73 Oral - Cell Biology II
Friday April 08, 10:45 AM - 11:00 AM

Authors:
Anna Yeh ¹; Julian Eskin ²; Bruce Goode ²; Adam Martin ¹

Affiliations:
1) MIT; 2) Brandeis University

Keywords:
a. cytoskeleton; d. compartments and boundaries

Actin networks undergo dynamic rearrangements that promote morphogenesis in the developing embryo. Therefore, actin network dynamics must be tightly regulated in space and time. The range of mechanisms that control actin network assembly and organization during development is still not fully understood. The Drosophila Synaptotagmin-like protein, Bitesize (Btsz), has been shown to organize actin at epithelial cell apical junctions in a manner that is thought to depend on its interaction with the actin-binding protein, Moesin. Through the maternal depletion of Btsz by RNA interference (RNAi), we discovered that Btsz functions at earlier, syncytial stages of development. In the syncytial embryo, nuclei separated by metaphase furrows undergo rounds of synchronous divisions. Btsz-RNAi disrupts these metaphase furrows, leading to spindle collisions and nuclear division defects, similar to mutants in the formin Diaphanous. Interestingly, we identified an amino acid motif in Btsz, that is similar to a formin elongation effector domain (FEED) found in yeast formin regulators. Additionally, purified Btsz protein containing FEED stimulates formin activity and directly interacts with F-actin through the C-terminal half of the protein in vitro. To test the functional requirement of Btsz isoforms that contain this motif, we used CRISPR/Cas9 to engineer a btsz mutant, that specifically targets FEED-containing isoforms. Our preliminary data suggest FEED-containing isoforms and to a lesser extent, MBD-containing isoforms are important for the syncytial stages of development. This work suggests a novel mechanism regulating actin assembly during animal development.