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The Genom of Homo sapiens.pdf

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498 OLSONbacterial lineages prospered by piggybacking on the hugeexpansion <strong>of</strong> the human population that followed the development<strong>of</strong> agriculture.Although available data are much sparser for metazoans,analogous evolutionary processes appear to haveoccurred throughout the tree <strong>of</strong> life. Evolution appears toinvolve repeated cycles <strong>of</strong> specialization in which individualspecies and whole evolutionary lineages periodicallyshed genes that were present in more generalist ancestors.Koonin reported on large-scale comparisons <strong>of</strong>the gene content <strong>of</strong> available metazoan genomes. <strong>The</strong>secomparisons reveal a pattern <strong>of</strong> many, independent genelossevents on different lineages. This finding, which applieson a timescale <strong>of</strong> hundreds <strong>of</strong> millions <strong>of</strong> years, isreminiscent <strong>of</strong> S. Pääbo’s report <strong>of</strong> recent large-scale loss<strong>of</strong> olfactory receptor genes on the chimpanzee and humanlineages. In all likelihood, the recent loss <strong>of</strong> these genes issimply an instance <strong>of</strong> the general process described byKoonin (Rogozin et al.).Given the desirability <strong>of</strong> basing the comparative genomics<strong>of</strong> all evolutionary groups on comparisons <strong>of</strong>multiple whole-genome sequences, the meeting wasoddly lacking in serious assessments <strong>of</strong> the rate at whichsuch data will become available and the extent to whichthey will be <strong>of</strong> adequate quality to meet future needs. Thisvoid appears to have reflected lack <strong>of</strong> activity rather thanthe tastes <strong>of</strong> the organizers. E. Myers did report on incrementalprogress with his whole-genome assembler. Healso expressed the view that reasonable whole-genomeassemblies were only attainable when the sequence coveragewas at least 8x, a sampling depth higher than thatreached in many current whole-genome-shotgun projects.Gibbs (Gibbs and Weinstock) was a lone voice who actuallyaddressed the technical challenges associated withadding value to the raw output <strong>of</strong> whole-genome-shotgunprojects. His main message was that, although it may beimpractical to keep the army <strong>of</strong> finishers who producedthe current human-genome sequence in the field, thereare numerous lower-cost options for improving on rawwhole-genome assemblies.GENOME ANNOTATION AND RESOURCEDEVELOPMENTThis Symposium was dominated by the consumers, notthe producers, <strong>of</strong> genomic sequence. <strong>The</strong>se consumerswant, first and foremost, better annotation. Gerald Rubinemphasized challenges and successes in annotating theDrosophila genome. Challenges include the presence <strong>of</strong>hundreds <strong>of</strong> genes in heterochromatic regions that remaindifficult to sequence reliably, much less to annotate.<strong>The</strong>re are also many instances <strong>of</strong> genes embedded withingenes, transcribed either from the same or the oppositestrand, a theme also developed by Lipovich (Lipovichand King) for the human. Rubin’s emphasis on thesecomplex gene structures stimulated a lively exchangewith Brent about the prospects <strong>of</strong> detecting and disentanglingoverlapping and embedded genes computationally.Whereas Brent expressed optimism about the pace atwhich gene-detection programs are improving, Rubincountered with the observation that “sequencing is gettingcheaper.” <strong>The</strong> implication <strong>of</strong> cheaper sequencing isthat the comparative genomics <strong>of</strong> Drosophila speciesmay provide the best path toward comprehensive geneidentification for D. melanogaster. Rubin forcefully advocatedthe view that annotation and resource creation(e.g., full-length cDNA clones, comprehensive collections<strong>of</strong> transposon mutations) should be taken to thesame level <strong>of</strong> completion as the sequence itself.Many talks emphasized the breadth <strong>of</strong> commitment tothis goal, at least for intensively studied organisms.Hayashizaki described impressive progress on development<strong>of</strong> a full-length-cDNA resource for the mouse. Indeed,he indicated that the resource is now sufficientlyrich that more attention is needed to distribution mechanisms.Hayashizaki (Hayashizaki) illustrated the increasingdisparity between the ease <strong>of</strong> distributing data and thedifficulty <strong>of</strong> distributing biological resources by describinghis experiences sending out the FANTOM2 set <strong>of</strong>60,770 mouse full-length-cDNA clones packaged with100 kg <strong>of</strong> dry ice. To solve this problem, the Riken grouphas developed DNA-printing technology that may allowroutine distribution <strong>of</strong> DNA samples, designed for easyPCR amplification, on printed pages. Perhaps this applicationwill provide a long-term future for hard-copy editions<strong>of</strong> biological journals!Other examples <strong>of</strong> large-scale biological resources includedFriddle’s (Friddle et al.) report on high-throughputmouse-knockout technology. His talk described an insertion-mutagenesisprotocol based on retroviral constructsthat disrupt mouse transcription units. This method hasyielded over 200,000 ES cell lines containing unique insertionevents, which disrupt the function <strong>of</strong> ~60% <strong>of</strong>mouse genes. <strong>The</strong> positions <strong>of</strong> the insertions are determinedby sequencing the exon downstream from the insertionsite following PCR amplification <strong>of</strong> reverse transcripts<strong>of</strong> mRNAs transcribed from a promoter within theinserted element. RNAi <strong>of</strong>fers a potential alternative toknockout technology for functional annotation <strong>of</strong>genomes. Hannon reported on major progress in understandingthe mechanism <strong>of</strong> RNAi, a step that should facilitateincreased reliance on this relatively cheap alternativeto traditional gene-inactivation methods.High-throughput in situ hybridization to developingembryos provides still another experimental means <strong>of</strong>functional annotation. Roe (Roe et al.) described a projectto gather such data for the zebrafish, with an initial focuson the orthologs <strong>of</strong> genes present on human Chromosome22. This talk was <strong>of</strong> technical interest in that Roe, agenome-sequencing veteran, retooled his sequencingpipeline for this purpose. Malek (Malek et al.) describeda way <strong>of</strong> coupling sequencing technology even more directlyto functional annotation. In his system, which hasbeen pioneered on the bacterium Rickettsia sibirica, thesubclone libraries that provide sequencing templates forwhole-genome-shotgun sequencing are constructed in avector that supports their use as “bait” and “prey” sequencesin a bacterial implementation <strong>of</strong> the two-hybridmethod for detecting protein–protein interactions. Hence,simply as a by-product <strong>of</strong> genome sequencing, one obtainsa saturating collection <strong>of</strong> sequenced clones for usein protein–protein-interaction mapping.

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