From the issue dated May 22, 1991
Slugs Provide Models for Researchers Studying Mucus
By Peter Monaghan
Seattle, Washington -- While the mere mention of slugs disgusts most people, Ingrith J. Deyrup-Olsen has looked beyond their slimy surfaces and discovered unappreciated qualities in the much-maligned gastropods.
Ms. Deyrup-Olsen, an emeritus professor of zoology, is one of several researchers here at the University of Washington who have demonstrated that slugs are not only of interest to zoologists, but a particularly useful model for biological research. Whether they can convince the slug-shy that they are aesthetically pleasing is another matter.
"If you want to study methods of mucus secretion, production, and control, the slug is the animal," says Daniel L. Luchtel, associate professor of environmental health.
So convinced is Ms. Deyrup-Olsen of the animal's usefulness to research that she chafes at hearing it called "lowly." "The slug is," she notes, "the top of the line in land mollusks."
She and her colleagues point out that in biology many animals have belied their apparent lowliness. "Most of what we know about nerves today," says Pedro J. Verdugo, professor of bioengineering and biostructure, "has come from a cousin of the slug, the squid." (Other cousins include the clam, the snail, and the oyster.)
But winning financial support for slug research is tough, not just because of the cultural bias against slugs and mucus. Researchers say granting agencies have biases against research that uses invertebrates, or even non-mammalian species, to explore human diseases or other features of human life.
So, when applying for grants, slug researchers stress that the results of their studies could be used to improve treatments for human diseases associated with impaired secretion of mucus, asthma, gastric ulcers, and even the common cold. Ms. Deyrup-Olsen concedes, however, that at this point "our work is still very theoretical" and important mainly to others engaged in basic research.
Ms. Deyrup-Olsen has brought together scientists from a variety of disciplines and demonstrated to them that their work can be aided by research on slugs. She persuaded Mr. Luchtel, for instance, by showing him how slugs could help his work on the protective role of mucus in the respiratory system.
The general problem Ms. Deyrup-Olsen and her colleagues are looking at is how mucus is formed. They believe knowledge of that process will illuminate many puzzles in health and basic research.
Ms. Deyrup-Olsen says that, as far as she knows, the University of Washington is the only institution in the world where slug mucus is being studied as a general model of mucus formation -- which is fitting, since the Northwest is a major natural source of gastropods. The region is home to two dozen of the world's 500 species of slugs.
Schoolchildren to whom Ms. Deyrup-Olsen makes presentations, and adults who come to her laboratory here, quickly become intrigued by slugs. Ms. Deyrup-Olsen confronts, head on, aversions to mucus -- by showing visitors just how slimy the animals are.
As Ms. Deyrup-Olsen places a large, greyish-olive banana slug on a Petri dish, she invites visitors to touch the animal lightly on the back. The effect is extraordinary: Instantly the finger is covered with a thick ooze that, when rubbed between the fingers, resembles rubber cement. Ms. Deyrup-Olsen recommends not washing it off just then -- the mucus may swell to up to 50 times its initial volume.
Also surprising is the size of the slug, and how distinct its features are. The head is large and clearly set off from the torso. At its side is a breathing hole, or pneumostome. Unseen is the animal's tongue-like scraper, the radula, and the 27,000 minute teeth that cover it.
However strong the average person's aversion to slugs and their slime, that feature first sparked Ms. Deyrup-Olsen's interest.
"The slug found me," she says. In 1978 a colleague, Arthur W. Martin, now also a professor emeritus of zoology here, was trying to measure blood volume in slugs by injecting hemoglobin into one.
He ran into an unexpected problem: The hemoglobin oozed out, all over the slug's body. He had discovered that slugs were able to extrude toxic matter all over their bodies from cells with pores that go from inside the body to outside.
Recalls Ms. Deyrup-Olsen: "That was so spectacular that I became enchanted with them."
Research performed since then, she says, has shown that slugs "have a lot of remarkable and ingenious devices." For example, they form their mucus in cells that are gigantic by comparison with other animals -- and much easier to observe through a microscope. The cells are in effect packets of slime, enclosed in membranes.
The animals' skin, unlike that of humans and most other land animals, is a layer of living cells protected by mucus, rather than by many layers of dead cells. The mucus may be very slippery, the perfect vehicle for, say, sliding along at about 12 yards an hour. And it may emerge as a thick, sticky substance to trap and repel viruses and other foreign matter.
After Ms. Deyrup-Olsen retired in 1990, the department of zoology gave her continuing use of the office where she and Mr. Martin study slugs and rally others to their cause. Their major focus is the signaling system that causes mucus to be released, or to malfunction in cases of disease.
Ms. Deyrup-Olsen also breeds slugs for research projects her colleagues run. The subspecies of choice is the banana slug, Ariolimax columbianus, one of the largest slug varieties. It grows to about seven inches in length in the laboratory and more than half as much again in its natural, forest habitats. The banana slug is so named because the California variety resembles the fruit in color and size.
From these animals, Ms. Deyrup-Olsen prepares samples of mucus granules, packages of mucus molecules within the mucus-producing cell. She uses some of that material in her own research, and also passes samples on to other researchers.
Mr. Verdugo, the professor of bioengineering and biostructure, is examining the way mucous material is packaged, and what happens when it is released. In addressing the nature of a variety of human diseases, the question he asks is, How can mucus be made to come out in the right amounts at the right time? Abnormal release, for example, can cause cystic fibrosis, a congenital condition in which the malfunctioning of mucus glands harms the pancreas and lungs and suffocates its victims.
Mr. Luchtel, the associate professor of environmental health, is examining the structure of mucus cells to see how that might throw light on such health hazards as pollution. He and Rodman Miller, a senior fellow in the department of oral biology, are trying to determine what happens in the cells when mucus is released.
The key, they suspect, is an elegant fusing of double membranes around the mucus granules inside the mucus cells. But a definitive explanation of the process remains years off. Why is the going so slow? "The damn mucus is in the way," Mr. Miller explains.
Ms. Deyrup-Olsen says, "One thing that fascinates me about mucus is that people tend to be so negative about it, but it's so crucial to survival." Mucus or mucus-like materials are found throughout both the animal and plant worlds as protection for living surfaces that encounter the outside world. Mucus is essential to such functions as digestion and reproduction.
Who, after developing ulcers due to interference of mucus function, asks Ms. Deyrup-Olsen, "would ever stop, when feeling the pain, to say, `I wish my mucus was working properly?' "
Three years ago, perhaps noticing that Ms. Deyrup-Olsen had a sense of humor about her work, David Letterman, the late-night television comedian renowned for his friendly mockery of guests, invited Ms. Deyrup-Olsen to his show as "The Slug Lady." She says Mr. Letterman proved genuinely interested in her gastropods.
Not to overcome aversion, but to supplement diet, some biologists advocate eating slugs, as the French do snails. Slugs are rich in protein, and they don't need to be plucked or chased down.
One last point about slugs: Yes, says Ms. Deyrup-Olsen, slugs will eat your flowers, and can ruin large areas of crops. But the reason they are so hard to get rid of in gardens and under kitchen sinks is that they are, in their basic biological chemistry, so akin to humans.
"Anything that harms slugs," she warns, expressing her comradeship with them in one more way, "harms humans."
Copyright © 1991 by The Chronicle of Higher Education
