The salivary protein Saglin facilitates efficient midgut colonization of Anopheles mosquitoes by malaria parasites

Abstract

Malaria is caused by the unicellular parasite Plasmodium which is transmitted to humans through the bite of infected female Anopheles mosquitoes. To initiate sexual reproduction and to infect the midgut of the mosquito, Plasmodium gametocytes are able to recognize the intestinal environment after being ingested during blood feeding. A shift in temperature, pH change and the presence of the insect-specific compound xanthurenic acid have been shown to be important stimuli perceived by gametocytes to become activated and proceed to sexual reproduction. Here we report that the salivary protein Saglin, previously proposed to be a receptor for the recognition of salivary glands by sporozoites, facilitates Plasmodium colonization of the mosquito midgut, but does not contribute to salivary gland invasion. In mosquito mutants lacking Saglin, Plasmodium infection of Anopheles females is reduced, resulting in impaired transmission of sporozoites at low infection densities. Interestingly, Saglin can be detected in high amounts in the midgut of mosquitoes after blood ingestion, possibly indicating a previously unknown host-pathogen interaction between Saglin and midgut stages of Plasmodium. Furthermore, we were able to show that saglin deletion has no fitness cost in laboratory conditions, suggesting this gene would be an interesting target for gene drive approaches.

A population modification gene drive targeting bothSaglinandLipophorinimpairsPlasmodiumtransmission inAnophelesmosquitoes

“…Despite the absence of physical linkage between the two transgenes, DsRed-only individuals were strikingly absent from all early populations, indicative of the lethality of the SagGD vasa transgene in the absence of a protected Lp allele. Importantly, toxicity of SagGD vasa was due to its destructive action on the Lp locus rather than to a fitness cost of its disrupted Saglin host locus, since individuals carrying both DsRed and GFP thrived in all populations, and consistent with the reported absence of obvious fitness cost of Saglin mutants (Klug et al, 2023). Several populations (notably populations 1, 3, 4, 5, 6, 7) rapidly seemed fixed for Lp::Sc2A10.…”

“…To host a GD promoting the spread of Lp::Sc2A10 , we turned our attention to the mosquito Saglin locus, which encodes a Plasmodium agonist (Okulate et al, 2007; Ghosh et al, 2009; O’Brochta et al, 2019; Klug et al, 2023). Indeed, while not leading to complete Plasmodium transmission blockage, the loss of Saglin reduces parasite prevalence and loads, reduces transmission, is homozygous viable and has no obvious fitness cost at least in laboratory conditions (Klug et al, 2023). Similar to an antimicrobial combination therapy, combining Sc2A10 expression with the knockout of Saglin can be expected to reinforce the transmission-blocking properties of each strategy taken alone.…”

Circadian rhythms mediate malaria transmission potential

“…When expression of these genes is knocked down, the efficiency of the mosquito bloodmeal has been shown to decline 41 . Additionally, genes encoding SG1 family proteins, such as SAG (Saglin), TRIO (triple functional domain protein), and GILT (mosquito gamma-interferon-inducible lysosomal thiol reductase), that are associated with infection by malaria parasites 18–20 also showed a cycling profile (Fig. 2A).…”

“…2A). Saglin binds the parasite microneme TRAP (Thrombospondin Related Anonymous Protein) protein and is relevant for parasite invasion of the mosquito midgut and presence in the salivary glands 20,42,43 . Immunization against the Anopheles TRIO protein can reduce the parasite burden in the host after mosquito transmission, suggesting this protein is also important for parasitic infection 21 .…”

Peptides with Antimicrobial Activity in the Saliva of the Malaria Vector Anopheles coluzzii

“…Investigating the complexity of salivary components posed the question of whether saliva might contain antimicrobial activities protecting the mouthparts and the initial phases of blood-or sugar-feeding processes. In fact, salivary proteins are reingested by blood-feeding insects [14,15,63] and, therefore, could be involved in minimizing the bacterial growth in both sugar meal (stored in the crop) and blood meal (digested in the gut). In this work, we started a search for antimicrobial activities in mosquito saliva and, employing a catalogue of A. gambiae salivary proteins, we selected a short list of candidates according to the following criteria: (i) the absence of sequence similarity to any known protein; (ii) the presence of sequence/structural features typical of antimicrobial peptides; and (iii) the tissue-and sex-specific expression profile.…”