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Antagonistic functions of Par-1 kinase and protein phosphatase 2A are required for localization of Bazooka and photoreceptor morphogenesis in Drosophila.

ABSTRACT: Establishment and maintenance of apical basal cell polarity are essential for epithelial morphogenesis and have been studied extensively using the Drosophila eye as a model system. Bazooka (Baz), a component of the Par-6 complex, plays important roles in cell polarity in diverse cell types including the photoreceptor cells. In ovarian follicle cells, localization of Baz at the apical region is regulated by Par-1 protein kinase. In contrast, Baz in photoreceptor cells is targeted to adherens junctions (AJs). To examine the regulatory pathways responsible for Baz localization in photoreceptor cells, we studied the effects of Par-1 on Baz localization in the pupal retina. Loss of Par-1 impairs the maintenance of AJ markers including Baz and apical polarity proteins of photoreceptor cells but not the establishment of cell polarity. In contrast, overexpression of Par-1 or Baz causes severe mislocalization of junctional and apical markers, resulting in abnormal cell polarity. However, flies with similar overexpression of kinase-inactive mutant Par-1 or unphosphorylatable mutant Baz protein show relatively normal photoreceptor development. These results suggest that dephosphorylation of Baz at the Par-1 phosphorylation sites is essential for proper Baz localization. We also show that the inhibition of protein phosphatase 2A (PP2A) mimics the polarity defects caused by Par-1 overexpression. Furthermore, Par-1 gain-of-function phenotypes are strongly enhanced by reduced PP2A function. Thus, we propose that antagonism between PP2A and Par-1 plays a key role in Baz localization at AJ in photoreceptor morphogenesis.

SUBMITTER: Nam SC

PROVIDER: S-EPMC1975814 | biostudies-literature | 2007 Jun

REPOSITORIES: biostudies-literature

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Antagonistic functions of Par-1 kinase and protein phosphatase 2A are required for localization of Bazooka and photoreceptor morphogenesis in Drosophila.

Nam Sang-Chul SC Mukhopadhyay Bibhash B Choi Kwang-Wook KW

Developmental biology 20070401 2

Establishment and maintenance of apical basal cell polarity are essential for epithelial morphogenesis and have been studied extensively using the Drosophila eye as a model system. Bazooka (Baz), a component of the Par-6 complex, plays important roles in cell polarity in diverse cell types including the photoreceptor cells. In ovarian follicle cells, localization of Baz at the apical region is regulated by Par-1 protein kinase. In contrast, Baz in photoreceptor cells is targeted to adherens junc ...[more]

PMID: 17475233

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Project description:The location of proteins that contribute to synaptic function has been widely studied in vertebrate synapses, far more than at model synapses of the genetically manipulable fruit fly, Drosophila melanogaster. Drosophila photoreceptor terminals have been extensively exploited to characterize the actions of synaptic genes, and their distinct and repetitive synaptic ultrastructure is anatomically well suited for such studies. Synaptic release sites include a bipartite T-bar ribbon, comprising a platform surmounting a pedestal. So far, little is known about the composition and precise location of proteins at either the T-bar ribbon or its associated synaptic organelles, knowledge of which is required to understand many details of synaptic function. We studied the localization of candidate proteins to pre- or postsynaptic organelles, by using immuno-electron microscopy with the pre-embedding method, after first validating immunolabeling by confocal microscopy. We used monoclonal antibodies against Bruchpilot, epidermal growth factor receptor pathway substrate clone 15 (EPS-15), and cysteine string protein (CSP), all raised against a fly head homogenate, as well as sea urchin kinesin (antibody SUK4) and Discs large (DLG). All these antibodies labeled distinct synaptic structures in photoreceptor terminals in the first optic neuropil, the lamina, as did rabbit anti-DPAK (Drosophila p21 activated kinase) and anti-Dynamin. Validating reports from light microscopy, immunoreactivity to Bruchpilot localized to the edge of the platform, and immunoreactivity to SUK4 localized to the pedestal of the T-bar ribbon. Anti-DLG recognized the photoreceptor head of capitate projections, invaginating organelles from surrounding glia. For synaptic vesicles, immunoreactivity to EPS-15 localized to sites of endocytosis, and anti-CSP labeled vesicles lying close to the T-bar ribbon. These results provide markers for synaptic sites, and a basis for further functional studies.

Dataset Information

Antagonistic functions of Par-1 kinase and protein phosphatase 2A are required for localization of Bazooka and photoreceptor morphogenesis in Drosophila.

Publications

Antagonistic functions of Par-1 kinase and protein phosphatase 2A are required for localization of Bazooka and photoreceptor morphogenesis in Drosophila.

Similar Datasets

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