The researchers, to discuss the cloning project this week at the American Association for the Advancement of Science annual meeting, said increasing calcium levels in the fluid surrounding cloned equine embryos proved the key to equine cloning.
Dr Gordon Woods from University of Idaho-Utah State University began to focus on calcium after becoming interested in why horses appear to be more resistant to some forms of cancer. It is not unusual for light-coloured horses to develop melanomas or skin cancers that do not metastasise and the cancer mortality rate for horses is approximately 8 per cent compard to 24 per cent for humans, said Woods.
Blood samples from men and stallions heightened his interest in calcium. Tests showed intracellular calcium concentrations in horse red blood cells were 2.3 times less than in human red blood cells. Extracellular calcium concentrations were reversed, with 1.5 times greater calcium concentrations outside cells in equines than in humans.
The lower concentrations of calcium within horse cells supported a model proposed by Woods. He postulated the equine system was 'slower' physiologically than the human system. The lower cancer rates in equines appeared to support that idea.
Woods connected that hypothesis to embryonic development. "There are electrifying similarities between cancer metastasis and embryo division," he commented.
The researcher and his team agreed to try stimulating embryonic development by increasing calcium concentrations in the surrounding medium. The results were immediate, Woods said, generating a seven-fold increase in the two-week pregnancy rate of transferred clone embryos.
Only two pregnancies lasted two weeks without manipulating calcium levels. Nineteen pregnancies lasted two weeks or more with calcium treatments. Of 21 pregnancies detected at two weeks, 11 lasted 30 days and five lasted 45 days. Three pregnancies lasted past 60 days, and all of them survived full term and resulted in normal births.
The work also provides insight into calcium's role in cell signaling. As some human diseases progress, calcium levels escalate.
"The connection between calcium and many forms of human disease is well documented," said Dr Woods.
Calcium functions as a universal intracellular messenger, controlling processes as diverse as gene transcription, muscle transcription and cell proliferation, he noted.
A breakdown in calcium regulation is implicated in diseases ranging from cancer to diabetes, heart disease and neurological disorders.