Chromatin Remodeling and Male Killing Figure 4. Nuclear condensation defects are amplified at cellularization. Embryos are stained for DNA (left panels) and microtubules (right panels). Cellular blastoderm is usually formed by evenly spaced nuclei at the same condensation stage and of the same size and dimensions (A) surrounded by honeycomb microtubular baskets (A9). Abnormal cellular blastoderms are characterized by small (arrow in B) or larger (arrows in C) clusters of picnotic nuclei scattered among normal looking blastoderm nuclei; the honeycomb microtubular baskets are often altered in these embryos (arrowheads in B9, C9). Scale bar is 15 mm. doi:10.1371/journal.pone.0030045.g004 or three polar body spindles (Fig. 7G,G9). Many microtubules converged to the poles of these meiotic-like spindle structures (Fig. 7F9,G9), where bacteria clustered. To verify whether the astral arrays of microtubules were nucleated by true centrosomes, we looked at the localization of centrosomin (Cnn), a master protein required for centrosome organization and maturation [29] and c-tubulin that dictates the nucleation of polarized microtubular arrays [30]. Antibodies against both of these centrosomal proteins recognized distinct spots at the poles of the mitotic spindles (Fig. 8 A,B). The foci of the cytoplasmic asters contained more or less large aggregates of Cnn (Fig. 8C) and c-tubulin (Fig. 8D) suggesting that these microtubule arrays were nucleated by discrete centrosomal material. At the end of meiosis, unfertilized oocytes can retain the large central aster that characterizes the female meiotic spindle. A Cnn aggregate was found in the remnant of the central aster (Fig. 8E). Surprisingly, thin clusters of Cnn material surrounded the periphery of the multi-spindle structures (Fig. 8F), where bacteria accumulated. By contrast, no evidence of Cnn material was associated with the poles of isolated meiotic-like spindles (inset, Fig. 8F), despite the observation that some microtubule bundles were found in aster-like disposition. These findings suggest that these microtubules are not nucleated at the spindle poles and may have an acentrosomal origin. Discussion It has been shown that female insects infected by some species of endosymbiotic bacteria, including the genera Wolbachia and Spiroplasma produce very strong female-biased progeny when PLoS ONE | www.plosone.org 7 January 2012 | Volume 7 | Issue 1 | e30045