The role of juvenile hormone in the specification of reproductive fate in the pea aphid

Posted May 12th, 2010 at 3:11 pm.

Emma Hedman

Mentor: Dr. Greg Davis

Recently, Aphids are becoming more and more important as model organisms ind evelopmental biology due to a wide range of polyphenisms, including the so-called reproductive polyphenism. During the summer aphids exist as exclusively female, asexual clonal populations. Female aphids which give rise to more asexual females are known as virginoparae. During the fall, when aphids are exposed to long nights, they will asexually produce a new generation of females known as sexuparae. Sexuparae reproduce asexually, but give rise to females which must reproduce sexually. The details of this process are foggy, and understanding it could be a major step in developmental biology by giving insight into what sorts of molecular responses are responsible for polyphenisms in nature. We do know is that an active signal exists that promotes the production of asexual females, though the nature of the signal is unknown.

One candidate is Juvenile Hormone (JH), as application of JH has been shown to turn sexuparae back into virginoparae. Since previous research continues to show that JH is sufficient to cause the switch from producing sexuals to asexuals, my goal is to prove that it is also necessary. I plan to do this by conducting experiments opposite to the current research, and trying to induce production of sexual offspring in mothers which would typically give rise to asexual offspring by targeting JH production as exclusively as possible. Since JH is suspected of being the asexual signal, it would follow that blocking the production of JH in asexual mothers would make them incapable of continuing the production of asexual offspring in favor of sexuals. We will first try to accomplish this using the new technology of in vivo morpholinos. These are unique molecules which can move between cells and block translation. I will investigate the expression of the gene Juvenile Hormone Acid Methyl Transferase (JHAMT) using the morpholino, and hope to see a drop in JH production in the offspring of the mother injected. I also hope to use RNA interference to block the mRNA produced by JHAMT, preventing the production of the protein which is thought to be the rate-determining step in the biosynthesis of JH. By using these two methods, I hope to either credit or discredit JH as a major contributor in the sexual polyphenism. If this research was successful, it would be a major contribution to understanding the underlying role of hormones on phenotypic expression and development.

Filed under: 2009,Davis, Dr. Gregory,Hedman, Emma by Ann Dixon

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