Trees of Knowledge

 

 

Are some contemporary Jewish men descended from the biblical Aaron? Are all cancer metastases derived from the same primary tumor? These are the kinds of questions addressed by Prof. Karl Skorecki, a Rambam Medical Center physician who recently spent his sabbatical leave in the Weizmann Institute's Computer Science and Applied Mathematics Department.

 

Why would a physician choose to spend his sabbatical among computer scientists? Skorecki splits his time between treating patients at Rambam and conducting research in population genetics as Director of the Rappaport Research Institute at the Technion – Israel Institute of Technology. He believes that interaction with computer scientists can help him solve biological problems in "out of the box" ways. Skorecki came to Weizmann because he was fascinated by the work of Institute computer scientist Prof. Ehud Shapiro, who has developed an innovative computational approach to tackling biological questions. Besides, Skorecki had already spent a sabbatical at Weizmann in 1991 before immigrating to Israel from Canada.

 

The approach developed by Shapiro's team takes advantage of certain markers on the DNA molecule to trace the origins, or lineage, of body cells. In particular, DNA regions called microsatellites, which contain numerous repeated genetic "letters," are especially prone to accumulating mistakes – just as a word like "Mississippi" could easily be misspelled as, say, "Missississippi." By assessing such genetic misspellings, scientists can tell how many divisions a cell has undergone and trace the lineage relations among cells.

 

The cells Skorecki studied during his sabbatical at the Weizmann Institute, in collaboration with postdoctoral fellow Dr. Shalev Itzkovitz, included different types of cancer cells. The goal of one collaborative study, for example, was to determine the number of divisions undergone by leukemia cells, which in turn can help assess the aggressiveness of the cancer.

 

These studies, Skorecki says, resemble the population genetics research he has been conducting for many years: "You are looking at the relatedness of cells rather than people, but in both cases you are using DNA analysis to build lineage trees that reveal common origins and different branches." In one study, he analyzed the Y chromosome, which determines male gender and is helpful for tracing ancestry because it is passed on intact from father to son. The analysis revealed that contemporary Jewish men traditionally belonging to the Cohanim tribe might have had a common male ancestor who lived 2,000 to 3,000 years ago – a finding that appears to support the Jewish tradition according to which following the exodus from Egypt, all Jewish priests, the Cohanim, are male descendants of Moses' brother Aaron. In another study, Skorecki and his colleagues found that nearly half of all Ashkenazi Jews can trace their ancestry back to just four women who lived close to 2,000 years ago. Skorecki has also recently revealed that genetic features of the Druze population in northern Israel and its neighboring countries lend credence to the Druze belief about the diverse origins of this ancient minority.

 

Skorecki: "The Weizmann Institute is making an enormous contribution to Israeli medicine by bringing physicians into its labs and teaching them to think like scientists. The more the physicians are trained in critical scientific thinking, the more effective they will be in treating patients. We need to realize the limits of our knowledge and always seek to learn more."