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Title: A P element excision-derived mutation in Drosophila melanogaster
Author: Adam, Margaret M.
Awarding Body: University of Glasgow
Current Institution: University of Glasgow
Date of Award: 1995
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The purpose of the work described in this Thesis was to isolate and mutate novel genes essential in the development of the Drosophila melanogaster nervous system. Two marked P element enhancer trap strains were found to express the reporter gene lacZ in spatially and temporally regulated patterns in the nervous system. Excisions of the P element construct in one of these strains, A22, were detected in approximately 68% of the A22-derived progeny which were recognised by the loss of the rosy gene. 19 strains were subsequently found to have a recessive mutant phenotype believed to be a result of imprecise excision of the P element. This represents a mutation rate of approximately 24%. Each of these 19 strains had a recessive mutation that resulted in abnormal wing development. Other mutant phenotypes were not detected in any of the excision-derived strains. No similar mutations are known to be located at the site of P element insertion of the ancestral A22 strain and therefore these excision-derived mutants are considered novel. Four excision-derived mutants were selected for further characterisation and these were found to be cold-sensitive. The severity and frequency of the mutant phenotype was increased when these four strains were raised at 20°C rather than 25°C. When raised at 16°C, these four mutants were found to have a recessive pupal lethal phenotype. Complementation analysis using all possible combinations of these four mutants confirm each strain is mutant at the same locus. The mutant phenotype indicates no disruption to embryonic neurogenesis at the temperatures investigated. In addition, the mesothoracic disc of the A22 ancestral strain gives no evidence of reporter gene activity. Thus the lacZ expression pattern of the A22 P element insertion strain can not be correlated with the abnormal wing development. Reporter gene activity was detected in the larval and adult central brain. This may indicate the cold-sensitive pupal lethality results from abnormal CNS development during metamorphosis. The available data at this time suggests the gene disrupted by P element imprecise excision may not be the gene regulated by the enhancer element directing lacZ expression during embryonic development. Further analysis of these four mutant strains when raised at both 20°C and 25°C, show they are able to jump, excluding the possibility of abnormal leg development. Flight ability tests show these homozygous mutants are unable to fly when raised at the higher temperature of 25°C while those raised at 20°C have normal flight behaviour. Those homozygous progeny raised at the lower temperature of 20°C with phenotypically normal wings are able to initiate and maintain flight, while those raised at 25°C with apparently normal wings are unable to fly. Characterisation of these four mutants show imprecise excision of the A22 P element has resulted in the generation of a paradoxical phenotype where normal development during the pupal stages is cold-sensitive and flight behaviour is heat-sensitive.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available