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Vol. 18, Issue 11, 4625-4636, November 2007

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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^,, and Mark S. Mooseker^*,,

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

Submitted March 1, 2007; Revised August 14, 2007; Accepted August 31, 2007
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 green fluorescent protein-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 terminal deoxynucleotidyl transferase dUTP nick-end labeling-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 P. 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.

The online version of this article contains supplemental material at MBC Online (http://www.molbiolcell.org).

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

Abbreviations used: BB, brush border; GFP, green fluorescent protein; MV, microvillus/i/ar; Myo1B, myosin IB; TUNEL, terminal deoxynucleotidyl transferase dUTP nick-end labeling.

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