomal amplification in CML. Short-term cell cultures of p210BCR-ABL-negative (NHDF, UROtsa, HL-60, U937), positive (K562, LAMA-84) and inducible (U937p210BCR-ABL/c6 (Tet-ON)) human cell lines were treated with therapeutic doses of IM and analyzed by qRT-PCR, Western blot analysis and quantitative Separase activity assays. Decreased Separase protein levels were observed in all cells treated with IM in a dose dependent manner. Accordingly, in all p210BCR-ABL-negative cell lines, decreased proteolytic activity of Separase was found. In contrast, p210BCR-ABL-positive cells showed increased Separase proteolytic activity. This activation of Separase was consistent with changes in the expression levels of Separase regulators (Separase phosphorylation at serine residue 1126, Securin, CyclinB1 and PP2A). Our data suggest that regulation of Separase in IM-treated BCR-ABL-positive cells occurs on both the protein expression and the proteolytic activity levels. Activation of Separase proteolytic activity exclusively in p210BCR-ABL-positive cells during IM treatment may act as a driving force for centrosomal amplification, contributing to genomic instability, clonal evolution and resistance in CML.

Antigens in chronic myeloid leukemia: implications for vaccine development

Treatment with imatinib mesylate and other tyrosine kinase inhibitors (TKI) revolutionized the therapy of chronic myeloid leukemia (CML). However, it alone does not cure this disease. Moreover, some patients develop resistance or adverse effects to this therapy. As successful treatment of a portion of CML patients by hematopoietic stem cell transplantation (HSCT) suggests the importance of immune mechanisms in the elimination of leukemic cells, including leukemia stem cells, TKI administration or HSCT might be combined with vaccination to cure CML patients. However, antigens implicated in the immune responses have not yet been sufficiently identified. Therefore, in this report, we compiled and characterized a list of 165 antigens associated with CML (CML-Ag165) and analyzed the expression of the corresponding genes in CML phases, subpopulations of leukemic cells, and CML-derived cell lines using available datasets from microarray transcriptional-profiling studies. From the CML-Ag165 list, we selected antigens most suitable for vaccine development and evaluated their appropriate characteristics.

A clinical overview of centrosome amplification in human cancers

The turn of the 21st century had witnessed a surge of interest in the centrosome and its causal relation to human cancer development - a postulate that has existed for almost a century. Centrosome amplification (CA) is frequently detected in a growing list of human cancers, both solid and haematological, and is a candidate "hallmark" of cancer cells. Several lines of evidence support the progressive involvement of CA in the transition from early to advanced stages of carcinogenesis, being also found in pre-neoplastic lesions and even in histopathologically-normal tissue. CA constitutes the major mechanism leading to chromosomal instability and aneuploidy, via the formation of multipolar spindles and chromosomal missegregation. Clinically, CA may translate to a greater risk for initiation of malignant transformation, tumour progression, chemoresistance and ultimately, poor patient prognosis. As mechanisms underlying CA are progressively being unravelled, the centrosome has emerged as a novel candidate target for cancer treatment. This Review summarizes mainly the clinical studies performed to date focusing on the mechanisms underlying CA in human neoplasia, and highlights the potential utility of centrosomes in the diagnosis, prognosis and treatment of human cancers.

Internuclear chromosome distribution of dysplastic megakaryocytes in myelodysplastic syndromes is dependent on the level of ploidy

Megakaryopoiesis is largely disturbed in myelodysplastic syndromes (MDS), and megakaryocytes (MKs) frequently show multinucleation. Here, we investigated dysplastic mono-, bi-, and multinuclear MKs (n = 169) of seven patients with MDS and one patient with myelodysplastic/myeloproliferative neoplasm by sequential multilocus FISH. Analysis of binuclear MKs with a combined DNA content of 4 N (n = 46) indicated a significantly even (symmetric) chromosome distribution between the two separate nuclei (p = 0.0223), which suggests bipolar spindle orientation and symmetric chromosome segregation during the first endomitotic cell cycle. In contrast, multinuclear MKs of higher ploidy (>4 N, n = 108) demonstrated a significantly uneven (asymmetric) chromosome distribution between the separate nuclei (p = 0.0248). Thus, the internuclear chromosomal distribution of dysplastic MKs depends on the level of ploidy. In addition, centrosomal aberrations were not found in dysplastic MKs. Our results indicate that megakaryocytic multinucleation in MDS originates from dysregulated endomitosis, including restoration of karyokinesis.

Pericentrin in cellular function and disease

Pericentrin is an integral component of the centrosome that serves as a multifunctional scaffold for anchoring numerous proteins and protein complexes. Through these interactions, pericentrin contributes to a diversity of fundamental cellular processes. Recent studies link pericentrin to a growing list of human disorders. Studies on pericentrin at the cellular, molecular, and, more recently, organismal level, provide a platform for generating models to elucidate the etiology of these disorders. Although the complexity of phenotypes associated with pericentrin-mediated disorders is somewhat daunting, insights into the cellular basis of disease are beginning to come into focus. In this review, we focus on human conditions associated with loss or elevation of pericentrin and propose cellular and molecular models that might explain them.