Oocyte destruction is activated during viral infection

Abstract

Summary: Viral infection has been associated with a starvation-like state in Drosophila melanogaster. Because starvation and inhibiting TOR kinase activity in vivo result in blocked oocyte production, we hypothesized that viral infection would also result in compromised oogenesis. Wild-type flies were injected with flock house virus (FHV) and survival and embryo production were monitored. Infected flies had a doseresponsive loss of fecundity that corresponded to a global reduction in Akt/TOR signaling. Highly penetrant egg chamber destruction mid-way through oogenesis was noted and FHV coat protein was detected within developing egg chambers. As seen with in vivo TOR inhibition, oogenesis was partially rescued in loss of function discs large and merlin mutants. As expected, mutants in genes known to be involved in virus internalization and trafficking [Clathrin heavy chain (chc) and synaptotagmin] survive longer during infection. However, oogenesis was rescued only in chc mutants. This suggests that viral response mechanisms that control fly survival and egg chamber survival are separable. The genetic and signaling requirements for oocyte destruction delineated here represent a novel host-virus interaction with implications for the control of both fly and virus populations. genesis 50:453-465, 2012. V V C 2011 Wiley Periodicals, Inc.

piRNA pathway is not required for antiviral defense in Drosophila melanogaster

“…and (v) no vpiRNAs are detected during infection with DmelSV, DXV, and FHV, shown to infect ovarian cells (51,52). Taken together, these results indicate that the piRNA pathway is not involved in the antiviral response mediated by vpiRNAs.…”

“…IIV-6 and FHV are not natural Drosophila viruses. Nevertheless, both are able to replicate in D. melanogaster under experimental conditions (49)(50)(51). IIV-6 is commonly used as a DNA virus model, and we thought that vpiRNAs could originate from a DNA source, as is the case for endogenous piRNAs.…”

Immune response costs are associated with changes in resource acquisition and not resource reallocation

“…The reduction in metabolic rate was significantly greater in males than females, whereas feeding reductions were similar in both sexes. We hypothesize that females mobilized energetic resources by resorbing eggs from the ovarioles, as has been shown in both Drosophila and mosquitoes suffering infections (Ahmed & Hurd ; Thomson, Schneemann & Johnson ). Egg resorption may provide females with additional energetic reserves, not available to males, which support metabolism when food acquisition is restricted during immune responses.…”

Viruses and antiviral immunity in Drosophila

“…It is interesting to note that ATP-sensitive potassium channels mediate resistance to FHV in the heart (Croker et al, 2007; Eleftherianos et al, 2011). FHV can also be detected in most if not all cell types and developmental stages of the egg chamber including the germarium (Thomson et al, 2012). FHV infection results in decreased TOR activity in FHV-infected flies and ovaries and leads to the downregulation of Drosophila inhibitor of apoptosis 1 (DIAP1), rendering cells susceptible to apoptotic death (Liu et al, 2013; Settles and Friesen, 2008).…”