TITLE:
Spontaneous and Bleomycin-Induced γH2AX Signals in CHO9 Metaphase Chromosomes
AUTHORS:
María Vittoria Di Tomaso, Silvia Basso, Laura Lafon-Hughes, Gustavo Saona, Beatriz López-Carro, Ana Laura Reyes-Ábalos, Pablo Liddle
KEYWORDS:
H2AX Phosphorylation on Serine 139, γH2AX Signals, Metaphase Chromosomes, Homologous Chromosome Regions, CHO9 Chinese Hamster Cell Line
JOURNAL NAME:
Advances in Bioscience and Biotechnology,
Vol.5 No.7,
June
10,
2014
ABSTRACT:
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.