Xenopus Oocyte Polarity and Meiotic Maturation

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The Xenopus oocyte, after undergoing a prolonged period of growth, remains in a state of developmental arrest in the ovary. In response to progesterone, the oocyte resumes meiosis, is released from the surrounding follicle cells, and becomes a fertilizable egg. This process has been shown by Dr. Robinson not to invlove an increase in calcium, at least insofar as can be detected by calcium microelectrodes or aequorin. Using his modified fluorescence microscope and the calcium indicator fura 2, he propose to probe the cortical region to a depth of about 10microm. underneath the plasma membrane and determine if there are increases or decreases in calcium during the maturation process. Dr. Robinson will also look for gradients of calcium associated with the animal-vegetal axis of the oocytes. These measurements will be extended to the smaller oocytes that are in the process of developing and expressing the primary polarity axis. Using the method of fluorescence polarization, Dr. Robinson will measure membrane fluidity during maturation induced by steroid and non-steroid agonists, with the aim of identifying a common mechanism of action. In collaboration with Dr. Susan Strome, Dr. Robinson will extend the calcium and vibrating probe measurements to the early development of Caenorhabditis elegans oocytes and zygotes. The significance of this research lies to two areas. The first is that of the mechanism of steroid hormone interaction with cells. It has long been thought that steroid hormones exert their effects directly on the genetic machinery. In the amphibian oocyte on the other hand, progesterone is known to have its effect at the surface of the cell, although the nature of the surface-hormone interaction is unknown. Recently, it has become apparent that a surface effect is a general feature of steroid hormone action. The second aspect of this work addresses the important problem of pattern formation.