November 10, 2011

Mistakes happen. If you are as special as DNA, then you have someone to point out those mistakes and fix them for you. That sounds like your PI editing your manuscript, doesn’t it? Today’s stunning image is from a paper describing DNA repair in meiotic divisions.

When double-strand breaks happen to DNA, the cell has an efficient pathway that recognizes and repairs the breaks to both DNA strands. Two kinase proteins, ATM and ATR, play pivotal roles by phosphorylating numerous key proteins involved in this process. The roles of these two proteins are well-studied in mitosis, but their function in meiosis is not clear. Meiosis is the reductive cell division that results in gametes (ooctyes or sperm). A recent paper describes the role of ATM and ATR in the meiotic cell divisions of fruit fly ovaries. Both ATM and ATR phosphorylate a protein called histone H2AV at the site of DNA breaks, providing a handy and fluorescently-labeled output of ATM and ATR activity. Joyce and colleagues found that ATR plays a role in regulating the cell cycle checkpoint machinery that halts cell cycle progression in the presence of DNA breaks, while ATM is required for the DNA repair of meiotic double strand breaks. As seen in the images above, H2AV levels (red, phosphorylated and unphosphorylated) decreased in the developing oocyte (green) until it was almost undetectable by stages 4 and 5 of oogenesis (see bottom row for higher magnification). These results suggest that either ATM/ATR does not respond to DNA damage at these stages or that repair occurs before these stages (before the first meiotic division).

Joyce, E., Pedersen, M., Tiong, S., White-Brown, S., Paul, A., Campbell, S., & McKim, K. (2011). Drosophila ATM and ATR have distinct activities in the regulation of meiotic DNA damage and repair originally published in The Journal of Cell Biology, 195 (3), 359-367 DOI: 10.1083/jcb.201104121