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MBC in Press, published online ahead of print September 12, 2007
Mol. Biol. Cell 10.1091/mbc.E07-02-0191

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Submitted on March 1, 2007
Revised on August 14, 2007
Accepted on August 31, 2007

Roles for Drosophila melanogaster Myosin IB in Maintenance of Enterocyte Brush Border Structure and Resistance to the Bacterial Pathogen, Pseudomonas entomophila

Peter S. Hegan,* Valerie Mermall,* Lewis G. Tilney,{dagger}{ddagger} and Mark S. Mooseker*{ddagger}{sect}

*Department of Molecular, Cellular, and Developmental Biology, Yale University, New Haven, CT 06520; {dagger}Department of Biology, University of Pennsylvania, Philadelphia, PA 19104; {ddagger}Marine Biological Laboratory, Woods Hole, MA 02543; {sect}Departments of Cell Biology and Pathology, Yale School of Medicine, New Haven, CT 06511

Monitoring Editor: M. Bishr Omary

Drosophila myosin IB (Myo1B) is one of two class I myosins in the Drosophila genome. In the larval and adult midgut enterocyte, Myo1B is present within the microvillus (MV) of the apical brush border (BB) where it forms lateral tethers between the MV membrane and underlying actin filament core. Expression of GFP-Myo1B tail domain in the larval gut showed that the tail domain is sufficient for localization of Myo1B to the BB. A Myo1B deletion mutation exhibited normal larval gut physiology with respect to food uptake, clearance and pH regulation. However, there is a threefold increase in TUNEL-positive enterocyte nuclei in the Myo1B mutant. Ultrastructural analysis of mutant midgut revealed many perturbations in the BB, including membrane tethering defects, MV vesiculation and membrane shedding. The apical localization of both singed (fascin) and Dmoesin is impaired. BBs isolated from mutant and control midgut revealed that the loss of Myo1B causes the BB membrane and underlying cytoskeleton to become destabilized. Myo1B mutant larvae also exhibit enhanced sensitivity to oral infection by the bacterial pathogen, Pseudomonas entomophila, and severe cytoskeletal defects are observed in the BB of proximal midgut epithelial cells soon after infection. Resistance to Pseudomonas entomophila infection is restored in Myo1B mutant larvae expressing a Myo1B transgene. These results indicate that Myo1B may play a role in the local midgut response pathway of the Imd innate immune response to Gram-negative bacterial infection.

Address correspondence to: Peter S. Hegan (peter.hegan{at}yale.edu)






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