Novel In Vivo CometChip Reveals NDMA-Induced DNA Damage and Repair in Multiple Mouse Tissues

The comet assay is a versatile assay for detecting DNA damage in eukaryotic cells. The assay can measure the levels of various types of damage, including DNA strand breaks, abasic sites and alkali-sensitive sites. Furthermore, the assay can also be modified to include purified DNA glycosylases so that alkylated and oxidized bases can be detected. The CometChip is a higher throughput version of the traditional comet assay and has been used to study cultured cells. Here, we have tested its utility for studies of DNA damage present in vivo. We show that the CometChip is effective in detecting DNA damage in multiple tissues of mice exposed to the direct-acting methylating agent methylmethane sulfonate (MMS) and to the metabolically activated methylating agent N-nitrosodimethylamine (NDMA), which has been found to contaminate food, water, and drugs. Specifically, results from MMS-exposed mice demonstrate that DNA damage can be detected in cells from liver, lung, kidney, pancreas, brain and spleen. Results with NDMA show that DNA damage is detectable in metabolically competent tissues (liver, lung, and kidney), and that DNA repair in vivo can be monitored over time. Additionally, it was found that DNA damage persists for many days after exposure. Furthermore, glycosylases were successfully incorporated into the assay to reveal the presence of damaged bases. Overall, this work demonstrates the efficacy of the in vivo CometChip and reveals new insights into the formation and repair of DNA damage caused by MMS and NDMA.

Abstract LB-289: Genomic instability and the development of high-grade gliomas

Genome stability is crucial for normal mammalian development. Broadly, genome maintenance is carried out by two distinct mechanisms; functional integration of DNA replication and DNA damage response signaling. Neural cells are particularly sensitive to DNA strand breaks and defective DNA damage responses can result in detrimental effects to the nervous system, including neurodegenerative disease and cancer. It remains unclear which DNA repair pathways are critical for preventing DNA damage accumulation in stem and progenitor cells. The same mechanisms that protect progenitor genomes also suppress DNA mutations that can result in cancer. A primary objective of the current study is delineation of key factors for genome stability that prevent tumorigenesis during cortical neurogenesis. We have compared the differential effects of inactivation of homologous recombination (HR) and non-homologous end-joining (NHEJ) towards tumorigenesis by directing their deletion specifically to early cortical progenitors in mouse models. We recently found that coincident loss of either of these repair pathways result in high-grade glioma formation. Furthermore, modelling histone H3 mutations found in human high-grade glioma, specifically the H3.3 K27M mutation, we found that gliomagenesis was accelerated after defective HR (Brca2 loss) or NHEJ (Lig4 loss), although the resultant cancers showed distinct differences in penetrance and diffusion throughout the cortex. Interestingly, gliomas resulting from NHEJ inhibition were more penetrant and diffuse than brain tumors subsequent from HR loss. Gene expression analysis through RNA sequencing is currently being used to identify causative events that drive these individual tumor identities. Embryonic analysis has further shown that inhibition of these repair pathways in combination with the H3.3 K27M mutation results in distinct spatiotemporal DNA damage early in cortical development. Our recent discoveries support cortical progenitor susceptibility to genomic damage is not only influenced by a critical early period of development but also the suppression of specific tumorigenic mutations involving DNA damage repair pathways and histone modifications during neurogenesis.

Citation Format: Lee J. Pribyl, Susanna M. Downing, Cristel V. Camacho, Jon D. Larson, Suzanne J. Baker, Peter J. McKinnon. Genomic instability and the development of high-grade gliomas [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr LB-289.

Method for obtaining primary ovarian cancer cells from solid specimens

Reliable tools for investigating ovarian cancer initiation and progression are urgently needed. While the use of ovarian cancer cell lines remains a valuable tool for understanding ovarian cancer, their use has many limitations. These include the lack of heterogeneity and the plethora of genetic alterations associated with extended in vitro passaging. Here we describe a method that allows for rapid establishment of primary ovarian cancer cells form solid clinical specimens collected at the time of surgery. The method consists of subjecting clinical specimens to enzymatic digestion for 30 min. The isolated cell suspension is allowed to grow and can be used for downstream application including drug screening. The advantage of primary ovarian cancer cell lines over established ovarian cancer cell lines is that they are representative of the original specific clinical specimens they are derived from and can be derived from different sites whether primary or metastatic ovarian cancer.

D-elg, a member of the Drosophila ets gene family: sequence, expression and evolutionary comparison

We have cloned a cDNA from the Drosophila elg gene, a new member of the ets family of genes. The D-elg gene is located at 97D on chromosome 3R and is expressed as a 2.0kb RNA in the embryos, pupae and adults, with no detectable expression in third instar larvae. D-elg expression is observed in all cells of early stage embryos, prior to transcriptional activation of the zygotic genome, and is maintained throughout embryogenesis with no regional localization. The cDNA encodes a predicted protein of 15.4kD that has an 86 amino acid sequence with 72% similarity to the carboxy terminal region of the Drosophila ets-2 gene. Comparison with all known ets genes allows us to define a minimal region required for assignment to the ets gene family.

The Drosophila ets-2 gene: molecular structure, chromosomal localization, and developmental expression

The cellular homologs of the ets gene from the avian erythroblastosis retrovirus E26 have been studied in chickens, humans, mice, and cats. In this report a further evolutionary step is taken by isolating and characterizing a Drosophila ets-related genomic clone. Sequence analysis of this clone has shown it to contain the 3' end of the v-ets gene, called ets-2, corresponding to the last two exons of chicken ets. The predicted amino acid sequence was found to have over 90% homology when compared to that of v-ets. This is the highest level of conservation observed for any previously characterized Drosophila oncogene homolog. Expression of the ets-2 gene occurs throughout development, but is highest during the embryonic and pupal stages. By in situ hybridization, the ets-2 chromosomal position was determined to be 58A/B which corresponds to no known phenotypic mutant. As this is a highly conserved gene, the Drosophila model system should prove useful for the determination of the ets gene function.