Abstracts - Society for Developmental Biology

37
Program/Abstract # 113
Requirement of microtubule based processes in dendrite maintenance
Lee, Jiae, University of Washington, Seattle, United States
Development of a cell into its proper shape is critical for its function. This is especially true in neurons, which display a
great diversity in morphologies. I am using the Drosophila melanogaster peripheral nervous system (PNS) neurons to
identify the cellular machinery involved in ensuring that dendrites maintain their proper shape. I carried out an EMSinduced
mutagenesis screen to unravel the intrinsic factors involved in dendrite establishment and maintenance. From this
screen, I have identified mutants that the dendrite branches distal from the cell body were lost, whereas the proximal area
towards the cell body showed exuberant branching. This demonstrates the presence of distinct domains within the
dendrites is required for proper maintenance of dendrite arborization. For further characterization of these genes, I
monitored the progressivity of the phenotype, and the velocity and intracellular distribution of trafficking organelles. Since
defects in dendrite maintenance have obvious implications for neuronal function and pathologies that are hallmarks of
many neurodevelopmental diseases, understanding of the intrinsic signals will likely facilitate therapeutic intervention in
MR and neurodevelopmental diseases with progressive dendrite pathologies.
Program/Abstract # 114
Talin: A master regulator of Cell-ECM adhesion-dependent morphogenesis
Ellis, Stephanie; Fairchild, Michael; Czerniecki, Stefan; Pines, Mary; Tanentzapf, Guy, University of British Columbia,
Vancouver, Canada
Morphogenesis of a complex body plan requires coordinated regulation of cell adhesion molecules and the cytoskeleton to
form distinct, organized tissues. Integrin adhesion receptors mediate ECM attachment and connect to the cytoskeleton
through the adapter protein, talin. Talin interacts with many binding partners including integrin and F-actin. A delicate
balance of these multiple interactions offers a means of fine-tuning integrin function and linkage to the cytoskeleton. Using
targeted point mutations, we systematically investigate the role of different domains of talin during Drosophila
embryogenesis. Our results suggest that morphogenetic events requiring short term, transient adhesions, such as germband
retraction and dorsal closure, are highly sensitive to mutations in talin that compromise the ability to quickly disassemble
adhesive contacts and linkage to the cytoskeleton. Conversely, in the embryonic and larval musculature, where
myotendinous junctions form adhesive contacts that grow and persist over several days, talin interactions that strengthen
attachment between integrins and the surrounding ECM are of greatest importance. Finally, using FRAP in the living
embryo, we find that disruption of key domains in talin alters the dynamics of talin at adhesions, suggesting talin may be a
master regulator of adhesion stability and cytoskeletal dynamics. Altogether, we demonstrate how the ability of talin to
switch between multiple binding partners comprises an essential mechanism for modulating integrin function to elicit
distinct developmental outcomes.
Program/Abstract # 115
Regulation of nonmuscle myosin II during Drosophila cellularization
Thomas, Jeffrey; Chougule, Ashish; Rosales, Rafael, Texas Tech University Health Sciences Center, Lubbock, United
States
The Drosophila cellular blastoderm is formed by the enclosure of approximately 6,000 peripheral syncytial nuclei by
plasma membrane. The bases of the newly formed cells are partially closed by the constriction of a network of actomyosin
rings at the leading edge of membrane addition. We find that nonmuscle myosin II activity is required for both contraction
and formation of these actomyosin rings. Mutation of the regulatory subunit of nonmuscle myosin II, myosin regulatory
light chain (MRLC, Sqh), causes severe cytoskeletal defects during cellularization: actomyosin rings do not properly form,
are disorganized, and do not contract. A number of different serine/threonine kinases, including Rho kinase (Rok), myosin
light chain kinase (MLCK), and citron kinase, can phosphorylate and activate MRLC. We are investigating the roles of
these potential MRLC regulators in controlling actomyosin dynamics at the cellularization front. Rok has been shown to be
a key regulator of actomyosin during many morphogenetic events in Drosophila. Most of the defects in the cellularization
actomyosin cytoskeleton in rok mutant embryos are caused by earlier embryonic defects; however, cellularization-specific
defects to appear to be present. Mutation of one of the Drosophila MLCK genes, Strn-Mlck, produces no actomyosin
cytoskeletal defects during cellularization. Mutation of another Drosophila MLCK gene, drak, cause striking defects in the
organization of actomyosin rings and abrogates most MRLC phosphorylation during cellularization. Our results suggest
that specific changesin the actomyosin cytoskeleton during cellularization are controlled by the regulation of myosin II
activity by specific MRLC regulatory proteins.