In May.25, 2008, Dr. Edward Arthur Kravitz was invited to give a lecture at Room 101, Life Sciences Building, Peking University. Edward A. Kravitz Ph.D. is the George Packer Berry Professor of Neurobiology at Harvard Medical School. Early in his scientific career Ed and colleagues demonstrated that gamma-aminobutyric acid (GABA) functions as a neurotransmitter. In addition, he and Tony Stretton were the first to use the intracellular dye procion yellow to visualize neuronal architecture. Later, Ed’s work with neuroamines demonstrated that serotonin and octopamine act as synaptic modulators. Ed continued to explore the function of amines using Homarus americanus, the American lobster, as a model organism to study aggression. He currently works on aggressive behavior using the genetically manipulable model organism, Drosophila melanogaster, the fruit fly.

The title of Dr. Edward A. Kravitz’s lecture is, “Genetic manipulations in the fruit fly fight club: love and war in a single gene and other stories”. The first part is the behavior issue. Dr. Kravitz began with three questions: Why flies? Do flies fight? How do we get them to fight? For the first question the answer was, fruit fly is an organism whose genome was sequenced and where genetic methods were available for solving sophisticated problems. Then he showed by video the aggression stimulated by food or headless mating targets between different pairs of fruit flies, that is male and male, virgin and virgin, mated female and mated female, as the answers to the other two questions. He further described the diverse and distinctive fighting patterns of male and female fruit flies, and the methods and relative definitions to analyze their aggressive behavior. One of the interesting differences between male and female aggression was that the hierarchical relationship only formed in males’ fights but not in females’. The critical point of their study was that those fruit flies were isolated, i.e. no social interaction experience, until they were tested, recorded and analyzed, which demonstrated that their fighting patterns were determined by genes and their fighting ability and trends were innate. As following, Dr. Kravitz discussed the learning and memory of fruit flies during and after the aggression tests. It was found that flies alter their fighting strategies after a hierarchical relationship is established. Flies could remember their previous opponents and the defeated ones showed a “loser” mentality or effect, which may be employed as a model for study on depression. In the microarray analysis in the heads of winners, losers and control flies, his group found the gene expression differed, only the losers showed significant difference while winner and control ones were almost the same.

Then Dr. Kravitz came into the second part, i.e. the issue that “the same gene specifies who flies court and how they fight”. He firstly introduced briefly the powerful genetic tool in fruit flies, the GAL4/UAS system; then he mainly discussed the gender-related fly gene fruitless(fru), which encoded a class of transcript factors. Some previous studies had demonstrated the critical function of fru in gender determination and courtship behavior. In wild type fruit flies, the males own fruM and females own fruF. These sex specific subtypes produced the sex specific behavior in aggression and courtship. Dr. Kravitz’s group interchange fru between male and female flies and found that fruM females and fruF males behaved like males and females, and showed some interesting and strange patterns, which meant they gained the brain of the opposite sex. Dr. Kravitz showed couples of such behaviors by videos. For instance, fruM females would court wild-type females and tasted the latter continuously.

When finishing the issue of fru, Dr. Kravitz began to talk about “how flies decide what to court and to fight”. The key mechanism here involved octopamine, a special neuroamine. It was found that low octopamine in the brain stimulated oct-mutant male fruit flies to court wild-type males more frequently, while between wild-type males fight was dominant. What’s more, males lack of octopamine could not distinguish female and male, and would response to stimulus more quickly but produce more mistakes. Dr. Kravitz found that fru and oct both expressed in three neurons in fruit flies, and their function was relevant to olfactory system. Dr. Kravitz also mentioned other critical genes involved in gender specific behaviors, doublesex and tra for instance. Their future work will focus on these three neurons, attempting to manipulate one or more of them, evaluate their activity and analyze the gene expression in diverse circumstances.

At the end of his lecture, Dr. Kravitz discussed with audience on several questions, such as the application of studies on fruit fly aggression for mammal issues, the mechanism of tra functioning on fru, and the potential interaction of fru and oct. Although most of these questions had no answers because they were still being studied, Dr. Kravitz guided us to think in logical and inspired way, which helped students to understand relative issues more comprehensively.

Overall, this lecture was successful and impressive. Dr. Kravitz’s group were doing interesting researches and he presented them perfectly both in general and specific aspects. Combined with one previous lecture given by Dr. Miczek, which also talked about aggression but of rats, we get a more thorough vision on the study of aggression behavior. 

Zhang, Ling

    2008-05-25