Evolution of photoreceptors: insights from amphioxus

Abstract

Souhrn Problematikaevoluceokaprov6zievoludnibiologii od samdhopod6tku.JiZve sv6 klrrize,,o pfivodu druhfi" se charles Darwin zmiiuje o oku jako o orginu ,,exfidmnl dokonalosti"a vyjadiuje obavy, zda je mofu6 vysv6tlit vznik takto dokonaldhoorg6nu ptirodnimv;fbErem.I nejjednodu55i,,proto-oko"sloZen6pouzez jedn(:pigmentovdbunkya jedn6 bunky sv6tlodivn6potiebuje pro svou funkci nesdetrf podet gent k6dujicich komponentyfototansdukdnikaskidy,pienosusignriluapigmentace. SvEtlodivndbunkylze na zildadEmorfologierozddlitdo dvou zakladnichtypt na bunkyciliirni arhabdomerick6.Rhabdomerick6svdtlodivndbuf,kytvoii nejdastEjisitnici oka bezobratllfch,zatimcocilirirni typ bundkwoff sitnici obratlovctia Zahavcri.DtleZitou rilohu v pochopenievolucesvEtlodirmfchbundkhraji opsinovdgenya Gc podjednotky,kterdjsou zodpovEdn6za absorpcifotonua prvni lrok fototransdukdnikask6dy.Pro regulaciexprese tdchto struktumichkomponentridasfiricichse biochemiclcjchprocest a pro f6dny vyvoj celdhoodniho orgrinuje zapotiebitdsn6spolupricemnohareguladnichgenri.V pnibdhu poslednichlet bylo zji5tEno,Zeurdit6tanskripdnifaktoryhrajici zisadniflohu vevfvoji oka a svEtlodivnlichbundkjsou totoZndi u evoluCndvelmi vzditenlch organismt.Jednimz nich je ranskripdnifaktorPax6,ktetyje v tomtoohledunejldpeprostudovanf,av5akukazujese, LePax6nenijedinf...

The topic of eye evolutionwas touchedas early as at the very beginningof the evolutionarytheoryitself.In his book'On theOrign of Species'CharlesDarwinexpresses concemsfor theexplanationof theocclurenceof complexeyesby naturalselection.Eventhe simplest'proto-eye'composedof a singlephotoreceptorcellanda shadingpigmentrequires properfrrnctioningof dozensof genesinvolvedin the phototansductioncascade,signal transmissionand pigmentation.Photoreceptorcells can be classifiedaccordingto their morphology as ciliary or rhabdomeric.Primary observationsrevealedthe rhabdomeric photoreceptorsbeing predominantlypresentin the eyes of invertebrates,whereasthe vertebrateandcnidarianseyesemploytheciliary type.Key componentsof thephotoreceptor cells arevisualpigments(opsins)andassociatedGa subunitsresponsiblefor absorptionof photonandthefirst stepof aphotoffansductioncascade.To properlyorchesftatetheassembly of thesestructuralgenesmediatingbiochemicalprocessesinto a functionalorgan,a tight regulationby a dedicatedsetof tanscriptionfactorsis required.Oneof themostremarkable andbeststudiedexamplesof geneswith anevolutionaryconservedrole in eyeorganogenesis is a paired-homeoboxgenePax6.However,availableliteraturepointsto othertranscription factors participatingin photoreceptordevelopmentacrossanimal phyla, for examplea...