In vivo and in vitro analyses of a Bombyx mori nucleopolyhedrovirus mutant lacking functional vfgf

Abstract

All lepidopteran baculovirus genomes sequenced to date encode a viral fibroblast growth factor homolog (vfgf), suggesting that vfgf may play an important role in the infection cycle of lepidopteran baculoviruses. Here, we describe the characterization of a Bombyx mori nucleopolyhedrovirus (BmNPV) mutant lacking functional vfgf. We constructed a vfgf deletion mutant (BmFGFD) and characterized it in BmN cells and B. mori larvae. We observed that budded virus (BV) production was reduced in BmFGFD-infected BmN cells and B. mori larvae. The larval bioassays also revealed that deletion of vfgf did not reduce the infectivity; however, the mutant virus did take 20 h longer to kill B. mori larvae than wild-type BmNPV, when tested either by BV injection or by polyhedrin-inclusion body ingestion. These results suggest that BmNPV vfgf is involved in efficient virus production in BmN cells and B. mori larvae.

Viral fibroblast growth factor, matrix metalloproteases, and caspases are associated with enhancing systemic infection by baculoviruses

“…Slower time of death implies that vfgf accelerates the rate of infection and insect death. Evidence for this is shown here and with another baculovirus (14).…”

“…Hosts infected with AcBAC-vfgfKO take longer to die, especially following oral infection (7,14). Slower time of death implies that vfgf accelerates the rate of infection and insect death.…”

Open reading frame Bm21 of Bombyx mori nucleopolyhedrovirus is not essential for virus replication in vitro, but its deletion extends the median survival time of infected larvae

“…It has been demonstrated that deletion of the egt gene from certain baculovirus genomes increases the speed of killing of the baculoviruses (O'Reilly & Miller, 1991;Flipsen et al, 1995;Chen et al, 2000). Fibroblast growth factor gene (fgf) is conserved in baculoviruses (Katsuma et al, 2004) and is involved in efficient BV production and stimulation of migration of insect cells (Katsuma et al, 2006;Detvisitsakun et al, 2007). The deletion of fgf delayed the time of death of infected larvae (Katsuma et al, 2006;Detvisitsakun et al, 2007).…”

“…Fibroblast growth factor gene (fgf) is conserved in baculoviruses (Katsuma et al, 2004) and is involved in efficient BV production and stimulation of migration of insect cells (Katsuma et al, 2006;Detvisitsakun et al, 2007). The deletion of fgf delayed the time of death of infected larvae (Katsuma et al, 2006;Detvisitsakun et al, 2007). Baculovirus chitinase is involved in the liquefaction of infected larvae.…”

Recent Advances in Our Knowledge of Baculovirus Molecular Biology and Its Relevance for the Registration of Baculovirus-Based Products for Insect Pest Population Control

“…Conserved only in alphabaculoviruses and betabaculoviruses, but absent in midgut-restricted gammabaculoviruses and deltabaculoviruses, viral FGF (vFGF) has been shown to accelerate BV exit from midgut cells and secondary infection by rerouting the host respiratory system to the midgut epithelium by mimicking host FGF. Although not essential for host infection per se, the difference in speed of establishment of systemic infection and speed of kill (Detvisitsakun et al, 2007;Katsuma et al, 2006) is thought to impact the capacity of any given virus to infect different hosts (Passarelli, 2011).…”