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Genetic and developmental analysis of a temperature-sensitive minute mutation of Drosophila melanogaster
Abstract:
A temperature-sensitive (ts) third chromosome Minute (M) mutation, designated Q-III, has been recovered and characterized. Q-III heterozygotes raised at 29 degrees exhibit all of the dominant traits of M mutants including small bristles, rough eyes, prolonged development, reduced viability and interactions with several unrelated mutations. Q-III homozygotes raised at 29 degrees are lethal; death occurs primarily during the first larval instar. When raised at 22 degrees, Q-III heterozygotes are phenotypically normal and Q-III homozygotes display moderate M traits. In addition, Q-III elicits ts sterility and maternal-effect lethality. As is true of M lesions, the dominant traits of Q-III are not expressed in triploid females raised at 29 degrees. Complementation tests suggest that Q-III is a ts allele of M(3)LS4, which is located in 3L near the centromere.--Reciprocal temperature-shift experiments revealed that the temperature-sensitive period (TSP) of Q-III lethality is polyphasic, extending from the first instar to the latter half of pupation. Heat-pulse experiments further resolved this into two post-embryonic TSPs: one occurring during the latter half of the second larval instar, and the other extending from the larval/pupal boundary to the second half of pupation. In addition, heat pulses elicited a large number of striking adult phenotypes in Q-III individuals. These included pattern alterations such as deficiencies and duplications and other morphological defects in structures produced by the eye-antennal, leg, wing and genital imaginal discs and the abdominal histoblasts. Each defect or pattern alteration is associated with a specific TSP during development.--We favor the interpretation that most of the major Q-III defects, particularly the structural duplications and deficiencies, result from temperature-induced cell death in mitotically active imaginal anlagen, while the small macrochaete phene probably results from the direct effects of Q-III on bristle synthesis. The hypothesis that the Q-III locus specifies a component required for protein synthesis is discussed, and it is concluded that this hypothesis can account for the pleiotropy of Q-III, and that perhaps it can be extended to M loci in general.
Insights
A new temperature-sensitive mutation, Q-III, causes lethal developmental defects in fruit flies at higher temperatures. This mutation affects multiple tissues and suggests a role in protein synthesis for Minute loci.
Area of Science:
- Developmental Biology
- Genetics
- Molecular Biology
Background:
- Minute (M) mutations in Drosophila melanogaster are characterized by dominant traits like small bristles and rough eyes.
- These mutations often exhibit temperature-sensitive (ts) properties and can be lethal.
- The genetic basis and developmental roles of M loci are not fully understood.
Purpose of the Study:
- To characterize a novel temperature-sensitive third chromosome Minute mutation, Q-III.
- To determine the temperature-sensitive periods (TSPs) for Q-III lethality and associated developmental defects.
- To investigate the molecular basis and pleiotropic effects of the Q-III mutation.
Main Methods:
- Characterization of Q-III heterozygotes and homozygotes at different temperatures (22°C and 29°C).
- Complementation tests to identify the specific locus of Q-III.
- Reciprocal temperature-shift and heat-pulse experiments to define TSPs.
- Analysis of adult phenotypes resulting from temperature-induced developmental disruptions.
Main Results:
- Q-III exhibits dominant M traits at 29°C and is lethal in homozygotes, with death occurring in early larval stages.
- Q-III homozygotes are viable and show moderate M traits at 22°C.
- Lethality has a polyphasic TSP from first instar to late pupation, with two major post-embryonic TSPs identified.
- Heat pulses induce diverse adult phenotypes, including pattern alterations and morphological defects in imaginal discs and histoblasts, each linked to specific TSPs.
- Q-III also shows temperature-sensitive sterility and maternal-effect lethality.
Conclusions:
- The Q-III mutation likely results from temperature-induced cell death in imaginal discs and histoblasts, leading to structural defects.
- The small bristle phenotype may arise from direct effects on bristle synthesis.
- The pleiotropic effects of Q-III support a hypothesis that the Q-III locus encodes a component essential for protein synthesis, potentially applicable to M loci generally.