Hey guys can you read this?

[425nm]

So for the term paper of my Genetics 408 class (at the UofA) I decided to write my paper on a genetic phenomenon in Octocorals!
The instructions for the paper were to write an article that anyone could read on a topic related to Genetics, so since Canreef has a diverse array of posters I was wondering if you guys could give me some feedback?
If you guys could skim through and post about anything you didn't understand or would like expanded on that'd be awesome.
Its due on Monday (I only just finished this quasi-final draft) so if I could get some feedback by Sunday evening that'd be awesome. If not I'd still be interested in knowing what people think of it.
Thanks!
Liam Brinston.


The Octocorals: a story of genetic nesting dolls



Corals capture the imagination with their bizarre appearance and their ability to photosynthesize. It is often a surprise for many to learn despite their photosynthetic abilities corals are in fact animals. The ability of Corals to photosynthesize is derived from a partnership with zooxanthellae, small algae that lives in the coral skeleton (8). These algae provide the coral with energy from photosynthesis and the coral provides the zooxanthellae with shelter and other nutrients. Corals are also considered Eukaryotes, meaning they possess mitochondria. The mitochondria are the organs of the cell, they are the power house of the cell as they generate energy for the cell. Scientists believe that mitochondria to have once been a free living bacterium that formed a partnership with a bigger organism. This partnership is similar to the partnership between corals and their zooxanthellae. Over time the mitochondria’s partnership became so close that it became part of the bigger organism, giving rise to Eukaryotes. Due to their free living past, mitochondria have retained their own set of DNA or genome, called the mitochondrial genome (mtGenome). This mtGenome contains instructions for the running of the mitochondria but not its building. As the partnership progressed many of the genes from the mtGenome were exported to the nuclear genome of its partner. The nuclear genome is what is conventionally thought of as the blue print of the cell and also contains the instructions for building mitochondria. The mtgenome is shared by all Eukaryotes but often differs somewhat in size and less often in gene order but rarely does it differ in the genes.

Corals are a sort of genetic nesting doll. Corals house zooxanthellae which is a separate organism, possessing its own genome. The Zooxanthellae themselves contain organelles similar to the plastids of plants, the photosynthetic cellular organ of plants which like mitochondria may have once been free living. Corals also possess mitochondria, which has its own genome and was once a separate organism. In one group of corals, the Octocorals which are comprised of the gorgonians, sea pens and soft corals, this nesting goes one step deeper. The mtGenome of the Octocorals possess an additional gene. The addition of a gene to the mtGenome has not been observed in any other group of organisms (1). Interestingly the Octocoral sister sub-family, the Hexacoralia: anemones, zoanthids, and the stony corals (6), lacks this gene but it has been found in every Octocoral to date. This confirms that the Octocoralia and Hexacoralia are genetically distinct from one another. The presence of this gene in all Octocorals suggests that it is providing some advantage to the Octocorals, however its absence in all other corals tells us that it is not essential for the function of coral mitochondria (1).

The gene in question is a copy of MutS. A gene originally found in E. coli, also present in Humans (refered to as MSH – MutS Homolog in humans) this gene is part of a DNA repair system. In E. coli MutS detects DNA damage, and signals to other proteins to repair it but is not able to repair the damage itself (5). The Octocorallian mitochondrial MutS (mtMutS) appears to have acquired a modification that will allow mtMutS to potentially carry out the repair process by itself (1). The presence of a gene does not necessarily mean that it is working however Bilewitch and Degnan (1) were able to detect the expression of mtMutS in three separate Octocoral species. If a working mtMutS is being produced it may explain why the mtGenome of the Octocorals appears to be evolving slower than the mtGenome of the Hexacorallia. Alternatively this slower change in the Octocoral genome can be viewed as indirect evidence of mtMutS working. Interestingly the mtMutS gene itself seems to be evolving faster than the rest of the mtGenome but not as fast as the mtGenome of the Hexacorallia. How exactly mtMutS is stabilizing the Octocoral mtGenome is unclear. It is likely that the stabilization effect is the result of mtMuts carrying out DNA repair as it retains the necessary components to do so (1). A similar stabilizing effect is seen in plants that lose a copy of the nuclear MutS that is made outside of the mitochondria then transported to the mitochondria. These plants have an increase in reshuffling of mitochondrial genes resulting from double strand breaks in mitochondrial DNA (10). It is possible that mtMutS is preventing such breaks in the DNA from occurring in the mtGenome of the Octocorals. Despite inversions, reversal of gene order, being rather rare in the Octocoral mtGenome, it has occurred at least three times (9). These inversions are speculated to have occurred by misalignment of double stranded DNA leading to a double strand break (9). This is a very similar situation to the damage suppressed by MutS in plants (10).

When mtMutS was first discovered it was thought that it was the ancestral copy of MutS from the mitochondria’s time as a free living bacterium (3). However this has recently been called into question by Ogata et al. (7) who showed that the mtMutS is more closely related to a MutS genes belonging to NucleoCytoplasmic Large DNA Viruses (NCLDV) and epsilonproteobacteria, than either the E. coli or the Human MutS. The E. coli copy of mutS would be more similar to mtMutS if it was a relic of the bacterial mitochondria MutS. Additionally the NCLDV MutS also possess the same component believed to allow mtMutS to operate independently (7). Both Bilewitch and Degnan (1) and Ogata et al. (8) showed that together the Octocoral mtMutS, NCLDV mutS, and epsilonproteobacteria mutS form a unique subfamily of mutS proteins, the mutS7. These two studies provide strong support for mtMutS having arisen from a transfer of the MutS gene from either the NCLDV or an epsilonproteobacteria to the ancestral Octocoral mitochondria. This passing of DNA from one organism to another is called a Horizontal Gene Transfer (HGT). HGT are rare however NCLDVs are highly abundant in marine environments (Claverie et al. 2009) and corals are well known for their association with a diverse array of microorganisms including the Proteobacteria (4). This viral introduction of the mtMutS gene additionally calls into question the origin of Human mutS which was until now assumed to have come from the ancestral mitochondria.

It is currently unknown if NCLDVs are able to infect Octocorals, however there is evidence that they are able to infect sponges (2). The means by which mtMutS would have made its way from an NCLDV to the mitochondria of the Octocoral is also unclear, as NCLDVs have yet to demonstrate the ability to infect mitochondria. Mitochondrial infecting viruses are known infect terrestrial fungi. This unique evolutionary event provides a tool for identifying any coral that belongs to the Octocorals. The variability of the mtMutS gene may also assist scientists in determining the species boundaries within the Octocorals, as currently morphological groupings provide an incomplete picture. The occurrence of such a rare event bears significant repercussions for the understanding of evolution. Previous to this discovery a HGT event occurring in the mitochondrial was considered so unlikely it was never considered a possibility. The role that NCLDVs have played and currently are playing in the evolution of marine organisms has yet to be fully grasped.


Literature Cited:

1. Bilewitch P. J., and Degnan M. S. 2011. A unique horizontal gene transfer event has provided the octocoral mitochondrial genome with an active mismatch repair gene that has potential for an unusual self-contained function. BMC Evolutionary Biology. 11: 228. 1471-2148.
2. Claverie J-M., Grzela R., Lartigue A., Bernadac A., Nitsche S., Vacelet J., Ogata H., and Abergel C. 2009. Mimivirus and Mimiviridae: Giant viruses with an increasing number of potential hosts, including corals and sponges. Journal of Invertebrate Pathology. 101. 172-180.
3. Culligan M. K., Meyer-Gauen G., Lyons-Weiler J., and Hays B. J. 2000. Evolutionary origin, diversification and specialization of eukaryotic MutS homolog mismatch repair proteins. Nucleic Acids Research. 28:2. 463-471.
4. Lee O. O., Yang J., Bougouffa S., Wang Y., Batand Z., Tian R., Al-Suwailem A., and Qian P-Y. 2012. Spatial and Species Varaitions in Bacterial Communities Associated with Corals from the Red Sea Revealed by Pyrosequencing. Applied and Environmental Microbiology. 78:20. 7173-7184.
5. Malik S. H. and Henikoff S. 2000. Dual recognition-incision enzymes might be involved in mismatch repair and meiosis. TIBS 25. 414-418.
6. McFadden S. C., Sanchez A. J., and France C. S. 2010. Molecular Phylogenetic Insights into the Evolution of Octocorallia: A Review. Integrative and Comparative Biology. 50: 3. 389-410.
7. Ogata H., Ray J., Toyoda K., Sandaa R-A., Nagasaki K., Bratbak G., and Claverie J-M. 2011. Two new subfamilies of DNA mismatch repair proteins (MutS) specifically abundant in the marine environment. International Society for Microbial Ecology. 5. 1143-1151.
8. Stat M., Baker C. A., Bourne G. D., Correa M. S. A., Forsman Z., Huggett J. M., Pochon X., Skillings D., Toonen J. R., van Oppen J. H., and Gates D. R. 2012. Molecular Delineation of Species in the Coral Holobiont. Advances in Marine Biology. 63. 1-65.
9. Uda K., Komeda Y., Koyama H., Koga K., Fujita T., Iwasaki N., and Tomohiko S. 2011. Complete mitochondrial genomes of two Japanese precious corals, Paracorallium japonicum and Corallium konojoi (Cnidaria, Octocorallia, Coralliidae): Notable differences in gene arrangement. Gene. 476. 27-37.
10. Xu Y., Arrieta-Montiel P. M., Virdri S. K., de Paula B.M. K., de Paula B.M. W., Widhalm R. J., Basset J. G., Davila I. J., Elthon E. T., Elowasky G. C., Sato J. S., Clemente E. T., and Mackenzie A. S. 2011. MutS HOMOLOG1 Is a Nucleoid Protein That Alters Mitochondrial and Plastid Properties and Plant Response to High Light. The Plant Cell. 23: 3428-3441.