Small non-coding RNAs produced by a 'selfish' B chromosome in the jewel wasp
Patrick Ferree
B chromosomes are considered to be genome parasites in thousands of plant and animal species. Our research group has been studying a B chromosomes known as PSR (for Paternal Sex Ratio) that is present in the genome of the jewel wasp, Nasonia vitripennis. PSR is transmitted through the sperm to new progeny, and its presence causes the complete elimination of the sperm's hereditary material immediately after fertilization, causing female-destined diploid embryos to become haploid males, the PSR-transmitting sex. The ability to cause genome elimination is absolutely essential for the survival of this B chromosome, and our group is interested in understanding mechanistically how this process occurs. In a recently published study we tested the hypothesis that PSR produces its own specialized set of small non-coding RNAs, which generally have been implicated in a number of different chromatin-based processes, including genome elimination, in other organisms. We identified a subset of small RNAs produced by PSR in the wasp testis. One of these small RNAs in particular matches a highly abundant satellite DNA that is spread across the PSR chromosome and is not found at all in the wasp's genome. Moreover, this small RNA represents 64% of all small RNA reads produced by PSR. This expression level is at least ten-fold higher than any other repeat-associated small RNA that we know of that is produced by the wasp's normal genome. We propose that these PSR-expressed small RNAs, and perhaps long transcripts that our group previously identified, play an active role in PSR's ability to cause genome elimination in the wasp. We are currently testing this hypothesis through directed experiments.  


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