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First published online 3 October 2007
doi: 10.1242/dev.011361

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Cortical granule exocytosis in C. elegans is regulated by cell cycle components including separase

¹ University of Wisconsin-Madison, Laboratory of Molecular Biology, 1525 Linden Drive, Madison, WI 53706, USA.
² Laboratory of Biochemistry and Genetics, NIDDK, National Institutes of Health, Building 8, Room 323, 8 Center Drive, Bethesda, MD 20892-0840, USA.
³ Growth and Development, Biozentrum, University of Basel, Klingelbergstrasse 50/70, CH-4056 Basel, Switzerland.

^* Author for correspondence (e-mail: jbembenek{at}wisc.edu)

Accepted 13 August 2007

In many organisms, cortical granules undergo exocytosis following fertilization, releasing cargo proteins that modify the extracellular covering of the zygote. We identified cortical granules in Caenorhabditis elegans and have found that degranulation occurs in a wave that initiates in the vicinity of the meiotic spindle during anaphase I. Previous studies identified genes that confer an embryonic osmotic sensitivity phenotype, thought to result from abnormal eggshell formation. Many of these genes are components of the cell cycle machinery. When we suppressed expression of several of these genes by RNAi, we observed that cortical granule trafficking was disrupted and the eggshell did not form properly. We conclude that osmotic sensitivity phenotypes occur because of defects in trafficking of cortical granules and the subsequent formation of an impermeable eggshell. We identified separase as a key cell cycle component that is required for degranulation. Separase localized to cortically located filamentous structures in prometaphase I upon oocyte maturation. After fertilization, separase disappeared from these structures and appeared on cortical granules by anaphase I. RNAi of sep-1 inhibited degranulation in addition to causing extensive chromosomal segregation failures. Although the temperature-sensitive sep-1(e2406) allele exhibited similar inhibition of degranulation, it had minimal effects on chromosome segregation. These observations lead us to speculate that SEP-1 has two separable yet coordinated functions: to regulate cortical granule exocytosis and to mediate chromosome separation.

Key words: Anaphase promoting complex, Cortical granule exocytosis, Egg activation, Separase, Spindle assembly checkpoint, C. elegans, Meiosis

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Development 2007 134: e2103. [Full Text]  

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