Epsilon Open Archive

Abstract

Mosquitoes are vectors of numerous pathogens that cause human diseases, putting
more than half of the world’s population at risk. These diseases are transmitted when a
mosquito takes a blood meal following the successful seeking of a human host. Hostseeking
is highly state dependent and predominantly mediated by olfactory cues. The
goal of this thesis is to describe the neuropeptidergic regulation of the state dependent
odour-mediated host-seeking behaviour.
In order to identify and characterize the neuropeptides that are modulated by feeding
and are involved in host-seeking, I analysed the antennal lobes, the primary olfactory
centre, of Aedes aegypti, using semi-quantitative MALDI-TOF mass spectrometry.
Functional evidence for the involvement of the identified neuropeptides in the
regulation of host-seeking was provided using neuropeptide injections. I demonstrated
that short neuropeptide F-2 (sNPF-2) and allatostatin-A-5 (AstA-5) are regulated upon
blood feeding and that the injection of a binary mix of sNPF-2 and AstA-5 inhibited
host-seeking in non-blood fed mosquitoes, mimicking the effect of a blood meal. I next
characterized the sNPF and AstA receptors (sNPFR and AstAR) from Ae. aegypti and
two other important disease vectors, Culex quinquefasciatus and Anopheles coluzzii
assessing the receptor conservation and function as well as the regulation of the
receptors in response to blood feeding. Within the AstA signalling system, I described a
dipteran-specific duplication of the AstARs (R1 and R2) in mosquitoes. Functional
characterization revealed that the AstAR2s show a higher sensitivity to AstAs
compared to AstAR1s in the culicine mosquitoes Ae.aegypti and Cx. quinquefasciatus.
In contrast, both AstARs in An. coluzzii showed a similar sensitivity to the AstA
ligands, which suggests a divergence in the AstA signalling in mosquitoes. This is in
contrast to the sNPFRs in the three species, which showed a high conservation in
structure and receptor sensitivity. Blood feeding results in a selective regulation of
transcript abundance of the more sensitive AstAR2 and the sNPFR in Cx.
quinquefasciatus, but not in Ae. aegypti or An. coluzzii. This is indicative of differences
in the regulatory mechanisms for AstA and sNPF in Cx. quinquefasciatus compared
with the other species.
In this thesis, I provide strong evidence that host-seeking is regulated by complex
mechanisms involving at least two neuropeptidergic systems. These findings may shed
new light on previous results and should encourage further investigation of other
neuropeptide families. The functional characterization of the AstA and sNPF receptors
leads to a better understanding of the conservation and regulation of neuropeptide
signalling system and provides new targets for future research.