Analysis of chicken genome offers new insights

The first detailed analysis of the chicken genome has identified a chicken counterpart to an important human immune system protein and revised scientists’ assessment of the chicken’s sense of smell, among other insightful findings.

The analysis, reported in the Dec. 9 issue of Nature by the International Chicken Genome Sequencing Consortium, includes the identification of genes that affirm the chicken’s value as a model for study of developmental disorders like cleft palate and diseases like muscular dystrophy.

Richard Wilson
Richard Wilson

The genome provides several firsts: It is the first bird, the first agricultural animal and the first descendant of the dinosaurs to have its genome sequenced.

The consortium is directed by Richard K. Wilson, Ph.D., director of the Genome Sequencing Center (GSC), professor of genetics and associate professor of molecular microbiology.

Wilson and other project leaders predict that the chicken genome will help biomedical researchers seeking to better understand the human genome in order to improve diagnosis and treatment of human disease.

Scientists found the chicken genome has about the same number of genes as the human genome: 20,000-23,000 versus the human genome’s estimated 20,000-25,000 genes.

However, those genes are contained in only 1 billion DNA base pairs, barely a third of human DNA’s 2.8 billion base pairs.

Scientists identified a chicken gene for interleukin 26, an important immune response protein only previously seen in humans.

Researchers hope that further study of the chicken’s immune system will lead to the development of better ways to control the spread of viruses, such as the bird flu in Asia. These viruses sometimes jump across species and infect humans.

“With both the human and the chicken genome sequences completed, we can ask more questions about what types of resistance to viral infections and other pathogens are possible for humans and chickens,” Wilson said.

The chicken has traditionally been regarded as having a poor sense of smell, but an assessment of the number of smell receptors in the chicken genome has scientists reconsidering.

By function, one area of strong chicken-to-human similarity was in genetic sequences related to early development. Several developmental genes, including genes linked to disorders that cause limb loss or deformity, were found.

“Because it’s so easy to look at and manipulate gene activity as an embryo develops in the egg, scientists often use the chicken in studies of development,” said lead author LaDeana Hillier, GSC senior research scientist.

“The finding that some of these ultraconserved regions are involved in development affirms the chicken as a valuable model for these studies.”

Analysis of the chicken’s telomeres, cap-like structures on the ends of chromosomes, revealed that they are more similar to human telomeres than rodent telomeres.

Scientists believe telomeres shorten the DNA slightly every time a cell divides, eventually making it impossible for the cell to divide. This inability to renew through cell division is thought to be a primary component of the structural and functional breakdowns produced by aging.

Increased telomere similarity may mean that the chicken, already a valuable tool for study of the earliest stages of life, also will become useful for study of its final stages.

Wilson says the chicken genome and other genomes are like Rosetta stones that scientists use to better understand the human genome.

As life on Earth evolved over time, genes have been created, kept, discarded or deactivated, and reorganized. At the particular point in evolutionary time over which a species first develops, these processes may have changed a gene in ways that allow scientists to use it to get a better fix on the human version of the gene.

“For every human gene, there’s a gene in another species that’s going to be most helpful in understanding the human version,” Wilson said.

“For some human genes, we might be able to learn more by looking at the genome of the mouse; for others, we might have to look at the version of the gene found in the chicken.”

Based on their initial look at the chicken genome, scientists have suggested that they may need to alter the proposed starting point for as many as 2,000 human genes.

The International Chicken Genome Sequencing Consor-tium includes scientists from 12 nations.