Epigenetics

Argonaute slicing is required for heterochromatic silencing and spreading. Irvine, D. V. et al. Science 313, 1134–1137 (2006)

It has been proposed that small interfering RNA (siRNA)-guided histone H3 dimethylation on lysine 9 (H3K9me2) might be caused by an interaction of siRNA with DNA and the recruitment of modified histones by the RITS complex. Alternatively, siRNAs might guide histone modification by base-pairing with RNA. Working in fission yeast, Irvine et al. provide support for the second mechanism. They show that the endonucleolytic cleavage motif of Argonaute is required for heterochromatic silencing and for 'slicing' mRNAs that are complementary to siRNAs. They also show that spreading of silencing requires read-through transcription, as well as slicing.

Technology

Trans-kingdom transposition of the maize Dissociation element. Emelyanov, A. et al. Genetics 1 September 2006 (doi:10.1534/genetics.106.061184)

Transposons are useful tools for genetic manipulation, but the range of hosts for any given transposon system is restricted. These authors report that the maize Dissociation (Ds) element transposes in zebrafish, yielding high germline transmission rates, and in mammalian cells, in which it can carry large inserts and still transpose accurately and at high frequency. This is the first example of a mobile element that can transpose in hosts from both the plant and animal kingdoms, making Ds a versatile genetic tool.

Population genetics

Global genetic change tracks global climate warming in Drosophila subobscura. Balanyá, J. et al. Science 31 August 2006 (doi:10.1126/science.1131002)

Global warming over the last 2–3 decades has altered gene frequencies in the fruitfly Drosophila subobscura. The frequency of a chromosomal inversion in this species varies clinally with latitude because of temperature differences. The authors compared data sets that had been collected, on average, 24 years apart from North American, South American and European populations. They found that in most populations the frequency distribution had shifted in favour of the low-latitude, warm-climate genotype, and that the average shift was 70 miles closer to the equator.

Development

The dwarf phenotype of the Arabidopsis acl5 mutant is suppressed by a mutation in an upstream ORF of a bHLH gene. Imai, A. et al. Development 133, 3575–3585 (2006)

This study reveals a role for upstream open reading frames (uORFs) in plant development. Loss-of-function mutations in the Arabidopsis thaliana ACL5 gene cause dwarfism. Imai and colleagues show that a mutation in SAC51 suppresses the ACL5 mutant phenotype. The SAC51 mutation causes premature termination of a short uORF, which results in increased translation of the main ORF. The authors provide evidence that wild-type ACL5 functions by overcoming the inhibition of translation of SAC51 mRNA that is mediated by its uORF.