Science / Medicine : DNA Fingerprints : This technique not only can solve crime, but researchers are now using it in medical treatments and even to help zoologists to breed condors.
In science, a finding is only as good as the proof. Thus when a team of scientists at the German Cancer Research Center in Heidelberg made an unusual discovery last year, their work did not stop until they employed a technique that lately is better known for its role as a courtroom prosecutor’s tool.
The scientists, led by cell biologist Petra Boukamp, successfully cultured a healthy human skin cell so that it multiplied itself, creating dozens of generations of other healthy, long-living skin cells that could be used for laboratory research on skin and skin ailments.
Moreover, the researchers found that the cell could be genetically engineered to become cancerous, something scientists have had a very difficult time doing with human cells in the lab.
Boukamp suspected immediately that the scientific community might doubt her team’s findings. Cell culture has a history of great discoveries that have turned into greater disappointments. Cell lines that have appeared at first to be new and unusual have turned out many times only to be variations of HeLa cells, a pervasive laboratory contaminant.
“There are more cross-contaminations in (cell) lines than you would think there are,” Boukamp said during a recent telephone interview from UC Irvine, where she was completing a three-month visit.
The German team needed something that would prove beyond a doubt that their cell line was new and unique. Boukamp turned to molecular geneticist Alex Markham of the British firm ICI Diagnostics to apply DNA fingerprinting, a 3-year-old discovery that “reads” part of the genetic code of an organism and creates a pattern that is unique to the organism.
The pattern reflects inherited characteristics and allows a scientist to verify an organism’s parentage. For the German team, fingerprinting proved that the original human skin cell they cultured was the “parent” of the cells growing in the lab 140 generations later. Contaminants had not intervened to create the cell’s unusually hardy characteristics.
In March, the team’s research was published in the respected Journal of Cell Biology.
The article is apparently the first published account of scientists using DNA fingerprinting to verify the purity of a laboratory-cultured cell line. However, there are already signs that other labs may adopt the procedure routinely.
Since March, 1985, when British geneticist Alec Jeffreys first reported his discovery of DNA fingerprinting, it has been embraced mostly by forensics experts because it is much more reliable than conventional analyses.
The variation in DNA fingerprints from one person to the next is so great that the probability of two people sharing the same print is almost zero. And unlike hand fingerprints, which are often difficult to gather at a crime scene, a DNA “fingerprint” can be taken from very small samples of blood or semen, or even a single hair.
In November, DNA fingerprinting had its first major court test. A Florida man was convicted of rape after a small sample of semen taken from the victim’s vagina was fingerprinted and found to match the DNA fingerprint of the man’s blood.
Yet these courtroom applications may be just the tip of the iceberg for this technology. DNA fingerprinting holds other medical and laboratory promise, and a handful of scientists in the United States and Europe are quietly exploring other applications.
“As one of my friends says, this is sort of like ‘give a kid a new hammer and he’ll find everything to pound,’ ” said Bruce Kovacs, an assistant professor of obstetrics and gynecology at USC and a research scientist at the City of Hope National Medical Center in Duarte. “That’s exactly what we have here. I have a new hammer and I’m trying to find everything that needs to be hammered.”
So far, these scientists have used fingerprinting for tasks as disparate as guiding captive breeding programs for cheetahs and monitoring the success of human bone marrow transplants.
DNA fingerprinting relies on a conglomeration of techniques that have been used for a number of years in genetic study.
Every living cell has its own double strand of deoxyribonucleic acid, or DNA. Within a single individual, every double strand of DNA is believed to be identical to the next. Often called the body’s blueprint, DNA holds the genes that instruct the body how to form and operate.
To make a fingerprint, scientists begin with a sample of cells from an organism. They then break open the cell, extract the DNA and introduce an enzyme that cuts the DNA strand at specific sites. The fragments of DNA are then separated with an electric charge run through a bed of gel.
A radioactive chemical combination called a probe is added to the DNA segments. The probe is designed to find many specific sites on the DNA chain and effectively allows the fingerprint to be picked up on film and read.
The fingerprint pattern has 20 to 30 small bars of varying widths lined up in a row. The pattern has been described as resembling the pricing bar code used on supermarket products.
Every individual’s bar pattern is a mix of his or her parents’ bar patterns. Except for identical twins, who share identical genes, even siblings have different patterns.
The few scientists exploring DNA fingerprinting say it could eventually have broad medical--especially diagnostic--applications.
Already, doctors at several hospitals, including UCLA Medical Center, have begun using a variation of fingerprinting in bone marrow patients to determine whether the donor’s marrow is working, enabling them to respond earlier if the transplant isn’t taking. Scientists are also exploring DNA fingerprinting’s power to help understand and identify genetic mutations. And Kovacs sees a potential use for DNA fingerprinting in early cancer diagnosis and prevention.
In the last year, by studying fingerprints of people who do not have any apparent disorders, Kovacs and Jeffreys have separately determined that the rate of occurrence of mutations at specific sites using specific probes is about one in 20. This suggests that there is a sort of background mutation rate, Kovacs said, a finding that provides an important base for other mutation research.
Researchers have also found that DNA fingerprinting may help solve problems in the animal kingdom. Inbreeding of certain species at zoos and animal parks has led to creation of a genetic pool within each breed that has very little differentiation.
Scientists at the San Diego Zoo have already used fingerprinting in their captive breeding program for condors. That lack of differentiation could ultimately make an entire breed susceptible to ailments or defects that could wipe it out.
With fingerprinting information, scientists hope captive breeding programs will be able to more carefully pair animals to increase the differentiation.
For at least one litter of potential show puppies, fingerprinting secured their reputation, said molecular geneticist Markham of ICI Diagnostics, which markets certain DNA fingerprinting probes. The puppies’ mother had escaped during her breeding period. By running DNA fingerprints on the dogs and comparing them with the puppies’ DNA fingerprints, the true parentage was determined.
“Her honor was upheld,” Markham said of the puppies’ mother.
The champion dog was indeed the father.
DEVELOPING A DNA FINGERPRINT
Every living cell has its own double strand of deoxyribonucleic acid, or DNA. Within a single individual, every double strand of DNA is believed to be identical to the next. Often called the body’s blueprint, DNA holds the genes that instruct the body how to form and operate.
To make a fingerprint, scientists begin with a sample of cells from an organism. They then break open the cell, extract the DNA and introduce an enzyme that cuts the DNA strand at specific sites.
The fragments of DNA are then separated with an electric charge run through a bed of gel. The shorter fragments rise toward the electric charge more quickly, longer segments more slowly.
A radioactive chemical combination called a probe is added to the DNA segments. The probe is designed to find many specific sites on the DNA chain and effectively allows the fingerprint to be picked up on film and read.
The fingerprint pattern has about 20 to 30 small bars of varying widths lined up in a row. The pattern has been described as resembling the pricing bar code used on supermarket products. The darkness of a band increases with the concentration of like-size segments at a particular level. The width of the band increases when there are several segments within a close range of lengths. The pattern of bands resulting is the individual’s DNA fingerprint.
