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Programmed cell death shown to be 550 million years old

A network of Acropora polyps.
RevolverOcelot - Own work CC BY-SA 3.0 Permission is hereby granted to use and/or modify this image for any purpose.

One of the major pathways of apoptosis or programmed cell death seen in humans has been found in coral that dates to the Cambrian explosion. Steven D. Quistad from San Diego State University in San Diego, California and colleagues have proven that the tumor necrosis factor proteins that cause cell death are 550 million years old. The research was reported in the June 9, 2014, edition of the journal Proceedings of the National Academy of Sciences.

The coral species Acropora digitifera has been found to have more tumor necrosis factor proteins than any other organism including man. The researchers substituted human tumor necrosis factor proteins into coral and produced coral bleaching and cell death. Substitution of tumor necrosis factor proteins from coral into healthy human cells produced cell death.

The similarity in action of the same type of proteins from two very different organisms indicates that the tumor necrosis factor proteins have been evolutionarily conserved for at least half a billion years. Tumor necrosis factor proteins have been traced back to the earliest known arthropod species. It is unusual for a protein to have been preserved over such a vast period of time. The function of the protein also appears to have been preserved for the same time with minimal changes.

The research contradicts presently accepted theory that the complexity of life has steadily increased since the Cambrian explosion. This is the first evidence that a protein has been conserved in form and function for this period of time and probably as early as the Precambrian era. The multiple added forms of tumor necrosis factor proteins in coral may have a function in preventing cell death in humans.

The researchers do not express any opinion about the potential for human cells being a factor in coral bleaching and death. Diving around coral is a common human activity. Human cells with their tumor necrosis factor proteins are certainly lost around coral when people dive around coral. The fact that tumor necrosis factor proteins from humans produce cell death in coral could be a small factor in coral death.