Plant technology

Targeted mutagenesis using zinc-finger nucleases in Arabidopsis. Lloyd, A. et al. Proc. Natl Acad. Sci. USA 102, 2232–2237 (2005)

Existing methods of targeted mutagenesis in plants that are based on homologous recombination are generally inefficient. These authors used an engineered zinc-finger nuclease to generate double-strand breaks at specific target sites in the Arabidopsis genome. Repair of these breaks led to a high frequency of mutations in the target sequence, potentially providing a new high-efficiency method for introducing targeted mutations in plant genomes.

Development

Four-cell stage mouse blastomeres have different developmental properties. Piotrowska-Nitsche, K. et al. Development 132, 479–490 (2005)

Piotrowska-Nitsche et al. have tested the theory that all blastomeres of the four-cell-stage mouse embryo have equivalent developmental properties. By tracing the origins of the blastomeres with respect to earlier cell divisions, they were able to make chimeric embryos that consist of just one of the four types of blastomere. The authors showed that although all four cells have the same developmental potential, they have distinct developmental properties with respect to their abilities to differentiate in different contexts.

Genome evolution

Evidence for widespread degradation of gene control regions in hominid genomes. Keightley, P. D. et al. PLoS Biol. 3, e42 (2005)

These authors examined the conservation of non-coding regulatory regions in hominids by comparing these regions in the human and chimpanzee genomes. Surprisingly, they found that there has been little selective constraint in the sequences compared with the equivalent regions of murid (mouse and rat) genomes. They conclude that natural selection on these non-coding regions has exerted only weak effects in humans and chimpanzees, and that this might be due to the effects of small population sizes.

Epigenetics

Epigenetic memory of active gene transcription is inherited through somatic cell nuclear transfer. Ng, R. K. & Gurdon, J. B. Proc. Natl Acad. Sci. USA 102, 1957–1962 (2005)

Following somatic cell nuclear transfer, genes from donor nuclei lose their epigenetic mark and are reprogrammed to adopt an embryonic expression pattern. Ng and Gurdon now show that this process is not complete. When using endoderm and neuroectoderm donor nuclei for transfer, they noticed that genes that would normally be expressed in the donor nuclei are also expressed, inappropriately, in some transplant embryos. It seems that epigenetic memory is established in differentiating cells and only applies to transcriptionally active genes.