Novel Functions for Adherens Junction Components Prior to Gastrulation. D.T. Fox ¹, E.E. Grevengoed ², M.A. Peifer ^1,2. 1) Department of Biology, University of North Carolina, Chapel Hill, NC; 2) Curriculum in Genetics, University of North Carolina, Chapel Hill, NC.

   Within an epithelial sheet, adherens junctions (AJs) establish cell-cell adhesion and transduce cytoskeletal forces. Loss of the AJ component Armadillo (Arm; beta-catenin) from Drosophila embryos disrupts adhesion, polarity, and the cytoskeleton in epithelial cells immediately following AJ establishment at cellularization. Subsequently, gastrulation fails. Thus, AJs provide an essential function following establishment of a cellular blastoderm. Surprisingly, AJ components are also present in the syncitial embryo. Both cadherin, alpha-catenin, and Arm localize to both metaphase furrows during the syncytial divisions and to specific structures during cellularization. This localization led us to examine the function of these proteins prior to gastrulation. During the syncytial nuclear divisions, arm maternally mutant embryos exhibit nuclear fallout due to defects in tethering of microtubules to the cell cortex. Furthermore, embryos maternally mutant for abl kinase, which genetically interacts with arm, exhibit cytoskeletal defects during the syncytial divisions and cellularization, which coincide with a mislocalization of Arm. To determine the full extent of AJ function during early embryogenesis, we are examining embryos maternally and zygotically mutant for either arm or shotgun, the fly ortholog of the AJ component E-Cadherin. We will determine the effect of loss of one AJ component on the localization of other components or F-actin. In addition to identifying early functions for AJ components, this analysis will determine whether loss of AJ function is the primary cause of defects in abl maternally mutant embryos.