Autophagic cell death restricts chromosomal instability during replicative crisis.

Replicative crisis is a senescence-independent process that acts as a final barrier against oncogenic transformation by eliminating pre-cancerous cells with disrupted cell cycle checkpoints1. It functions as a potent tumour suppressor and culminates in extensive cell death. Cells rarely evade elimination and evolve towards malignancy, but the mechanisms that underlie cell death in crisis are not well understood. Here we show that macroautophagy has a dominant role in the death of fibroblasts and epithelial cells during crisis. Activation of autophagy is critical for cell death, as its suppression promoted bypass of crisis, continued proliferation and accumulation of genome instability. Telomere dysfunction specifically triggers autophagy, implicating a telomere-driven autophagy pathway that is not induced by intrachromosomal breaks. Telomeric DNA damage generates cytosolic DNA species with fragile nuclear envelopes that undergo spontaneous disruption. The cytosolic chromatin fragments activate the cGAS-STING (cyclic GMP-AMP synthase-stimulator of interferon genes) pathway and engage the autophagy machinery. Our data suggest that autophagy is an integral component of the tumour suppressive crisis mechanism and that loss of autophagy function is required for the initiation of cancer.

Topokaryotyping demonstrates single cell variability and stress dependent variations in nuclear envelope associated domains.

Analysis of large-scale interphase genome positioning with reference to a nuclear landmark has recently been studied using sequencing-based single cell approaches. However, these approaches are dependent upon technically challenging, time consuming and costly high throughput sequencing technologies, requiring specialized bioinformatics tools and expertise. Here, we propose a novel, affordable and robust microscopy-based single cell approach, termed Topokaryotyping, to analyze and reconstruct the interphase positioning of genomic loci relative to a given nuclear landmark, detectable as banding pattern on mitotic chromosomes. This is accomplished by proximity-dependent histone labeling, where biotin ligase BirA fused to nuclear envelope marker Emerin was coexpressed together with Biotin Acceptor Peptide (BAP)-histone fusion followed by (i) biotin labeling, (ii) generation of mitotic spreads, (iii) detection of the biotin label on mitotic chromosomes and (iv) their identification by karyotyping. Using Topokaryotyping, we identified both cooperativity and stochasticity in the positioning of emerin-associated chromatin domains in individual cells. Furthermore, the chromosome-banding pattern showed dynamic changes in emerin-associated domains upon physical and radiological stress. In summary, Topokaryotyping is a sensitive and reliable technique to quantitatively analyze spatial positioning of genomic regions interacting with a given nuclear landmark at the single cell level in various experimental conditions.

Multicolor karyotype analyses of mouse embryonic stem cells.

The manipulation of embryonic stem (ES) cells to introduce directional genetic changes into the genome of mice has become an important tool in biomedical research. Monitoring of cell morphology before and after DNA manipulation and special culture conditions are a prerequisite to preserve the pluripotent properties of ES cells and thus their ability to generate chimera and effective germline transmission (GLT). It has been reported that prolonged cell culturing may affect the diploid chromosomal composition of cells and therefore the percentage of chimerism and GLT. Herein, we report multicolor-fluorescence in situ hybridization (M-FISH) analysis of four different ES cell lines/clones. Although the morphology of all four ES cell lines/clones appeared normal and all four expressed the early markers Oct-3/4 and Nanog, two cell lines presented consistent numerical and structural chromosome aberrations. We demonstrate that M-FISH is a sensitive and accurate method for a comprehensive karyotype analysis of ES cells and may minimize time, costs, and disappointments due to inadequate ES cell sources.

High resistance to X-rays and therapeutic carbon ions in glioblastoma cells bearing dysfunctional ATM associates with intrinsic chromosomal instability.

PURPOSE: To investigate chromosomal instability and radiation response mechanisms in glioblastoma cells. METHODS AND MATERIALS: We undertook a comparative analysis of two patient-derived glioblastoma cell lines. Their resistance to low and high linear energy transfer (LET) radiation was assessed using clonogenic survival assay and their intrinsic chromosome instability status using fluorescence in situ hybridization. DNA damage was analyzed by pulsed-field gel electrophoresis and by γ-H2AX foci quantification. Expression of DNA damage response proteins was assessed by immunoblot. RESULTS: Increased radioresistance to X-rays as well as carbon ions was observed in glioblastoma cells exhibiting high levels of naturally occurring chromosomal instability and impaired Ataxia-telangiectasia mutated (ATM) signaling, as reflected by lack of phosphorylation of ATM, CHK2 and p53 after double-strand breaks induction. CONCLUSION: Our results indicate the existence of highly radioresistant glioblastoma cells, characterized by dysfunctional ATM signaling and high levels of intrinsic chromosomal instability.

Defined conditions for the isolation and expansion of basal prostate progenitor cells of mouse and human origin.

Methods to isolate and culture primary prostate epithelial stem/progenitor cells (PESCs) have proven difficult and ineffective. Here, we present a method to grow and expand both murine and human basal PESCs long term in serum- and feeder-free conditions. The method enriches for adherent mouse basal PESCs with a Lin(-)SCA-1(+)CD49f(+)TROP2(high) phenotype. Progesterone and sodium selenite are additionally required for the growth of human Lin(-)CD49f(+)TROP2(high) PESCs. The gene-expression profiles of expanded basal PESCs show similarities to ESCs, and NF-kB function is critical for epithelial differentiation of sphere-cultured PESCs. When transplanted in combination with urogenital sinus mesenchyme, expanded mouse and human PESCs generate ectopic prostatic tubules, demonstrating their stem cell activity in vivo. This novel method will facilitate the molecular, genomic, and functional characterization of normal and pathologic prostate glands of mouse and human origin.

Comparison of genomic abnormalities between BRCAX and sporadic breast cancers studied by comparative genomic hybridization.

Very little is known about the chromosomal regions harbouring genes involved in initiation and progression of BRCAX-associated breast cancers. We applied comparative genomic hybridization (CGH) to identify the most frequent genomic imbalances in 18 BRCAX hereditary breast cancers and compared them to chromosomal aberrations detected in a group of 27 sporadic breast cancers. The aberrations observed most frequently in BRCAX tumours were gains of 8q (83%), 19q (67%), 19p (61%), 20q (61%), 1q (56%), 17q (56%) and losses of 8p (56%), 11q (44%) and 13q (33%). The sporadic cases most frequently showed gains of 1q (67%), 8q (48%), 17q (37%), 16p (33%), 19q (33%) and losses of 11q (26%), 8p (22%) and 16q (19%). Losses of 8p and gains 8q, 19 as well as gains of 20q (with respect to ductal tumours only) were detected significantly more often in BRCAX than in sporadic breast cancers. Analysis of 8p-losses and 8q-gains showed that these aberrations are early events in the tumorigenesis of BRCAX tumors. The findings of this report indicate similarities between BRCAX and BRCA2 tumours, possibly suggesting a common pathway of disease. These findings need confirmation by more extensive studies because only a limited number of cases were analysed and there are relatively few reports published.

Study of 30 patients with unexplained developmental delay and dysmorphic features or congenital abnormalities using conventional cytogenetics and multiplex FISH telomere (M-TEL) integrity assay.

Cryptic subtelomeric chromosome rearrangements are a major cause of mild to severe mental retardation pointing out the necessity of sensitive screening techniques to detect such aberrations among affected patients. In this prospective study a group of 30 patients with unexplained developmental retardation and dysmorphic features or congenital abnormalities were analysed using the recently published multiplex FISH telomere (M-TEL) integrity assay in combination with conventional G-banding analysis. The patients were selected by one or more of the following criteria defined by de Vries et al.: (a) family history with two or more affected individuals, (b) prenatal onset growth retardation, (c) postnatal growth abnormalities, (d) facial dysmorphic features, (e) non-facial dysmorphism and congenital abnormalities. In addition, we included two patients who met these criteria and revealed questionable chromosome regions requiring further clarification. In four patients (13.3%) cryptic chromosome aberrations were successfully determined by the M-TEL integrity assay and in two patients with abnormal chromosome regions intrachromosomal aberrations were characterized by targetted FISH experiments. Our results accentuate the requirement of strict selection criteria prior to patient testing with the M-TEL integrity assay. Another essential precondition is high-quality banding analysis to identify structural abnormal chromosomes. The detection of familial balanced translocation carriers in 50% of the cases emphasizes the significance of such an integrated approach for genetic counselling and prenatal diagnosis.