| Several years ago, while attending
a seminar, reproductive physiologist Kurt A. Zuelke, who heads the Beltsville
lab, heard about a new, computerized, digital method for practicing functional
genomics. It's called SAGE (Serial Analysis of Gene Expression), and Zuelke
has since found it to be spectacularly effective for researching livestock
"In terms of today's genetics research, functional genomics is
where the rubber meets the road," says Zuelke. His team is using
SAGE to study alterations in gene expression when turkey sperm are present
Expressed genes are those genes that are "switched on"that
is, making important proteinsat a given time. Using the SAGE method,
the researchers can count the number of RNA transcripts, or copies,
made by expressed genes. Many transcripts signal high expression; few
transcripts suggest low expression.
"The beauty of SAGE is that it counts close to exactly the number
of transcripts of every expressed gene in the entire turkey genome at
a particular moment by using digital technology," says Zuelke.
"If you have 20 transcripts, then in theory you have 20 SAGE tags."
Improving Sperm Preservation
To maintain a fertility rate of 90 percent or more on turkey farms,
each hen is inseminated once a weekwith about 200 to 300 million
sperm each timefor 5 months. Each collected dose of turkey semen
yields about 9 billion to 12 billion sperm per milliliter.
"Lengthening the time that these sperm stay alive outside the
tom would translate into significant savings for the commercial turkey
industry," says Zuelke.
The first breakthrough study was conducted by Zuelke, reproductive
physiologist Julie Long, and ARS researchers at the Bovine Functional
Genomics Laboratory, also in Beltsville.
The scientists ran two SAGE analyses-one on tissue taken from
turkey SSTs when sperm were present and one when sperm were not present.
They reported that more than 214 genes were expressed at different levels
within SSTs when sperm were present compared to when sperm were not
This was the first report in scientific literature that indicated that
the presence or absence of sperm in the reproductive tract could affect
gene expression within the SSTs. The breakthrough lays a foundation
for understanding which proteins are produced from the expressed genes.
"SAGE technology allows us to study thousands of genes simultaneously,
measure their expression, and quickly identify genetic differences between
cells in the presence and absence of sperm," says Zuelke.
During the study, the team found a particular gene, named "avidin,"
which corresponded to a SAGE tag. Avidin had already been identified
and well studied in chickens. Since the SAGE technique had never been
used in poultry before, avidin was chosen to help validate SAGE in turkeys.
"Now that we have the avidin gene, we can use it as a model for
analyzing other genes expressed in the presence of sperm," he says.
Learning which genes are switched on when sperm are present in the
SSTs can help identify which proteins are produced under those special
circumstances. Those proteins could then be put into extenders to help
prolong the life of sperm outside the SSTs.
The scientists consider the milestone of identifying key expressed
genes as opening a door to further research. They hope that their discoveries
will lead to further knowledge that will eventually allow them to freeze
"If we could extend their survival rate to 24 hours, allowing
them to stay viable overnight, that would open wider transportation
and storage options for better reproductive management," says Zuelke.
The newly developed turkey SAGE tag data has been donated to a database
called SAGE-Map, which is maintained by the National Center for Biotechnology
Information, part of the National Institutes of Health, in Bethesda,
Maryland. SAGE-Map is available to both public and private scientists
for further research and can be accessed at www.ncbi.nih.gov.By
Rosalie Marion Bliss,
Agricultural Research Service Information Staff.
This research is part of Food Animal Production, an ARS National
Program (#101) described on the World Wide Web at www.nps.ars.usda.gov.
Kurt A. Zuelke is
with the USDA-ARS Biotechnology
and Germplasm Laboratory, Bldg. 200, Room 124, BARC-East, 10300
Baltimore Ave., Beltsville, MD 20705-2350; phone (301) 504-5161, fax
"Revolutionizing Turkey Production: Functional genomics is
the driving force" was published in the September
2004 issue of Agricultural Research magazine.