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General Information
D. melanogaster
FlyBase ID
Feature type
Associated gene
Associated Insertion(s)
Carried in Construct
Also Known As
Key Links
Allele class
Nature of the Allele
Allele class
Mutations Mapped to the Genome
Additional Notes
Nucleotide change:


Amino acid change:

G274E | comt-PA; G274E | comt-PB

Reported amino acid change:



Site of nucleotide substitution in mutant inferred by FlyBase based on reported amino acid change.

Associated Sequence Data
DNA sequence
Protein sequence
Progenitor genotype
Nature of the lesion

Amino acid replacement: G274E.

Single missense mutation due to at GC to AT transition.

Expression Data
Reporter Expression
Additional Information
Marker for
Reflects expression of
Reporter construct used in assay
Human Disease Associations
Disease Ontology (DO) Annotations
Models Based on Experimental Evidence ( 1 )
Modifiers Based on Experimental Evidence ( 0 )
Comments on Models/Modifiers Based on Experimental Evidence ( 0 )
Disease-implicated variant(s)
Phenotypic Data
Phenotypic Class
Phenotype Manifest In
Detailed Description

comt4/comt4 mutants exhibit severely reduced lifespans when reared at 29[o]C, and a milder reduced lifespan phenotype when reared at 22[o]C; display neurodegeneration, as assessed by presence of vacuoles in the neuropil after 48-hr exposure to 29[o]C; display normal climbing ability when reared at 22[o]C, but loss of climbing ability after shifting to 29[o]C; and decreased survival during prolonged starvation during adulthood at 22[o]C, as compared with wild type flies.

At the restrictive temperature of 33[o]C, comt4 mutants exhibit a wild-type excitatory postsynaptic current (EPSC) in response to stimulus. However, subsequent stimulation produces a marked activity-dependent reduction in EPSC amplitude relative to wild-type.

At the restrictive temperature of 33[o]C, comt4 synapses exhibit a two-component recovery time course indistinguishable from that of wild-type.

After 5Hz stimulation at 33[o]C, Snap25ts DLM neuromuscular synapses exhibit marked activity-dependent reduction in EPSC amplitude with respect to wild-type. The EPSC amplitude declines progressively over 100 stimuli to 21% of the first amplitude. The initial time course of depression closely resembles that of wild-type over the first five stimuli. Recovery in comt4 exhibits a similar time constant to the slow component in PP experiments.

comt4 mutants exposured to 38oC exhibit a delay before paralysis.

Hemizygous male larvae take much longer than wild type to roll from lying on their dorsal surface to their ventral surface.

Wild-type larvae incubated at 37oC show conversion of larval clusters of vesicles and tubules in the Golgi areas of leg and wing discs into Golgi cisternae. This formation of Golgi cisternae is blocked in homozygous female and hemizygous male comt4 larvae incubated at 37oC (which have been fed ecdysone) and is also blocked in comt4 discs incubated in vitro at 37oC (in the presence of ecdysone).

Electroretinograms taken from the retina at 38oC reveal losses of on/off transients in mutants. Retinal axon terminals are filled with synaptic vesicles that have not fused with the membrane.

The action potentials of the dorsal longitudinal flight muscle (DLM) are indistinguishable from wild-type at the permissive temperature (20oC). At the restrictive temperature, the first stimulus produces a wild-type action potential, but subsequent stimuli result in a reduction and then loss of the DLM action potential. A slowing of the synaptic current kinetics is seen. The number of docked vesicles per active zone is higher than wild-type in the neuromuscular synapses of the coxal muscles (at the restrictive temperature).

In ERG assay, mutants lose the on/off transients at 38oC, though over a slower time course than for Syx1A3-69. Recovery of transients at 20oC is slower than for Syx1A3-69. ERG phenotypes correlate with paralytic phenotypes: time course of paralysis and recovery for Syx1A mutants is more rapid than for comt mutants. Ultrastructural studies reveal that the number of synaptic vesicles in photoreceptor terminals in the optic cartridge is increased. Clear inreases occur in the number of vesicles clustered round T-bars. Number of docked vesicles is increased compared to wild type.

Paralysis normally occurs within 1-2 minutes of exposure to 38oC. comt4 flies bearing P{hsp70-NSF} exposed to heat shock, followed by one day recovery, are highly resistant to exposure to 38oC.

Reversible heat induced paralysis.

External Data
Show genetic interaction network for Enhancers & Suppressors
Phenotypic Class
Enhanced by

comt4 has paralytic | recessive | heat sensitive phenotype, enhanceable by ovr1

comt4 has paralytic | heat sensitive phenotype, enhanceable by cacS

Suppressed by

comt4 has paralytic | heat sensitive phenotype, suppressible by Scer\GAL4elav-C155/Nsf2UAS.cGa

comt4 has abnormal neuroanatomy | heat sensitive phenotype, suppressible by shi1

NOT suppressed by

comt4 has short lived | heat sensitive phenotype, non-suppressible by sei2/sei2

Phenotype Manifest In
Suppressed by

comt4 has synapse | heat sensitive phenotype, suppressible by shi1

Additional Comments
Genetic Interactions

sei2/sei2 does not significantly change the severity of the shortened lifespan phenotype of comt4/comt4 mutants at 29[o]C.

cacTS2 comt4 double mutant males generate song pulses whose intrapulse cycle (CPP) values are within the normal range.

comt4, parats1 double mutant animals exposed to 38oC for 5 minutes show a rapid recovery from the paralysis phenotype when returned to the permissive temperature. After rapid recovery and normal behaviour, these flies suddenly re-paralyse several minutes later at the permissive temperature. Retinal axon terminals in comt4 shi1 are devoid with synaptic vesicles and show an increase in larger vacuolar-type structures.

ovr1 accelerates the paralysis observed in comt4 animals at 36oC (the time for 50% paralysis is reduced). cacS comt4 double mutants show faster paralysis than comt4 single mutants at both 36o and 38oC.

Xenogenetic Interactions
Complementation and Rescue Data
Images (0)
Stocks (1)
Notes on Origin

Siddiqi and Benzer.


The G274E mutation alone is responsible for the temperature sensitive paralytic phenotype of comt4.

Results from response to cervical stimulation, intracellular recordings of flight muscles and direct excitability of muscle cannot distinguish if the mutant phenotype is due to a slowing of nerve induction, delayed transmitter release at the nerve terminal or a defect in muscle response to chemical excitation.

External Crossreferences and Linkouts ( 0 )
Synonyms and Secondary IDs (6)
References (17)