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Fig. 2. klp67A mutants exhibit karyokinetic and cytokinetic failure during meiosis. (A) Phase-contrast image of onion-stage spermatids taken from a klp67A mutant. Unlike wild-type control spermatids which contain a single nucleus and phase dense Nebenkern, those in the mutants may contain two nuclei of equal or varying sizes, indicative of cytokinetic failure and in the latter case, of segregation defects as well. (B-I) A gallery of spindles taken from the wild type and klp67A mutant primary spermatocytes; tubulin is shown in green, DNA in blue and the centriole marker, Centrin in red. In klp67A mutants the centrosomes separate and form highly aberrant bipolar spindles. Unlike control spindles seen during metaphase (B) and anaphase (E), those in klp67A mutants are poorly organised (C,D,F-I). Ectopic MTs are present in the regions of the spindle as well as in the surrounding cytoplasm. The astral MTs are more robust than in wild-type cells and may form bundles that run around the cell periphery (C). The chromosomes sometimes appear entangled in the increased numbers of MTs found in the spindle. Kinetochore fibres in klp67A mutants could be hard to discern and often have an elongated and bent morphology (arrowheads in C). In contrast to wild-type anaphase/telophase cells (E) mutants lack a distinct central spindle but are filled with ectopic MTs and abnormal MT structures (F-I). Note how the chromosomes appear to segregate in unequal masses and initiate decondensation at non-polar locations. Some chromosomes may be linked together by non-centrosomal MT bundles (arrow in H) or have MT bundles oriented in opposite directions, suggestive of merotelic malorientation (arrowhead in I). Bars, 10 µm.
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