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Title: Tissue specificity of a baculovirus expressed, basement membrane-degrading protease in larvae of Heliothis virescens

Author
item TANG, HAILIN - IOWA STATE UNIV
item LI, HUARONG - IOWA STATE UNIV
item LEI, SAMANTHA - IOWA STATE UNIV.
item GATEHOUSE, JOHN - DURHAM UNIV.
item Harrison, Robert - Bob
item BONNING, BRYONY - IOWA STATE UNIV.

Submitted to: Tissue and Cell
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/23/2007
Publication Date: 12/1/2007
Citation: Tang, H., Li, H., Lei, S. M., Harrison, R. L., Bonning, B.C. 2007. Tissue specificity of a baculovirus-expressed, basement membrane-degrading protease in larvae of Heliothis virescens. Tissue and Cell. 39:431-443.

Interpretive Summary: Insect pests cause billions of dollars of damage to crops each year. The use of chemical insecticides to control insect pests can have negative ecological, environmental, and health consequences. Baculoviruses are insect viruses that can kill harmful insects on plants without the need to use chemical insecticides. However, the success of baculoviruses for insect control is limited by their slow speed of action against insect pests. A gene has been inserted into a baculovirus that caused the baculovirus to kill insect pests faster. The gene causes the baculovirus to make a new protein that quickly kills the insect. In this study, the effects of this new protein on the insect’s body were examined. The information in this study will help researchers develop baculovirus strains with better insecticidal activity. Baculoviruses have a wide range of applications in addition to their use in controlling insects, and this study will be of interest to scientists in academia, government, and industry who work with this group of viruses.

Technical Abstract: ScathL is a cathepsin L-like cysteine protease from flesh fly Sarcophaga peregrina, which digests components of the basement membrane during insect metamorphosis. A recombinant baculovirus (AcMLF9.ScathL) expressing ScathL kills larvae of the tobacco budworm, Heliothis virescens, significantly faster than the wild type virus and triggers melanization and tissue fragmentation shortly before death. The tissue fragmentation was assumed to be a direct consequence of basement membrane degradation by ScathL. The goal of this study was to investigate the tissue specificity of ScathL when expressed by AcMLF9.ScathL using light, transmission and scanning electron microscopy. Baculovirus expression of ScathL resulted in damage to the basement membrane overlying the midgut, fat body and muscle fibers in larvae infected with AcMLF9.ScathL, but not in larvae infected with the control virus AcMLF9.ScathL.C146A or wild type virus AcMNPV C6. Injection of recombinant ScathL and high levels of baculovirus-mediated expression of ScathL resulted in complete loss of the gut. Extensive damage to the basement membrane mediated by ScathL likely resulted in loss of viability of the underlying tissue and subsequent death of the insect. These results confirm the conclusion of an earlier study (Philip et al, Insect Biochem. Molec. Biol. 2007) of the remarkable specificity of this protease.