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FIGURE 14.3 (Color Ýgure follows p. 206.) Wolbachia distribution and proliferation within cysts during
meiosis and sperm elongation from D. melanogaster (DMB, top row) and D. simulans (DSR, bottom row).
Each of three images shows progressively later stages of spermatogenesis: left, 16-cell spermatocyt; middle,
beginning of spermatid elongation; right, apical region of fully elongated spermatid. DNA is shown as red
(propidium iodide), and Wolbachia are seen as small punctate dots varying in color from yellow to green,
depending on the relative staining intensity of the propidium and the FITC-labeled secondary antibody. In
DMB at the 16-cell spermatocyst stage (top left), essentially no Wolbachia are present, while DSR (bottom
left) display abundant Wolbachia (yellowÏgreen), which are present in numbers great enough to obscure
spermatocyte nuclei (red). During early stages of spermatid elongation (middle) DSR (bottom) contain a
substantial number of Wolbachia at either end of the spermatid, while DMB (top) spermatids contain few, if
any, bacteria. Fully elongated spermatids of both (right) contain Wolbachia , although DSR (bottom) have
substantially greater numbers than DMB (top). All scale bars = 10 nm. [Adapted from Clark, M.E., Veneti,
Z., Bourtzis, K., and Karr, T.L. (2002). Mech. Dev. 111: 3Ï15.]
Cell Biology of Wolbachia -Induced CI
Cytological Studies
CI results in early egg lethality following sperm entry (Jost, 1970; OÔNeill and Karr, 1990;
Reed and Werren, 1995; Callaini et al., 1996; Lassy and Karr, 1996). As a central element of
the ÑmodiÝcationÒ portion of the mod/resc model, understanding how and when Wolbachia
affect sperm function during spermatogenesis is of primary interest. However, manifestation of
the ÑmodiÝcationÒ that results in sperm dysfunction occurs only during and following fertili-
zation. One of the earliest observed defects is chromosomal abnormalities at the Ýrst division
(Callaini et al., 1997). However, this early phenotype is not fully penetrant, and numerous other
developmental abnormalities are present. These additional developmental anomalies include
 
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