St.
Louis, MO (4/9/99)- Put Jordan under pressure and then watch for the jump
shot, say Washington University researchers. In this case they are talking
biology, not basketball.
Photo: Michael
Jordan- Jumping Genes
Cell biologists David Kirk, Ph.D., and Stephen Miller, Ph.D., have named
a a transposon, sometimes called a 'jumping gene' after the former Chicago
Bulls star. The two researchers have managed a first, developing a new technique
for controlling the activity of one kind of transposon, a discovery that should
open new avenues in genetic research .
A transposon is a type of gene found in most living organisms. Under certain
circumstances, this type of gene literally jumps from one chromosome to another.
The researchers discovered what makes a transposon gene in Volvox, a green
alga, want to jump. Moreover, by regulating the temperature of its environment
they can make the Volvox gene jump on command.
"We found that simply by growing cultures of Volvox at lower temperatures,
we can increase Jordan's jumping 30- to 50-fold. It's important to have Jordan
jumping frequently because for every thousand times it jumps in Volvox, maybe
only once will it land in a gene we're interested in," said Dr. Kirk.
After Jordan jumps, the scientists can determine where it lands by tracking
its characteristic genetic signature.They can use the jumping Jordan gene
to isolate genes of interest and study their form and function. The Jordan
jumping gene has already helped the team to discover and analyze two important
genes that play key roles in cell replication and specialization.
"Jordan has two special genetic sequences at its ends that permit the gene
to cut its way out of a cell at one location and reinsert itself at another.
That's what's called jumping. We can recognize the Jordan mutation in the
gene where it lands, and then extract that gene's preexisting DNA and study
it. Having Jordan in a gene gives us a handle to pull out the DNA of interest.
That's how we found these two genes, and their discovery has led to a far
deeper understanding of Volvox than we've ever had before." Explains Kirk.
The genes Jordan landed in are called glsA and regA. The first,
glsA is essential for asymmetric division in Volvox, whereby only large
cells become germ cells and only small cells become body cells. The glsA
gene has a counterpart in humans called MPP11, which also plays a role
in cell division. The human gene is more than 50 percent homologous with the
Volvox gene.
"This was astonishing to us. The similarity is really close for organisms
separated by at least one billion years of evolution. Only five other genes
similar to glsA have been found throughout the biosphere, three in
mammals and one each in fungi and algae," said Kirk.
The other gene Jordan jumped on is RegA. It prevent the body cells
from becoming germ cells by harnessing the activity of 18 other genes that
inhibit the formation of chloroplasts in the body cells. Volvox is a green
alga, so it gets its energy from photosynthesis. Without the formation of
new chloroplasts, the body cells have just a limited time to carry out their
function and then they die.
"Volvox interests biologists because it has only two cell types, somatic
or body cells that fulfill their functions and die within five days, and germ
cells, which reproduce. This is what makes Volvox an important system. We're
trying to get a big picture of basic cell development with just two cell types
as opposed to trying to understand the basics in mammals where as many as
200 different cell types are developing all at once," explained Kirk.
An improved understanding of transposons could lead to using them as vectors
for gene therapy. The work also has implication for cancer research since
50 percent of all spontaneous mutations are due to transposon insertions into
other genes.
Transposons were first identified by Barbara McClintock in maize in 1943.
She won the Nobel prize for this work in 1983.
The research appears in a recent issue of the journal Development.
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