Evolution of piRNA clusters in Anopheles gambiae M and S forms. Phillip George¹, Igor Sharakhov¹, Chantal Vaury², Silke Jensen². 1) Department of Entomology, Virginia Tech, Blacksburg, VA, USA; 2) Laboratoire Génétique, Reproduction et Développement (GReD), Clermont-Ferrand, France.

   The piRNA pathway is known to be an important mechanism in the suppression and control of transposable element (TE) mobilization in many genomes including the fruit fly, Aedes mosquitoes and mice. Hybrid dysgenesis in Drosophila is caused by a lack of maternally loaded piRNAs, which was absent in the non TE-carrying female. However, a role of the piRNA pathway in reproductive isolation between species is not yet established. Members of the Anopheles gambiae complex (including incipient species M and S) represent a promising system for addressing this gap. We have sequenced piRNAs from the Mali strain (M form) and Zanu strain (S form) of A. gambiae. A library of total small RNAs ranging from 20-35 nt was taken from the total RNA pool. 26-32 nt sequences were kept, and redundant RNA sequences were removed. A program NucBase was used to count and map the RNAs that interacted with the PEST, S and M genomes of A. gambiae. The highest piRNA clusters are found in the pericentromeric and intercalary heterochromatin. We have also identified the top 15 piRNA clusters. They have been further analyzed to determine the TE content difference between the M and S forms. The clusters are similar, but there are noticeable differences in the TE classes and the non-TE content in the clusters. The number of piRNAs that uniquely map to these clusters also is visibly different. We hypothesize that the divergence in the piRNA pathway in the malaria mosquito plays an important role in speciation due to the protection or lack of protection toward conferred TEs in offspring. The TE derepression in F1 hybrids, although not documented in A. gambiae as of yet, could be one possible mode of speciation.