By disabling its genes, U geneticist Mario Capecchi and postdoctoral fellow Deneen Wellik created a mouse with a rib cage similar to a snake’s.
The mouse has ribs all the way to the end of its tail.
The findings may lead to a better understanding of skeletal birth defects in humans.
The study shows why mammals, including humans, don’t need the extra ribs.
The study is a blueprint of our physical evolution.
Capecchi’s work indicates which genes control what parts of the body, helping doctors discover why some babies are born with limb abnormalities.
Capecchi’s study was published this summer in the journal Science and shows that less ribs allow mammals to be faster and more agile, important both as prey and as predator.
Less ribs also allowed for development of sacral vertebrae and the pelvis, making mammal reproduction possible.
Using his “gene targeting” method, Capecchi disabled different genes in a mouse.
By doing this, he discovered which genes helped form limbs.
According to Wellik, the coding regions of these genes are more than 95 percent identical between mouse and human.
Because these genes are identical, it is likely that an abnormality created by a gene in a mouse would create a similar abnormality in a human.
A mouse with the “Hox10” genes disabled can show abnormalities, such as malformed legs or missing kneecaps.
That gene, therefore, is attributed to developing the upper leg, according to the research.
A human with a mutated gene might suffer from an incorrectly formed thigh bone.
Capecchi discovered the lower leg forms under the control of different genes, named “Hox11.” A mutated Hox11 gene in a human could cause abnormally sized or missing toes.
Capecchi disabled an entire family of genes to create the mouse with ribs all the way to its tail. The study concluded that 16 of the 39 genes found in mammals play an important role in the evolution of the vertebrate.
By identifying each of these genes, scientists have a better understanding of how human limbs and spines function.
These findings may have important implications in understanding how many skeletal birth defects in humans occur.
One out of every 1,000 babies is born with some limb defect, Wellik said.
Capecchi has been both nationally and internationally recognized through numerous awards for his contributions to the medical and science fields, including the National Medal of Science and the Wolf Prize in Medicine.
Wellik is pursuing gene research at the University of Michigan Medical School this fall.