Molecular Biology

Keeping the Genome Safe

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Science  09 Sep 2011:
Vol. 333, Issue 6048, pp. 1360
DOI: 10.1126/science.333.6048.1360-b

The germ line of an organism must necessarily be sacrosanct; this, after all, is the genetic information transmitted to all subsequent generations. Germline integrity is preserved by a specialized RNA interference system involving Piwi proteins and tiny noncoding RNAs (piRNAs), which suppress the activity of transposable elements (TEs): parasitic DNA elements that are abundant in many eukaryotic genomes. piRNAs are derived from clusters of derelict and defunct TEs in the genome, which are bundled up into heterochromatin.

Rangan et al. show that this normally repressive heterochromatin wrapper is critical for the proper expression of the piRNA clusters. Mutation of the Drosophila histone methyl transferase dSETDB1 results in the loss of repressive heterochromatin marks as well as piRNA cluster transcription, and subsequent activation of TEs. TEs, in turn, suppresses germline stem cell differentation. During normal development, gene transcription is broadly activated in the germ line to promote differentiation, and the heterochromatic piRNA clusters are expressed at the same time, to smother any chance activation of TEs.

Curr. Biol. 21, 1373 (2011).

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