The study found that when a development gene named Hoxb1 worked in a mouse's brain but not in the developing facial tissues, nerves extended outward from the brain but failed to reach the facial muscles, leaving the mouse unable to blink its eyes, flatten its ears or make other facial movements.
"The question is how the nerves form a circuit from the brain to the target tissue and back to the brain" as an embryo develops, says Mario Capecchi, professor and co-chair of human genetics at the University of Utah School of Medicine and an investigator for the Howard Hughes Medical Institute.
The new study "is the first time it has been shown that the same genes involved in making the nerves that go from the brain to the face also are found in the cells making the tissues of the face," Capecchi says. "That might be a way nerves know where to go and then recognize the target tissue" within facial muscles.
Because mice are so similar genetically to other mammals, the findings in mice likely hold true in humans, he adds.
Benjamin Arenkiel, a human genetics doctoral student who conducted the research under Capecchi's supervision, says the study shows "Hoxb1 is involved in generating the nerves that go to the face as well as the facial tissues themselves. Hoxb1 helps the brain get wired to and control the muscles of the face."
Arenkiel adds: "If this gene controls the nerves and the targets facial tissues this simple genetic code also might work to wire up the body from head to foot. Other Hox genes may act along the length of the body to control nerve circuits at each particular level of the body."
Capecchi agrees: "You are using the same gene outside and inside the brain to allow nerves to make the appropriate cir