Rutgers scientists changed one gene in tiny worms to test a human kidney disease clue; the altered nerve protein fell to 15% of normal and missed its target

A genetic test can reveal that a person carries a DNA change linked to an inherited disease, but understanding what that change actually does inside the body is not always easy. Some changes alter the ability of the protein to function, while others may leave it functioning normally. That difference can make a difference for families with indeterminate genetic status.

Researchers at Rutgers University have looked at an odd organism for research on the question of why such genetic differences occur: a tiny roundworm that lacks kidneys altogether. By changing one small part of the worm's DNA, researchers discovered that a protein linked to human kidney disease fell to just 15% of its normal level and could no longer reach the place where it was supposed to work. The findings, published in the journal Genetics in [insert publication year] and described by Rutgers, offer a new way to examine genetic changes that may cause disease.

A tiny worm with a connection to human kidneys


The organism used in the experiment is a nematode known as Caenorhabditis elegans or C. elegans. The small roundworms have been popular subjects of biological research because their genes, cells, and behavior can be precisely controlled. The study focused on autosomal dominant polycystic kidney disease (ADPKD), which is an inherited disorder characterized by fluid-filled cysts that form in the kidneys. As these cysts develop, they can cause the kidneys to malfunction and eventually cause kidney failure.

In most cases of this disease, two genes, called PKD1 and PKD2, get changed. These genes encode for proteins called polycystin-1 and polycystin-2 that function within cells. Worms lack kidneys, but they have accessory proteins that represent counterparts of kidney proteins. The proteins are used in small structures in their bodies called cilia. These hair-like projections help cells detect signals from the environment.

One genetic change caused a major protein problem

To find out what the suspected disease-related change actually did, researchers used CRISPR, a gene-editing tool that allows scientists to make precise changes to DNA. The team brought in a human equivalent of a worm gene change that was found to be likely to cause disease. The change involved only a single building block of the worm's version of polycystin-2.

The experiment revealed a major change in the altered protein. The amount of altered polycystin-2 in the main part of the nerve cell dropped to about 15% of the normal level. Most importantly, the protein could not be found in the cilia where it normally works. This meant that the issue wasn't just a change in the protein. It was also not getting to its proper place within the cell.

The damage also affected its partner protein

The researchers found another problem inside these modified worms. The level of the protein polycystin-1, which functions with the protein polycystin-2, also decreased significantly. It was also lacking in the cilia. This suggested that changing one member of the protein partnership could affect the other, disrupting a system that normally depends on both. These changes were also reflected in the behavior of animals. Male C. elegans use signals detected by their nerve cells to locate and mate with hermaphrodites, the primary reproductive form of the species.

In the experiment, only 20 percent of males with the altered gene initiated the typical mating behavior after meeting a partner. All the normal males in the comparison group showed the expected behavior. Researchers tested 60 males in each group. This gave the team a way to connect what was happening inside individual cells with a measurable change in the animals' behavior.

A healthy gene copy made a difference

The next part of the experiment gave a significant result. Researchers wanted to know whether the altered protein could also interfere with a healthy version of the same protein. They inserted both versions into the same worm, and then traced them with different fluorescent dyes. The altered protein glowed green, whereas the healthy protein glowed red. The healthy protein had still reached the cilia and was still functioning normally. The altered protein was still not able to get to its target. Mating tests with the worms also showed that they were normal. This indicated that while one normal gene copy could handle the functions that were tested in the experiment, the other copy could be altered.

Why genetic test results need closer examination

Autosomal dominant polycystic kidney disease (ADPKD) affects between one in 400 and one in 1,000 people, according to the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK). The National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) estimates that it affects between one in 400 and one in 1,000 people. Doctors commonly diagnose it between the ages of 30 and 50, when symptoms often begin to appear. In most individuals with the condition, there is a defect in the gene known as PKD1, and in about 1 in 7 or 8, there is a defect in the gene called PKD2. The Rutgers experiment did not produce kidney disease in worms or test a treatment. It showed how scientists can use a living animal to examine what a specific genetic change does to a protein.