Developmental piRNA profiles of the invasive vector mosquito Aedes albopictus.

BACKGROUND: In eukaryotic organisms, Piwi-interacting RNAs (piRNAs) control the activities of mobile genetic elements and ensure genome maintenance. Recent evidence indicates that piRNAs are involved in multiple biological pathways, including transcriptional regulation of protein-coding genes, sex determination and even interactions between host and pathogens. Aedes albopictus is a major invasive species that transmits a number of viral diseases in humans. Ae. albopictus has the largest genome and the highest abundance of repetitive sequences when compared with members that belong to Culicidae with a published genome. Analysis of piRNA profiles will provide a developmental and evolutionary perspective on piRNAs in Ae. albopictus.

METHODS: piRNAs were identified and characterized during the development of Ae. albopictus, and piRNA expression patterns in adult males and females as well as sugar-fed females and blood-fed females were compared.

RESULTS: Our results reveal that, despite the large genome size of Ae. albopictus, the piRNA pool of Ae. albopictus (1.2 × 10(7)) is smaller than those of Aedes aegypti (1.7 × 10(7)) and Drosophila melanogaster (1.6 × 10(7)). In Ae. albopictus, piRNAs displayed the highest abundance at the embryo stage and the lowest abundance at the pupal stage. Approximately 50 % of the piRNAs mapped to intergenic regions with no known functions. Approximately 30 % of the piRNAs mapped to repetitive elements, and 77.69 % of these repeat-derived piRNAs mapped to Class I TEs; 45.42 % of the observed piRNA reads originated from piRNA clusters, and most of the top 10 highest expressed piRNA clusters and 100 highest expressed piRNAs from each stage displayed biased expression patterns across the developmental stages. All anti-sense-derived piRNAs displayed a preference for uridine at the 5' end; however, the sense-derived piRNAs showed adenine bias at the tenth nucleotide position and a typical ping-pong signature, suggesting that the biogenesis of piRNAs was conserved throughout development. Our results also show that 962 piRNAs displayed sex-biased expression, and 522 piRNAs showed higher expression in the blood-fed females than in the sugar-fed females.

CONCLUSIONS: Our results suggest that piRNAs, aside from silencing transposable elements in Ae. albopictus, may have a role in other biological pathways.