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5-350 (38)

Patterning a Simple System

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University of Windsor
Biological Sciences
Asish Mukhopadhyay

Patterning a Simple Systemdeterminedcells cannot alter their anteriorposterior identity early in development though they can alter proximal distal identityHOX genesdetermine mammalian anteriorposterior fateHOXlocated on chromosome in same order as they are expressed homeotic genesdetermine Drosophila anteriorposterior fatehomeoticsimilar to HOX genesUnfertilized Drosophila eggMATERNAL expression bicoidmRNA expressed at headbicoid nanosmRNA expressed at tailnanosboth code for MORPHOGENSsubstances present in a gradientmorphogenspecify different cell fates at different concentrations both are TFsEarly Drosophila embryo is a SYNCITIUMsyncitium before cellularization when cells reform gradients form bicoid expression leads to HUNCHBACK protein txnexpressionHb a threshold of bicoid is needed to activate Hb txn nanos codes for a transcriptional REPRESSOR no nanosHb is expressed throughout ENTIRE embryobicoid and nanos create a gradient of Hb which is itself a TFHunchback regulates expression of other TFsGAP genesgap geneskruppel hunchback activateskrknirpshunchback repressesknigiant hunchback repressesgthigh hunchback expressionall repressed60 of egg lengthkruppel activated other repressed45kruppel inactive knirps active giant repressed30kruppel inactive knirps REPRESSED giant active 0 kruppel inactive knirps repressed giant REPRESSEDwhat represses knirps and giant repression in absence of Hb embryonic TAILLESStailless
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