Abstract
The Drosophila protein kinase Par-1 is expressed throughout Drosophila development, but its function has not been extensively characterized because of oocyte lethality of null mutants. In this report, we have characterized the function of Par-1 in embryonic and post-embryonic epithelia. Par-1 protein is dynamically localized during embryonic cell polarization, transiently restricted to the lateral membrane domain, followed by apicolateral localization. We depleted maternal and zygotic par-1 by RNAi and revealed a requirement for Par-1 in establishing cell polarity. Par-1 restricts the coalescing adherens junction to an apicolateral position and prevents its widespread formation along the lateral domain. Par-1 also promotes the localization of lateral membrane proteins such as Delta. These activities are important for the further development of cell polarity during gastrulation. By contrast, Par-1 is not essential to maintain epithelial polarity once it has been established. However, it still has a maintenance role since overexpression causes severe polarity disruption. Additionally, we find a novel role for Par-1 in Notch signal transduction during embryonic neurogenesis and retina determination. Epistasis analysis indicates that Par-1 functions upstream of Notch and is critical for proper localization of the Notch ligand Delta.
Highlights
The distribution of cellular components in asymmetric patterns produces polarized cells, which are critical for the building and maintenance of multicellular organisms
We present evidence that Par-1 is essential for restriction of the adherens junction (AJ) within the blastoderm
Par-1 is expressed throughout embryonic development and in imaginal discs The first embryonic epithelium in Drosophila to develop is the blastoderm, which forms by cellularization
Summary
The distribution of cellular components in asymmetric patterns produces polarized cells, which are critical for the building and maintenance of multicellular organisms. The Drosophila Par-1 kinase acts within the developing fly oocyte to establish the anteroposterior axis of the resulting embryo through localization and stabilization of polarized mRNAs and proteins that pattern the embryo (Riechmann and Ephrussi, 2004; Riechmann et al, 2002; Shulman et al, 2000; Tomancak et al, 2000). Reduction of Par activity in hypomorphic mutant oocytes results in embryos with abnormal posterior patterning and missing germ cells (Shulman et al, 2000; Tomancak et al, 2000). Analysis of null par-1 alleles has shown that Par-1 is critical for earlier events during oogenesis such as the maintenance of oocyte fate (Huynh et al, 2001)
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