Cloning

Oct4 distribution and level in mouse clones: consequences for pluripotency.Boiani, M. et al. Genes Dev. 16, 1209–219 (2002)

The transcription factor Oct4 is essential for early embryonic mouse development and is expressed only during embryogenesis and in germ cells. It is, therefore, a good marker to assess genome reprogramming in cloned blastocysts derived from somatic-cell nuclei. Here, Boiani et al. report that cultured cells derived from cloned blastocysts that were generated from cumulus-cell nuclei rarely express Oct4 correctly or at levels required for normal embryonic development. The frequency of this abnormal expression alone can account for the low rates of post-implantation survival of clones.

Multifactorial genetics

Simultaneous detection and fine mapping of quantitative trait loci in mice using heterogeneous stocks.Mott, R. & Flint, J. Genetics 160, 1609–1618 (2002)

Determining the molecular basis of a quantitative trait remains a challenge as current protocols for fine-mapping QTL involve scoring a large number of individuals or following the trait over many generations. The authors have used a computer simulation to show that, by examining only ∼1,500 F2 progeny from a cross between an inbred line and a heterogeneous stock of mouse (a genetic mosaic of eight known strains), a QTL can be mapped to within ∼3 cM by screening with ∼100 markers followed by a focused scan on the candidate regions.

Gene regulation

Identification of tissue-specific microRNAs from mouse.Lagos-Quintana, M. et al. Curr. Biol. 12, 735–739 (2002)

MicroRNAs (miRNAs) are non-coding RNAs that are thought to modulate gene expression at the post-transcriptional level. Here, the authors report the identification and cloning of 34 novel miRNAs from mouse, many of which are conserved in other vertebrate genomes, including human. Many of these miRNAs are expressed in a tissue-specific manner, perhaps indicating their involvement in tissue specification or cell-lineage decisions.

Gene expression

Regulation of noise in the expression of a single gene.Ozbudak, E. M. et al. Nature Genet. 31, 69–73 (2002)

Biochemical reactions are sensitive to changes in molecular concentrations. By measuring the expression levels of a fluorescent reporter gene on a Bacillus subtilis chromosome in different translational and transcriptional mutants, the authors quantify the extent to which molecular fluctuations in single cells explain the differences in gene expression in a genetically identical population (which they call “phenotypic variation”). Their results show that translational efficiency is the main source of phenotypic variation.