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Fig. 6. Furrow ingression in wild-type spermatocytes. (A) DIC images and (B) corresponding images from a time-lapse series of a wild-type primary spermatocyte expressing GFP-tagged ß-tubulin (Inoue et al., 2004). Fluorescence shown is the maximum intensity projection and the DIC image is from the central-most focal plane. Time is shown in minutes relative to anaphase onset (0). During metaphase I the nucleus is surrounded by a double-nuclear membrane, three to five layers of double parafusorial membranes and mitochondria which lie just outside, although parallel, to this membrane system (Fuller, 1993) that can be seen as parallel contrasting structures by DIC optics. As the cell enters anaphase the spindle elongates, central spindle microtubules form and the cleavage furrow is initiated (8 minutes, arrows). The furrow ingresses, and compresses the central spindle microtubules. A ring canal, detected in this cell at 19 minutes (arrow), encircles the parafusorial membranes (19 minutes, arrowheads). Dissolution of the aligned parafusorial membranes occurs on average 4 minutes before cleavage (23 minutes), which occurs at 28 minutes as assessed by the appearance of GFP-ß-tubulin at the cell periphery and by the complete breakdown of the parafusorial membranes seen by DIC. The central spindle microtubules are compacted to a maximal point at around 19 minutes and appear to gradually `degrade' as cleavage progresses (19-36 minutes GFP panels). See supplementary material, Movie 1. Bar, 10 µm.
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