Both EcR112/EcRM554fs and EcR139/EcRM554fs third instar larvae have the same number of Burs-immunoreactive CCAP neurons as wild-type controls. At 24-48 hours after puparium formation, both EcR112/EcRM554fs and EcR139/EcRM554fs animals show more Burs-immunoreactive abdominal CCAP neurons than +/EcRM554fs controls. Some CCAP neurons retain larval features such as small soma size and larva-like projections.
Homozygous embryos do not hatch and show incomplete head involution and abnormal midgut morphogenesis at late stage 16. Most mutant embryos show incomplete dorsal closure and develop bloated tracheal dorsal trunks.
EcRM554fs/+ flies have wings of wild-type appearance.
An EcR-A mutant (EcR112/EcRM554fs) does not protect normal Crz-expressing ventral-nerve cord neurons from programmed cell death.
The severity of cocaine-induced follicle degeneration in EcRM554fs/+ females is indistinguishable from that observed in wild-type females.
EcR112/EcRM554fs and EcR139/EcRM554fs mutants show a range of lethal phases and a loss of coordination of larval wandering and pupariation behaviour. Both EcR112/EcRM554fs and EcR139/EcRM554fs larvae survive to the third larval instar stage but show abnormal larval wandering behaviour. Unlike wild-type larvae, both types of transheterozygote mutant third instar larvae continue feeding and often fail to wander in search of a suitable pupariation site, resulting in their pupariation on food. The mutants seem to physically resist pupariation and their aberrant movement causes the formation of a misshapen puparium. The predominant lethal period for EcR112/EcRM554fs mutants is pupal stage P5 and a subset survive to later pupal stages. EcR112/EcRM554fs pupae retain swollen salivary glands at more than 48 hours post pupariation, while wild-type salivary glands undergo autophagy at 14 hours post pupariation. Other internal structures, such as gastric cecae and larval midgut cells are not affected in the mutant pupae. Only ~2% of EcR112/EcRM554fs mutants survive to the pharate adult stage and such mutants rarely eclose. These pharate adults have a range of defects, including abnormal operculum formation, heads that are compacted into the anterior portion of the puparium, larval mouth hooks that have not been ejected during pupal development and legs that have shortened, rounded tarsal segments with kinked femurs. Over 60% of EcR139/EcRM554fs mutants survive to pupal stage P5 and most progress through head eversion, eye development, and leg and wing extension. Dessication and necrosis of the pupa is frequently evident at this stage. Additionally, puparium formation is defective; the puparium fails to shorten and tan normally, and the cuticle fails to harden to wild-type levels. Around 15% of EcR139/EcRM554fs mutants survive to pharate adult stage P15, but these animals fail to eclose and degenerate within the pupal case. EcR139/EcRM554fs pharate adults have abnormally short legs, with rounded tarsal segments and kinked femurs. 98% of EcR94/EcRM554fs mutants fail to pupariate. Instead, the internal tissues of these animals become unstable and undergo necrosis. In the 2% of mutants that pupariate, eversion of the anterior spiracles occurs in an abnormal position, the pupal case is sometimes misshapen and after 24 hours, pupae undergo desiccation.
Heterozygotes are viable and morphologically normal.
The embryonic lethality caused by heat treating EcRhs.T:Scer\GAL4/+ embryos at 3 to 5 hours after egg laying is increased from 60% to 96% penetrance if the embryos are also heterozygous for EcRM554fs. The penetrance and expressivity of the germ band retraction defect is also increased in these embryos. Expression of EcRB1-ΔC655.F645A.Scer\UAS under the control of Scer\GAL469B or Scer\GAL4c381 in an EcRM554fs/+ background results in 23% or 15% respectively of the embryos having germ band retraction defects.
Homozygous clones at the posterior margin of the eye disc or in the centre of the eye disc are normal or have very minor defects. EcRM554fs/EcRV559fs larvae rescued through the moult to the third instar by repeated heat shocks (resulting in expression of EcRB2.hs) show normal anterior progression of retinal differentiation in the eye discs. Discs are seen in which the furrow has traversed the entire eye field, reaching the antennal boundary (this represents a late stage of eye disc development that is normally only reached following pupariation). Homozygous clones in the adult eye result in a scar.
EcRA483T/EcRM554fs animals show strong survival at either 22o or 25oC, but do not survive when raised at 29oC. EcRA483T/EcRM554fs females raised at 22o and then shifted to 29oC and mated to wild-type males for 2 days show a progressive reduction in fecundity over a 3 day period of egg collections, culminating in a 75% reduction on the third day. Fecundity is affected to a greater degree (more than 90% reduction) in EcRA483T/EcRM554fs females shifted to 29oC during the prepupal period and retained at 29oC for mating. EcRA483T/EcRM554fs females raised at 22o and then shifted to 29oC show an excess of mature stage 14 egg chambers and a decrease in the number of vitellogenic egg chambers between stages 7 and 14 relative to control siblings (decreases in mid- (stage 10) and late (stages 11-13) vitellogenic stages are seen). Ovarioles containing more than one stage 14 egg chambers in the most posterior portions of the ovariole are seen. Defective egg chambers are also seen. Some defective egg chambers contain very few follicle cells, while others have defects that are limited to nurse cell nuclei. Two types of nurse cell defect are seen; an apparent breakdown of the nuclei of stage 8 and 9 egg chambers and nurse cell nuclei that are dramatically smaller than normal (this defect is seen in both previtellogenic and early vitellogenic egg chambers).
Only 2% of EcRM554fs/EcRV559fs animals survive to the first instar stage, and these survivors die as early first instar larvae.
EcRM554fs/EcRV559fs animals which have been rescued to the first larval instar stage by expression of EcRB2.hs during embryogenesis have normal appearance and movement until the end of the first instar stage. If no further heat pulses are given, they arrest as first instar larvae. The arrested larvae survive for 1-2 days. Most rescued larvae arrest with both first and second instar mouth parts and posterior spiracles. Arrested larvae also appear to retain the first instar cuticle as well as the newly formed second instar cuticle.
EcRM554fs/EcRV559fs animals which have been rescued to the second larval instar stage by expression of EcRB2.hs during embryogenesis and the first larval instar stage have normal appearance and movement until the end of the second instar stage. If no further heat pulses are given, they arrest as second instar larvae. Most rescued larvae arrest with duplicated larval cuticle and both second and third instar mouth hooks and posterior spiracles. The arrested larvae survive for 1-2 days.
EcRM554fs/EcRV559fs animals which have been rescued to the third larval instar stage by expression of EcRB2.hs during embryogenesis, first and second larval instar stages appear normal at the beginning of the third instar stage. Progression through the third instar stage is significantly delayed. The mutant larvae generally stop feeding and begin wandering 48-72 hours following the second to third instar moult (wild-type larvae stop feeding and begin wandering 24-36 hours after the previous moult). Most mutant wandering larvae are able to clear their gut of food (as occurs in wild type). Most mutant larvae become stationary within 24-36 hours after beginning wandering (this occurs 12-24 hours after initiation of wandering in wild-type larvae) but retain their larval morphology without outward signs of pupariation. The mutant larvae can initially resume crawling and mouthpart movements if stimulated with a needle ("stage 1b"). Subsequent phenotypes are not seen in wild-type larvae. The larvae become incapable of resuming mouthpart movement or locomotion when stimulated with a needle ("stage 2"). This stage can be divided into three parts. In "stage 2a" the mutant larvae wriggle the posterior portion of the body, although the anterior tip of the larva appears to be fixed to the side of the culture vial. In "stage 2b" the mutant larvae have ceased wriggling but will resume wriggling if stimulated by a needle. At this stage, brown spots that may indicate necrosis begin to appear on the cuticle of some larvae. "Stage 2c" mutant larvae do not resume posterior wriggling when stimulated by a needle. Most stage 2c larvae have brown areas present on the cuticle. Throughout stage 2, mutant larvae continue to show dorsal medial abdominal contraction (ie. heart pumping), which is no longer detectable in wild-type larvae between 1-7 hours after pupariation. "Stage 3" mutants lack any response to stimulation and have ceased dorsal medial abdominal contraction. Necrotic patches of tissue continue to accumulate and the larvae ultimately deteriorate. Imaginal discs from mid-third instar EcRM554fs/EcRV559fs animals which have been rescued to the third larval instar stage by expression of EcRB2.hs during embryogenesis, first and second larval instar stages are indistinguishable from wild type. Leg discs initiate elongation in the mutant larvae but arrest shortly afterwards. The gastric caeca from mid-third instar mutant larvae appears normal and shortening of the gastric caeca is initiated. However, gastric caeca shortening is not completed, and appears to arrest at a stage comparable to 2 hours after pupariation in wild type. The larval salivary glands persist in mutants. The midgut imaginal cells appear normal in mid-third instar mutant larvae, but do not proliferate.
A small number of females containing homozygous germline clones lay eggs 2-4 days after eclosion. Although few in number, the eggs appear to be normal in shape and size. Egg laying ceases after 4-5 days. Many of the clonal egg chambers are arrested at stage 6 or 7.
Homozygous embryos do not hatch.