Trypanosomal histone γH2A and the DNA damage response

DNA damage and repair in trypanosomatids impacts virulence, drug resistance and antigenic variation but, currently, little is known about DNA damage responses or cell cycle checkpoints in these divergent protozoa. One of the earliest markers of DNA damage in eukaryotes is γH2A(X), a serine phosphorylated histone H2A (variant). Here, we report the identification and initial characterization of γH2A in Trypanosoma brucei. We identified Thr130 within the replication-dependent histone H2A as a candidate phosphorylation site and found that the abundance of this trypanosomal γH2A increased in vivo in response to DNA damage. Nuclear γH2A foci mark the sites of putative natural replication fork stalling, sites of meganuclease-induced DNA double strand breaks and sites of methyl methanesulphonate-induced DNA damage. Naturally occurring and meganuclease-induced γH2A and RAD51 double-positive repair foci are typically found in S-phase or G2 nuclei. The results link trypanosomal γH2A, with an unusual histone modification motif, to DNA damage sensing and mitotic checkpoint signaling.

105Highlights► Histone H2A phosphorylated at Thr130 is identified as trypanosomal γH2A. ► γH2A nuclear foci mark the putative sites of replication fork stalling. ► γH2A nuclear foci form in response to meganuclease or chemical-induced DNA damage. ► Trypanosomal γH2A and RAD51 positive damage and repair foci are most often seen in S-phase and G2. ► The findings implicate γH2A in mitosis-entry checkpoint signaling.