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Splicing with inverted order of exons occurs proximal to large introns
~]ONITOR Vavil0v Institute scientists heroically preserve world plant genetic resources collections during World War II siege of Leningrad S.M. ALEXANYANAND V.I. KRIVCHENKO
Diversity 7, 10-13 If you were dying of starvation, would you preserve several thousand packets of genetically diverse rice grain? D.S. Ivanov did, as with other scientists at Leningrad's renowned Vavilov Institute of Plant Industry (VIR) he struggled to save a priceless collection of plant germ plasm, representing more than 187 000 varieties, during the siege of Leningrad. The stow is recounted in the latest issue of Diversity, a quarterly news journal for the international plant genetic resources community. In the autumn of 1941, VIR scientists gathered their crop of potato tubers under enemy fire, and managed to preserve them through the harsh winter of 1941M2 until the collection was eventually transported across the frozen Lake Ladoga 'Road of Life' to storage in the Ural Mountains. The Institute's seed collection was divided into several replicate sets stored in different parts of the Institute building, and guarded literally with its keepers' lives, not just against rats and extreme cold, but against the starving populace. Ironically, the VIR was spared direct bombing because it was near the Astoria Hotel, where Hitler planned to hold a victory banquet. Those scientists who survived the 1941-42 winter (and many did not) faced new problems in the spring as the seeds began to deteriorate. Propagation was essential and, amazingly, was achieved on plots of land on the outskirts of the city. By early 1944 it was possible to transfer most of the VIR collection to the Urals station; there it began once more to grow and was returned to Leningrad after the war./z
Human p53 and CDC2Hsgenes combine to inhibit the proliferation of Saccharomyces cerevisiae J.M. NIGRO, R. SIKORSK1, S.1. REED AND B. VOGELSTEIN
Mol. Cell. Biol. 12, 1357-1365 It has become one of the great cliches of yeast genetics papers that these unicellular fungi provide a genetically manipulable system for studying cellular processes that are fundamental to all eukaryotes - but it keeps on being true! In this paper, Nigro et al. show that the mammalian tumour suppressor gene p53, which is inactivated in many tumour types and appears to have a role in control* ling cell cycle progression, can slow
Splicing with inverted order of exons occurs proximal to large introns C. COCQUERELLE E TA L.
EMBOJ. 11, 1095-1098 Splicing links exons together in a strict 5' to 3' direction. However, there have been two recent examples of exon shuffling during splicing: in the DCC (deleted in colorectal carcinomas) gene and, as discussed here, in the human ETS gene. The odd couple was discovered b y accident. Chicken c-ets-1 has two alternatively spliced exons, ot and [3. Using primers to the human al exon and to the chicken [3 exon, Cocquerelle et al. tried to amplify a human fragment corresponding to an alternative exon. Sequencing revealed that their fragment was
Inducible cell ablation in Drosophila by c01d-sensitive ricin A chain
in fact the d exon from further down the gene linked to the al exon; d and !3 are similar and PCR was carried out at low stringency. The RNA was present in the poly(A)- pool only, and genuine splice sites had been used. It was not a PCR artefact either: RNase protection assays also identified the abnormally spliced species and suggested that it is present at -1% of the levels of normal transcripts. Attempts to identify other abnormal splices by PCR provided only one other example: a c to al join. Of potential significance, the intron before al and that after d are huge (30 and 15 kb, respectively). An understanding of this unusual exon scrambling could perhaps help to resolve the mechanism of alternative splicing. /z
Development 114, 787-796 Cell ablation is a valuable weapon in the developmental biologist's armoury, providing clues about the origin, fate and function of cells. Physical ablation techniques have obvious drawbacks when dealing with complex organisms. Toxigenic approaches are thus becoming more popular, and these two papers describe schemes based on the ablation of cells by temperature-sensitive toxins; the major advantage is that the time of ablation can be controlled by temperature shift. Moffat et al. generated cold-sensitive mutants of ricin toxin A chain in yeast. Then they linked a cold-sensitive toxin gene to the sevenless promoter, and transformed Drosophila
embryos. At permissive temperatures, transgenic flies had greatly disrupted eyes while at the restrictive temperature, only 1-2% of ommatidia showed any defect. Scanning electron microscopy confirmed that the defects were on the whole consistent with ablation of cells that normally express sev. Bellen et al. took much the same line, generating temperature-sensitive mutant diphtheria toxins in yeast, and expressing them under the control of the ninaE promoter in R1-R6 photoreceptors. The usefulness of the technique could be expanded if a twostep system was used. The toxin could be expressed under the control of a UASGAL element, expression from which requires the yeast GAL4 activator. Toxin would then be made only when flies were crossed with a GAL4expressing strain - and enhancer traps could be used to generate lines expressing P-GAL4 fusions in a wide range of cells, permitting cell ablation of practically any cell type without the need to generate new transgenic fly lines for each cell type. /~
the growth rate of yeast cells, even though no p53 homologue has yet been found in yeast. Either wild-type human p53, or a p53 mutant known to be oncogenic in human cells, was introduced into yeast under the control of the inducible GALl promoter. Under inducing conditions, colonies containing wild-type p53 grew much more slowly than controls, while two different p53 mutants caused either a slight reduction in growth rate or an intermediate rate. Since p53 activity is thought to be regulated in part by phosphorylation by the human CDC2Hs kinase, the next experiment was to introduce both p53 and CDC2Hs genes into yeast: still further inhibition of growth occurred, and
morphological and flow cytometry studies showed that the cells arrested mainly in G1. Somewhat disappoint ingly, though, no differences in phosphorylation of p53 have yet been found between cells expressing just p53 and cells expressing p53 plus CDC2tts. Perhaps a more indirect effect is operating; the authors suggest that p53 functioning as a transcriptional regulator (which it is known to be able to do in yeast) might activate genes that inactivate CDC2Hs, or inactivate CDC2! ts activators. If the yeast factors that interact with human p53 and/or CDC2Hs can be identified, they may point to new players in the mare malian system.
K.G. MOFFAT E TA L.
Development 114, 681-.-687
Isolation of temperature-sensitive diphtheria toxins in yeast and their effects on Drosophila cells H.J. BELLEN ETAL.
TIG MAY 1 9 9 2 VOL. 8 NO. 5
15"
Diversity 7, 10-13 If you were dying of starvation, would you preserve several thousand packets of genetically diverse rice grain? D.S. Ivanov did, as with other scientists at Leningrad's renowned Vavilov Institute of Plant Industry (VIR) he struggled to save a priceless collection of plant germ plasm, representing more than 187 000 varieties, during the siege of Leningrad. The stow is recounted in the latest issue of Diversity, a quarterly news journal for the international plant genetic resources community. In the autumn of 1941, VIR scientists gathered their crop of potato tubers under enemy fire, and managed to preserve them through the harsh winter of 1941M2 until the collection was eventually transported across the frozen Lake Ladoga 'Road of Life' to storage in the Ural Mountains. The Institute's seed collection was divided into several replicate sets stored in different parts of the Institute building, and guarded literally with its keepers' lives, not just against rats and extreme cold, but against the starving populace. Ironically, the VIR was spared direct bombing because it was near the Astoria Hotel, where Hitler planned to hold a victory banquet. Those scientists who survived the 1941-42 winter (and many did not) faced new problems in the spring as the seeds began to deteriorate. Propagation was essential and, amazingly, was achieved on plots of land on the outskirts of the city. By early 1944 it was possible to transfer most of the VIR collection to the Urals station; there it began once more to grow and was returned to Leningrad after the war./z
Human p53 and CDC2Hsgenes combine to inhibit the proliferation of Saccharomyces cerevisiae J.M. NIGRO, R. SIKORSK1, S.1. REED AND B. VOGELSTEIN
Mol. Cell. Biol. 12, 1357-1365 It has become one of the great cliches of yeast genetics papers that these unicellular fungi provide a genetically manipulable system for studying cellular processes that are fundamental to all eukaryotes - but it keeps on being true! In this paper, Nigro et al. show that the mammalian tumour suppressor gene p53, which is inactivated in many tumour types and appears to have a role in control* ling cell cycle progression, can slow
Splicing with inverted order of exons occurs proximal to large introns C. COCQUERELLE E TA L.
EMBOJ. 11, 1095-1098 Splicing links exons together in a strict 5' to 3' direction. However, there have been two recent examples of exon shuffling during splicing: in the DCC (deleted in colorectal carcinomas) gene and, as discussed here, in the human ETS gene. The odd couple was discovered b y accident. Chicken c-ets-1 has two alternatively spliced exons, ot and [3. Using primers to the human al exon and to the chicken [3 exon, Cocquerelle et al. tried to amplify a human fragment corresponding to an alternative exon. Sequencing revealed that their fragment was
Inducible cell ablation in Drosophila by c01d-sensitive ricin A chain
in fact the d exon from further down the gene linked to the al exon; d and !3 are similar and PCR was carried out at low stringency. The RNA was present in the poly(A)- pool only, and genuine splice sites had been used. It was not a PCR artefact either: RNase protection assays also identified the abnormally spliced species and suggested that it is present at -1% of the levels of normal transcripts. Attempts to identify other abnormal splices by PCR provided only one other example: a c to al join. Of potential significance, the intron before al and that after d are huge (30 and 15 kb, respectively). An understanding of this unusual exon scrambling could perhaps help to resolve the mechanism of alternative splicing. /z
Development 114, 787-796 Cell ablation is a valuable weapon in the developmental biologist's armoury, providing clues about the origin, fate and function of cells. Physical ablation techniques have obvious drawbacks when dealing with complex organisms. Toxigenic approaches are thus becoming more popular, and these two papers describe schemes based on the ablation of cells by temperature-sensitive toxins; the major advantage is that the time of ablation can be controlled by temperature shift. Moffat et al. generated cold-sensitive mutants of ricin toxin A chain in yeast. Then they linked a cold-sensitive toxin gene to the sevenless promoter, and transformed Drosophila
embryos. At permissive temperatures, transgenic flies had greatly disrupted eyes while at the restrictive temperature, only 1-2% of ommatidia showed any defect. Scanning electron microscopy confirmed that the defects were on the whole consistent with ablation of cells that normally express sev. Bellen et al. took much the same line, generating temperature-sensitive mutant diphtheria toxins in yeast, and expressing them under the control of the ninaE promoter in R1-R6 photoreceptors. The usefulness of the technique could be expanded if a twostep system was used. The toxin could be expressed under the control of a UASGAL element, expression from which requires the yeast GAL4 activator. Toxin would then be made only when flies were crossed with a GAL4expressing strain - and enhancer traps could be used to generate lines expressing P-GAL4 fusions in a wide range of cells, permitting cell ablation of practically any cell type without the need to generate new transgenic fly lines for each cell type. /~
the growth rate of yeast cells, even though no p53 homologue has yet been found in yeast. Either wild-type human p53, or a p53 mutant known to be oncogenic in human cells, was introduced into yeast under the control of the inducible GALl promoter. Under inducing conditions, colonies containing wild-type p53 grew much more slowly than controls, while two different p53 mutants caused either a slight reduction in growth rate or an intermediate rate. Since p53 activity is thought to be regulated in part by phosphorylation by the human CDC2Hs kinase, the next experiment was to introduce both p53 and CDC2Hs genes into yeast: still further inhibition of growth occurred, and
morphological and flow cytometry studies showed that the cells arrested mainly in G1. Somewhat disappoint ingly, though, no differences in phosphorylation of p53 have yet been found between cells expressing just p53 and cells expressing p53 plus CDC2tts. Perhaps a more indirect effect is operating; the authors suggest that p53 functioning as a transcriptional regulator (which it is known to be able to do in yeast) might activate genes that inactivate CDC2Hs, or inactivate CDC2! ts activators. If the yeast factors that interact with human p53 and/or CDC2Hs can be identified, they may point to new players in the mare malian system.
K.G. MOFFAT E TA L.
Development 114, 681-.-687
Isolation of temperature-sensitive diphtheria toxins in yeast and their effects on Drosophila cells H.J. BELLEN ETAL.
TIG MAY 1 9 9 2 VOL. 8 NO. 5
15"