|Feature type||allele||Associated gene||Dmel\Mhc|
|Also Known As||Ifm(2)RU1|
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|Nature of the Allele|
|Mutations Mapped to the Genome|
|Associated Sequence Data|
|Nature of the lesion|
Amino acid replacement: E1570K.
|Phenotype Manifest In|
dorsal medial muscle & myofibril
4-5 day old Mhc[E1570K] mutant homozygotes show severe dorsal longitudinal muscle (DLM) abnormality, with intact fibres attached through thin strands at both ends. Muscle deformity (reduced birefringence) is also present, although the tearing and bundling of fibres associated with a typical hypercontraction phenotype is not observed. Sarcomeres show some of the repetitive structure seen in wild type but there is considerable disarray, with severe disruption of the filament lattice. The lattice is almost totally absent except for small patches where myofilaments are seen, and individual scattered thick and thin filaments are present. In some areas, clumps of Z-disc-like structures are linked by what appear to be thin filaments. These Z-discs are smaller and more variable in shape, with short spacing compared to wild type. DLM defects are also detected during development. Z discs of an irregular shape and size are first detectable at 42-46h after puparium formation and the myofibrils appear wider at this stage. The dorsal longitudinal muscle (DLM) fibres in newly eclosed Mhc[E1570K]/+ flies appear similar to wild type, with areas of reduced birefringence. However, by two days these heterozygous flies show a more typical complete hypercontraction phenotype; the fibres have detached and bundled to one side as a result of tearing, especially at the anterior muscle attachment site. The thick/thin filament lattice is clearly present, but is irregular and loosely packed. Repeating sarcomeric structures are seen but are short and irregular compared to wild type. M-bands and Z-discs are irregular, and I-bands and H-zones are not seen. No defects are detected in the DLMs of pupal stage Mhc[E1570K]/+ mutants The dorsal longitudinal muscles of Mhc[E1570K]/Mhc[L1736P] transheterozygotes show fibre thinning at both the anterior and posterior ends. The flies are flightless.
All homozygotes have a drooping wing phenotype, in some cases so severe that it interferes with walking. Muscle fibre defects are seen in the early developing indirect flight muscles (IFMs); the fibres appear spongy with aberrant structures 22 hours after puparium formation (APF) and at 30-32 hours APF the defect is very prominent in the margins of the muscle fibre, where the attachment to the epidermis takes place. In the adult, the IFMs are totally disorganised, with the muscle fibres appearing thin, disrupted and constricted to a small region of the thorax. The phenotype is completely penetrant, although the expressivity varies. Thinning of the dorsal longitudinal muscles (DLMs) is seen toward either end of the thorax, whereas in some extreme cases, a whole DLM appears as thin strips. The myofibrils appear to be easily broken with no demarcation of the muscle bands. Heterozygous flies also show a slight drooping of the wings and the DLMs are affected to varying extents; in some flies 1 or 2 DLMs are disorganised and in others the posterior regions have degenerated. The dorsoventral muscles (DVMs) are also usually disorganised or degenerated. The myofibrils of heterozygotes appear more or less like those of homozygotes, except that the Z bands are preserved. Homozygotes are completely flightless, and most heterozygotes are also completely flightless, although some show weak flight ability. Homozygous males show an inability to court with wild-type females. Homozygotes have significantly reduced viability. Ifm(2)RU11/Df(2L)H20 flies have a more severe wing and muscle phenotype than Ifm(2)RU11 homozygotes.
|Phenotype Manifest In|
|Complementation & Rescue Data|
|Fails to complement|
|Partially rescued by|
Expression of two copies of Mhc[+t41.9] rescues the dorsal longitudinal muscle thinning seen in homozygous Mhc[E1570K] mutants, with flies instead showing a similar hypercontraction phenotype to that seen in Mhc[E1570K] heterozygotes. Expression of Mhc[+t41.9] partially suppresses the sarcomere disruption seen in Mhc[E1570K] mutants. Expression of Mhc[+t41.9] partially rescues the hypercontraction phenotype seen in Mhc[E1570K]/+ mutants, with flies displaying less fibre tearing. One copy of Mhc[2D] suppresses the defects in dorsal longitudinal muscle morphology seen in Mhc[E1570K] mutant flies.
|Stocks ( 0 )|
|Notes on Origin|
|External Crossreferences & Linkouts|
|Synonyms & Secondary IDs ( 5 )|
|Secondary FlyBase IDs|
|References ( 3 )|