Abundant expression of somatic transposon-derived piRNAs throughout Tribolium castaneum embryogenesis

作者：Ninova Maria; Griffiths Jones Sam^*; Ronshaugen Matthew^*

来源：Genome Biology, 2017, 18(1): 184.

DOI：10.1186/s13059-017-1304-1

• piRNA
• Short-germband development
• Maternal-zygotic transition
• Maternal transcripts
• Ping-pong pathway
• Transposons
• Tribolium castaneum

Background: Piwi-interacting RNAs (piRNAs) are a class of short (similar to 26-31-nucleotide) non-protein-coding RNAs expressed in the metazoan germline. The piRNA pathway in arthropods is best understood in the ovary of Drosophila melanogaster, where it acts to silence active transposable elements (TEs). Maternal loading of piRNAs in oocytes is further required for the inheritance of piRNA-mediated transposon defence. However, our understanding of the diversity, evolution and function of the piRNA complement beyond drosophilids is limited. The red flour beetle, Tribolium castaneum, is an emerging model organism separated from Drosophila by similar to 350 million years of evolution that displays a number of features ancestral to arthropods, including short germ embryogenesis. Here, we characterize the maternally deposited and zygotically expressed small RNA and mRNA complements throughout T. castaneum embryogenesis.
Results: We find that beetle oocytes and embryos of all stages are abundant in heterogeneous similar to 28-nucleotide RNAs. These small RNAs originate from discrete genomic loci enriched in TE sequences and display the molecular signatures of transposon-derived piRNAs. In addition to the maternally loaded primary piRNAs, Tribolium embryos produce secondary piRNAs by the cleavage of zygotically activated TE transcripts via the ping-pong mechanism. The two Tribolium piRNA pathway effector proteins, Tc-Piwi/Aub and Tc-Ago3, are also expressed throughout the soma of early embryos.
Conclusions: Our results show that the piRNA pathway in Tribolium is not restricted to the germline, but also operates in the embryo and may act to antagonize zygotically activated transposons. Taken together, these data highlight a functional divergence of the piRNA pathway between insects.

• 出版日期2017-9-26