Though scientists have known since the late 19th century of the existence of the centrosome, an organelle crucial to replication in animal cells, until recently they could do little more than view it through a microscope. In the 1990s, ground-breaking discoveries were made that revealed the centrosome’s importance in anti-cancer and fertility control research. Now one of the authorities on centrosomes, Robert Palazzo, professor of molecular biosciences at the University of Kansas, is working to uncover the secrets of their structure and function.

Palazzo will be among the many researchers to take advantage of the resources and facilities that will become available as a result of the National Institutes of Health Center of Biomedical Research Excellence (COBRE) grant recently awarded to KU. Palazzo, Richard Himes of Molecular Biosciences, and Gunda Georg, director of the Drug Discovery Program at HBC spearheaded the grant. The High-throughput Screening Core Facility of the COBRE project,which Palazzo will help establish and lead, will develop biological assays to identify novel compounds, such as Taxol, that Georg’s Combinatorial Chemistry Core Facility will synthesize . Together these cores will work to identify synthetic organic compounds and natural products that could serve as potential anti-cancer agents, more specifically anti-mitotic agents that interfere with cell replication and the spread of cancer.

Molecular biosciences professor Bob Palazzo began his groundbreaking work with centrosomes by researching the cells of the Atlantic surf clam.

Halting cell replication
When a cell commits to division, it must replicate and segregate its chromosomes. Consequently, any agent that disrupts this process could halt cell division. Cancer cells, which have a high rate of proliferation and undergo frequent mitosis, would be particularly sensitive to such agents. The question for scientists then has been what are potential targets within the cell that an agent could act upon to halt mitosis?

Enter the centrosome. In 1888, cytologist Theodor Boveri described the centrosome as a centroplasm serving as the central point of attachment for fibrous "astral rays." Now called microtubules, these "rays" are actually protein polymers made up of alpha and beta tubulin subunits found in eukaryotic cells. By organizing these microtubules, the centrosome also organizes a dynamic structure called the mitotic apparatus which segregates the chromosomes. During cell replication, equal halves of the cell’s chromosomes move along the microtubules toward two poles formed in the centrosome. After replication both daughter cells inherit a complete and identical set of chromosomal DNA and one centrosome; each is ready to go through the replication cycle again. In short, if you inhibit the centrosome’s function, you halt cell replication.

During cell replication, equal halves of the cell's chromosomes move along the microtubules toward two poles formed in the centrosome.

Solving the mystery
Though soon after its discovery the centrosome was indeed suspected as a key player in cell replication, its exact function remains elusive after more than 100 years of research. Scientists still know very little about its molecular components or about the mechanisms by which animal cells control centrosome replication.

Since each animal cell has only one, infinitesimally small centrosome, the major barrier to studying its molecular structure has been an inability to isolate sufficient quantities from any animal system for in-depth analysis. However, in the 1990s, centrosomes were isolated and purified from a few plentiful sources, one of them being the oocytes or eggs of the Atlantic surf clam, Spisula solidissima.

Palazzo received a National Institutes of Health grant in 1989 to begin his ground-breaking centro-somal research with the Atlantic surf clam at the Marine Biological Laboratory in Woods Hole, Massachusetts. "I was intrigued by the Atlantic surf clam because I knew I’d need plenty of material for study," he said. "There in Woods Hole, the ocean turned out to be my incubator. I found vast, unmatched quantities of research specimens that would be useful for centrosome research. The clams are commercially harvested daily along the Atlantic coast, from Newfoundland down to Virginia." While at the Marine Biological Laboratory, Palazzo and KU graduate Jackie Vogel, now at Yale University, developed methods for the purification of centrosomes and demonstrated that they could isolate sufficient quantities for biochemical analysis.

In 1992, Palazzo chose to relocate his research base to the University of Kansas for several reasons. One, he needed to find an environment that would allow him to conduct important research in basic cell biology. Also, he wanted to integrate his research with that of other scientists with overlapping interests.

"I was intrigued by KU’s expertise in tubulin and microtubule research," Palazzo said, "particularly with Dr. Himes who had been a recognized figure in the field for many years. Also, I was impressed with the university’s strengths in medicinal and pharmaceutical chemistry. I thought that work in these disciplines could ultimately be applied to the problems I was working on. Now, the collaboration I had hoped for has materialized in the COBRE proposal and the Experimental Therapeutics Program effort. By collaborating with Dr. Georg and other scientists, I now have the opportunity to conduct novel, basic research while seeking to identify novel reagents that could help me to understand the centrosome and hopefully serve as potential therapeutic agents as well."

Plentiful research opportunities
The field of centrosome research is expanding exponentially, thanks to efforts by Palazzo and a few colleagues. For example, in 1997 he and Dr. John Kilmartin of the Medical Research Council in Cambridge, England, organized the first international meeting on the topic. Kilmartin has isolated related structures from yeast cells and is a pioneer in the field. The interest in the conference from the scientific community was overwhelming. "Everybody seemed to be interested in this meeting," Palazzo said. "The number of people who attended was almost twice what we expected."

In 2000, Palazzo and Gerald Schatten of the University of Oregon edited The Centrosome in Cell Replication and Early Development, a comprehensive collection of research articles about centrosomes written by experts in the field. Working with Trisha Davis of the University of Washington, Palazzo has edited his second book which outlines methods used by researchers. "Hopefully, these books will be useful for biomedical researchers and students interested in entering this area of research in the future," Palazzo said. "Before the 1990s, we were limited to basically looking at centrosomes through microscopes. But now centrosome research is exploding."

Palazzo said the current challenge for researchers is discovering how all of the centrosome’s components interact and identifying which components are common in a broad variety of cells, from yeast to human. Those conserved components could very well turn out to be important targets for centrosome-specific chemotherapeutic agents in the fight against cancer.