PgmNr W4032: Cortical microtubule dynamics in C. elegans oocytes.

Authors:
C.-H. Chuang; B. Bowerman


Institutes
University of Oregon, Eugene, OR.


Keyword: Other ( Oocyte meiotic spindle assembly )

Abstract:

In many animal oocytes, meiotic spindles assemble in the absence of centrosomes to segregate chromosomes; yet, little is known about the origin of the spindle microtubules and the proteins that regulate spindle microtubule dynamics. We recently showed that in the absence of the microtubule depolymerizing kinesin KLP-7, extra microtubules accumulated around the oocyte chromosomes1. As others have reported2, we also have observed a dramatic increase in microtubule levels throughout the oocyte cortex during meiosis I in klp-7(-) mutant oocytes. To further investigate microtubule dynamics, we are using spinning disc confocal microscopy in live oocytes to image GFP::β-tubulin during meiosis I in both wild-type and klp-7(-) mutants. In klp-7(-) oocytes, we found that microtubule foci were formed at the cortex during prometaphase; some foci moved towards each other and then merged as larger microtubule organizing centers, while other foci moved into the assembling meiotic spindles. In wild-type oocytes, we observed that smaller and less dense of microtubule foci assembled in the cortex area; some foci still merged together, but fewer foci were recruited to the spindles relative to klp-7(-) mutants. We then used a GFP fusion to a spindle pole protein ASPM-1 to further investigate the dynamics of cortical microtubules in wild-type oocytes, and found that GFP::ASPM-1 also was present as multiple foci at the cortex. We are currently making an mKate2 fusion to ASPM-1 to further investigate the interplay of cortical microtubules and ASPM-1. In addition, we have found that the microtubule motor protein complex dynein influences oocyte cortical microtubule dynamics and is essential for proper organization of the oocyte meiotic spindle. In dhc-1(-) oocytes, cortical microtubules were present but did not appear to aggregate as microtubule foci. Moreover, in contrast to the barrel-shaped wild-type spindle, dhc-1(-) spindles collapsed soon after they started to assemble. After collapsing, the spindle microtubules spread around the cortex. Similarly, chromosomes distributed around the cortex, rather than aligning at the equator of the spindle barrel, based on analysis of an mCherry::Histone 2B fusion. We are currently further investigating how cortical microtubules and dynein contribute to oocyte meiotic spindle assembly.



Wormbase Genetic Index
1. klp-7
2. aspm-1
3. dhc-1