The origins of introns and their evolutionary role remain unclear. In the November 6 Proceedings of the National Academy of Science, Alexei Fedorov and colleagues describe the use of a computer program, called INTRONMAP to present evidence for the existence of ancient introns (Proc Natl Acad Sci USA 2001, 98:13177-13182).They used the program to map intron positions onto homologous genes encoding proteins for which the three-dimensional structure is known. They applied the program to 665 nonredu

An international project is replacing each yeast open reading frame (ORF) with a drug-resistance cassette containing two 20-mer oligonucleotide 'barcodes' that can be used as hybridization tags for each gene. In the November 8 Sciencexpress, Siew Loon Ooi and colleagues describe the use of this resource to screen for mutants defective in nonhomologous end-joining (NHEJ) (10.1126/science.1065672).They used a transformation-based plasmid-repair assay to screen for NHEJ activity. They prepared hapl

The mouse is being widely used as a model organism in microarray studies, yet little is known about the range of normal physiological variance in gene expression in complex systems in vivo. In the November 6 Proceedings of the National Academy of Sciences, Colin Pritchard and colleagues at the Fred Hutchinson Cancer Research Centre describe a study of normal variation of gene expression levels in mouse tissues (Proc Natl Acad Sci USA 2001, 98:13266-13271).They analysed the expression of over fiv

The extraembryonic lineage is the first to differentiate in mammals following fertilization. In the November 6 Proceedings of the National Academy of Sciences, Myriam Hemberger and colleagues at the Department of Biochemistry and Molecular Biology, University of Calgary, report the use of cDNA subtraction and microarray hybridisation to screen for genes implicated in placentogenesis (Proc Natl Acad Sci USA 2001, 98:13126-13131).They isolated the ectoplacental cone region of mouse conceptuses at

Microarray analysis using an inducible expression system identifies genes regulated by the PTEN tumour suppressor.

The DrosophilaY chromosome has several features (including its heterochromatic state) that have made mapping and sequencing difficult. The Y chromosome contains genes directly involved with male fertility. In the November 6 Proceedings of the National Academy of Sciences, Antonio Carvalho and colleagues describe a search for more novel Y-linked genes (Proc Natl Acad Sci USA 2001, 98:13225-13230).They used a strategy involving staggered TBLASTN screening of 500,000 proteins against the armU datab

Exposure to light induces photoreceptor cell death and retinal degeneration in animal models. The absence of some genes (for example, arrestin or rhodopsin kinase) can sensitize the retina to light damage. In the November 6 Proceedings of the National Academy of Sciences, Sangdun Choi and researchers at the California Institute of Technology report the use of gene expression profiling to investigate light-induced apoptosis (Proc Natl Acad Sci USA 2001, 98:13096-13101).They isolated retinal tissu

Hammerhead ribozymes with self-cleaving properties have been found in a range of organisms, including plants, newts, schistosomes and cave crickets. In the i November Nature, Salahi-Ashtiani and Szostak of the Howard Hughes Medical Institute and Massachusetts General Hospital describe an in vitro system to address the origins of hammerhead ribozymes (Nature 2001, 413:82-84).They used a DNA collection encoding large random-sequence RNAs to select self-cleaving RNAs. Repeated rounds of selection l

Misregulation of autocrine signalling loops may contribute to cancer phenotypes. In November Nature Genetics, Thomas Graeber and David Eisenberg of the Howard Hughes Medical Institute and the University of California, Los Angeles describe a computer-based strategy to identify receptor-ligand pairs and autocrine loops in large datasets (Nat Gen 2001, 29:295-300).They compiled a Database of Ligand-Receptor Partners (DLRP) that is based on the published literature and contains 452 ligand-receptor p

Libraries containing as many as nine trillion different peptide sequences can be used to select numerous high-affinity RNA-binding peptides.

Dendritic cells (DCs) are stalwarts of the immune response, activating both the innate and acquired immune systems. In the October 26 Science Qian Huang and colleagues at the Whitehead Institute for Biomedical Research describe the use of oligonucleotide microarrays to examine how DCs respond to different pathogens (Science 2001, 294:870-875).They exposed human monocyte-derived DCs to Gram-negative bacteria (Escherichia coli), fungi (Candida albicans) or an RNA virus (influenza virus), and then

Fruitfly biologists have developed some elaborate genetic tricks to express transgenes in a spatially restricted manner. The bipartite GAL4/UAS system exploits the yeast GAL4 transcriptional activator and the upstream activating sequence (UAS) to which it binds to drive transgene expression. In the October 23 Proceedings of the National Academy of Sciences, Thomas Osterwalder and colleagues at Yale University describe an enhanced conditional, tissue-specific expression system that can take advan