Mixing the correct cellular soup for survival

(January 19, 1998 00:13 a.m. EST http://www.nando.net) - Genes are the
blueprint of life. Or perhaps not.

Some embryologists -- scientists who study how a single fertilized egg
develops -- are proposing an alternative theory: that genes are like building
regulations, and it's growing cells that are the cutting edge of evolution.

The idea has arisen out of some weird observations. A chimpanzee's genes are
99 percent the same as human genes. Even one-third of yeast genes have
counterparts in humans.

The curiosity is not how alike humans, chimpanzees and yeast must somehow be,
but how different they actually are when they have so many genes in common.

Another observation is that bacteria have evolved to live on just about any
energy source. Some live in darkness, others in volcanic vents, and yet others
on your teeth.

Other living creatures are differently diverse. They give electric shocks,
fly, or write symphonies, but their food is more or less the same.

The two are linked because eating is about the biochemistry of energy. Fruit
flies, which have many genes in common with humans, are genetically and
biochemically similar to people. There are even biotechnology companies
studying fruit fly genetics to help understand human biochemistry.

What may have happened in prehistory is that bacteria came first and learned
how to evolve biochemically. Two billion or so years later came other living
creatures, which evolved through changing shape and behavior.

John Gerhart of the University of California-Berkeley and Marc Kirschner at
Harvard Medical School have just published their summary of modern embryology,
"Cells, Embryos and Evolution" (Blackwell Science, $69.95).

It proposes that the vehicles for much of this second type of evolution are
cells, and they are especially interested in one type called neural crest
cells. These are cells that, during embryo development, can turn into any of
an enormous variety of more specialized ones.

They include bones, bird beaks, human vocal cords, sense organs and blood
vessels -- many of the distinguishing features of species. The job of neural
crest cells is to explore.

Blood vessels grow in patterns that are not determined by genes, and are often
different in identical twins. Elk antlers, hummingbird beaks and elephants'
trunks are all derived from neural crest cells.

These cells have been studied for decades, but as Gerhart and Kirschner
surveyed embryologists' work, increasingly informed by discoveries in more
basic science such as molecular biology, it seemed that evolution itself
depended on such cells.

Is that enough to consider displacing genes from the center of the
evolutionary universe? No. But it does begin to suggest genes should share the
center stage with cells.

To see how the two work together, let us take another look at how genes work,
in the light of molecular and cell biology.

Genes cause cells to make proteins such as insulin and hemoglobin. These
proteins make the body work. But genes don't make proteins all the time:
they're switched on and off by what is happening around them. Insulin is made
only when the conditions are right, perhaps when sugar is eaten.

Every cell in your body has the same genes, but every gene has a set of
switches which make sure, for example, that your skin cells do not start
making insulin.

The switches work in response to the environment. But their environment is the
cell. So genes and cells affect each other.

Take deer antlers. Genes create a biochemical soup in which cells grow. During
the animal's development, these cells "explore" new shapes.

The size and shape of the antlers vary how the elk reacts to its environment:
it may find it hard to eat leaves growing high, or easier to challenge rivals
for the low-growing leaves.

Either way, the food the animal eats affect where and when genes get switched
on -- that is, they affect the biochemical soup.

If the combination of genes and cells works well, the animal is successful and
the soup's recipe is passed on to the next generation.

What the embryologists are saying does not contradict traditional Darwinian
evolution. Richard Dawkins, for example, has said the ability to evolve better
is itself the result of evolution. Cells that evolve quickly would be one way
of doing this.

This also implies there can be different kinds of evolution, as in bacteria
and their biochemical diversity, and animals and their shape diversity.

Gerhart and Kirschner tentatively suggest there can be psychological
evolution, too.

Other scientists have suggested prehistoric man was what we would now describe
as schizophrenic, given the evidence of remorse-free killings prompted by
divine "voices", for example, described by Homer.

Even this does not exclude genes, whose functioning is affected by the outside
world.

Schizophrenia appears to be related to a protein in the brain called dopamine.
This is, of course, made by a gene.

So genes tell cells what they can and cannot do. In return, cells call on the
resources of genes to enable them to act.

Perhaps the best analogy is that we are driving a car. The genes are the gears
and engine while the cells are the bodywork and wheels. Lots of different car
designs are possible.

By DANIEL GREEN, The Financial Times
Copyright 1998 Nando.net
Copyright 1998 Scripps Howard

janet paterson / 50-9 / sinemet-selegiline-prozac / [log in to unmask]