Gene copy number and function of the APL1 immune factor changed during Anopheles evolution

Abstract

Background: The recent reference genome assembly and annotation of the Asian malaria vector Anopheles stephensi detected only one gene encoding the leucine-rich repeat immune factor APL1, while in the Anopheles gambiae and sibling Anopheles coluzzii, APL1 factors are encoded by a family of three paralogs. The phylogeny and biological function of the unique APL1 gene in An. stephensi have not yet been specifically examined. Methods: The APL1 locus was manually annotated to confirm the computationally predicted single APL1 gene in An. stephensi. APL1 evolution within Anopheles was explored by phylogenomic analysis. The single or paralogous APL1 genes were silenced in An. stephensi and An. coluzzii, respectively, followed by mosquito survival analysis, experimental infection with Plasmodium and expression analysis. Results: APL1 is present as a single ancestral gene in most Anopheles including An. stephensi but has expanded to three paralogs in an African lineage that includes only the Anopheles gambiae species complex and Anopheles christyi. Silencing of the unique APL1 copy in An. stephensi results in significant mosquito mortality. Elevated mortality of APL1-depleted An. stephensi is rescued by antibiotic treatment, suggesting that pathology due to bacteria is the cause of mortality, and indicating that the unique APL1 gene is essential for host survival. Successful Plasmodium development in An. stephensi depends upon APL1 activity for protection from high host mortality due to bacteria. In contrast, silencing of all three APL1 paralogs in An. coluzzii does not result in elevated mortality, either with or without Plasmodium infection. Expression of the single An. stephensi APL1 gene is regulated by both the Imd and Toll immune pathways, while the two signaling pathways regulate different APL1 paralogs in the expanded APL1 locus. Conclusions: APL1 underwent loss and gain of functions concomitant with expansion from a single ancestral gene to three paralogs in one lineage of African Anopheles. We infer that activity of the unique APL1 gene promotes longevity in An. stephensi by conferring protection from or tolerance to an effect of bacterial pathology. The evolution of an expanded APL1 gene family could be a factor contributing to the exceptional levels of malaria transmission mediated by human-feeding members of the An. gambiae species complex in Africa.

Clusters of polymorphic transmembrane genes control resistance to schistosomes in snail vectors

“…For example, the PR-locus mediating bacterial resistance in Daphnia via matching-allele interactions also features haplotypes of vastly different sizes (differences > 60 kb at both this locus and PTC2) with large non-homologous sections, and these contain glycosyltransferase genes that could mediate host-pathogen compatibility ( Bento et al, 2017 ). Similarly, the APL1 immune factor impacting Plasmodium development in Anopheles consists of adjacent paralogs that differ in copy number among species and show extreme diversity within species ( Rottschaefer et al, 2011 ; Mitri et al, 2020 ). Thus, while invertebrates lack the acquired immunity of vertebrates and its associated adaptive genetic variation ( Spurgin and Richardson, 2010 ), their defenses can show similar nuance conveyed by molecular diversity ( Loker et al, 2004 ; Cerenius and Söderhäll, 2013 ).…”

A chromosome‐level assembly of the black tiger shrimp (Penaeus monodon) genome facilitates the identification of growth‐associated genes

“…Besides the fact that gene duplication could be beneficial by increasing the expression of immune genes (Palmer & Jiggins, 2015), neofunctionalization of the duplicated gene might occur and subsequently affect pathogen resistance as reported in Anopheles spp. (Mitri et al, 2020). Specially,…”

“…As the copy number variation of immune genes has been linked to pathogen tolerance in arthropods (Mitri et al, 2020), we compared the copy number of genes in the Toll pathway, an essential immune response to defend pathogen invasion, in P. monodon and L. vannamei. Most members of the Toll pathway had higher copy numbers in L. vannamei than in P. monodon with the exception of MyD88 (Figure 3c).…”

“…A. stephensi with a single copy of leucine-rich repeat immune factor (Apl1) gene and A. gambiae with three copies of Apl1 showed the expanded Apl1 genes contribute to tolerance of Plasmodium infection (Mitri et al, 2020). Thus, these higher copy numbers of immunerelated genes in L. vannamei might enhance its defence against pathogens, potentially contributing to higher degrees of disease resistance in L. vannamei (Briggs et al, 2004;Rungrassamee et al, 2016).…”

Delimiting cryptic morphological variation among human malaria vector species using convolutional neural networks

“…Although An. gambiae complex members largely retain their species identity through hybrid male sterility [11], there is evidence of some gene flow between them [12]. Complex members also vary in several traits expected to influence vectorial capacity including larval ecology, adult habitat, behaviors that impact bloodfeeding such as resting location, and human biting [13][14][15].…”