See the embryonic expression pattern of qtc at the Berkeley Drosophila Genome Project Patterns of Gene Expression Site.
The qtc enhancer trap line was originally identified by virtue of its reporter gene expression in the olfactory system, with limited expression also detected in the brain. To determine whether the qtc gene is expressed in the olfactory system and brain, Northern blots and in situ hybridizations to RNA were performed in tissue sections (Gaines, 2000).
A 2.4-kb transcript in heads and antennae is observed to hybridize to a qtc probe. The transcript is present in both males and females, in comparable amounts. Quantitative RNase protection experiments reveal no differences between male and female antennae in qtc transcript levels. In another experiment, the 2.4-kb transcript was also observed in bodies from which heads had been removed and in embryos, although the intensity of hybridization was less than that to head RNA. Following long exposure, an additional band of 4.4 kb can be observed in the head RNA track (Gaines, 2000).
The qtc mutations were found to affect the 2.4-kb transcript. Specifically, the P-element insertion in qtc1, which introduces ~14 kb of DNA into the third intron of the qtc gene, greatly reduces the intensity of labeling and affects the band pattern; the same alterations are observed for the parental insertion line qtc1 b pr. The qtcEx1 deletion mutation, generated by imprecise excision of the P-element insertion, also reduces the intensity of labeling and alters the band pattern. The changes in band pattern presumably reflect changes in the length of the transcription unit, the deletion or addition of splice junctions, and stability of the mRNAs: rapid degradation of other disrupted transcripts by mRNA surveillance pathways has been demonstrated. In contrast, wild-type levels of the adjacent L37a gene expression are observed in both qtc1 insertion lines and in the deletion mutant line qtcEx1 (Gaines, 2000).
Localization of the qtc transcript was confirmed and extended by in situ hybridization to RNA in tissue sections. A qtc antisense probe hybridizes to sections of the antenna and the maxillary palp, another olfactory organ of the fly head. Within the antenna, expression is seen in both the second and third segments and is concentrated near the cuticle, where the cell bodies of sensory neurons are located. Expression in the maxillary palp also appears near the cuticle. These hybridization results show that the gene is expressed in two olfactory organs: the third antennal segment and the maxillary palp. However, they also show that expression is not limited to olfactory cells, since the second antennal segment contains no olfactory sensilla (Gaines, 2000).
Abundant expression is also seen in the CNS within the head, consistent with the strong hybridization to head RNA in Northern blots. There are high levels of expression in the visual system: expression is seen in the retina and the optic lobe. Uniform expression is also seen in the cortex of the brain, where the cell bodies of brain neuropil are located (Gaines, 2000).
The probe also hybridizes to sections from the thorax and abdomens of males and females. In both sexes, expression is seen in the ventral ganglion within the thorax. In males, expression is seen near the tip of the abdomen, closely associated with the ejaculatory bulb and testis. In females, expression is also observed in the distal end of the abdomen, likely associated with the reproductive system (Gaines, 2000).
Several aspects of the sexual behavior of qtc males and females are normal, in comparison to CS males and females. Mature qtc1 males perform normal levels of courtship toward CS virgin females during the observation period: the CI of qtc1 males paired with CS females was 75 ± 3, compared with 78 ± 3 for CS males paired with CS females. Moreover, mutant males performed 'advanced' courtship behaviors toward CS females: qtc1 males showed wing vibration in all of 20 cases, and in most cases they showed licking of female genitalia and curling of the abdomen to attempt copulation. Moreover, qtc1 and CS males that began to mate with females during the 10-min observation period had copulation latencies that were not significantly different. qtc1 females elicit as much courtship from CS males as do CS females. Immature qtc1 males elicite the same level of courtship from CS males as do immature CS males. qtc1 females are as likely to mate with CS males (65%) during the observation period as are CS females (67%), and the mutant females' copulation latencies are normal. During courtship tests of qtc1 males with CS females, qtc1 males are observed to perform the full repertoire of wild-type courtship behaviors (Gaines, 2000).
In addition, sensory function of qtc1 appears normal in limited testing of visual and olfactory physiology by electroretinogram and electroantennogram recordings and in tests of both adult and larval olfactory behavior. Detailed examination of qtc mutants did not reveal any general behavioral defects in such activities as walking or grooming (Gaines, 2000).
Gaines, P., Tompkins, L., Woodard, C. T. and Carlson, J. R. (2000). quick-to-court, a Drosophila mutant with elevated levels of sexual behavior, is defective in a predicted coiled-coil protein. Genetics 154(4): 1627-1637. 10747058
date revised: 30 July 2001
Home page: The Interactive Fly © 1997 Thomas B. Brody, Ph.D.
The Interactive Fly resides on the
Society for Developmental Biology's Web server.