A Tiny Worm Challenges Evolution

A Tiny Worm Challenges Evolution

I do set My bow in the cloud

The entire genome of the tiny nematode C. Elegans has recently been sequenced. This is the first complete genome of a multi-cellular organism to be sequenced. It contained about 100 million base pairs and about 20,000 genes. However, this achievement poses some problems for the theory of evolution.

The first problem is that some of the genes of C. Elegans are so similar to those for humans that scientists have substituted the human genes for the nematode genes, and the human genes have worked fine. According to accepted evolutionary theory, nematodes and humans split more than 600 million years ago. This means that since the common ancestor of humans and nematodes, these genes have changed so little that one can be substituted for the other. These genes are really living fossils, then! During all this time, when evolutionary pressures have supposedly led to so many other changes, including the development of whole new organs, we find that these particular genes have hardly changed at all! If these genes are so locked in that they do not change appreciably, then how can we expect such drastic changes in the other ones to take place?

Another problem is with the size of the most recent common ancestor of humans and nematodes. Of the 5000 best known human genes, three fourths have close analogues in the nematode. This implies that these roughly 3700 genes were represented in the most recent common ancestor of humans and nematodes. This is about the number of genes in the E. Coli bacterium, and much less than one finds in yeast. But there are many more human genes that are not known yet, so the real number must be much higher. So this most recent common ancestor of humans and nematodes would have to have at least 5000 or more genes, in all probability. This is quite a large number for such a supposedly primitive creature, but still not as many as are found in yeast. But as more and more organisms are studied, this number will probably increase significantly. For example, the eye genes in humans and fruit flies are very similar, implying such a gene in their most recent common ancestor.

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Friday December 11, 1998 1:50 a.m. EST

Researchers Map Worm's Entire Genetic Code; Could Lead to Cures for Diseases WASHINGTON (AP) -- Researchers have mapped the entire gene pattern of a tiny soil worm, a feat that some say is the biological equal to landing on the moon and a major milestone toward finding new ways to cure disease.

The worm, a type of nematode called Caenorhabditis elegans, is as common as dirt. Thousands live in a typical handful of garden soil.

But the small creature also is a complex, multicelled organism that carries many genes that also exist in humans, and function in the same way.

As a result, the worm provides a crucial keyhole view of the vast world of genetics, said Robert H. Waterston, who led a team at the Washington University Medical School in St. Louis that joined with British scientists to map the worm's genes.

``This worm is really an animal just as we are,'' said Waterston. ``It has muscles and many different kinds of cells. And it also ages, just as we do. By and large, it uses the same genes that we do.''

By studying genes shared by worm and human, researchers will learn at a molecular level what can go wrong and how to fix it. Such microscopic studies are virtually impossible in humans.

``Half of the disease genes in humans have identifiable counterparts in this worm,'' said Dr. Francis Collins, director of the National Human Genome Research Institute. He said researchers into many human diseases will be able to use the humble worm as a way of learning how to prevent, treat and cure the illnesses of man.

``I don't think that it is an overstatement to say that the hopes of the parents of a child with a birth defect, the hopes of a young man with a family history of cancer and the hopes of a couple caring for aging parents are advanced'' by this new understanding of the C. elegans, Collins said.

In fact, researchers studying the worm identified genes that have been linked to Alzheimer's disease, to aging and to some forms of cancer, Waterston said.

``The only reason we know about some proteins in Alzheimer's disease is because there are related proteins in the worms, and the function of these proteins had been determined,'' he said.

In terms of the gene-mapping's significance to science in general and to biology in particular, Collins said: ``This is like landing on the moon.''

Earlier researchers had completed gene patterns for single-cell organisms and for yeast, but this is the first mapping of an animal with many cells.

Dr. Harold Varmus, head of the National Institutes of Health, called the worm gene mapping ``a significant event in the history of biology.''

``The unveiling of this genetic blueprint is giving us our first real picture of what it is like to understand a multicellular, complex organism like ourselves,'' said Varmus. ``Researchers into many diseases will make use of this advance.''

Waterston's team and a group at the Sanger Centre in Cambridge, England, worked together for eight years to identify the worm's nearly 20,000 genes. To do this, they had to find and sequence about 97 million DNA base pairs, a task that required labs to work around the clock.

Collins said that by understanding what happens in the worm cells, researchers also learn what happens in human cells. Of the 5,000 best-known human genes, 75 percent have matches in the worm, Collins said.

The human genetic pattern, or genome, has 80,000 genes arranged in 3 billion DNA molecule pairs. About 7 percent of the human genome has been mapped, Collins said.

The worm is a clear-skinned creature whose biological functions can be easily monitored by microscope. A dozen of the animals could perch on a pinhead, but within each is a complex world of genes that perform the same functions as in humans.

``With modern techniques, you can actually watch the action of individual proteins inside this worm,'' said Waterston. ``If that function happens in the worm, then you know the same thing is happening in humans.''

Some worm genes are so similar to human genes that researchers have experimentally inserted human genes into the animal and watched as the implant worked perfectly, he said.

Genes for muscles ``map almost one to one'' when comparing human and worm, Waterston said. In the nervous system, some genes discovered first in the worm were later found to be in humans, even though the worm has only 302 neurons compared with a human's millions.

Scientists began studying the worm after a British researcher identified it as an ideal way to study the nervous system. It has only 959 cells yet reproduces, grows into a mature adult, eats, excretes and dies with many of the cellular interactions of other animals.

Since the studies began in the 1960s, researchers have plotted the development and demise of virtually every cell in the worm's body. They have monitored worm embryos as they grew, cell by cell, into an adult and then have watched the cells age and die.

Such work, Collins said, provided insights into basic functions common to virtually all multicelled creatures.

By PAUL RECER, AP Science Writer

Copyright )1998 Associated Press. All rights reserved. This material may not be published, broadcast, rewritten, or distributed.

Copyright )1995-1998, Capitol Broadcasting Company, Raleigh, NC.

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