CYCLIC ASSEMBLY DISASSEMBLY OF CORTICAL MICROTUBULES DURING MATURATION AND EARLY DEVELOPMENT OF STARFISH OOCYTES

An extensive array of cortical microtubles in oocytes of the starfish P. ochraceus undergoes multiple cycles of disappearance and reappearance during maturation and early development. These events were studied in isolated fragments of the oocyte cortex stained with antitubulin antibodies for indirect immunofluorescence. The meshwork of long microtubules is present in the cortex of immature oocytes (i.e., before treatment with the maturation-inducing hormone 1-methyladenine), for 10-20 min after treatment with 1-methyladenine, after formation of the 2nd polar body (in reduced numbers in unfertilized oocytes), and in the intermitotic period between 1st and 2nd cleavage divisions. The array of cortical microtubules is absent in oocytes undergoing germinal vesicle breakdown, during the 2 meiotic divisions (polar body divisions), and during mitosis of the 1st and, perhaps, subsequent cleavage divisions. The cycle of assembly-disassembly of cortical microtubules is synchronized to the cycle of nuclear envelope breakdown and reformation and to the mitotic cycle; specifically, cortical microtubules are present when a nucleus is intact (germinal vesicle, female pronucleus, zygote nucleus, blastomere nucleus) and are absent whenever a meiotic or mitotic spindle is present. Findings are discussed in terms of microtubule organizing centers in eggs, possible triggers for microtubule assembly and disassembly, eccentric location of the germinal vesicle and regulation of oocyte maturation and cell division.