New Insights into Limb Formation

Significantly, these discoveries were made using a novel mouse model in which the production of HA is blocked in a tissue-specific manner.

The Yamaguchi laboratory genetically modified the Has2 gene, which is a critical enzyme for HA synthesis, so that the gene can be “conditionally” disrupted in mice. This is the first time a conditional Has2 knockout mouse has been created, a breakthrough that opens vast possibilities for future research. The paper was published online in the journal Development on July 24.

HA is a large sugar molecule that is produced by every cell in the body and has been thought to play a role in joint disease, heart disease and invasive cancers. Yu Yamaguchi, M.D., Ph.D., a professor in the Sanford Children’s Health Research Center at Burnham and Robert Kosher, Ph.D., a professor in the Center for Regenerative Medicine and Skeletal Development at U.C.H.C. and colleagues showed that transgenic mice, in which Has2 was inactivated in the limb bud mesoderm, had shortened limbs, abnormal growth plates and duplicated bones in the fingers and toes.

“Because hyaluronic acid is so prevalent in the body, it has been difficult to study,” said Dr. Yamaguchi. “Systemic Has2 knockout mice died mid-gestation and could not be used to study the role of HA in adults. By inactivating Has2 in specific tissues, we give ourselves the opportunity to study the many roles HA plays in biology. This mouse model will be useful to study the role of HA in various age-related diseases and conditions, such as arthritis and skin aging, as well as cancer.”

To create the conditional knockout mice, the Yamaguchi laboratory genetically engineered the Has2 gene to create the Has2flox allele. The team then added the Prxl1-Cre transgene, which is associated with early limb bud mesenchyme to produce the conditional Has2 knockout mice.

The research was funded by grants from the National Institutes of Health.

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Burnham Institute for Medical Research is dedicated to discovering the fundamental molecular causes of disease and devising the innovative therapies of tomorrow. Burnham, with operations in California and Florida, is one of the fastest-growing research institutes in the country. The institute ranks among the top four institutions nationally for NIH grant funding and among the top 25 organizations worldwide for its research impact. For the past decade (1999-2009), Burnham ranked first worldwide in the fields of biology and biochemistry for the impact of its research publications (defined by citations per publication), according to the Institute for Scientific Information.

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