Sea Slug Eats Algae and Becomes Plant-Like
A common garden slug, Arion lusitanicus, eating (note: the subject of these experiments was a sea slug) photo credit: Håkaan Svensson, Xauxa
After two weeks of a strict algae-only diet, a one-inch, green sea slug species (Elysia chlorotica) was somehow able to incorporate the plants chloroplasts (the cell-like organelles that trap solar energy and convert it to sugar), and then live out the rest of their single-year lives without eating.
The slug, a snail-like mollusk without a shell, was able to photosynthesize, just as plants do. Scientists are not sure exactly how it is able to pull this trick off, but they do know that the slug is able to harness the DNA found within the alga’s chloroplasts (note: chloroplasts in plants are like mitochondria, in that each has its own DNA apart from the DNA found in the cell’s nucleus). But this DNA only encodes a small percentage of the genes (and their proteins) needed for complete photosynthesis. The rest of the needed genes (in particular the nuclear osbO gene) are in the algae cell’s nuclear DNA. Not to worry, somehow, the slug is able to “steal” those genes as well, and incorporate them into their germ line cells–allowing them to pass this new capability on to their off-spring.
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Cell biologist are quite familiar with the phenomenon of “jumping genes” –genes which are able to transfer to another genome (or to another chromosome or germ cell) and insert a copy of themselves (also related to “cheating” genes). However, in the case of jumping genes, the DNA is inactive. This is not the case with the algae-fed sea slug, for its off-spring possess a functional photosynthetic capability.
The phenomenon is referred to as horizontal gene transfer . The researchers speculate that “foreign organelle retention generates metabolic novelty” (or “green animals”), caused by an anastomosis (a joining of two separated parts) of “two branches of the tree of life driven by predation and horizontal gene transfer”.
Discovering the key mechanisms involved in this “horizontal transfer” holds promise for transgenic science which seeks to uncover the novel trait conferring abilities of genes and incorporate these into other organisms. Sometimes this is done to enhance an ability already present, and sometimes to confer a new ability or trait (phenotype). This has led to some rather bizarre outcome such as female goats that produce silk threads in their milk, but also animals that produce important drugs in their urine.
It some genetic experiments, it is the opposite: whole genes or gene sequences are “knocked out” to see the effect of this loss on the animals’ functioning. Some of these “knock-out” creatures (typically, they are mice) have led to the discovery of important genes that control human diseases. In other cases, defective mutations result. Obviously, these practices has raised many ethical questions and is perhaps the central issue in Bio Ethics.
Researchers Rumpho, et al reported their findings earlier this year in the on-line publication of Proceedings of the National Academy of Sciences
photo credit: Håkaan Svensson, Xauxa
