Direct association of Bazooka/PAR-3 with the lipid phosphatase PTEN reveals a link between the PAR/aPKC complex and phosphoinositide signaling
2005
Cell polarity in Drosophila epithelia, oocytes and neuroblasts is
controlled by the evolutionarily conserved PAR/aPKC complex, which consists of
the serine-threonine protein kinase aPKC and the PDZ-domain proteins Bazooka
(Baz) and PAR-6. The PAR/aPKC complex is required for the separation of apical
and basolateral plasma membrane domains, for the asymmetric localization of
cell fate determinants and for the proper orientation of the mitotic spindle.
How the complex exerts these different functions is not known. We show that
the lipid phosphatase PTEN directly binds to Baz in vitro and in vivo, and
colocalizes with Baz in the apical cortex of epithelia and neuroblasts. PTEN
is an important regulator of phosphoinositide turnover that antagonizes the
activity of PI3-kinase. We show that Pten mutant ovaries and embryos
lacking maternal and zygotic Pten function display phenotypes
consistent with a function for PTEN in the organization of the actin
cytoskeleton. In freshly laid eggs, the germ plasm determinants oskar
mRNA and Vasa are not localized properly to the posterior cytocortex and pole
cells do not form. In addition, the actin-dependent posterior movement of
nuclei during early cleavage divisions does not occur and the synchrony of
nuclear divisions at syncytial blastoderm stages is lost. Pten mutant
embryos also show severe defects during cellularization. Our data provide
evidence for a link between the PAR/aPKC complex, the actin cytoskeleton and
PI3-kinase signaling mediated by PTEN.
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