Gene expression

Evidence that processed small dsRNAs may mediate sequence-specific mRNA degradation during RNAi in Drosophila embryos. Yang, D. et al. Curr. Biol. 10, 1191–1200 (2000)

RNA interference (RNAi) is a process by which an introduced double-stranded (ds)RNA specifically silences the expression of genes through degradation of their cognate mRNA. Experiments in vitro indicate that the introduced dsRNA is converted into 21–23 nucleotide 'guide RNAs', which label the target mRNAs to be destroyed by nuclease digestion. Using a quantitative RNAi assay based on measuring luciferase expression in Drosophila melanogaster embryos, the authors show that the 21–23 nucleotide RNAs also mediate RNAi in vivo, with the antisense strand determining substrate specificity. [PubMed]

Human genetics

Small evolutionarily conserved RNA, resembling C/D box small nucleolar RNA, is transcribed from PWCR1 , a novel imprinted gene in the Prader–Willi deletion region, which is highly expressed in brain. de los Santos, T. et al. Am. J. Hum. Genet. 67, 1067–1082 (2000)

Paternal inheritance of a deletion in the 15q11–q13 region causes the neurodevelopmental disorder, Prader–Willi syndrome (PWS). Several genes in this region are imprinted and are expressed only from the maternally or paternally derived allele. PWCR1 is such a gene — it encodes an untranslated small nucleolar RNA (snoRNA) that is transcribed only from the paternal allele and is highly expressed in human and mouse brain. Its expression is abolished in PWS brains and its loss might contribute to PWS pathology. [PubMed]

Developmental biology

Conservation of the sequence and temporal expression of let-7 heterochronic regulatory RNA. Pasquinelli, A. E. et al. Nature 408, 86–89 (2000)

In Caenorhabditis elegans, a small 21-nucleotide RNA molecule encoded by the let-7 gene regulates the late developmental transitions in the worm's life cycle. Now it seems that the worm let-7 gene is shared by all the main groups of bilaterally symmetrical animals (including humans), where it is expressed at important developmental transitions, such as before fly metamorphosis. Small RNAs such as let-7 probably function by pairing with target RNAs and preventing their translation. This study also shows that the genetic targets of let-7 have been evolutionarily conserved. [PubMed]