Just as raging hormones² are part of the process of a child's maturation through the teen years to adulthood³, juvenile⁴ hormones, a group of insect isoprenoids（类异戊二烯） , play an important role as butterflies, fruit flies and mosquitoes transform their body structures as they molt⁵ from larva to pupa（蛹） and then adults. Unlike humans, in insects the juvenile hormone¹ inhibits⁶ development of adult characteristics until the insects reach a proper stage. Juvenile hormones also play a prominent role in regulating reproductive maturation in adult insects and synthetic⁷（合成的） juvenile hormone mimics⁸ have been widely used as pesticides⁹ for mosquito controls.

Virginia Tech researchers have discovered an important step in the activation¹⁰ of juvenile hormone target genes¹¹. "Understanding the molecular¹² details in the juvenile hormone signaling may lead to discovery of novel chemicals that target mosquitoes with more selectivity," said Jinsong Zhu, assistant professor of biochemistry with the Fralin Life Science Institute at Virginia Tech.

The research is reported in the early online edition of the Proceedings¹³ of the National Academy of Sciences the week of Dec. 27.

"The secretion¹⁴ of juvenile hormone is drastically（彻底地，激烈地） reduced in the final larval stage, as a result of which the larva is transformed into a pupa. While an insect protein, Methoprene-tolerant (Met), has been postulated¹⁵ as the top candidate for juvenile hormone receptor, it remains¹⁶ unclear how this protein is activated¹⁷ by juvenile hormone," said Zhu.

He and his group believe that studying the hormone-regulated reproduction have a better chance of elucidating¹⁸（阐明，说明） the molecular action of juvenile hormones. They discovered a protein partner for Met in the yellow fever mosquito Aedes aegypti. This protein, named FISC, forms a complex with Met when juvenile hormone is present. Binding¹⁹ of these two proteins to the regulatory regions of some juvenile hormone target genes is closely correlated with the expression levels of those target genes in the newly emerged adult mosquitoes. Reducing the protein levels of Met or FISC by genetic²⁰ approaches leads to dampened expression of the juvenile hormone target genes, and decreased egg production after the female mosquitoes take a blood meal.

The study by Zhu's group clearly demonstrates that formation of Met-FISC complex is a critical step in juvenile hormone signaling pathway. Evidence presented in the Proceedings of the National Academy of Sciences paper also suggests that fruit flies use the same mechanism²¹ in mediating²² juvenile hormone responses during molting²³.

Zhu is now collaborating²⁴ with Professor David Bevan's group in the biochemistry department to analyze²⁵ the structure-function relationship of the Met protein.