Marine Research Division

D. John Faulkner Laboratory

The graduate students at Scripps are expected to direct their own research projects after they have passed their qualifying examination. In this research group, students are involved in all aspects of their research program from collecting the marine organisms, performing chemical studies and, whenever possible, screening the chemicals for bioactivity. It is not unusual for students to do research in other laboratories that have specialized equipment needed for a particular aspect of their research program. As a result, students in this group obtain a very broad research background that is, however, firmly based in organic chemistry.

"When we go to a coral reef and find animals that look like large chunks of food-poorly protected, soft-bodied, sessile or slow-moving and easy to grab-we assume that it has physical protection. The chemicals responsible for the animal's survival are often those that we seek for biomedical research."

The quotation above provides an apt description of the appearance and behavior of marine sponges, tunicates, soft corals, gorgonians, nudibranchs and sea hares, all of which are studied by this research group. We have tended to specialize in studies of marine sponges because Mary Kay Harper, who manages the collections for the group, has a professional interest in sponge biology and taxonomy. Our biomedical interests include anti-cancer, anti-fungal and anti-bacterial agents, inhibitors of HIV-1 integrase (with Rick Bushman, Salk Institute), anti-inflammatory agents (with Robert Jacobs, UC Santa Barbara) and agents to treat tropical diseases such as leishmaniasis (with Dr. Reinaldo Compagnone, Venezuela). We are part of a National Cooperative Drug Development Program with Bill Fenical (SIO), Yuzuru Shimizu (Rhode Island) and Bristol-Myers Squibb to discover new anticancer agents from marine sources.

In collaboration with Vivek Malhotra (Biology, UCSD), we have been studying marine natural products that cause vesiculation of Golgi membranes in a process that resembles that which occurs during mitosis. Since the Golgi plays a vital role in protein sorting and trafficking within the cell, chemicals that influence the role of the Golgi may have significant biomedical potential. At present we are more concerned with using marine natural products, such as ilimaquinone, to study the signaling pathways that control Golgi vesiculation.

A recent collaboration with Larry Goldstein (Pharmacology, UCSD) resulted in the discovery that adociasulfate-2, produced by a marine sponge, inhibits the activity of motor proteins, which are responsible for the transport of proteins along the microtubule network within the cell. Adociasulfate-2 also caused apoptosis in Drosophila melanogaster embryos.

How does the production of natural products by marine invertebrates influence their relationships with other species? Has chemical protection allowed organisms to dispense with shells, spines and other physical defenses? Do marine invertebrates use chemicals to prevent their competitors from reproducing successfully, either at the stage of fertilization or at the later stage of settlement of larvae from the water column? Do marine invertebrates have specific food sources and, if so, how do they find their food? All these and many similar questions form the basis of research on the chemical ecology of marine invertebrates.

The earliest research performed in this laboratory clearly demonstrated that the defensive chemicals in the sea hare Aplysia californica, which were usually distasteful rather than toxic, were derived from a diet of specific chemically-rich red algae. Extending this research to other shell-less molluscs, we demonstrated that nudibranchs relied on consuming sessile marine invertebrates, usually sponges, bryozoans or tunicates, to provide their defensive chemicals. We found that the nudibranchs often stored only a few selected compounds from their dietary sources and that they could modify chemicals to make them more effective as chemical defense agents.

Together with Michael Ghiselin, Dr. Faulkner proposed that the acquisition of a chemical defense mechanism allowed the ancient shelled molluscs to evolve into the nudibranchs of today by gradual loss of their shells. This gives the nudibranch much greater mobility than its shelled cousins but makes them very dependent on locating their food source.

By studying three nembrothid nudibranchs of different sizes, all of which depended on the same suite of chemicals, we were able to show that the nudibranchs could differentiate between the small concentrations of the chemicals that are released by their food source and the greater concentrations that are exuded by a nudibranch that is being attacked.

The advantage of studying the chemistry of nudibranchs and other shell-less molluscs is that they usually concentrate the most biologically-active compounds available to them through their diet. Thus the molluscs have done a great job in directing chemists toward the most rewarding chemistry.

The rich diversity of sponge chemistry undoubtedly has its origins in the need to provide sponges with a chemical defense mechanism. As the most primitive metazoans, sponges must have used their chemical talents to ensure their survival. We rely on this hypothesis to guide our collection of sponges for biomedical research.

Do microbial symbionts produce any of the natural products attributed to their hosts and hence contribute to the chemical defense of the association? Symbiosis can be defined as an association between two organisms that is beneficial to both. Many associations between marine invertebrates and microorganisms appear to be quite specific and may be considered as symbiotic associations. As chemists, we believe that chemistry plays a vital role in the establishment and preservation of symbiotic relationships in marine organisms. Our particular interest is to demonstrate the role of micro-organisms in producing chemicals that are beneficial to the host. However, so many marine natural products, particularly those from sponges, have been attributed to undefined "symbionts" that we feel obliged to investigate the veracity of some of these claims.

Our strategy is to select a specific chemical or class of chemicals and determine their location at the cellular level. This assumes that the chemicals are not made in one cell type only to be completely translocated to another. The strategy has the advantage that one does not start with the daunting task of culturing symbionts, which are considered to be among the most difficult microbes to culture and which may not produce the desired compounds in the absence of the host.

We have studied two associations between the sponge Dysidea herbacea and the cyanobacterium Oscillatoria spongeliae, which can constitute half of the mass of the sponge. Each of these sponge/cyanobacterium associations produced different chemicals. Using a specimen from the Great barrier Reef, we showed that chlorinated amino acid-derived metabolites were produced by the cyanobacteria and terpenes were produced by the sponge. In a second specimen from Palau, Western Caroline Islands, we found that the major metabolites were polybrominated biphenyl ethers and that these were produced by cyanobacteria. We still do not understand why Oscillatoria spongeliae produces two different classes of halogenated compounds.

Studies of the lithistid sponge Theonella swinhoei resulted in the discovery that complex bicyclic peptides were produced by filamentous bacteria and that the cytotoxic metabolite swinholide A was found in a fraction containing many unicellular heterotrophic bacteria: the sponge appears to produce no useful chemicals. In contrast, the sponge Oceanapia sagittaria contains the pyridoacridine alkaloid dercitamide in high yield. This immediately suggests that it is a sponge metabolite because microorganisms are not that abundant in the sponge. Since dercitamide is fluorescent, we used laser confocal microscopy to locate the dercitamide in a specific type of sponge cell.

• Selected Publications
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