Date Published: February 1, 2015
Source: The Journal of Experimental Biology
Summary: A study was conducted to investigate how the effects of day length
on the Culex pipiens' circadian clock components trigger their
diapause.
The Northern house mosquito, Culex pipiens, faces a
reproductive shut down during the winter time. This "reproductive shut
down" that occurs is also known as diapause and it occurs when the amount
of time the day lasts reaches a certain length – which in the case of C.
pipiens occurs during the winter time. And after shutting down during
the winter, C. pipiens resume their reproductive activity in
the spring.
The cause of diapause has been researched in the past in numerous
other species. This previous research has proved that circadian clocks, an
internal clock that is in rhythm with daylight and darkness of the night,
regulates body function within many organisms. In C. pipiens however,
no definitive explanation to prove what particular mechanism helps these mosquitoes
in measuring the day length and how that data triggers diapause is unknown. Megan
Meuti from The Ohio State University and her colleagues: Mary Stone, Tomoko
Ikeno, and David Denlinger studied C. pipiens to prove how
their circadian clocks are affected by day length. Along with proving the role
of circadian clocks, the team noted that C. pipiens are also carriers
for deadly diseases. And with the discovery of what mechanisms trigger
diapause, the team hopes to prevent disease transmission by controlling the
mosquitoes' reproductive activity.
To prove their hypothesis, the researchers broke down the internal
clock into five parts: clock, cycle, period, timeless, and cryptochrome2. They
analyzed that each of the levels fluctuate in response to daylight. In the
case of the C. pipiens, researchers aimed to discover if during the
time of diapause, these parts of the clock continued to still run. By using
adult mosquitoes (each of which were exposed to different times and length of
daylight) the team discovered that the mRNA levels, even during winter, were uninterrupted. This proved to the team of researchers that without the clock, the
insects would never know when and when not to be in diapause. This proves that
the clock serves as a mechanism to help measure the length of day and night.
The researchers also made note of the cryptochrome, which after
diapause began to hit peaks at night time. Thus proving when the mosquitoes were active the most,
which was during daytime.
After attesting the influence circadian clocks have on diapause,
the team decided to concentrate on the five components mentioned previously. To
better understand each of their particular roles, researchers wanted to know
how reduced mRNA levels would affect the adult female mosquitoes in their
ability to reproduce. In order to do this, an RNA molecule designed to stop
mRNA from its continuous cycle and prohibit transcription of particular parts
of the circadian clock, was injected. The researchers then observed how females
exposed to short daylight failed to regulate diapause when the mRNA levels of
the last three regulators of the circadian clock were reduced. However, when
another part of the circadian clock not mentioned previously, pigment
dispersing factor, was also turned off, it initiated diapause when in fact
they should have been fertile. This further substantiated that components of
the circadian clock do play a vital role in diapause.
After completing their experiment, the researchers concluded how the
results paint a bigger picture in the world of ecology than initially
anticipated. Aside from the reproductive aspects of C. pipiens,
these mosquitoes, as mentioned previously, are in fact a major
carrier for diseases like: the West Nile virus, St. Louis encephalitis, and
filariasis. With new knowledge on the components of the internal clock needed
to be inactivated in order to initiate and halt diapause, researchers hope to
prohibit the spread of these diseases in order to create a safe ecological
environment.
Citation:
Meuti, M. E., Stone, M., Ikeno, T. and Denlinger, D. L. 2015.
Functional circadian clock genes are essential for
the overwintering diapause of the Northern house mosquito, Culex
pipiens. The Journal of Experimental Biology 218: 412-422.
