Loy E Volkman

Professor
Ph.D.  Microbiology    University of Washington, Seattle, 1973
B.A.   Zoology    University of California, Riverside, 1967

111 Koshland Hall
Berkeley, California 94720
lvolkman@nature.berkeley.edu
office: 510-642-4500   lab: 510-642-5676   fax:  510-642-4995

     Recent publications     

Our group studies pathogenesis induced by a virus that infects the larvae of lepidopteran insects (moths/butterflies) called Autographa californica M nucleopolyhedrovirus (AcMNPV). The study of this virus provides an opportunity to contribute to the development of biological alternatives to chemical pesticides, as well as to gain insight into the molecular and cell biology of the target organisms and virus-cell interactions.

AcMNPV is the best-studied member of Baculoviridae, a family of viruses restricted to arthropod hosts. Perhaps because of the strict co-evolution of these viruses with their invertebrate hosts, certain aspects of their replicative strategy are not shared by viruses of vertebrates or plants. One unique property recently established, for example, is that actin is essential for the assembly of AcMNPV nucleocapsids. While actin has long been known to be involved in the budding of many enveloped viruses, such a dependence on actin for the assembly of a virus in the nucleus has never been reported before.

One focus of current research is the elucidation of the viral gene products involved in the manipulation of the actin cytoskeleton. The availability of the complete AcMNPV genome sequence and evidence that two viral structural proteins (components of the capsid) are actin-binding proteins provide convenient vantage points from which to investigate this problem. In addition to assembly, evidence suggests that actin is also involved in the transport of AcMNPV nucleocapsids to the nucleus. This problem is also under investigation.

Another focus of research is the comparison of viral pathogenesis in larval insect hosts of varying susceptibilities. Our approach is to use recombinant viruses equipped with reporter genes to compare the progress of infection in susceptible and resistant hosts. This approach has yielded valuable information about important benchmarks of the infection process, as well as identifying resistance barriers in less susceptible hosts. For example, we have learned that decreasing susceptibility of aging insects is a midgut-related phenomenon; that the midgut is cleared of infection during molting; that the insect's tracheal (respiratory) system, the second tissue infected, is the conduit used by the virus for spreading infection within the host and that within highly susceptible hosts, infection of the tracheal system portends death.

Infection of tracheal cells leads to infection of hemocytes, and recently we determined that the inability of hemocytes of the corn ear worm, Helicoverpa zea, to support AcMNPV replication accounts for the majority of the extreme resistance to mortal infection observed in that host. In the fall armyworm, Spodoptera frugiperda, it is the midgut cells that confer organismal protection to infection, as other cell types are highly susceptible. We are using various genetic and cell biological approaches to elucidate the underlying cause of the observed tissue-specific resistances in both hosts.

Finally, the hallmark of baculovirus-induced pathology is liquefaction of the host. This dramatic ending is coincident with death and is mediated by two virus-encoded enzymes, a cathepsin and a chitinase. We are interested in illuminating the interaction and regulation of these two enzymes.

Ohkawa T, Washburn JO, Sitapara R, Sid E, Volkman LE.Specific binding of Autographa californica M nucleopolyhedrovirus occlusion-derived virus to midgut cells of Heliothis virescens larvae is mediated by products of pif genes Ac119 and Ac022 but not by Ac115. J Virol. 2005 Dec;79(24):15258-64.

Zhang JH, Ohkawa T, Washburn JO, Volkman LE. Effects of Ac150 on virulence and pathogenesis of Autographa californica multiple nucleopolyhedrovirus in noctuid hosts. J Gen Virol. 2005 Jun;86(Pt 6):1619-27.

Haas-Stapleton EJ, Washburn JO, Volkman LE. Spodoptera frugiperda resistance to oral infection by Autographa californica multiple nucleopolyhedrovirus linked to aberrant occlusion-derived virus binding in the midgut. J Gen Virol. 2005 May;86(Pt 5):1349-55.

Haas-Stapleton EJ, Washburn JO, Volkman LE. P74 mediates specific binding of Autographa californica M nucleopolyhedrovirus occlusion-derived virus to primary cellular targets in the midgut epithelia of Heliothis virescens Larvae. J Virol. 2004 Jul;78(13):6786-91.

Zhang JH, Washburn JO, Jarvis DL, Volkman LE. Autographa californica M nucleopolyhedrovirus early GP64 synthesis mitigates developmental resistance in orally infected noctuid hosts. J Gen Virol. 2004 Apr;85(Pt 4):833-42.

Haas-Stapleton EJ, Washburn JO, Volkman LE. Pathogenesis of Autographa californica M nucleopolyhedrovirus in fifth instar Spodoptera frugiperda. J Gen Virol. 2003 Aug;84(Pt 8):2033-40.

Milks ML, Washburn JO, Willis LG, Volkman LE, Theilmann DA. Deletion of pe38 attenuates AcMNPV genome replication, budded virus production, and virulence in heliothis virescens. Virology. 2003 Jun 5;310(2):224-34.

Washburn JO, Trudeau D, Wong JF, Volkman LE. Early pathogenesis of Autographa californica multiple nucleopolyhedrovirus and Helicoverpa zea single nucleopolyhedrovirus in Heliothis virescens: a comparison of the 'M' and 'S' strategies for establishing fatal infection. J Gen Virol. 2003 Feb;84(Pt 2):343-51.

Washburn JO, Chan EY, Volkman LE, Aumiller JJ, Jarvis DL. Early synthesis of budded virus envelope fusion protein GP64 enhances Autographa californica multicapsid nucleopolyhedrovirus virulence in orally infected Heliothis virescens. J Virol. 2003 Jan;77(1):280-90.

Ohkawa T, Rowe AR, Volkman LE. Identification of six Autographa californica multicapsid nucleopolyhedrovirus early genes that mediate nuclear localization of G-actin. J Virol. 2002 Dec;76(23):12281-9

Hom LG, Ohkawa T, Trudeau D, Volkman LE. Autographa californica M nucleopolyhedrovirus ProV-CATH is activated during infected cell death. Virology. 2002 May 10;296(2):212-8.

Machesky LM, Insall RH, Volkman LE. WASP homology sequences in baculoviruses. Trends Cell Biol. 2001 Jul;11(7):286-7

Washburn JO, Wong JF, Volkman LE. Comparative pathogenesis of Helicoverpa zea S nucleopolyhedrovirus in noctuid larvae. J Gen Virol. 2001 Jul;82(Pt 7):1777-84.

Trudeau D, Washburn JO, Volkman LE. Central role of hemocytes in Autographa californica M nucleopolyhedrovirus pathogenesis in Heliothis virescens and Helicoverpa zea. J Virol. 2001 Jan;75(2):996-1003.

Washburn JO, Haas-Stapleton EJ, Tan FF, Beckage NE, Volkman LE. Co-infection of Manduca sexta larvae with polydnavirus from Cotesia congregata increases susceptibility to fatal infection by Autographa californica M Nucleopolyhedrovirus. J Insect Physiol. 2000 Feb;46(2):179-190.

Hom LG, Volkman LE. Autographa californica M nucleopolyhedrovirus chiA is required for processing of V-CATH. Virology. 2000 Nov 10;277(1):178-83.

Hoover K, Washburn JO, Volkman LE. Midgut-based resistance of Heliothis virescens to baculovirus infection mediated by phytochemicals in cotton. J Insect Physiol. 2000 Jun 1;46(6):999-1007