Submitted September 5, 2006
Returned for revision October 12, 2006
Accepted February 2, 2007
Gamete Biology
Allocation of Gamma-Tubulin Between Oocyte Cortex and
Meiotic Spindle Influences Asymmetric Cytokinesis in the
Mouse Oocyte
Susan L. Barrett
and
David F. Albertini *
* To whom correspondence should be addressed. E-mail: dalbertini{at}kumc.edu.
Abstract
In oocytes, asymmetric cytokinesis represents a conserved
strategy for karyokinesis during meiosis to retain
ooplasmic maternal factors needed after fertilization.
This study focused on gamma-tubulin as a key regulator of
asymmetric cytokinesis in mouse oocytes given its role in
cell cycle progression and microtubule dynamics.
Gamma-tubulin properties were studied using multiple-label
digital imaging, western blots, quantitative RT-PCR and
microinjection strategies in mouse oocytes matured in vivo
(IVO) or in vitro (IVM). Quantitative image analysis
established that IVO oocytes extrude smaller first PBs,
contain smaller spindles and more cytoplasmic microtubule
organizing centers (MTOCs) relative to IVM oocytes.
Maturation in culture was shown to alter gamma-tubulin
distribution evidenced by incorporation throughout the
meiotic spindle and within the first PB. Western blot
analysis confirmed that total gamma-tubulin content
remained elevated in IVM oocytes compared to IVO oocytes.
Analysis of gamma-tubulin mRNA during maturation revealed
fluctuations in IVO oocytes whereas IVM oocytes maintained
relatively stable at lower levels for the time points
examined (0-16hrs). Selective reduction of gamma-tubulin
mRNA by injection of siRNA diminished both spindle and
polar body size whereas overexpression of
pEGFP-gamma-tubulin had the opposite effect. Together,
these studies reinforce the notion that limiting
gamma-tubulin availability during meiotic maturation
ensures coordination of karyokinesis and cytokinesis and
conservation of gamma-tubulin as an embryonic reserve.
Key words:
Cumulus cells •
Follicle-stimulating hormone •
Meiosis •
Oocyte development •
Ovum
