MEETXNG REPORTS

the University of California (Davis), working with the author, has proto- typed a system that consists of a simple drawing tool, specialized for sketching automata, and a code generation ‘back end’ that automati- cally compiles the visual program into an actual functioning align- ment algorithm4.

This raks .wme faxinaring pc&bilities. While this automaticAy generated code is far slower than hand-written code, it more than suf- fices for experimentation in a rapid prototyping mode; promisiig resului cm be hand-optimized at leisure. A tool that permits easy design and test- ing of highly complex models of

mutation and alignment, tin hy non-programmers. would further encourage incorpomtion of biologi- cal knowledge. We have done so with models that, for examptc, better account for certain forms of insenion and deletion, such as those z.so& ated with microsatellite repeaW. In cases such as this. a picture can he worth a thousand lines of ctdr.

David B. SearIs DJvid_B._Searls@si~phrd.com

Plant chromosomes unite

A few years ago the proqxct of unifying plant genomes that l-J”@ over seveml orders of magnitude in size would have seemed remole. Now, as presentations at a meeting held recently in Cambridge showed, not only is unity emerging but it has very pnctical conxquences, both for evolutionary and for genetic studies as well as for plant breeding.

The big story will be familiar to mders of Trends in Genelid2. namely that there is widespread conservation of gene order (synteny) between related plant species. For instance, in the gt?tSXs (ranging from cereals. such as rice, wheat and maize. to crops, such as sugar cane) the genomes cm be considrrrvl s descended from a common genome much like present-day rice, which has been cut up in slightly different ways in the different crops and distributed amon@ diRerent numben of chromosomes. This was strikingly illustrated by Mike Gale (John Innes InsliNle, UK) with a representation of the RFLP linkage maps of a cereal genome as a circle with the chromosomes laid end to end on the circumference. A series of concentric circles can then be drawn (with few rearrangements) representing the Renames of the other gmsses with the rice genome as the innernmst circle and syntenic sequences from other grasses aligned on the ndiij. Most strikingly, when the known lorations of genes (such

29-31 ARWT 1995.

;ui ligtrlrss from rice, maize and barley) are entered on the diagnm rhcy lit on the same radius. A similar pattern of lying on a comtnon radius (implying syntenic positioning in different grasses) occurs for genes regulating photoperiodism. dwalfism and vivipry. Viewed In this way it should be pns+blr to pre&t the locltion of genes affecting phenotype from interpolation from other crops. The importance for crop geneticists is clcx; thq can no longer :,tudy their crop in kwlation but in the context of olher plans with which it has genome synteny. For the molecular biologisr. it might he possible to clone genes positionally from the large genomr C-IS hy walking in the chromosome of a smaller genome. For thii to be a reality, gencme similarity must exi.. on the microscale as well as the gross scale alluded to abrwr. Jeff &nnetzen (Purdue, USA) showed that this is the c3se for the genes sb2and rrl. which are in the mme orientation in maize (where they are l4Okb apart). and in sorghum and rice (20 kh and 19 kh apan respxtively~. The intervening se- quences were composed of rqxtkive DNA (which comprises the majority of the genome of must plants). In maize. these repeats are derived from retroposons (and often retmposom within retmposons). These retmposons have been active in recent history: a comparison of modem inbred maize lines shows that while gene order 1s thy FCIIIIC.

TIC JAF~UARY 1996 VOL. 12 No. 1

37

the intergenic repeats are vastly different. Unfortunately foi the gene walkers. microsynteny c3n be complicated by segmental chromosome duplications bt%vt!n species. For instance. despite its smaller g-me. sorghum ha5 a duplinted version of the R&J Iocu~, which is sin&z copy in maize. Nevettheles, Andrezj Kilian (Pullman. USA) targeted the barley stem rust- resistance gene Rpfl (Ref. 4). Using subclones from ordered rice YACs probed with barley cDNA% he showed that the Ias1 6.54 of chromosome Ip of barley was symentic at the microscale with the mnst renninal 2.7cM of rice chromosome 6. As a result of the pmctic31 use of micmsynteny he believes he is within 35 kb of the gene.

Synteny is not confined to the grasses: microsynteny has been observed between Arahidopsis and the 5rasricu.s (Derek Lydiate, John lnnes Centre, UK; Michel Delsney, Perpignan, France) although gross synteny between chromosomes is complicated by rearraqements and duplications in the Brussica genome. A common gene order is, however, seen over much of the potato and tomato genomes. Christian Gebhardt (MPI, Germany) showed that many of the disease resistance loci in tomato are in sy!teny with similar loci in potato. Reasoning that if the gene

MEETING REPORTS

An excellent bag of nerves

Lklhc?*13) and FizI R;whid-Doulrll (Institute of Rychiitry. Iorxbn) showed with Mdn-positive murine stem cells ttit rhe htr of ccn!mI nrrwus system (CNS) wlls cxn he Iwmipukuerl in cukurc wing diffwddion hctors. Significantly. thaw cultud stem cells slain sufftcient plasticiIy to inIeRrJtr into the murine hipporxmpus folkwinH injcxdon and IO f0ll0w IO‘-Jl dilfrrrntiarkm cut% a Ixxm for t~J~S,ht resarchers.

F~JII~ Walsh WMDS, London) &cussed axonog~twis and the intriguing interactions he~wren the cell adhesion m&u-&. SCAM. and the fihrohb growth fucror (FGF) Iyrosine kinw receptor. Hewn1 work with 3 dominant-newtive FGF weptor prwides further evidence 11raI this rc’cc’*tor in1crJction is z~ prerequisiIe for CAGivcn neurite gro&. &wing :~xons musr aIn) Iw guided IO their Inr~vt.. ;md %Jmh Guthrie (LILIDS. London) tlemonsIrJIed IhJl motor 3XWl\ cxn Iw enperimenlally misrouted II) target muscles usinR rhdx)merc wcrsal. Although rhomlwmere n~rw rrnaa mubt. thrreforc. bharc .wme [wrmidve fv;llureh for thcsc molar lilxeh. Ihe neuron* Ihat have misrour~cl ;wm ultim;Wly tlic. prcbum;d~ly

thro”_gh mismatching of trophic support. Studies of awn regrowth aftrr CNS d;lmagc were addr~sxd hy MarIin Schwh (Zurich) using Ihr my&n- nxtive IN-l antibody. He show& that r3Ls with spimd cd ldons Wd impbJtXs of this antihdy cwkl rwovc’r significant mom* activity in previously fxm~ly.sd hindlimhs. Although Ihe molwular action of this antihdy during axon rrgro~h rw~ins uncktr. this continues to he an interesting model of spinal cord repair.

FimJRy. Stt?e MchIahon (St Thomas’ Hwpitd. London~ rqx~~I Ihe ~m~rk~hlr &c~~ of NGF on adult ncricqtors ttxin rwgors). Suhcutuna~us administmtion of a fusion protein am~p~idr~g the NGF rwpmr TrkA and th& duces Ixh knd SCF leveb md. significantly. Icxd pin .wnsitivity. thus, offering novel therqwutic

l#3tersto~Editor We welcome ktterx on any topic of interest to geneticists and

rkvelgmental biologists. Write to : 12 Mark PavXioll,

Trends In G??nt?lb, Ebevier Trends Jcxlmds, 68 Hills Road, Cambridge, UK CU2 lLA.enuil: 1%

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TIC JANUAWY 1996 VOL. I2 No. I

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