Journal club: A new hint to the evolution of the nucleus?
Saturday, January 14, 2017 at 9:54AM One of the fundamental divisons of life is between prokaryotes and eukaryotes. Prokaryotes, including both Archaea and bacteria, have a very simple cell, with no major subcellular compartments. Eukaryotes, essentially all over living things (plants, animals, fungi, amoeba, etc), have much more complex cells, with a nucleus and dedicated organelles (mitochondria, chloroplasts, etc).
Exactly how eukaryotes evolves from prokaryotes is one of the biggest questions in evolution. It is clear that some organelles, such as mitochondria and chloroplasts, evolved by endosymbosis. Essentially, one bacteria swallowed another, which survived inside and took on specialised functions. The nucleus has been a bigger mystery, with no clear preceeding structure in prokaryotes to build upon. Until now. In the lastest issue of Science, Chaikeeratisak et al discover a nucleus-like structure in bacteria. Interestingly, the structure is not part of the bacteria's normal lifecycle, instead it is assembled by a virus, bacteriophage 201φ2-1, as a structure for DNA replication and transcription, after which the RNA is sent to the cytoplasm of the bacteria for translation, exactly as occurs in eukaryotes.
There are many fascinating angles to this paper. Why does bacteriophage 201φ2-1 assemble this structure? Is it to protect the phage genome from bacteria attack by restriction enzymes and the like? Most importantly, could similar viruses have been the origin of the eukaryotic nucleus? One can easily imagine an ancestral prokaryote becoming permanently infected by such a virus, and rapidly evolving useful functions for a nucleus of its own.
Read the paper: Vorrapon Chaikeeratisak, Katrina Nguyen, Kanika Khanna, Axel F. Brilot, Marcella L. Erb, Joanna K. C. Coker, Anastasia Vavilina, Gerald L. Newton, Robert Buschauer, Kit Pogliano, Elizabeth Villa, David A. Agard and Joe Pogliano. 'Assembly of a nucleus-like structure during viral replication in bacteria'. Science 13 Jan 2017: Vol. 355, Issue 6321, pp. 194-197
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