Date: 28.05.2019

Changes in vitellogenin expression caused by nematodal and fungal infections in insects

This paper was selected by the editorial board as an 'Inside JEB' featured paper. The results proved protective effect of insect vitellogenin against nematodal and fungal infections.

Photo description: Direct inhibiting effect of vitellogenin on the growth of the Xenorhabdus spp. bacteria tested by the disc diffusion method (mean ± s.d.). Statistically significant difference between the vitellogenin and control groups at 1% level was evaluated by Student’s t-test **. The number above the bar represent fold-difference between vitellogenin and control groups.

Vitellogenins (Vgs) are well-known and well-characterized precursors of yolk proteins involved in the reproduction in the majority of oviparous animals including insects. In this study we examined the expression and role of Vg in the body of the firebug Pyrrhocoris apterus (Heteroptera, Insecta) during the infection elicited by two entomopathogenic organisms, the nematode Steinernema carpocapsae and the fungus Isaria fumosorosea. Infection by S. carpocapsae significantly up-regulated Vg mRNA expression in the male body. The corresponding increase in Vg protein expression was also confirmed by electrophoretic and immunoblotting analyses. Remarkably, the opposite tendency was found in females, where nematodal infection significantly reduced both Vg mRNA and Vg protein expression levels in fat body and haemolymph, respectively. We speculate that infection of reproductive females reduces Vg expression to the level, which is still sufficient for defence, but insufficient for reproduction. This circumstance reduces energy expenditure and helps the individual to cope with the infection. Importantly, purified Vg significantly inhibited growth of Xenorhabdus spp., an entomotoxic bacteria isolated from S. carpocapsae. On the other hand, the effect of Vg against I. fumosorosea was not so obvious. The fungus significantly stimulated Vg gene expression in males, however, a similar increase was not recapitulated on the protein level. Nevertheless, in females, both mRNA and protein Vg levels were significantly reduced after the fungal infection. The obtained data demonstrate that Vg is likely an important defence protein, possibly with a specific activity, which considerably expands the known spectrum of Vg functions.

Kodrík D., Ibrahim E., Gautam U.K., Čapková-Frydrychová R., Bednářová A., Krištůfek V. and Jedlička P. (2019) Changes in vitellogenin expression caused by nematodal and fungal infections in insects. J. Exp. Biol. 222, jeb202853. doi:10.1242/jeb.202853




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