Evidence for karyogamy and exchange of genetic material in the binucleate intestinal parasite Giardia intestinalis.

The diplomonad parasite Giardia intestinalis contains two functionally equivalent nuclei that are inherited independently during mitosis. Although presumed to be asexual, Giardia has low levels of allelic heterozygosity, indicating that the two nuclear genomes may exchange genetic material. Fluorescence in situ hybridization performed with probes to an episomal plasmid suggests that plasmids are transferred between nuclei in the cyst, and transmission electron micrographs demonstrate fusion between cyst nuclei.

Kinesin-13 regulates flagellar, interphase, and mitotic microtubule dynamics in Giardia intestinalis.

Microtubule depolymerization dynamics in the spindle are regulated by kinesin-13, a nonprocessive kinesin motor protein that depolymerizes microtubules at the plus and minus ends. Here we show that a single kinesin-13 homolog regulates flagellar length dynamics, as well as other interphase and mitotic dynamics in Giardia intestinalis, a widespread parasitic diplomonad protist. Both green fluorescent protein-tagged kinesin-13 and EB1 (a plus-end tracking protein) localize to the plus ends of mitotic and interphase microtubules, including a novel localization to the eight flagellar tips, cytoplasmic anterior axonemes, and the median body.

Three-dimensional analysis of mitosis and cytokinesis in the binucleate parasite Giardia intestinalis.

In the binucleate parasite Giardia intestinalis, two diploid nuclei and essential cytoskeletal structures including eight flagella are duplicated and partitioned into two daughter cells during cell division. The mechanisms of mitosis and cytokinesis in the binucleate parasite Giardia are poorly resolved, yet have important implications for the maintenance of genetic heterozygosity. To articulate the mechanism of mitosis and the plane of cell division, we used three-dimensional deconvolution microscopy of each stage of mitosis to monitor the spatial relationships of conserved cytological markers to the mitotic spindles, the centromeres and the spindle poles.

The fission yeast homolog of the human transcription factor EAP30 blocks meiotic spindle pole body amplification.

Centrosome aberrations caused by misregulated centrosome maturation result in defective spindle and genomic instability. Here we report that the fission yeast homolog of the human transcription factor EAP30, Dot2, negatively regulates meiotic spindle pole body (SPB, the yeast equivalent of centrosome) maturation. dot2 mutants show excess electron-dense material accumulating near SPBs, which we refer to as aberrant microtubule organization centers (AMtOCs).