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Provisional bilateral symmetry in Xenopus eggs is established during maturationDorsal-ventral patterning in the Xenopus egg becomes established midway through the first cell cycle during a 30 degree rotation of the subcortical yolk mass relative to the egg cortex. This 'rotation of symmetrisation' is microtubule dependent, and its direction is thought to be cued by the usually eccentric sperm centrosome. The fact that parthenogenetically activated eggs also undergo a directed rotation, despite the absence of a sperm centrosome, suggests that an endogenous asymmetry in the unfertilised egg supports the directed polymerisation of microtubules in the vegetal cortex, in the way that an eccentric sperm centrosome would in fertilised eggs. Consistent with this idea, we noticed that the maturation spot is usually located an average of more than 15 degrees from the geometric centre of the pigmented animal hemisphere. In parthenogenetically activated eggs, this eccentric maturation spot can be used to predict the direction of rotation. Although in most fertilised eggs the yolk mass rotates toward the sperm entry point (SEP) meridian, occasionally this relationship is perturbed significantly; in such eggs, the maturation spot is never on the same side of the egg as the SEP. In oocytes tilted 90 degrees from upright during maturation in vitro, the maturation spot developed 15 degrees or more from the centre of the pigmented hemisphere, always displaced towards the point on the equator that was up during maturation. This experimentally demonstrated lability is consistent with an off-axis oocyte orientation during oogenesis determining its eccentric maturation spot position, and, in turn, its endogenous rotational bias.
Document ID
20050000309
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
Authors
Brown, E. E.
(Oregon Health Sciences University Portland 97201-3097, United States)
Margelot, K. M.
Danilchik, M. V.
Date Acquired
August 22, 2013
Publication Date
August 1, 1994
Publication Information
Publication: Zygote (Cambridge, England)
Volume: 2
Issue: 3
ISSN: 0967-1994
Subject Category
Life Sciences (General)
Distribution Limits
Public
Copyright
Other
Keywords
NASA Discipline Number 40-20
NASA Discipline Developmental Biology
NASA Program Space Biology
Non-NASA Center

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