Cloning conundrums

Credit: courtesy Science

Two recent papers provide insight into the low rates of success and high rates of phenotypic abnormalities that characterize animal cloning. A study on rhesus monkey cells by Gerald Schatten and coworkers (Science 300, 297, 2003) suggests that primate cloning may face insuperable obstacles if current methods are not improved. Imaging of the chromosomes and microtubules of cloned embryos revealed malformed mitotic spindles and aberrant chromosome segregation leading to aneuploidy (see inset). The abnormalities were linked to the absence of two proteins involved in mitotic spindle pole assembly, NuMA and HSET, which are lost during the initial enucleation of oocytes. In non-primate species, by contrast, cloned embryos seem to escape such gross chromosomal defects but are prone to abnormal gene expression. Rudolf Jaenisch and colleagues (Development 130, 1673–1680, 2003) report that cloned mouse embryos often fail to activate genes essential for embryonic development. Only 62% of blastocysts derived from somatic cells exhibited normal expression of the Oct4 gene (required for development of the pluripotent cells of the inner cell mass) and ten other Oct4-related genes. In comparison, 100% of blastocysts derived from embryonic stem cells showed normal expression of these genes. KA

Vancomycin-resistance exposed

Scientists from The Institute for Genomic Research report the complete genome sequence of the first vancomycin-resistant strain of Enterococcus faecalis, strain V583, isolated in 1987 from a St. Louis hospital (Science 299, 2074–2077). Although E. faecalis is a natural inhabitant of the human gut, often found in sewage and water, it can frequently cause serious infections and has been shown to be a reservoir for vancomycin resistance, a particular problem in hospital settings where vancomycin is the antibiotic of last resort. The genome sequence revealed that mobile elements and exogenously acquired genes account for over a quarter of the bacterium's genome. This is believed to represent the highest percentage of mobile elements in a bacterial genome. The mobile elements include 3 plasmids, 7 phage regions, 38 insertion elements, many transposable elements, and a pathogenicity island. A new transposable element harboring vancomycin resistance genes was discovered, as well as a plasmid encoding a novel pheromone inhibitor. The bacterium's penchant for incorporating mobile elements may contribute to the rapid development and expansion of antibiotic resistance. LD

A better parts list

Researchers have attempted to experimentally define all the genes in the microscopic worm Caenorhabditis elegans and to create a functional proteomics resource for this important model organism. Marc Vidal and coworkers (Nat. Genet. 34, 35–41, 2003) use PCR primers to amplify each of the 19,477 predicted or known genes and to clone them into a highly flexible recombination-based cloning system. They successfully assembled 11,984 open reading frames (ORFs) into the C. elegans ORFeome version 1.1, which is available to the research community. Over 4,000 of the ORFs had not been identified by random cDNA sequencing or expressed sequence tags. The identification of these previously untouched genes may indicate that a substantial proportion of unpredicted genes could also be present in other organisms. In addition, more than 50% of genes predicted by genome annotation tools such as GeneFinder may need to be corrected because of mispredictions of intron-exon structure. When ORFs were cloned into a yeast two-hybrid vector and screened against 116 bait proteins, the ORFeome screen reached saturation with fewer yeast clones and identified more links than cDNA library screens. Finally, the resource makes it possible to produce approximately 8,800 proteins for applications such as proteome chips. MS


Building nanometer-scale structures has become a major challenge in the manufacture of novel materials for the electronic industry. Susan Lindquist and colleagues at the University of Chicago (Proc. Natl. Acad. Sci. USA 100, 4527–4532, 2003) now show how to build nanowire elements using a self-assembled protein matrix as the guiding template. The authors triggered the auto-assembly of Saccharomyces cerevisiae amyloid protein to generate 10-nm-wide fibers containing reactive cysteine residues. These fibers were placed on electrodes and the cysteine residues allowed to react with colloidal gold particles. The gaps between fixed particles were filled by a highly specific reductive gold and silver deposition procedure resulting in silver and gold wires of an average diameter of approximately 100 nm. The length of the reduction deposition step determined wire thickness. Whereas the naked protein fibers themselves acted as electrical insulators, the metal-coated fibers exhibited low resistance electric conduction and linear current-voltage curves. These nanowires might be modified with a variety of biological functionalities and fiber interconnections to ultimately enable the fabrication of complex electronic circuits at the nanoscale. GTO

One order of rice, extra tillers

The production of rice grains (tillering) is a complex developmental process that is not well understood, despite the existence of numerous mutants with defects in this process. Now Chinese researchers, led by Jiayang Li, report the isolation of a key regulator of the process, the monoculm 1 gene (MOC1) (Nature 442, 618, 2003). Screening rice mutants, Li and his colleagues found a plant that produced a single culm (mother stem), which possesses a single recessive nuclear mutation mapping to a 20 kilobase region on chromosome 6 corresponding to the MOC1 gene. Wild-type MOC1, when introduced into mutant plants, complemented the mutation and resulted in enhanced tillering activity, presumably as a result of overexpression. Expression patterns of MOC1 suggest it plays a role in both the formation and outgrowth of tiller buds. Based on this, its homology to the GRAS family of transcription factors and nuclear localization, the authors conclude that MOC1 is a key regulator of this important process in rice. LD

Research News Briefs written by Kathy Aschheim, Laura DeFrancesco, Meeghan Sinclair, and Gaspar Taroncher-Oldenburg.