Finding an immune system in the social amoeba (Dictyostelium discoideum) is not only surprising but it also may prove a clue as to what is necessary for an organism to become multicellular, said the Baylor College of Medicine researcher who led the research that appears today in the journal Science.

Dictyostelium discoideum usually exists as a single-celled organism. However, when stressed by starvation, the single cells band together to form a slug that can move. Eventually the slug changes to produce cells that perform specific functions spores and stalks. In this new report, Dr. Adam Kuspa, chair of biochemistry and molecular biology at BCM, and his colleagues describe a new kind of cell they dubbed a sentinel cell.

Sentinel cells circulate within the slug, engulfing invading bacteria and sequestering poisons or toxins, eventually eliminating these from the slug. These cells often operate through a particular mechanism in the cells controlled by a Toll/Interleukin-1 Receptor domain protein (TirA), Kuspa and his team found.

This signaling pathway or a very similar one is present in plants and animals, he said. Now it has been identified in amoeba. It has not been found in fungi.

Amoeba have, in the last 10 years, become appreciated as one of the four main forms of life in the crown group of eukaryotic (multicellular) organisms plants, animals, fungi and amoeba, said Kuspa. What allowed them to become multicellular"

One way to estimate the characteristics of the organism that went before those that were multicellular is to look for characteristics that are present in two, three or all four of these main groups, he said.

Those were likely present in the progenitor organism, said Kuspa. Because three of the four major groups of organisms have this pathway, I argue that means that the progenitor of all multicellular organisms had this pathway. Since that organism was not likely multicellular, it must
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Contact: Kimberlee Barbour
kbarbour@bcm.edu
713-798-4712
Baylor College of Medicine
2-Aug-2007