Breaking symmetry: polarization of the C. elegans zygote Center for Developmental Biology

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Category	Seminar
Date and Time	2011-10-19 16:00 - 17:00
Venue	Seminar Room A7F
Speaker	Fumio Motegi
Affiliation	Dept of Molecular Biology and Genetics, Howard Hughes Medical Institute, Johns Hopkins University School of Medicine
Title	Breaking symmetry: polarization of the C. elegans zygote
Poster	click here to download(PDF)
Host	Shigeo Hayashi
Summary	A hallmark of polarized cells is the segregation of the PAR polarity regulators into asymmetric domains at the cell cortex. Antagonistic interactions involving two conserved kinases, atypical protein kinase C (aPKC) and PAR-1, have been implicated in polarity maintenance, but the mechanisms that initiate the formation of asymmetric PAR domains are not understood. Here, we describe one pathway used by the sperm-donated centrosome to polarize the PAR proteins in Caenorhabditis elegans zygotes. Before polarization, cortical aPKC excludes PAR-1 kinase and its binding partner PAR-2 by phosphorylation. During symmetry breaking, microtubules nucleated by the centrosome locally protect PAR-2 from phosphorylation by aPKC, allowing PAR-2 and PAR-1 to access the cortex nearest the centrosome. Cortical PAR-1 phosphorylates PAR-3, causing the PAR-3/aPKC complex to leave the cortex. Our findings illustrate how microtubules, independent of actin dynamics, stimulate the self-organization of PAR proteins by providing local protection against a global barrier imposed by aPKC.