A novel microRNA regulating gene expression in oocytes of the cockroach Blattella germanica

Abstract

The discovery of non-coding small RNAs, including miRNAs, deeply changed the knowledge about gene expression control. In insects, information on miRNAs is still fragmentary and predominantly focused in Drosophila melanogaster. In this species, the processes studied go from neural development, metamorphosis, growth and development, to oogenesis. Our research aims at unveiling how miRNAs are involved in controlling gene expression during oogenesis in the cockroach Blattella germanica, a phylogenetically basal species with panoistic ovaries. To this end, we recently obtained a library of small RNAs from B. germanica adult ovaries, and we used quantitative PCR (qPCR) techniques for small RNAs amplification. These two approaches provided us with thorough data about classical miRNAs and novel miRNA candidates that are highly expressed in B. germanica ovaries. The most abundant miRNA candidate discovered in B. germanica ovary, named Bge-candidate1, was selected for the present study. The expression profile of Bge-candidate1 was established with qPCR in nymphal and adult ovaries, and showed a peak during vitellogenesis. Studies of in situ hybridization indicated that Bge-candidate1 is exclusively found in germline cells, whereas it is completely absent in follicular cells. According to the genome data of Acyrtosiphon pisum, another insect with panoistic ovaries, a miRNA identical to Bge-candidate1 should occur in this aphid species. This coincidence in two species with the same ovary type, and the high peak of expression of Bge-candidate1 in B. germanica ovary during vitellogenesis, suggests that this miRNA is typical of panoistic ovaries, and that plays important roles in oocyte maturation.