Identification of a TNF-TNFR-like system in malaria vectors (Anopheles stephensi) likely to influence Plasmodium resistance

Abstract

Identification of Plasmodium-resistance genes in malaria vectors remains an elusive goal despite the recent availability of high-quality genomes of several mosquito vectors. Anopheles stephensi, with its three distinctly-identifiable forms at the egg stage, correlating with varying vector competence, offers an ideal species to discover functional mosquito genes implicated in Plasmodium resistance. Recently, the genomes of several strains of An. stephensi of the type-form, known to display high vectorial capacity, were reported. Here, we report a chromosomal-level assembly of an intermediate-form of An. stephensi strain (IndInt), shown to have reduced vectorial capacity relative to a strain of type-form (IndCh). The contig level assembly with a L50 of 4 was scaffolded into chromosomes by using the genome of IndCh as the reference. The final assembly shows a heterozygous paracentric inversion, 3Li, involving 8 Mbp, which is syntenic to the extensively-studied 2La inversion implicated in Plasmodium resistance in An. gambiae involving 21 Mbp. Deep annotation of genes within the 3Li region in the IndInt assembly using the state-of-the-art protein-fold prediction and other annotation tools reveals the presence of a tumor necrosis factor-alpha (TNF-alpha) like gene, which is the homolog of the Eiger gene in Drosophila. Subsequent chromosome-wide searches revealed homologs of Wengen (Wgn) and Grindelwald (Grnd) genes, which are known to be the receptors for Eiger in Drosophila. We have identified all the genes in IndInt required for Eiger-mediated signaling by analogy to the TNF-alpha system, suggesting the presence of a functionally-active Eiger signaling pathway in IndInt. Comparative genomics of the three type-forms with that of IndInt, reveals structurally disruptive mutations in Eiger gene in all three strains of the type-form, suggesting compromised innate immunity in the type-form as the likely cause of high vectorial capacity in these strains. This is the first report of the presence of a homolog of Eiger in malaria vectors, known to be involved in cell death in Drosophila, within an inversion region in IndInt syntenic to an inversion associated with Plasmodium resistance in An. gambiae.

Aeroplane Wing, a New Recessive Autosomal Phenotypic Marker in Malaria Vector, Anopheles Stephensi Liston

“…However, 50 % propionic acid is used usually for long-time preserved samples fixed in Carnoy's solution from field-collected mosquito samples. In this study, the 3Li inversion in ae mutant persists as in its parental line (T 6 ), with a reduced frequency (19.64 % in ae mutants and 47.45 % in iso T 6 lines) [25]. Notably, inversion is the most prominent adaptation mechanism for new biotic and abiotic environment.…”

Aeroplane wing, a new recessive autosomal phenotypic marker in malaria vector,Anopheles stephensiListon

“…Precise morphometric analysis of mutant eggs shows the egg-float ridge numbers ranged between 15 and 16, which is helpful in its classification under intermediate variants. The 3Li inversion in ae mutant persists as in its parental line (T6), however with a reduced frequency (19.64% in ae mutants and 47.45%, in Iso T6 lines) [25]. Notably, inversion is the most prominent adaptation mechanism for new biotic and abiotic environment.…”

TNF signaling mediates cellular immune function and promotes malaria parasite killing in the mosquitoAnopheles gambiae

“…gambiae, demonstrating the effects of TNF signaling in limiting malaria parasite survival and immune cell regulation. While further study is required to fully determine the influence of TNF signaling on mosquito physiology and immune function, there is significant evidence, in addition to that provided herein, that TNF signaling is a central component that defines mosquito vectorial capacity and the susceptibility to Plasmodium infection in natural mosquito populations [36]. As a result, our study represents an important contribution to our understanding of the mechanisms of malaria parasite killing and the collective efforts to develop novel approaches for malaria control.…”

“…Across vertebrate systems, components of TNF signaling have remained conserved, consisting of a TNF-α ligand and two receptors: the TNFR1 and TNFR2 [34]. Previous phylogenetic analyses have revealed the presence of orthologous TNF pathways in invertebrates [35,36], however few studies have examined TNF signaling beyond Drosophila . With the Drosophila TNF pathway comprising an analogous TNF ligand, Eiger , and the receptors, Wengen ( Wgn ) and Grindelwald ( Grnd ) [37], Drosophila TNF signaling regulates several physiological processes, including tissue growth regulation, cellular proliferation, development, and host defense [38], with significant contributions of hemocytes in mediating these functions [39,40].…”