Establishing cell polarity
The early embryo undergoes rapid nuclear cell divisions resulting in a syncytial blastoderm embryo, in which around 6000 nuclei share a common cytoplasm. The subdivision of this syncytial embryo into a cellular blastoderm embryo occurs during cellularization, which represents a concerted cytokinetic event combined with the establishment of a polarized blastoderm epithelium. We are using cellularization as a paradigm to study mechanisms for the generation of cell polarity.
Our current work is focussed on understanding the regulation of cell polarity complexes and microtubule transport during cellularization. We are focusing on maternal effect genes required for cellularization and identified both transcriptional (Lilliputian) and cytoskeletal (RhoGEF2) regulators. Our current work tries to elucidate the role of the maternal effect gene drop out (dop), which exhibits an exciting new phenotype, indicating a role for the gene product in membrane assembly and microtubule transport.
Cellularization of the Drosophila embryo: After 13 mitotic cell divisions, the syncytial blastoderm undergoes cellularization within about 60min at 23°C forming the blastoderm epithelium. In the syncytial embryo entering interphase of cycle 14, membrane insertion (green arrowheads) takes place apically (orange) and the original egg plasma membrane forms the tip of the invading membrane, called furrow canal (orange). At the same time, basal adherens junctions are formed (gray bar). Membrane growth continues at a relatively slow rate. In the last third, membrane growth accelerates to a fast rate at the time when the furrow canals passed the basal level of the nuclei. In addition to the basal junction, spot adherens junctions (black bars) form along the lateral cell surfaces with a bias towards the apical region. The predominant site for membrane insertion is now at the lateral membrane domain (green arrowheads). After cellularization a polarized epithelium has formed with apical (red) and basolateral (green) membrane domains, apical adherens junctions (black bars) and an adjacent subapical region (blue bars.
Cellularization in wildtype and drop out mutant embryos: Wildtype and drop out mutant embryos at progressing stages of cellularization stained with antibodies against Armadillo/beta-Catenin (red) labelling adherens junctions, peanut (septin homolog) labelling the furrow canal and DAPI (blue) labelling nuclear DNA.