JUN in Drosophila development: redundant and non-redundant functions and regulation by two MAPK signalling pathways

MONITOR Patterning the zebrafish neural axis Specificalion of Ihe zeblafishnervoussyslemhy n(lnaxlalsignals W0o, K, and Fraser, S.E Science 277, 254-257 Large~.a.'alemutagenesis and screening have recently nlimtl the exciting IXtssihility I)f exlen.sive study ol zehnd'ish embt3onic development al the genetic level. However. compared ~%itil more estai~lished experimental systems, such as Xetzopzl$. little is known alxltlt (lie hil.~ic mechanisms of zt..bmfish e m i r ' i v genesis. The emhryonic shield {ff the zebrafish gatstrttla Iingressing tissue that confflhute5 It) axial mesodeml and tilt' ventral CNS Icenlml ncnoLIs a}stelll)] has lx.'en called the equivalent of the A2.nopusdorsal bias(oil)re lip or ot~g.mizt.-r, The organizer (-an induce a second embryonic axis, and cum:m thinking

sLiggests tll;ll induction and Ixitleming nfthe .X'em~pusCNS :ira adlieved hy two signals fmnl organizer-derived tissues, an "a~xivaling' signal Item ingrc':.sing future anterior axial me~)denn, which indut'es a neur.d plate initkdly anlerit )r in L'halx.ttlor, and at sulxse(luem Inlnnfonning" signal from the nl~iochord thai gives a graded posterioriTaltion of the netlb ectoderm IRl~ever. Woo and Fraser sh(i%x that ztlhrafish anterinr neuret~l~ deml cannel I~" induced tt~ uxpre*s I x ~ tedor ~;tla.lt~ttlresand markers hy tmnsplantatilm {if tile enlbt3'
JUN at t h e l e a d i n g e d g e Coupling 01"JU',Iamln0-termin£klna~eand Deeapentaplegicsignallingpathway¢ in Drosopbfhl inorph0gertesis Gli.a...B ;lrld"/0se]li.S. GellesDez' I I, 173g-l'i7

DrosupbiluJUN relaD the JUg amino-temgmdkinas¢signalIransdudilmgalhwa) te the Decapentaplegi~signal tranMuction pathwayin regulating epithelia] cd[ sheet nl{~velnent Hou. "(5, et al Ge~lt,~Dee II, 172g-17~7 JCN in Drosophiladevdopll~ent:redundantand non-redundantfunctions and regulation hy two MAPKsignallingpath~ays bi~lckel, L et al I (;enesDeL 1L ]748~1758

DrosopbllaJUg kinaseiegulates expressionof dl'cape,tepht~ic ~ia the El'S-domaln protein AOPand the AP-ItranscriptielnI:actur DJUNduringdorsal d¢~sure Riesgo.Esr0~arJ lind Itaten E GellesBet' I I 1717-1727 "lklwalllSthe end of DnJ.¢ophfla enll)g'~l- II~tI.JNIis ;in etfecior in this pn,,:~x~, hy genes.is, the dorsal side of the etnhr3t~ characterizing it)~s(g lunctitm allel~s in I g o m e s enclosed with epklennis (dorDJull and by delnl)nstrdling lhal uhk Isal closure) through Ihe co ordinated tlitous exprc-~slon of ;in :t(tivaled JUN 111igratgmof ix;'o wmmetrical cell sheets rescuesJNK and JNKK mutant enlt}13"os ',vRh specialized cells at their leading JI'N is essential fi~r the explcssion of edges. A I~vy tff papem in Ge#tes a n d specific genes in the It-uding-edge cells Det~.lopmem R~cus on tile role lffJUN and. intelestingly, ia all{) needed fin in these leading-edge cells. Prexious the cycoskelelal chang~:s in these cells, studies established that dnrsal eh)sure indicating that the effects on ccd]ular requires l)*~:)gopbJ/a JUN N-terminal nlorpholt)g,y are not directly nl(KJulated klna.se (.INK) and JNK kinase ~JNKK). hy JNK One key tran%cripti(inal target ~llree of the recent patx'rs I H~)u el a#, ill JI.'N is decapettl~qlle, gk" (dpp). at Kockel el al., Riesgt>Encovar and "l'GF-[~ honlnklgue. ~xllich is normally Hafen) confirm that DnJ.~¢~pbila .IUN t:xpi'ensed in Icviding-edge cells iGlise

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nlargin gilt lk~rmsnonaxial mt.':,tvJerml, even fi-om diametri,:aliy oplx*situ tge dor:-ad axis, can cause Ix~steriorizatkln of the neurecgMerm During gasinlhltiOlI the I~.llUre forehrain shifts away from tilt" get'raring, while ttlttlre hindI l d n cell* mm'erge dorsally, but reinain tktke t(i, and (()tlld r,:tx:i~e a nldi:ll tlzmM~irnting signal frOllL thc-g~illlling. bFGF is a candidate tra ns~ianningneural ind tK'ur in XeHOpII& and overexpre~inn of a dominant-negative FGF rt.o:ptor in tile zOmlfish emhry
and NomllL }lou eq al. Riesgo-Escovar and IlafenL Furthermore. expression c~f an acliv:ged dpp recel)mr (TKVqa) in tile dorsal-moe,t epidenn;d cells can rescue I)JUN/JNK nmtants thou el al,), con[inning tile ilnporlance o[ I)PI' signalling here" A st'c(md targel gene is p . ( k e m d (Glise el a l l Milch is six'ci[ically expressed in [~ldill,~ edge calls. IntelL+~lingly the Puckered protein inighl he a negatwe regulator of the JUN,JNK palh'~.:ly, hccausc p . c nnutatkllLs result in eclopJcpllcand dpp eXl)lCXqUnThe tmn.~criplionall~.'l)re~.a)r encoded h} e.ltt'lqrJr a p e . I AOP/YAN ) appears to I)e a C(llllln,)n suh~trate of JNK and MAPK (Riesgc)-E~covar and llatenl. 'Milch is ina(iiVated I',y pit
month

Stephen Mathias. Vincent Cunlitte, Mark Rogers, Alison Snape a n d Sanlh P.ray

TiG O(TroBEe.1997 VOL. 13 NO. 10

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