Gene regulation

An extensive class of small RNAs in Caenorhabditis elegans. Lee, R. C. et al. Science 294, 862–864 (2001) [PubMed]

Identification of novel genes coding for small expressed RNAs. Lagos-Quintana, M. et al. Science 294, 853–858 (2001) [PubMed]

An abundant class of tiny RNAs with probable regulatory roles in Caenorhabditis elegans. Lau, N. C. et al. Science 294, 858–862 (2001) [PubMed]

Keen to expand the number of known small RNAs that are involved in developmental timing in the worm (so-called small temporal RNAs, stRNAs) and in RNA interference (small intermediate RNAs, siRNAs), the authors of these papers have together identified and cloned 91 novel 22–25-nucleotide RNAs from worm, fly and human. Genome sequence and expression studies indicate that these hitherto elusive micro (mi)RNAs are processed from larger RNA molecules and that some are conserved, even in vertebrates, and probably function in translational repression. The task ahead is to find the precise function and potential targets of the new miRNAs (see Sean Eddy's review on p 919).

Evolution

Pattern and timing of gene duplication in animal genomes. Friedman, R. & Hughes, A. L. Genome Res. 11, 1842–1847 (2001) [PubMed]

The existence of numerous multigene families in vertebrates has often been explained in terms of whole-genome duplication that might have occurred early in vertebrate evolution. Friedman and Hughes tested this hypothesis by analysing homologous multigene families from the genomes of human, worm, fly and yeast, and found little evidence of whole-genome duplication. Instead, their results support several independent duplications of individual genes and the occasional duplication of chromosomal blocks.

Epigenetics

Lsh , a member of the SNF2 family, is required for genome-wide methylation. Dennis, K. et al. Genes Dev. 15, 2940–2944 (2001) [PubMed]

This paper adds to the growing evidence that chromatin-remodelling proteins can influence DNA methylation, when once the opposite was believed to be true (see also accompanying Highlight on histone methylation). Dennis et al. knocked out Lsh — a member of the SNF2 family of chromatin remodelling proteins — in mice to create animals that develop normally but have genome-wide hypomethylation, indicating that altering chromatin structure can affect global genomic methylation, which appears not to be essential for mouse embryogenesis.