To help battle genetic diseases, scientists at USF are turning to the sea and a certain kind of slug that could unlock the secret to curing many human ailments.
Seventy-five to 80 percent of all human diseases are genetic. One way to cure these is gene replacement therapy — the insertion of healthy genes into cells – but this is biochemically and physiologically difficult, said Dr. Sidney Pierce, a professor and chair of the biology department. Consequently, biologists worldwide have been looking for gene transfers in nature. The process occurs in retroviruses like HIV and in bacteria and various microorganisms, but between two multi-cellular organisms it has been difficult to prove. Until now.
Pierce, who has done research on slugs for about ten years, along with Steve Massey, a post-doctoral student, and Nick Curtis, a biology graduate student, discovered a case of horizontal gene transfer between two different species found off the coast of Martha’s Vineyard, in the waters around the Keys and in the Caribbean.
Saccoglossan, or lettuce sea slugs, eat algae. Then cells that line the digestive tract collect and save chloroplasts, or chlorophyll containing organelles in the algae, Pierce said.
“This is called symbiosis cleptoplasty … when one organism steals from another,” he said.
Once the slugs have ingested the chloroplasts, two things occur. The slugs turn green and the chloroplasts continue photosynthesis for up to nine months. When a light is shone directly onto the slugs, they give off oxygen and respirate carbon dioxide, just like plants.
Pierce and his assistants have found an algal gene within the slugs’ genetic material, and vice versa. Based on the presence of retroviruses in both the slugs and the chloroplasts, Pierce suspects that the viruses may be the mode by which genes are transferred from the algae to the slugs.
Although he said he theorizes that the first gene transferal occurred as an accident, he is quick to recognize the potential benefits for gene therapy techniques. Since the retroviruses in the slugs and algae are less pathological than HIV, if the viruses could be duplicated, it could represent the first step toward the end of incurable hereditary diseases.
Sea slugs are gastropods, gastro referring to the stomach and pod referring to the feet. They are marine invertebrates with soft, unsegmented bodies that get around on one foot, which is attached to their stomachs. They lack a shell and gills, and they breathe through small fringe-like projections on their bodies. Saccoglossan, or Elysia crispata, is one of five living orders of the Subclass Opisthobranchia, or sea slugs. Saccoglossan are specialized feeders on algae. In particular, they enjoy a species of algae called Shaving Brush algae. They look like pieces of lettuce and vary in color from brown to green to yellow. They are found clinging to the algae in a semi-secret location off Grassy Key, Florida, near the Keys Marine Lab, a government funded marine laboratory.
During research, slugs that have photosynthesizing abilities are kept in a freezer at 8 degrees celsius. There are automated lights that shine on the slugs for 12 hours each day. These slugs are not fed algae.