Zebrafish blowout provides genetic evidence for Patched1-mediated negative regulation of Hedgehog signaling within the proximal optic vesicle of the vertebrate eye

摘要

Inthisstudy,wehavecharacterizedtheoculardefectsintherecessivezebrafishmutantemblowout/emthatpresentswithavariablypenetrantcolobomaphenotype.emblowout/emmutantsdevelopunilateralorbilateralcolobomasandasaresult,theretinaandretinalpigmentedepitheliumarenotcontainedwithintheopticcup.Colobomasresultfromdefectsinopticstalkmorphogenesiswherebytheopticstalkextendsintotheretinaandimpedesthelateraledgesofthechoroidfissurefrommeetingandfusing.Theexpressiondomainoftheproximalopticvesiclemarkerempax2a/emisexpandedinemblowout/emattheexpenseofthedistalopticvesiclemarkerempax6/em,suggestingthattheinitialpatterningoftheopticvesicleintoproximalanddistalterritoriesisdisruptedinemblowout/em.Lateraspectsofdistalopticcupformation(i.e.retinadevelopment)arenormalinemblowout/emmutants,however.Positionalcloningofemblowout/emidentifiedanonsensemutationinempatched1/em,anegativeregulatoroftheHedgehogpathway,astheunderlyingcauseoftheemblowout/emphenotype.ExpandeddomainsofexpressionoftheHedgehogtargetgenesempatched1/emandempatched2/emwereobservedinemblowout/em,consistentwithalossofPatched1functionandupregulationofHedgehogpathwayactivity.Moreover,colobomasinemblowout/emcouldbesuppressedbypharmacologicallyinhibitingtheHedgehogpathwaywithcyclopamine,andmaximalrescueoccurredwhenembryoswereexposedtocyclopaminebetween5.5and13hourspost-fertilization.TheseobservationshighlightthecriticalrolethatHedgehogpathwayactivityplaysinmediatingpatterningoftheproximal/distalaxisoftheopticvesicleduringtheearlyphasesofeyedevelopmentandtheyprovidegeneticconfirmationfortheintegralrolethatempatched1/em-mediatednegativeregulationofHedgehogsignalingplaysduringvertebrateeyedevelopment./p/div