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Molecular and functional characterization of the odorant receptor2 (OR2) in the tiger mosquito Aedes albopictus.

Scialò F, Hansson BS, Giordano E, Polito CL, Digilio FA - PLoS ONE (2012)

Bottom Line: Our data indicate that AalOR2 is narrowly tuned to indole, and inhibited by (-)-menthone.In agreement with this results, these two compounds elicit two opposite effects on the olfactory-based behavior of A. albopictus larvae, as determined through a larval behavioral assay.In summary, this work has led to the cloning and de-orphaning of the first Odorant Receptor in the tiger mosquito A. albopictus.

View Article: PubMed Central - PubMed

Affiliation: Institute of Genetics and Biophysics A. Buzzati-Traverso, CNR, Naples, Italy.

ABSTRACT
In mosquitoes, the olfactory system plays a crucial role in many types of behavior, including nectar feeding, host preference selection and oviposition. Aedes albopictus, known also as the tiger mosquito, is an anthropophilic species, which in the last few years, due to its strong ecological plasticity, has spread throughout the world. Although long considered only a secondary vector of viruses, the potential of its vector capacity may constitute a threat to public health. Based on the idea that an improved understanding of the olfactory system of mosquitoes may assist in the development of control methods that interfere with their behavior, we have undertaken a study aimed at characterizing the A. albopictus Odorant Receptors. Here we report the identification, cloning and functional characterization of the AalOR2 ortholog, that represents the first candidate member of the odorant receptor (OR) family of proteins from A. albopictus. AalOR2 is expressed in the larval heads and antennae of adults. Our data indicate that A. albopictus OR2 (AalOR2) shares a high degree of identity with other mosquito OR2 orthologs characterized to date, confirming that OR2 is one of the most conserved mosquito ORs. Our data indicate that AalOR2 is narrowly tuned to indole, and inhibited by (-)-menthone. In agreement with this results, these two compounds elicit two opposite effects on the olfactory-based behavior of A. albopictus larvae, as determined through a larval behavioral assay. In summary, this work has led to the cloning and de-orphaning of the first Odorant Receptor in the tiger mosquito A. albopictus. In future control strategies this receptor may be used as a potential molecular target.

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Behavioral assay on A.albopictus larvae.(A, B) Third and fourth instar larvae were kept in a pirex pan containing a ball of low melting agarose with 10 mM indole and a ball of low melting agarose (the red and blue spots, respectively, in B). The number of larvae were counted each 30 seconds for a maximum of 22 minutes. The histogram shows clearly that indole has an attractive effect for Aedes albopictus larvae. (C,D) Third and fourth instar larvae in the presence of a ball containing 10 mM (–)-menthone and a ball of low melting agarose (the green and blue spots, respectively, in D). Again, the larvae were counted each 30 seconds for a maximum of 22 minutes. Histogram C shows clearly that (–)-menthone evoked an avoidance behavior on the larvae. The result was calculated reporting the number of larvae just at a discrete15-min time-point. These values were compared with each other and analyzed for statistical significance by using a paired, two-tailed student’s t test considering p≤0.05 as significant (df = 4 and t0,05;4 = 44,28 for behavioral test A; df = 4 and t0,05;4 = 27,76 for behavioral test C. *** indicate statistical significant changes (two-tailed Student’s t-test, p<0.001). Error bars indicate S.E.M. for n = 5 separate trials per odorant.
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pone-0036538-g008: Behavioral assay on A.albopictus larvae.(A, B) Third and fourth instar larvae were kept in a pirex pan containing a ball of low melting agarose with 10 mM indole and a ball of low melting agarose (the red and blue spots, respectively, in B). The number of larvae were counted each 30 seconds for a maximum of 22 minutes. The histogram shows clearly that indole has an attractive effect for Aedes albopictus larvae. (C,D) Third and fourth instar larvae in the presence of a ball containing 10 mM (–)-menthone and a ball of low melting agarose (the green and blue spots, respectively, in D). Again, the larvae were counted each 30 seconds for a maximum of 22 minutes. Histogram C shows clearly that (–)-menthone evoked an avoidance behavior on the larvae. The result was calculated reporting the number of larvae just at a discrete15-min time-point. These values were compared with each other and analyzed for statistical significance by using a paired, two-tailed student’s t test considering p≤0.05 as significant (df = 4 and t0,05;4 = 44,28 for behavioral test A; df = 4 and t0,05;4 = 27,76 for behavioral test C. *** indicate statistical significant changes (two-tailed Student’s t-test, p<0.001). Error bars indicate S.E.M. for n = 5 separate trials per odorant.

Mentions: The olfactory molecules already play an important role for mosquitoes in the early larval stages. Previous works have shown that A.gambiae larvae respond to olfactory stimuli with specific behavioral responses that are mediated by the larval olfactory system [20], [27]. Since in A.albopictus, AalOR2 is expressed in the larval heads, as well as in the adult antennae, we decided to assay the odorant-specific responses of A.albopictus larvae groups. To achieve this aim, we used the simple mobility paradigm developed by Xia et al. [20] to assay the behavioral responses of A. albopictus larvae to indole and (–)-menthone, two odorants that evoked strong responses of AalOR2 in our SSR experiment. In our test, we used a videocamera to record the behavior of large groups of late instar larvae in response to a 10−2 M source dilution of indole and (–)-menthone. In our experimental arena we defined a test zone and a control zone each corresponding approximately to ¼ of the total area around the odor balls. The number of larvae in both the test and control zones were counted every 30 s over a 22-min assay. Although this end-point analysis does not allow a detailed characterization of the attractive and repulsive behavioral patterns, our data nevertheless provide preliminary evidence of larval olfactory-based behaviors to indole and (–)-menthone. The larvae responded strongly to indole, with about 54 larvae approaching the indole zone, at a discrete 15 min time point; the number of larvae near the indole zone decreased towards the end of the experiment. This behavior could be consistent with the effect of an attractant. Conversely, (–)-menthone elicited an avoidance behavior on larvae, with just a few of them approaching the menthone zone (Fig. 8A,B); moreover, although we did not measure the parameters associated with the directional movement of the larvae, it appeared clear that in response to (–)-menthone the larvae that approached the menthone zone displayed an increase in terms of overall movement and velocity, suggesting a repulsive effect.


Molecular and functional characterization of the odorant receptor2 (OR2) in the tiger mosquito Aedes albopictus.

Scialò F, Hansson BS, Giordano E, Polito CL, Digilio FA - PLoS ONE (2012)

Behavioral assay on A.albopictus larvae.(A, B) Third and fourth instar larvae were kept in a pirex pan containing a ball of low melting agarose with 10 mM indole and a ball of low melting agarose (the red and blue spots, respectively, in B). The number of larvae were counted each 30 seconds for a maximum of 22 minutes. The histogram shows clearly that indole has an attractive effect for Aedes albopictus larvae. (C,D) Third and fourth instar larvae in the presence of a ball containing 10 mM (–)-menthone and a ball of low melting agarose (the green and blue spots, respectively, in D). Again, the larvae were counted each 30 seconds for a maximum of 22 minutes. Histogram C shows clearly that (–)-menthone evoked an avoidance behavior on the larvae. The result was calculated reporting the number of larvae just at a discrete15-min time-point. These values were compared with each other and analyzed for statistical significance by using a paired, two-tailed student’s t test considering p≤0.05 as significant (df = 4 and t0,05;4 = 44,28 for behavioral test A; df = 4 and t0,05;4 = 27,76 for behavioral test C. *** indicate statistical significant changes (two-tailed Student’s t-test, p<0.001). Error bars indicate S.E.M. for n = 5 separate trials per odorant.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3351472&req=5

pone-0036538-g008: Behavioral assay on A.albopictus larvae.(A, B) Third and fourth instar larvae were kept in a pirex pan containing a ball of low melting agarose with 10 mM indole and a ball of low melting agarose (the red and blue spots, respectively, in B). The number of larvae were counted each 30 seconds for a maximum of 22 minutes. The histogram shows clearly that indole has an attractive effect for Aedes albopictus larvae. (C,D) Third and fourth instar larvae in the presence of a ball containing 10 mM (–)-menthone and a ball of low melting agarose (the green and blue spots, respectively, in D). Again, the larvae were counted each 30 seconds for a maximum of 22 minutes. Histogram C shows clearly that (–)-menthone evoked an avoidance behavior on the larvae. The result was calculated reporting the number of larvae just at a discrete15-min time-point. These values were compared with each other and analyzed for statistical significance by using a paired, two-tailed student’s t test considering p≤0.05 as significant (df = 4 and t0,05;4 = 44,28 for behavioral test A; df = 4 and t0,05;4 = 27,76 for behavioral test C. *** indicate statistical significant changes (two-tailed Student’s t-test, p<0.001). Error bars indicate S.E.M. for n = 5 separate trials per odorant.
Mentions: The olfactory molecules already play an important role for mosquitoes in the early larval stages. Previous works have shown that A.gambiae larvae respond to olfactory stimuli with specific behavioral responses that are mediated by the larval olfactory system [20], [27]. Since in A.albopictus, AalOR2 is expressed in the larval heads, as well as in the adult antennae, we decided to assay the odorant-specific responses of A.albopictus larvae groups. To achieve this aim, we used the simple mobility paradigm developed by Xia et al. [20] to assay the behavioral responses of A. albopictus larvae to indole and (–)-menthone, two odorants that evoked strong responses of AalOR2 in our SSR experiment. In our test, we used a videocamera to record the behavior of large groups of late instar larvae in response to a 10−2 M source dilution of indole and (–)-menthone. In our experimental arena we defined a test zone and a control zone each corresponding approximately to ¼ of the total area around the odor balls. The number of larvae in both the test and control zones were counted every 30 s over a 22-min assay. Although this end-point analysis does not allow a detailed characterization of the attractive and repulsive behavioral patterns, our data nevertheless provide preliminary evidence of larval olfactory-based behaviors to indole and (–)-menthone. The larvae responded strongly to indole, with about 54 larvae approaching the indole zone, at a discrete 15 min time point; the number of larvae near the indole zone decreased towards the end of the experiment. This behavior could be consistent with the effect of an attractant. Conversely, (–)-menthone elicited an avoidance behavior on larvae, with just a few of them approaching the menthone zone (Fig. 8A,B); moreover, although we did not measure the parameters associated with the directional movement of the larvae, it appeared clear that in response to (–)-menthone the larvae that approached the menthone zone displayed an increase in terms of overall movement and velocity, suggesting a repulsive effect.

Bottom Line: Our data indicate that AalOR2 is narrowly tuned to indole, and inhibited by (-)-menthone.In agreement with this results, these two compounds elicit two opposite effects on the olfactory-based behavior of A. albopictus larvae, as determined through a larval behavioral assay.In summary, this work has led to the cloning and de-orphaning of the first Odorant Receptor in the tiger mosquito A. albopictus.

View Article: PubMed Central - PubMed

Affiliation: Institute of Genetics and Biophysics A. Buzzati-Traverso, CNR, Naples, Italy.

ABSTRACT
In mosquitoes, the olfactory system plays a crucial role in many types of behavior, including nectar feeding, host preference selection and oviposition. Aedes albopictus, known also as the tiger mosquito, is an anthropophilic species, which in the last few years, due to its strong ecological plasticity, has spread throughout the world. Although long considered only a secondary vector of viruses, the potential of its vector capacity may constitute a threat to public health. Based on the idea that an improved understanding of the olfactory system of mosquitoes may assist in the development of control methods that interfere with their behavior, we have undertaken a study aimed at characterizing the A. albopictus Odorant Receptors. Here we report the identification, cloning and functional characterization of the AalOR2 ortholog, that represents the first candidate member of the odorant receptor (OR) family of proteins from A. albopictus. AalOR2 is expressed in the larval heads and antennae of adults. Our data indicate that A. albopictus OR2 (AalOR2) shares a high degree of identity with other mosquito OR2 orthologs characterized to date, confirming that OR2 is one of the most conserved mosquito ORs. Our data indicate that AalOR2 is narrowly tuned to indole, and inhibited by (-)-menthone. In agreement with this results, these two compounds elicit two opposite effects on the olfactory-based behavior of A. albopictus larvae, as determined through a larval behavioral assay. In summary, this work has led to the cloning and de-orphaning of the first Odorant Receptor in the tiger mosquito A. albopictus. In future control strategies this receptor may be used as a potential molecular target.

Show MeSH
Related in: MedlinePlus