Lawrence B. Salkoff, Ph.D., professor of neurobiology and of genetics, has received a four-year $1.2 million grant from the National Institute of Diabetes and Digestive and Kidney Diseases. He is taking a novel approach to studying the genes that encode certain bioelectronic components of the nervous system.
"This is the first attempt to use the complete DNA sequence of a multicellular organism to create a comprehensive picture of potassium channels in a single animal," Salkoff said. "Before this, we were like the blind man feeling one small part of an elephant. Now we hope to obtain a complete picture of all of the components necessary to make a nervous system function."
Potassium channels are membrane-associated proteins that function as electronic switches; when open, potassium usually flows out of the cell, altering the difference in electrical charge between its interior and exterior. Such ion movements enable nerve cells to transmit and process information, while defects in ion regulation underlie many disorders of nerve and muscle.
Salkoff and his colleagues are mining data from the University's Genome Sequencing Center, which is determining the complete DNA sequence of a roundworm called Caenorhabditis elegans. This DNA sequence contains the instructions both to build the animal and to regulate its physiological functioning. By year's end, the center will have determined the complete DNA sequence of all one hundred million base pairs that constitute the entire genome.
By analyzing the data, Salkoff and his colleagues have identified 80 genes encoding potassium channels, and there may be more to come.
The 80 genes fall into families, all of which are present in mammals and many even in the simplest animals with a nervous system, such as jellyfish. "This suggests that the basic components of the nervous system evolved a billion years ago," Salkoff said. "They're the fundamental components that make the nervous systems of all animals on earth function."
The gene families have persisted and expanded in mammals, suggesting that evolution has generated variations on a theme rather than designing totally new components. These similarities make the worm useful for clinically relevant research.
However, the functions of most of the 80 genes are not yet known. Therefore, Salkoff intends to study the collection systematically. To see when and where a gene normally becomes active, he tags its regulatory region with the gene for green fluorescent protein. If that gene is expressed in a particular tissue, the tissue will have a green glow easily visible through the worm's transparent body. Salkoff and colleagues will obtain additional clues about function by the expression of each channel gene in the eggs of frogs. Experiments then can determine how that particular channel changes the electrical properties of the frog egg membrane.
Salkoff and his colleagues have already made some surprising findings. For example, it was discovered that some of the roundworm's potassium channel genes are expressed in just a few cells. In one instance, one gene has most of its expression limited to a single cell. "If such patterns of expression prove to be similar in the human nervous system, it will mean that many human potassium channels with limited patterns of expression are still waiting to be discovered," Salkoff said. "So there will be a huge resource to explore."
Salkoff hopes his C. elegans project will set a precedent for using the human sequence data that now is coming off the press. "One of our ideas is to show how human genome data will be useful in obtaining a comprehensive picture of an entire gene family," he said.
