Blattella germanica piRNAs in materno-zygotic transition

Poster presented at the Eight International Symposium on Molecular Insect Science, held 7-10th July 2019 in Barcelona (Spain).
The Piwi-interacting RNAs (piRNAs) are a small non-coding RNAs involved in the maintenance of genome stability. piRNAs were described as expressed exclusively in germinal cells, but their presence in somatic cells has been taking relevance in the last years. We have identified the Blattella germanica piRNAs from 24 small RNA libraries, corresponding to different developmental stages (Llonga et al 2018 DOI: 10.1002/jez.b.22815). Now we focus on the identification of piRNAs from a maternal origin and the characterization of the piRNAs involved in the transition to the zygotic stage. The role of such piRNAs in the protection of the embryo genome and the relationship with their putative target RNAs (transposable elements and mRNAs) are key to the understanding of the general functions of these regulatory elements but also their particularities in hemimetabolous insects. The 24 small RNA libraries were aligned against the genome with Bowtie and R Statistical Software was used for expression analysis. Finally, ovary and early embryonic piRNA expressions were validated by qRT-PCR. The analysis of B. germanica individual small RNA libraries, corresponding to ovaries from 7-day-old adult females (OvD7), non-fertilized eggs (NFE), the zygote (ED0), and the first day of embryogenesis (ED1), show that piRNAs in these stages agree with the current model of two piRNA biogenesis pathways. The most expressed piRNAs in each library of this transition have been analyzed in order to identify specific functions for each stage. By mapping the sequence to the genome, we have identified the origin of these piRNAs and also a number of potential mRNAs targets.