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Tetracyclic terpenoid-derived natural products are a broad class of medically relevant agents that include well-known steroid hormones and related structures, as well as more synthetically challenging congeners such as limonoids, cardenolides, lanostanes, and cucurbitanes, among others. These structurally related compound classes present synthetically disparate challenges based, in part, on the position and stereochemistry of the numerous quaternary carbon centers that are common to their tetracyclic skeletons. While de novo syntheses of such targets have been a topic of great interest for over 50 years, semisynthesis is often how synthetic variants of these natural products are explored as biologically relevant materials and how such agents are further matured as therapeutics. Here, focus was directed at establishing an efficient, stereoselective, and molecularly flexible de novo synthetic approach that could offer what semisynthetic approaches do not. In short, a unified strategy to access common molecular features of these natural product families is described that proceeds in four stages: (1) conversion of epichlorohydrin to stereodefined enynes, (2) metallacycle-mediated annulative cross-coupling to generate highly substituted hydrindanes, (3) tetracycle formation by stereoselective forging of the C9–C10 bond, and (4) group-selective oxidative rearrangement that repositions a quaternary center from C9 to C10. These studies have defined the structural features required for highly stereoselective C9–C10 bond formation and document the generality of this four-stage synthetic strategy to access a range of unique stereodefined systems, many of which bear stereochemistry/substitution/functionality not readily accessible from semisynthesis.

Citation indices are tools used by the academic community for research and research evaluation which aggregate scientific literature output and measure scientific impact by collating citation counts. Citation indices help measure the interconnections between scientific papers but fall short because they only display paper titles, authors, and the date of publications, and fail to communicate contextual information about why a citation was made. The usage of citations in research evaluation without due consideration to context can be problematic, if only because a citation that disputes a paper is treated the same as a citation that supports it. To solve this problem, we have used machine learning and other techniques to develop a “smart citation index” called scite, which categorizes citations based on context. Scite shows how a citation was used by displaying the surrounding textual context from the citing paper, and a classification from our deep learning model that indicates whether the statement provides supporting or disputing evidence for a referenced work, or simply mentions it. Scite has been developed by analyzing over 23 million full-text scientific articles and currently has a database of more than 800 million classified citation statements. Here we describe how scite works and how it can be used to further research and research evaluation.

A general approach to the synthesis of 1,3-disubstituted-1,2-dihydroisoquinolines was achieved with pyrrole and various electron withdrawing groups as substituents. CuAAC reaction on enynes yielded the resulting 1,2,3-triazole which spontaneously decomposed to the corresponding ketenimine. Nucleophilic attack by pyrrole and subsequent intramolecular Aza-Michael cyclization generated 1,2-dihydroisoquinolines in moderate to good yields. The optimized conditions allow for a range of substituents with excellent reproducibility.

We should stop accepting crude citation counts as a proxy of quality for researchers, journals, and institutions. Here, we introduce smart citations—citations that show how a scientific paper has been cited by displaying the context of the citation and a classification describing whether it provides supporting or disputing evidence.

Wikipedia is a widely used online reference work which cites hundreds of thousands of scientific articles across its entries. The quality of these citations has not been previously measured, and such measurements have a bearing on the reliability and quality of the scientific portions of this reference work. Using a novel technique, a massive database of qualitatively described citations, and machine learning algorithms, we analyzed 1,923,575 Wikipedia articles which cited a total of 824,298 scientific articles, and found that most scientific articles (57%) are uncited or untested by subsequent studies, while the remainder show a wide variability in contradicting or supporting evidence (2-41%). Additionally, we analyzed 51,804,643 scientific articles from journals indexed in the Web of Science and found that most (85%) were uncited or untested by subsequent studies, while the remainder show a wide variability in contradicting or supporting evidence (1-14%).

Tetraploidy has long been of interest to both cell and cancer biologists, partly because of its documented role in tumorigenesis. A common model proposes that the extra centrosomes that are typically acquired during tetraploidization are responsible for driving tumorigenesis. However, this model is inconsistent with the observation that tetraploid cells evolved in culture lack extra centrosomes. This observation raises questions about how tetraploid cells evolve and more specifically about the mechanisms(s) underlying centrosome loss. Here, using a combination of fixed cell analysis, live cell imaging, and mathematical modeling, we show that populations of newly formed tetraploid cells rapidly evolve in vitro to retain a near-tetraploid chromosome number while losing the extra centrosomes gained at the time of tetraploidization. This happens through a process of natural selection in which tetraploid cells that inherit a single centrosome during a bipolar division with asymmetric centrosome clustering are favored for long-term survival.

The current crisis of veracity in biomedical research is enabled by the lack of publicly accessible information on whether the reported scientific claims are valid. One approach to solve this problem is to replicate previous studies by specialized reproducibility centers. However, this approach is costly or unaffordable and raises a number of yet to be resolved concerns that question its effectiveness and validity. We propose to use an approach that yields a simple numerical measure of veracity, the R-factor, by summarizing the outcomes of already published studies that have attempted to test a claim. The R-factor of an investigator, a journal, or an institution would be the average of the R-factors of the claims they reported. We illustrate this approach using three studies recently tested by a replication initiative, compare the results, and discuss how using the R-factor can help improve the veracity of scientific research.

Author(s): Cornish-Bowden, Athel; Cornish-Bowden, Athel; Rasnick, David; Heng, Henry H; Horne, Steven; Abdallah, Batoul; Liu, Guo; Ye, Christine J; Bloomfield, Mathew; Vincent, Mark D; Aldaz, C Marcelo; Karlsson, Jenny; Valind, Anders; Jansson, Caroline; Gisselsson, David; Graves, Jennifer A Marshall; Stepanenko, Aleksei A; Andreieva, Svitlana V; Korets, Kateryna V; Mykytenko, Dmytro O; Huleyuk, Nataliya L; Baklaushev, Vladimir P; Kovaleva, Oksana A; Chekhonin, Vladimir P; Vassetzky, Yegor S; Avdieiev, Stanislav S; Bakker, Bjorn; Taudt, Aaron S; Belderbos, Mirjam E; Porubsky, David; Spierings, Diana CJ; de Jong, Tristan V; Halsema, Nancy; Kazemier, Hinke G; Hoekstra-Wakker, Karina; Bradley, Allan; de Bont, Eveline SJM; van den Berg, Anke; Guryev, Victor; Lansdorp, Peter M; Tatche, Maria Colome; Foijer, Floris; Liehr, Thomas; Baudoin, Nicolaas C; Nicholson, Joshua M; Soto, Kimberly; Quintanilla, Isabel; Camps, Jordi; Cimini, Daniela; Durrbaum, M; Donnelly, N; Passerini, V; Kruse, C; Habermann, B; Storchova, Z; Mandrioli, Daniele; Belpoggi, Fiorella; Silbergeld, Ellen K; Perry, Melissa J; Skotheim, Rolf I; Lovf, Marthe; Johannessen, Bjarne; Hoff, Andreas M; Zhao, Sen; SveeStromme, Jonas M; Sveen, Anita; Lothe, Ragnhild A; Hehlmann, R; Voskanyan, A; Fabarius, A; Bocking, Alfred; Biesterfeld, Stefan; Berynskyy, Leonid; Borgermann, Christof; Engers, Rainer; Dietz, Josef; Fritz, A; Sehgal, N; Vecerova, J; Stojkovicz, B; Ding, H; Page, N; Tye, C; Bhattacharya, S; Xu, J

Since cancers have individual clonal karyotypes, are immortal and evolve from normal cells treated by carcinogens only after exceedingly long latencies of many months to decades-we deduce that carcinogenesis may be a form of speciation. This theory proposes that carcinogens initiate carcinogenesis by causing aneuploidy, i.e., losses or gains of chromosomes. Aneuploidy destabilizes the karyotype, because it unbalances thousands of collaborating genes including those that synthesize, segregate and repair chromosomes. Driven by this inherent instability aneuploid cells evolve ever-more random karyotypes automatically. Most of these perish, but a very small minority acquires reproductive autonomy-the primary characteristic of cancer cells and species. Selection for autonomy stabilizes new cancer species against the inherent instability of aneuploidy within specific margins of variation. The speciation theory explains five common characteristics of cancers: (1) species-specific autonomy; (2) karyotypic and phenotypic individuality; (3) flexibility by karyotypic variations within stable margins of autonomy; (4) immortality by replacing defective karyotypes from constitutive pools of competent variants or subspecies generated by this flexibility; and (5) long neoplastic latencies by the low probability that random karyotypic alterations generate new autonomous species. Moreover, the theory explains phylogenetic relations between cancers of the same tissue, because carcinogenesis is restricted by tissue-specific transcriptomes. The theory also solves paradoxes of other cancer theories. For example, "aneuploidy" of cancers is now said to be a "paradox" or "cancer's fatal flaw," because aneuploidy impairs normal growth and development. But if the "aneuploidies" of cancers are in effect the karyotypes of new species, this paradox is solved.

Cancers are clones of autonomous cells defined by individual karyotypes, much like species. Despite such karyotypic evidence for causality, three to six synergistic mutations, termed onco- genes, are generally thought to cause cancer. To test single oncogenes, they are artificially activated with heterologous promoters and spliced into the germ line of mice to initiate cancers with collab- orating spontaneous oncogenes. Because such cancers are studied as models for the treatment of natural cancers with related oncogenes, the following must be answered: 1) which oncogenes collaborate with the transgenes in cancers; 2) how do single transgenic oncogenes induce diverse cancers and hyperplasias; 3) what maintains cancers that lose initiating transgenes; 4) why are cancers aneuploid, over- and underexpressing thousands of normal genes? Here we try to answer these questions with the theory that carcinogenesis is a form of speciation. We postulate that trans- genic oncogenes initiate carcinogenesis by inducing aneuploidy. Aneuploidy destabilizes the karyo- type by unbalancing teams of mitosis genes. This instability thus catalyzes the evolution of new cancer species with individual karyotypes. Depending on their degree of aneuploidy, these cancers then evolve new subspecies. To test this theory, we have analyzed the karyotypes and phenotypes of mammary carcinomas of mice with transgenic SV40 tumor viruse and hepatitis B virusederived oncogenes. We found that (1) a given transgene induced diverse carcinomas with individual karyo- types and phenotypes; (2) these karyotypes coevolved with newly acquired phenotypes such as drug resistance; (3) 8 of 12 carcinomas were transgene negative. Having found one-to-one correlations between individual karyotypes and phenotypes and consistent coevolutions of karyotypes and phenotypes, we conclude that carcinogenesis is a form of speciation and that individual karyotypes maintain cancers as they maintain species. Because activated oncogenes destabilize karyotypes and are dispensable in cancers, we conclude that they function indirectly, like carcinogens. Such onco- genes would thus not be valid models for the treatment of cancers. 2010 Elsevier Inc. All rights reserved.

Aneuploidy is widely acknowledged as a leading cause of miscarriage and birth defects in humans, and is generally known to be deleterious to the survival of individual cells. However, aneuploidy is also ubiquitous in cancer and is found to arise as an adaptive response in certain contexts. This dichotomy of aneuploidy has attracted the interest of researchers for over a century, but many studies have reached conflicting conclusions. The emergence of new technology has allowed scientists to revisit the aneuploidy problem and has fueled a number of recent studies aimed at understanding the effects of aneuploidy on cell physiology. Here, we review these studies, in light of previous observations and knowledge, specifically focusing on the effects of aneuploidy on cellular homeostasis, chromosome stability, and adaptation.

Too many US authors of the most innovative and influential papers in the life sciences do not receive NIH funding, contend Joshua M. Nicholson and John P. A. Ioannidis.

Here we present various pieces of advice from startup founders, academic professors, research

© Nicholson This article is distributed under the terms of the Creative Commons Attribution 4.0 International License, which permits unrestricted use, distribution, and redistribution in any medium, provided that the original author and source are credited. Cancers are defined by abnormal karyotypes, displaying ever-changing structural and numerical abnormalities. Such plasticity of the karyotype underlies the evolution of cancer cells (Navin et al. 2011, Pavelka, Rancati, and Li 2010, Lee et al. 2011, Nicholson and Duesberg 2009). Karyotype alterations are also responsible for phenotypic variation and evolution in yeast (Rancati et al. 2008, Pavelka, Rancati, and Li 2010) and arguably of species in general (King 1993, McCarthy 2008). Because the alterations in the karyotypes of cancer cells have been shown to be non-random and stable within limits (Li et al. 2009, Nicholson and Duesberg 2009, Gebhart and Liehr 2000, Mertens et al. 1997), recently it has been proposed that carcinogenesis may be a form of speciation (Duesberg et al. 2011, Vincent 2010)

Aneuploidy is widely acknowledged as a leading cause of miscarriage and birth defects in humans, and is generally known to be deleterious to the survival of individual cells. However, aneuploidy is also ubiquitous in cancer and is found to arise as an adaptive response in certain contexts. This dichotomy of aneuploidy has attracted the interest of researchers for over a century, but many studies have reached conflicting conclusions. The emergence of new technology has allowed scientists to revisit the aneuploidy problem and has fueled a number of recent studies aimed at understanding the effects of aneuploidy on cell physiology. Here, we review these studies, in light of previous observations and knowledge, specifically focusing on the effects of aneuploidy on cellular homeostasis, chromosome stability, and adaptation.

© Nicholson This article is distributed under the terms of the Creative Commons Attribution 4.0 International License, which permits unrestricted use, distribution, and redistribution in any medium, provided that the original author and source are credited. The value of blogs and bloggers in science is well recognized. Blogs serve as an excellent form of post-publication peer review and host much of the scientific discussion that occurs on the web today. Indeed, it is probably true that more interaction between scientists and between scientists and the public occurs away from traditional scientific articles themselves and in “alternative” forums such as Twitter, Facebook, and of course, blogs. These mediums are becoming increasingly important in scholarly discourse and often times shape what is written in traditional scholarly articles themselves (i.e. they are often cited). But for all the benefits blogs provide they are not afforded an equal footing. They are superfluous and can disappear without a trace. We want to change that. The content of these discussions can sway opinion and act as authoritative sources in their own right. Blogs are without a doubt valuable and as such deserve to be archived and aggregated, just like traditional scholarly publications are. They deserve to “count,” to be elevated to a level that is not viewed as something extra but as something integral to scientific communication (Nicholson 2014, Nicholson 2015). We need to get around the notion that where you publish actually matters. It doesn’t. It is the content, not the wrapper, and the sooner we act accordingly, the better.

How we can align open communication seen on blogs with career-advancement garnered from publications. Three key aspects of scholarly communication need to be made available for bloggers: 1) DOIs, 2) Review, and 3) Archival. 1 2

Cancer cells display aneuploid karyotypes and typically mis-segregate chromosomes at high rates, a phenotype referred to as chromosomal instability (CIN). To test the effects of aneuploidy on chromosome segregation and other mitotic phenotypes we used the colorectal cancer cell line DLD1 (2n = 46) and two variants with trisomy 7 or 13 (DLD1+7 and DLD1+13), as well as euploid and trisomy 13 amniocytes (AF and AF+13). We found that trisomic cells displayed higher rates of chromosome mis-segregation compared to their euploid counterparts. Furthermore, cells with trisomy 13 displayed a distinctive cytokinesis failure phenotype. We showed that up-regulation of SPG20 expression, brought about by trisomy 13 in DLD1+13 and AF+13 cells, is sufficient for the cytokinesis failure phenotype. Overall, our study shows that aneuploidy can induce chromosome mis-segregation. Moreover, we identified a trisomy 13-specific mitotic phenotype that is driven by up-regulation of a gene encoded on the aneuploid chromosome. DOI: http://dx.doi.org/10.7554/eLife.05068.001, eLife digest The DNA in a human cell is divided between forty-six structures called chromosomes. Before a cell divides, it copies every chromosome so that each daughter cell will have the same DNA as the parent cell. These chromosomes align in the center of the cell and then the matching chromosomes are separated and pulled to opposite ends. However, in some cases the separation process does not work properly, which can produce cells that either have too many, or too few, chromosomes. Abnormal numbers of chromosomes within cells—called aneuploidy—is a leading cause of miscarriage and birth defects in humans. Aneuploidy is also a common feature of cancer cells. It is common for the chromosomes in cancer cells to be distributed unequally when the cell divides. This phenomenon is known as chromosomal instability, but the link between aneuploidy and chromosomal instability in cancer cells is not fully understood. Here, Nicholson et al. used live-cell imaging techniques to analyze healthy human cells and cancer cells that had either the normal forty-six chromosomes, or a defined extra chromosome. Nicholson et al. found that when the cells divided, the chromosomes in the cells that had an extra copy of chromosome 7 or 13 were more prone to distributing chromosomes unequally, compared to cells with a normal number of chromosomes. Nicholson et al. also observed that the cells with an extra chromosome 13 were unable to properly divide into two. These cells had increased levels of a protein called Spartin—which is important for the last stage in cell division—and this was responsible for the failure to produce two daughter cells. These findings show that aneuploidy can cause chromosomal instability in human cells. Furthermore, Nicholson et al. have identified a defect in cell division that is specifically caused by the presence of an extra chromosome 13 in human cells. A future challenge will be to determine how, and to what extent, different chromosomes can affect chromosome stability. This could be useful in the development of therapies against cancer cells with aneuploidy. DOI: http://dx.doi.org/10.7554/eLife.05068.002

This is an open letter concerning the recent launch of the new open access journal, Science Advances. In addition to the welcome diversification in journal choices for authors looking for open access venues, there are many positive aspects of Science Advances: its broad STEM scope, its interest in cross-disciplinary research, and the offering of fee waivers. While we welcome the commitment of the Association to open access, we are also deeply concerned with the specific approach. Herein, we outline a number of suggestions that are in line with both the current direction that scholarly publishing is taking and the needs expressed by the open access community, which this journal aims to serve.

The following are pre-publication peer reviews received on the manuscript: Will we cure cancer by sequencing thousands of genomes ( Nicholson 2013 ), which was initially rejected and later resubmitted and published in Molecular Cytogenetics 1

Scientists, institutions and journals have been increasingly evaluated statistically, by metrics that focus on the number of published reports rather than on their content, raising a concern that this approach interferes with the progress of biomedical research. To offset this effect, we propose to use the R-factor, a metric that indicates whether a report or its conclusions have been verified. 1 2

This is an open letter concerning the recent launch of the new open access journal, eNeuro. We welcome the diversification of journal choices for authors looking for open access venues, as well as the willingness of eNeuro to accept negative results and study replications, its membership in the Neuroscience Peer Review Consortium, the publication of peer review syntheses alongside articles, and the requirement that molecular data be publicly available. As strong supporters of open access, we welcome the commitment of the Society to making the works it publishes freely and openly available. However, we are concerned with several aspects of the specific approach, and outline herein a number of suggestions that would allow eNeuro to provide the full benefits of open access to the communities the journal aims to serve...

The promise to understand cancer and develop efficacious therapies by sequencing thousands of cancers has not occurred. Mutations in specific genes termed oncogenes and tumor suppressor genes are extremely heterogeneous amongst the same type of cancer as well as between cancers. They provide little selective advantage to the cancer and in functional tests have yet to be shown to be sufficient for transformation. Here I discuss the karyotyptic theory of cancer and ask if it is time for a new approach to understanding and ultimately treating cancer.

Cancer cells are typically characterized by complex karyotypes including both structural and numerical changes, with aneuploidy being a ubiquitous feature. It is becoming increasingly evident that aneuploidy per se can cause chromosome mis-segregation, which explains the higher rates of chromosome gain/loss observed in aneuploid cancer cells compared to normal diploid cells, a phenotype termed chromosomal instability (CIN). CIN can be caused by various mechanisms and results in extensive karyotypic heterogeneity within a cancer cell population. However, despite such karyotypic heterogeneity, cancer cells also display predominant karyotypic patterns. In this review we discuss the mechanisms of CIN, with particular emphasis on the role of aneuploidy on CIN. Further, we discuss the potential functional role of karyotypic patterns in cancer. NSFNational Science Foundation (NSF) [MCB-0842551]; HFSPHuman Frontier Science Program [RGY0069/2010] We would like to thank all the members of the Cimini Lab for useful discussion and helpful comments. We also thank Giulia Rancati (Institute of Medical Biology, A-STAR, Singapore) for providing useful information and reference to scientific literature, and Neil Ganem (Dana Farber Cancer Institute, Harvard Medical School, Boston, MA, USA) for providing clarifications on published data. Work in the Cimini Lab is supported by NSF grant MCB-0842551 and HFSP grant RGY0069/2010.

Funding agencies (and journals) seem to be discriminating against ideas that are contrary to the mainstream, leading to leading to the preferential funding of predictable and safe research over radically new ideas. To remedy this problem a restructuring of the scientific funding system is needed, e.g. by utilizing laymen--together with scientists--to evaluate grant proposals.

Since the discoveries of a putative AIDS virus in 1984 and of millions of asymptomatic carriers in subsequent years, no general AIDS epidemic has occurred by 2011. In 2008, however, it has been proposed that between 2000 and 2005 the new AIDS virus, now called HIV, had killed 1.8 million South Africans at a steady rate of 300,000 per year and that anti-HIV drugs could have saved 330,000 of those. Here we investigate these claims in view of the paradoxes that HIV would cause a general epidemic in Africa but not in other continents, and a steady rather than a classical bell-shaped epidemic like all other new pathogenic viruses. Surprisingly, we found that South Africa attributed only about 10,000 deaths per year to HIV between 2000 and 2005 and that the South African population had increased by 3 million between 2000 and 2005 at a steady rate of 500,000 per year. This gain was part of a monotonic growth trajectory spanning from 29 million in 1980 to 49 million in 2008. During the same time Uganda increased from 12 to 31 million, and Sub-Saharan Africa as a whole doubled from 400 to 800 million, despite high prevalence HIV. We deduce from this demographic evidence that HIV is not a new killer virus. Based on a review of the known toxicities of antiretroviral drugs we like to draw the attention of scientists, who work in basic and clinical medical fields, including embryologists, to the need of rethinking the risk-and-benefit balance of antiretroviral drugs for pregnant women, newborn babies and all others who carry antibodies against HIV.

Aneuploidy is a common feature of cancer cells, and is believed to play a critical role in tumorigenesis and cancer progression. Most cancer cells also exhibit high rates of mitotic chromosome mis-segregation, a phenomenon known as chromosomal instability, which leads to high variability of the karyotype. Here, we describe the nature, nuances, and implications of cancer karyotypic diversity. Moreover, we summarize recent studies aimed at identifying the mitotic defects that may be responsible for inducing chromosome mis-segregation in cancer cells. These include kinetochore attachment errors, spindle assembly checkpoint dysfunction, mitotic spindle defects, and other cell division inaccuracies. Finally, we discuss how such mitotic errors generate karyotypic diversity in cancer cells.

Aneuploidy is a common feature of cancer cells, and is believed to play a critical role in tumorigenesis and cancer progression. Most cancer cells also exhibit high rates of mitotic chromosome mis-segregation, a phenomenon known as chromosomal instability, which leads to high variability of the karyotype. Here, we describe the nature, nuances, and implications of cancer karyotypic diversity. Moreover, we summarize recent studies aimed at identifying the mitotic defects that may be responsible for inducing chromosome mis-segregation in cancer cells. These include kinetochore attachment errors, spindle assembly checkpoint dysfunction, mitotic spindle defects, and other cell division inaccuracies. Finally, we discuss how such mitotic errors generate karyotypic diversity in cancer cells.

Summary Chromosomal instability (CIN) is a common feature of most human neoplasms and was defined, in a seminal study by Vogelstein and colleagues [1], as persistently elevated rates of whole chromosome mis-segregation. Since then, it was shown that certain errors in mitosis, including defects in the spindle assembly checkpoint [2], sister chromatid cohesion [3], kinetochore-microtubule (kMT) attachments [4,5], and centrosome number [6] can cause chromosome mis-segregation in the form of merotelically attached anaphase lagging chromosomes — chromosomes that lag behind at the spindle equator while all the other chromosomes move toward the spindle poles [7] (Figure 1A). A recent study has suggested that pre-mitotic replication stress generates partially replicated chromosomes during mitosis, and that this results in both numerical and structural chromosome abnormalities through the formation of chromosome bridges and acentric chromosome fragments during anaphase [8]. To determine whether whole chromosome instability in cancer cells is caused by defects originating in mitosis (lagging chromosomes) or from ones originating pre-mitotically (chromatin bridges and acentric fragments), we compared a variety of CIN+ to CIN- cells to determine the types of segregation defects that phenotypically distinguish CIN+ from CIN- cells and whose abrogation can rescue whole chromosomal instability.

The chromosomes of cancer cells are unstable, because of aneuploidy. Despite chromosomal instability, however, cancer karyotypes are individual and quasi-stable, as is evident especially from clonal chromosome copy numbers and marker chromosomes. This paradox would be resolved if the karyotypes in cancers represent chromosomal equilibria between destabilizing aneuploidy and stabilizing selection for oncogenic function. To test this hypothesis, we analyzed the initial and long-term karyotypes of seven clones of newly transformed human epithelial, mammary, and muscle cells. Approximately 1 in 100,000 such cells generates transformed clones at 2-3 months after introduction of retrovirus-activated cellular genes or the tumor virus SV40. These frequencies are too low for direct transformation, so we postulated that virus-activated genes initiate transformation indirectly, via specific karyotypes. Using multicolor fluorescence in situ hybridization with chromosome-specific DNA probes, we found individual clonal karyotypes that were stable for at least 34 cell generations-within limits, as follows. Depending on the karyotype, average clonal chromosome numbers were stable within +/- 3%, and chromosome-specific copy numbers were stable in 70-100% cells. At any one time, however, relative to clonal means, per-cell chromosome numbers varied +/-18% and chromosome-specific copy numbers varied +/-1 in 0-30% of cells; unstable nonclonal markers were found within karyotype-specific quotas of

Aneuploidy is ubiquitous in cancer and has been causally linked to tumorigenesis.1 Although many decades of intense research have provided invaluable information on the causes and consequences of aneuploidy (reviewed in ref. 1), many questions still remain. For example, it is still unclear whether the degree of aneuploidy observed in cancer is the result of multiple subsequent losses/gains of one to few chromosomes, or if it is the result of an initial tetraploidization event followed by chromosome loss/gain events.2 Furthermore, although tetraploidy has been observed in certain pre-cancerous lesions, thus making it a potential tumor promoter, it is not clear how tetraploidy affects aneuploidization and tumorigenesis.1 In a recent study, Lv, et al. began to provide answers to these questions by characterizing the karyotypes and cell division defects of mouse ovarian surface epithelial (MOSE) cells, which spontaneously transform after in vitro passaging over time.3 Lv, et, al. showed that the rate of cytokinesis failure in MOSE cells increases with passage number, yielding more tetraploid cells.3 These tetraploid cells continue to proliferate, but they display higher rates of chromosome mis-segregation compared to their diploid progenitors, leading to the generation of numerous aneuploid daughter cells.3 Recent studies showing that clustering of supernumerary centrosomes is a major cause of chromosome mis-segregation4-6 support the findings of Lv, et al. To investigate how the observed cellular events affect tumorigenesis, Lv, et al. injected late-passage (p35) MOSE cells into syngenic mice and saw tumors in 100% of mice.3 The rapid transformation of MOSE cells with the concurrent generation of aneuploidy underscores the importance of aneuploidy in tumorigenesis. Indeed, it may be more appropriate to describe the transformation of MOSE cells as aneuploidy-induced instead of spontaneous, since passaging of chromosomally stable immortalized cells for a similar amount of time does not result in tumorigenesis.6 Similar to the study by Lv, et al., previous work in mouse mammary epithelial cells showed the same sequence of events: cytokinesis failure-tetraploidy-aneuploidy-tumorigenesis.7 However, unlike the work by Lv, et al., this sequence of events in mouse mammary epithelial cells relied upon p53 mutation or loss.7 It is unclear whether or not this is true for the MOSE cells used by Lv, et al. Preliminary microarray data indicate a decrease in p53 expression levels in MOSE cells during progression (Schmelz, personal communication), but loss of p53 in MOSE cells has not been reported to date. Thus, it is unlikely that p53 was spontaneously lost in the Lv, et al. and other independent studies using MOSE cells,8 adding to the controversy of a “tetraploidy checkpoint.”9 While more work may be needed to understand whether p53 plays any role in modulating a response to tetraploidy and in the MOSE cancer progression model, it is clear from the work by Lv, et al. that tetraploidy can occur early in tumorigenesis, act as an intermediate for aneuploidization and, ultimately, cause cancer (Fig. 1).3 Figure 1. Tetraploidy can act as an intermediate for aneuploidization and cause cancer. Cells undergoing normal cytokinesis (A) maintain a stable karyotype and exhibit normal growth. Cytokinesis failure (B) generates tetraploid cells whose karyotype ...