Global transcriptional dynamics of diapause induction in non-blood-fed and blood-fed Aedes albopictus

Abstract

Background: Aedes albopictus is a vector of increasing public health concern due to its rapid global range expansion and ability to transmit Dengue virus, Chikungunya virus and a wide range of additional arboviruses. Traditional vector control strategies have been largely ineffective against Ae. albopictus and novel approaches are urgently needed. Photoperiodic diapause is a crucial ecological adaptation in a wide range of temperate insects. Therefore, targeting the molecular regulation of photoperiodic diapause or diapause-associated physiological processes could provide the basis of novel approaches to vector control.

Methodology/principal findings: We investigated the global transcriptional profiles of diapause induction in Ae. albopictus by performing paired-end RNA-Seq of biologically replicated libraries. We sequenced RNA from whole bodies of adult females reared under diapause-inducing and non-diapause-inducing photoperiods either with or without a blood meal. We constructed a comprehensive transcriptome assembly that incorporated previous assemblies and represents over 14,000 annotated dipteran gene models. Mapping of sequence reads to the transcriptome identified differential expression of 2,251 genes in response to diapause-inducing short-day photoperiods. In non-blood-fed females, potential regulatory elements of diapause induction were transcriptionally up-regulated, including two of the canonical circadian clock genes, timeless and cryptochrome 1. In blood-fed females, genes in metabolic pathways related to energy production and offspring provisioning were differentially expressed under diapause-inducing conditions, including the oxidative phosphorylation pathway and lipid metabolism genes.

Conclusions/significance: This study is the first to utilize powerful RNA-Seq technologies to elucidate the transcriptional basis of diapause induction in any insect. We identified candidate genes and pathways regulating diapause induction, including a conserved set of genes that are differentially expressed as part of the diapause program in a diverse group of insects. These genes provide candidates whose diapause-associated function can be further interrogated using functional genomics approaches in Ae. albopictus and other insects.

Fig 1. Experimental design for RNA-Seq experiment and diapause incidence measurements.

SD indicates diapause-inducing short-day conditions, and LD indicates non-diapause-inducing long-day conditions (see text). BM indicates females that received a blood meal, and NB indicates females that did not receive a blood meal.

Fig 2. Multi-dimensional scaling plot of normalized gene expression values for photoperiodic (SD, LD) and blood feeding (BM, NB) treatments (see text for details).

Two-letter symbols as in Fig 1.

Fig 3. Log₂ fold-change expression against log abundance of TMM-normalized gene expression in A) females exposed to non-diapause-inducing long day lengths (left) and diapause-inducing short day lengths (right) under blood-fed (BM) vs. non-blood-fed (NB) conditions, and B) non-blood-fed (left) and blood-fed (right) females exposed to diapause-inducing short day lengths (SD) vs. non-diapause-inducing long day lengths (LD).

Each point represents an individual transcript, and positive values indicate up-regulation under blood-fed conditions (A) or diapause conditions (B). Significant differential expression (Benjamini-Hochberg corrected P < 0.05; absolute log₂ fold-change > 0.5) indicated in red.

Fig 4. Heat maps of DE genes in the A) cell cycle, B) DNA replication and C) oxidative phosphorylation pathways under non-diapause-inducing long-day photoperiods (LD) and diapause-inducing short-day (SD) photoperiods for non-blood-fed (NB) and blood-fed (BM) females.

Expression values are depicted as standardized Z-scores for each gene, where blue represents low expression and red represents high expression. “+” and “-” in Panel A indicate positive and negative cell cycle regulators, respectively.