Author(s)

María Vittoria Di Tomaso, Silvia Basso, Laura Lafon-Hughes, Gustavo Saona, Beatriz López-Carro, Ana Laura Reyes-Ábalos, Pablo Liddle

Environmental Quality Evaluation and Control Service, Municipality of Montevideo, Montevideo, Uruguay.
Genetics Department, Instituto de Investigaciones Biológicas Clemente Estable, Montevideo, Uruguay.

In eukaryotes, a cascade of events named DNA damage response (DDR) has evolved to handle DNA lesions. DDR engages the recruitment of signaling, checkpoint control, repair and chromatin remodeling protein complexes, allowing cell cycle delay, DNA repair or induction of apoptosis. An early DDR event involves the phosphorylation of the histone variant γH2AX on serine 139 (H2AX¹³⁹ phosphorylation) originating the so-called γH2AX. DDR-related H2AX¹³⁹ phosphorylation have been extensively studied in interphase nuclei. More recently, γH2AX signals on mitotic chromosomes of asynchronously growing cell cultures were observed. We performed a quantitative analysis of γH2AX signals on γH2AX immunolabeled cytocentrifuged metaphase spreads, analyzing the γH2AX signal distributions of CHO9 chromosomes harboring homologous regions both in control and bleomycin (BLM)-treated cultures. We detected γH2AX signals in CHO9 chromosomes of controls which significantly increase after BLM-exposure. γH2AX signals were uniformly distributed in chromosomes of controls. However, the γH2AX signal distribution in BLM exposed cells was significantly different between chromosomes and among chromosome regions, with few signals near the centromeres and a tendency to increase towards the telomeres. Interestingly, both basal and BLM-induced γH2AX signal distribution were statistically equal between CHO9 homologous chromosome regions. Our results suggest that BLM exerts an effect on H2AX¹³⁹ phosphorylation, prevailing towards acetylated and gene-rich distal chromosome segments. The comparable H2AX¹³⁹ phosphorylation of homologous regions puts forward its dependence on chromatin structure or function and its independence of the position in the karyotype.

H2AX Phosphorylation on Serine 139, γH2AX Signals, Metaphase Chromosomes, Homologous Chromosome Regions, CHO9 Chinese Hamster Cell Line

Di Tomaso, M. , Basso, S. , Lafon-Hughes, L. , Saona, G. , López-Carro, B. , Reyes-Ábalos, A. and Liddle, P. (2014) Spontaneous and Bleomycin-Induced γH2AX Signals in CHO9 Metaphase Chromosomes. Advances in Bioscience and Biotechnology, 5, 603-616. doi: 10.4236/abb.2014.57071.