Showing papers by "Jeremy A. Squire published in 2003"

Identification of a Cancer Stem Cell in Human Brain Tumors

Abstract: Most current research on human brain tumors is focused on the molecular and cellular analysis of the bulk tumor mass. However, there is overwhelming evidence in some malignancies that the tumor clone is heterogeneous with respect to proliferation and differentiation. In human leukemia, the tumor clone is organized as a hierarchy that originates from rare leukemic stem cells that possess extensive proliferative and self-renewal potential, and are responsible for maintaining the tumor clone. We report here the identification and purification of a cancer stem cell from human brain tumors of different phenotypes that possesses a marked capacity for proliferation, self-renewal, and differentiation. The increased self-renewal capacity of the brain tumor stem cell (BTSC) was highest from the most aggressive clinical samples of medulloblastoma compared with low-grade gliomas. The BTSC was exclusively isolated with the cell fraction expressing the neural stem cell surface marker CD133. These CD133+ cells could differentiate in culture into tumor cells that phenotypically resembled the tumor from the patient. The identification of a BTSC provides a powerful tool to investigate the tumorigenic process in the central nervous system and to develop therapies targeted to the BTSC.

Beckwith–Wiedemann syndrome demonstrates a role for epigenetic control of normal development

Abstract: The Beckwith-Wiedemann syndrome (BWS) is characterized by somatic overgrowth and a predisposition to pediatric embryonal tumors. It is associated with genetic or epigenetic abnormalities in a cluster of imprinted genes found within a genomic region of approximately one megabase on human chromosome 11p15. Imprinted genes are expressed preferentially or exclusively from either the paternal or maternal allele. The 11p15 region is organized into two imprinted domains in which genomic imprinting is controlled by separate 'imprinting control regions'. Twenty-five to 50% of BWS patients have biallelic rather than monoallelic expression of the insulin-like growth factor 2 (IGF2) gene. Another 50% of patients have an epigenetic mutation resulting in loss of imprinting of a transcript called KCNQ1OT1. Each of these genes resides in one of the two imprinted domains that appear to be subject to developmental dysregulation in BWS. In this review, we discuss the insights that the study of BWS have contributed to our understanding of the mechanisms of growth control, oncogenesis and genomic imprinting. Specifically, methylation and chromatin modification may coordinate the expression of closely linked imprinted genes. Finally, we discuss how knowledge of epigenetic mechanisms associated with the early stages of embryogenesis suggest caution in the current debate surrounding assisted reproductive and cloning technologies.

High-resolution mapping of amplifications and deletions in pediatric osteosarcoma by use of CGH analysis of cDNA microarrays.

Abstract: Conventional cytogenetic and comparative genomic hybridization (CGH) studies have shown that osteosarcomas (OSs) are characterized by complex structural and numerical chromosomal alterations and gene amplification. In this study, we used high-resolution CGH to investigate recurrent patterns of genomic imbalance by use of DNA derived from nine OS tumors hybridized to a 19,200-clone cDNA microarray. In six OSs, there was copy number gain or amplification of 6p, with a minimal region of gain centering on segment 6p12.1. In seven OSs, the pattern of amplification affecting chromosome arm 8q showed high-level gains of 8q12–21.3 and 8q22–q23, with amplification of the MYC oncogene at 8q24.2. Seven OSs showed copy number gain or amplification of 17p between the loci bounded by GAS7 and PMI (17p11.2–17p12), and three of these tumors also showed small losses at 17p13, including the region containing TP53. An in silico analysis of the distribution of segmental duplications (duplicons) in this region identified a large number of tracts consisting of paralogous sequences mapping to the 17p region, encompassing the region of deletions and amplifications in OS. Interestingly, within this same region there were clusters of duplicons and several genes that are expressed during bone morphogenesis and in OS. In summary, microarray CGH analysis of the chromosomal imbalances of OS confirm the overall pattern observed by use of metaphase CGH and provides a more precise refinement of the boundaries of genomic gains and losses that characterize this tumor. © 2003 Wiley-Liss, Inc.

Spectral karyotyping identifies recurrent complex rearrangements of chromosomes 8, 17, and 20 in osteosarcomas.

Abstract: Conventional cytogenetic studies have shown that osteosarcomas (OSs) are often highly aneuploid, with a large number of both structural and numerical chromosomal alterations. To investigate the complexity of OS karyotypes in detail, we applied spectral karyotyping (SKY) to a series of 14 primary OS tumors and four established OS cell lines. A total of 531 rearrangements were identified by SKY, of which 300 breakpoints could be assigned to a specific chromosome band. There was an average of 38.5 breakpoints identified by SKY per primary tumor. Chromosome 20 was involved in a disproportionately high number of structural rearrangements, with 38 different aberrations being detected. Chromosomal rearrangements between chromosomes 20 and 8 were evident in four tumors. FISH analysis using a 20q13 subtelomeric probe identified frequent involvement of 20q in complex structural rearrangements of OS cell lines. Characterization of the structural aberrations of chromosomes 8 and 17 by use of SKY demonstrated frequent duplication or partial gains of chromosome bands 8q23-24 and 17p11-13. Other chromosomes frequently involved in structural alteration were chromosomes 1 (47 rearrangements) and 6 (38 rearrangements). Centromeric rearrangements often involving chromosomes 1, 6, 13, 14, 17, and 20 were present. Four of the 14 primary OS tumors were characterized by nonclonal changes that included both structural and numerical alterations. In summary, OS tumors have a very high frequency of structural and numerical alterations, compounded by gross changes in ploidy. This intrinsic karyotype instability leads to a diversity of rearrangements and the acquisition of composite chromosomal rearrangements, with the highest frequency of alteration leading to gain of 8q23-24 and 17p11-13 and rearrangement of 20q. These findings suggest that specific sequences mapping to these chromosomal regions will likely have a role in the development and progression of OS.

Transcriptional profiling of medulloblastoma in children.

Abstract: Object. Although medulloblastoma is the most common malignant brain tumor found in children, little is known about its molecular pathogenesis. The authors have attempted to compare patterns of gene expression in medulloblastoma samples with those in the healthy cerebellum. Methods. The authors used complementary (c)DNA microarray analysis to compare the expression of genes in samples of medulloblastoma and normal cerebellum. The expression levels of a subset of genes were then verified by immunohistochemical analysis. Six genes were identified that were expressed at a much higher level in at least five of six medulloblastomas: ezrin, cyclin D2, high mobility group protein 2, MAPRE1, histone deacetylase 2, and ornithine decarboxylase 1. A number of potentially important genes whose expression was much lower in medulloblastomas than in control cerebellum were also identified: tenascin R, TRK-B, FGF receptor, and death receptor 3. The expression levels of a subset of the identified genes were confirmed by im...

De novo 1q32q44 duplication and distal 1q trisomy syndrome

Abstract: We report on an infant with minor anomalies and a de novo 1q duplication. The chromosomal abnormality was diagnosed prenatally after sonographic detection of cerebral ventriculomegaly and bilateral choroid plexus cysts in the fetus. The amniocentesis showed an abnormal male karyotype, 46,XY,dup(1)(q32q44), subsequently confirmed by fluorescence in situ hybridization using whole chromosome paint 1 and comparative genomic hybridization. The baby, born at 37 weeks of gestation, had wide cranial sutures and large fontanelles, sloping forehead, hypertelorism, short and downward-slanting palpebral fissures, a high-arched and narrow palate, malformed ears, and long feet with overriding second and third toes. This is the sixth case of known duplication involving the 1q32q44 segment; the physical findings in the case reported herein are similar to those of other patients reported previously, providing further evidence of the existence of the “distal 1q trisomy” phenotype. © 2003 Wiley-Liss, Inc.

Chromosomal imbalances detected in primary bone tumors by comparative genomic hybridization and interphase fluorescence in situ hybridization

Abstract: We applied a combination of comparative genomic hybridization (CGH) and fluorescence in situ hybridization (FISH), to characterize the genetic aberrations in three osteosarcomas (OS) and one Ewing's sarcoma. CGH identified recurrent chromosomal losses at 10p14-pter and gains at 8q22.3-24.1 in OS. Interphase FISH allowed to confirm 8q gain in two cases. A high amplification level of 11q12-qter was detected in one OS. The Ewing's sarcoma showed gain at 1p32-36.1 as the sole chromosome alteration. These studies demonstrate the value of molecular cytogenetic methods in the characterization of recurrent genomic alterations in bone tumor tissue.

Genetic Basis of Cancer Progression

Abstract: The current paradigm for the development of cancer is that it is a genetic disease, with the malignant phenotype resulting from an accumulation of genetic alterations. This model was first postulated by Cavenee et al. (1) and further developed by Fearon and Vogelstein (2). In the simplest situation of a hematologic neoplasm, such as chronic myeloid leukemia (CML), neoplasia arises as a direct result of the formation of the Philadelphia chromosome (1). This primary aberration is observed recurrently in CML, and the onset of the more aggressive acute phase of the disease is usually heralded by the acquisition of secondary chromosomal changes (3). Many hematologic neoplasms and sarcomas are characterized by the presence of consistent primary chromosomal rearrangements. However, for most carcinomas, a more complex pattern of acquisition of genomic aberration takes place. An advanced carcinoma may have undergone multiple genetic alterations involving both simple mutations in tumor suppressor genes and oncogenes, as well as extensive karyotypic aberrations. Genetic changes are accompanied by a spectrum of phenotypic changes, and, as the number of genetic aberrations increases, there appears to be a more marked histologic phenotype. Through studies of colon cancer, we understand that colorectal neoplasia arises as a result of the mutational activation of oncogenes coupled with the mutational inactivation of tumor suppressor genes (for a review see ref. 2). It is believed that the total number of genetic changes, rather than the sequence in which they occur, is a primary factor in the development of malignancy. Vogelstein and coworkers found that at least five distinct genetic events were required for colon cancer to develop (2). In this malignancy, the specific genetic changes that lead to the production of invasive carcinoma have been clearly identified: the combination of adenomatous polyposis coli (APC) gene mutations; methylation status alterations; K-ras mutations; DCC (deleted in colon cancer) gene mutations; and p53 mutations. Invasive carcinoma has more genetic alterations than a benign lesion like an adenoma, and, in turn, an adenoma has more genetic alterations than histologically normal epithelium (Fig. 1). This particular model has guided much of our current thinking about how cancer arises.

Advanced cancer genetics in neurosurgical research.

Abstract: RAPID ADVANCES IN the technology used to study nucleic acids have revealed a great deal regarding the underlying biology of cancer. Most cancers arise as a result of chromosomal rearrangements and deoxyribonucleic acid mutations that lead to the activation of proto-oncogenes and loss of function of tumor suppressor genes. There are a number of different molecular routes that lead to these common goals, necessitating several different techniques of mutational analysis. Although many of these techniques can be difficult in practice, most are conceptually simple. We discuss several of the current techniques in cytogenetics and molecular genetics that are widely used in cancer biology laboratories. Understanding the molecular events that lead to cancer should allow the future development of targeted, nontoxic therapeutics similar to modern-day antibiotics. These technologies are being progressively applied in clinical neurosurgery, where they will be used to detect, diagnose, stratify, and treat cancers of the nervous system. High demand from an increasingly educated patient population means that neurosurgeons will need to be familiar with many of these techniques.