When you conjure up an image of cells, what do you see? What do you think? You may see a snapshot of an animal tissue, perhaps with actively dividing cells. That’s understandable because, as animals ourselves, we’re aware that cells come from other cells, thus the need to undergo mitosis, or cell division, frequently.
But one kind of mammalian animal cell does not fit that image—nerve cells. They do not arrange themselves as cells in a typical tissue do. Nerve cells are singular, with a long, sometimes very long, threadlike extension called an axon. And they don’t undergo mitosis frequently, except in embryos. This apparent aberration in the world of cells has puzzled scientists and medical researchers. If one could get nerve cells to behave more like other cells in terms of regeneration, a host of nerve-related diseases and damage could be reversed.
ScienceDaily published a story on January 26, 2009, reporting on exactly that kind of breakthrough, New Hope For Restoring Injured Nerves. A group of researchers at the University of Utah uncovered a pathway (a chain of molecular events) involving a gene that, when forced to be overactive, leads to repair of severed nerve cells in nematode worms. The gene is also found in mammalian genomes; thus, the researchers predict they will be able to replicate the study in mammals.
Finding a gene that produces a protein that aids in nerve cell repair in worms is not surprising. Gene theory predicts just that in organisms known to regenerate portions of their anatomy. It also is not necessarily surprising to find the same gene in mammalian systems, since evolutionary theory reveals our common ancestry. What did surprise researchers was that the pathway that results in nerve cell regeneration is not found in developing embryos.
Scientists have puzzled over the fact that nerve cells are regenerated in mammalian embryos and very young, rapidly developing mammals, but not in adults. The question was, what did mammals lose along the way to maturity? The pathway discovered in the new study “is unique in that it is not used by the nervous system during normal embryo development, yet it is absolutely required for regeneration,” one of the researchers said.
How to Turn This News Event into an Inquiry-Based, Standards-Related Science Lesson
Middle school curriculum usually includes some study of cells, genetics, and body systems. This story provides background for some authentic discussions allowing students to apply and extend their knowledge in these three areas. At the same time, it provides opportunity to reinforce concepts in methods of science.
Ask students what happens to a worm that gets cut in half by a gardener’s shovel? To a starfish whose leg is bitten off by a predator? What is regeneration? Have they ever wondered why humans cannot do the same? Do they know that mammalian embryos and very young mammals do have the ability to regenerate? How might regeneration be related to the science of genes? What does the idea of regeneration have to do with curing paralysis in humans?
Remind students of cell theory and show them some visuals of cells, and cells in tissues, organs, and systems. Show them some nerve cells. If they’ve studied the nervous system, they already have some notions regarding nerve cell structure and function. Explain that in paralysis, the nerve is severed and, in adults, not easily repaired.
Point out that scientists have uncovered the worms’ pathway that enables their nerve cells to regenerate. Ask how such a discovery could possibly be useful in mammalian systems? Remind students that all living things share some common characteristics, like cellular structure, DNA, and the ability to respond to stimuli. Is it possible that mammalian genomes could contain the same or similar genes that enable regeneration in worms? As predicted by evolutionary theory, the answer is yes!
So why can’t we regenerate nerve cells? Remind students, or explain, that genes have to be turned on in order to produce the necessary proteins that participate in a pathway culminating in regeneration. In this study, scientists methodically “knocked out” genes, one by one, in worms until they found the one primarily responsible for nerve cell regeneration. (There actually are four genes working together.) When the scientists created conditions that enabled the gene to increase its activity, producing ample protein associated with regeneration, nerve cell regeneration was rapid in adult worms. This confirmed their hypothesis regarding the activity of a particular gene on regeneration. It also enabled them to uncover the steps in the pathway from gene to cell regeneration. Knowing the steps allows scientists to hypothesize possible ways to enhance the pathway in order to induce regeneration in mammals.
Using this story allows you to facilitate student synthesis of knowledge from perhaps three different units in their curriculum around three fundamental theories: cell theory, gene theory and evolutionary theory. It also reinforces concepts associated with the Life Science content standard of the National Science Education Standards, as well as the History and Nature of Science content standard.
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This post was originally written by Mary LeFever and published January 27, 2009 in the Connecting News to the National Science Education Standards blog. The post was updated 3/22/12 by Jessica Fries-Gaither.