Healthy Chickens

Hans H. Cheng, a geneticist at the ARS Avian Disease and Oncology Laboratory in East Lansing, Michigan, worked with Michigan State University's Jerry Dodgson, a microbiologist, to build the chicken genome map. Now, Cheng and his colleagues are using the map to identify resistance genes to Marek's disease. These genes can be used to breed chickens with superior resistance. At the same time, the scientists have made molecular clones of the virus that causes the disease-a crucial first step to building more effective vaccines through biotechnology.

Since the initial sequencing of the chicken genome, many chicken gene sequences have been entered into the National Center for Biotechnology Information's GenBank. This repository is one of the first places researchers look to see whether a gene sequence they are interested in has already been found and entered into the database.

Animal scientist Mark Richards, in the Animal Biosciences and Biotechnology Laboratory at Beltsville, is studying groups of genes involved in basic physiological functions, such as feed-intake regulation and nutrient use in poultry.

Of current interest is the gene that codes for the pancreatic hormone glucagon. Glucagon counterbalances insulin to regulate blood glucose levels in all vertebrates. It works to raise blood glucose that has been lowered by insufficient nutrition or stress.

The glucagon gene codes not only for glucagon, but also for other metabolic hormones, including the glucagon-like peptides 1 and 2 (GLP-1 and GLP-2). Each has unique physiological functions that are distinct from glucagon. Together, glucagon, GLP-1, and GLP-2 are contained in a precursor protein, called "proglucagon."

"The glucagon gene is an interesting one to study because it functions differently in chickens than in other vertebrate species," says Richards. For example, the glucagon gene is active in the pancreas of mammals, but in chickens, it's expressed in high levels in the stomach too. Another difference is the number of precursor proteins produced by the glucagon gene. In chickens and mammals, the gene codes for a precursor protein that contains glucagon, GLP-1, and GLP-2. Richards's team found that in chickens, it codes for an additional protein that contains just glucagon and GLP-1.

"The differences may be linked to the high levels of circulating glucose found in birds, which are more than twice the levels that are found in humans," says Richards. "Such differences may help explain why chickens appear to be more resistant to insulin than mammals."

ARS research is also shedding light on poultry pathogens, such as the parasite Eimeria. Eimeria causes coccidiosis, a disease that costs U.S. poultry producers more than $700 million annually. ARS immunologist Hyun Lillehoj is using genomics to decipher the molecular interactions between poultry and several strains of Eimeria that commonly infect poultry.

Working with her colleagues at the Animal Parasitic Diseases Laboratory in Beltsville, Lillehoj has identified key genes of poultry immune cells that respond to the presence of Eimeria. Some genes encode important cytokines and chemokines, molecules produced by white blood cells to kick-start the immune response after infection. These genes exhibit a heightened response the first time a bird is infected with Eimeria. But in later infections, these same genes have a much more modulated response. Sometimes their activity levels stay the same or even decrease below the levels observed in uninfected birds.

"Understanding how these different intestinal immune cells and molecular signals function in the face of Eimeria infection is a key step in developing new, effective vaccines," Lillehoj says. "These findings will go a long way towards helping us find ways to control coccidiosis without using antibiotics."

Agricultural Reasearch magazine, August 2008 Complete Article