Developmental effects of a temperature-sensitive RNA polymerase II mutation in Drosophila melanogaster☆

摘要

Drosophilamelanogasterpossessingatemperature-sensitive(ts)mutationthatmapstoanX-linkedlocus(RpII215)(thelocushasalsobeencalledl(1)L5andUltrabithorax-likeorUbl)encodingasubunitofRNApolymeraseIIarefertileat22?°Cbutbecomesterilewhenshiftedto29?°C.HomozygousRpII215tsadultfemalesshiftedto29?°Claystructurallynormaleggsfor24hr,afterwhichincreasingnumbersofeggsareabnormal.Eggslefttodevelopat29?°Cdieasmorphologicallynormallateembryosorfirstinstarlarvaewhenproducedbyfemalesmaintainedat29?°Cforlessthan6hr.However,eggsproducedbyfemalesundergoingoogenesisat29?°Cforlongerthan6hrdevelopabnormally,displayingholesprimarilyintheirventralcuticleandpossessinganabnormalpharyngealapparatus.Asexposureoffemalesto29?°Clengthensthereisanincreaseintheseverityofthesedefects.SomeoftheeggscanberescuedbyeithermatingRpII215tsfemalestowild-typemalesorshiftingtheeggsto22?°C.Thepercentageofeggsrescueddecreaseswithincreasedlengthofoogenesisat29?°C,upto20hr,atwhichpointtheyarenolongerrescuable.Theterminalphenotypeofeggsthatfailtoberescuedbytheaboveprocedureislessextremethanthatofeggsforwhichnorescueattemptwasmade.Holesintheventralcuticlearereducedorabsent,butpatternformationisdisruptedsuchthatsegmentsareoftenmissing,incorrectlyorientedorfused.BecausetheRpII215locusencodesasubunitofRNApolymeraseII,thedevelopmentaldefectsdescribedabovearemostlikelyduetoreducedoraberranttranscriptionduringoogenesisandearlyembryogenesis.Thispostulatedeffectontranscriptionresults,inpart,fromthematernalloadingofageneproduct(s)thatisthermolabileineggs.