Chromatin Remodeling and Male Killing Figure 7. The early arrested phenotype is not due to Wolbachia. Eggs at different times AED were fixed and incubated with antibodies against b-tubulin (green), acetylated-a-tubulin (blue), and counterstained with Hoechst 33258 (red). Unfertilized eggs showed cytoplasmic asters that increase in number with age (A,B,C, arrows); old eggs also display smaller cortical asters (arrowheads). (E) Occasionally a sperm tail is found within the eggs that show cytoplasmic asters (arrowheads). Bacteria are associated with the cytoplasmic arrays of microtubules (arrowheads, inset D). (F) Unfertilized eggs from the uninfected KOS1 females also contain cytoplasmic asters. Bacteria are also observed at the poles of the meiotic-like spindles (arrowheads, F,G), where aster-like microtubule arrays are found (arrows, F9,G9). Scale bar is 25 mm in A,B,E; 15 mm in C; 4 mm in D; 5 mm in F,G. doi:10.1371/journal.pone.0030045.g007 in addition to or as alternatives to the elements of the sex determination machinery. The observation that the bacterium Arsenophonus nasoniae inhibits the formation of maternal centro- somes thus leading to mitotic defects associated with embryo death in Nasonia, indicates that bacteria have evolved different mecha- nisms for inducing male-killing in arthropods [15]. Although the activity of Wolbachia on chromatin remodeling during male-killing in Drosophila bifasciata appears unquestionably based on the chromosome segregation/condensation defects we observed, it remains unclear whether the spectrum of defects we observed affect all the chromosomes within the same spindle, why only the chromatin of male embryos is affected, and which specific mechanisms are involved. PLoS ONE | www.plosone.org 10 January 2012 | Volume 7 | Issue 1 | e30045