The PIs will investigate recognition of self and kin in an amoeba, Dictyostelium discoideum. These single-celled amoebas come together to form a multicellular fruiting body, but they do so primarily with members of their own genetically identical clone, rejecting genetically different clones. The researchers will study the costs and benefits of recognition, particularly how it protects against exploitation by foreign clones. They will also investigate whether recognition simply involves avoidance of other clones, or whether it also leads to attacks on the foreign clone, analogous to tissue rejection. Finally, they will also identify the genes that cause recognition.
Recognition systems are vital to life. For example, self-recognition is what allows humans to detect and attack pathogens, and it also plays a critical role in organ transplantation. D. discoideum is a good single-celled lab organism, has a sequenced genome, shares many genes with humans, and has many molecular and genetic techniques developed for it. Therefore these investigations will result in a valuable model system for the study of recognition, leading to insights into general questions of how recognition works and evolves, that are not easily addressed in other organisms.
How and why organisms recognize their relatives may seem like an obscure topic, but it is actually vital for our well being in ways we describe below. We say that an organism has recognized a relative when it behaves differently towards a relative than it would towards a non-relative. In many organisms, these differences are based on shared experiences. For example, if you are about my age and in the same nest as me, being fed by the same set of parents, I will not be wrong very often if I treat you as a sister or brother. This is called an environmental cue. There may also be genetic cues of various sorts. If there were thousands of colors of hair, for example, you might know that your family members were the ones with the pink hair. Any other individual would not be in your family. The trouble with this sort of recognition and the cooperation that follows is that it has been thought to be vulnerable to the kind of cheating that arises when some individuals carry the trait, in this case pink hair, but then do not follow through with the altruism. This would cause this system to break down. Another problem with this kind of system is how so many different labels evolve and are stable. After all, if you are the common type, then you will be in larger cooperative networks, which should be a good thing. The social amoeba Dictyostelium discoideum is a great organism for studying this sort of issue, because the recognition genes have been identified, and called tiger genes. If you have matching tiger genes, you will fuse with others in a social way that results in some amoebae dying to help others. Interestingly, we have documented that high levels of variation in this system have been maintained. This is basic work without direct ties to human health, but the connections are not hard to imagine. Microbes that recognize each other and cooperate might be more detrimental to humans as they proliferate better. On the other hand, microbes that detect enemies and produce toxins against them could also harm humans. It is a complicated situation. We have looked at quite a few angles of these complicated relationships. One of the interesting things we have discovered is that some kinds of amoebae do not act entirely on their own. They also carry along bacteria that impact others. Exactly how this works is a major and interesting question. After all, we are eukaryotes, with cells with a nucleus and vulnerability to bacteria. This is a system where we can study some interactions without harming any animals. Another advantage to this system is that it has got us thinking about cooperation generally, and what limits it. We have written more conceptual papers, like one on the veil of ignorance. This is the idea that the person who cuts the cake should not get first pick. We think similar processes go on in amoebas. We have involved students of many levels in our research, from beginning first year students to postdoctoral fellows. We have them participate in all aspects of the work, and present their work in publications whenever possible, and certainly in poster sessions. We also write blogs and write for Wikipedia to share what we learn with the widest possible audience.
