Abstract
Unequal segregation of cell fate determinants at mitosis is a conserved mechanism whereby cell fate diversity can be generated during development. In Drosophila, each sensory organ precursor cell (SOP) divides asymmetrically to produce an anterior pIIb and a posterior pIIa cell. The Par6-aPKC complex localizes at the posterior pole of dividing SOPs and directs the actin-dependent localization of the cell fate determinants Numb, Partner of Numb (Pon) and Neuralized at the opposite pole. The plasma membrane lipid phosphatidylinositol (4,5)-bisphosphate (PIP2) regulates the plasma membrane localization and activity of various proteins, including several actin regulators, thereby modulating actin-based processes. Here, we have examined the distribution of PIP2 and of the PIP2-producing kinase Skittles (Sktl) in mitotic SOPs. Our analysis indicates that both Sktl and PIP2 reporters are uniformly distributed in mitotic SOPs. In the course of this study, we have observed that overexpression of full-length Pon or its localization domain (LD) fused to the Red Fluorescent Protein (RFP::PonLD) results in asymmetric distribution of Sktl and PIP2 reporters in dividing SOPs. Our observation that Pon overexpression alters polar protein distribution is relevant because RFP::PonLD is often used as a polarity marker in dividing progenitors.
Highlights
Ontogenesis of complex multicellular organisms involves the generation of different cell types
(A,A9), ENTH::GFP (B,B9) and GFP::Sktl (C,C9) was examined by live imaging (A–C0) or by antibody staining in dividing sensory organ precursor cell (SOP) expressing Red Fluorescent Protein (RFP)::PonLD (A0,B0,C0,D0). Both PIP2 reporters and GFP::Sktl (C; 83%; n = 18) localize at the posterior pole of dividing SOPs at prometaphase when co-expressed with RFP::PonLD
A fusion protein consisting of the Red Fluorescent Protein (RFP) fused to the Cterminal localization domain of Partner of Numb (Pon) (RFP::PonLD) [11,24] was coexpressed with the PIP2 reporters to reveal SOP polarity
Summary
Ontogenesis of complex multicellular organisms involves the generation of different cell types. Each mechanosensory bristle located on the notum of Drosophila is composed of four different cells. These cells originate from a single sensory organ precursor cell (SOP) via a fixed lineage comprising four stereotyped asymmetric cell divisions [3]. Two regulators of Notch receptor signaling, Numb and Neuralized (Neur), localize at the anterior cortex of dividing SOPs and segregate into the anterior daughter cell [5,6]. Numb inhibits Notch whereas Neur positively regulates the signaling activity of the Notch ligand Delta This leads to Notch inhibition in the anterior cell that adopts the pIIb fate and Notch activation in the posterior cell that becomes pIIa
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