0319 GMT December 11, 2019
In a study published in the US journal Science, researchers at Cincinnati Children's Hospital Medical Center reported that the brain-to-limb nerve connections that endow humans with great hand dexterity are also present in mice at birth, but are suppressed shortly afterward, news.xinhuanet.com wrote.
A protein called PlexA1 is to blame, according to the study led by Yutaka Yoshida of the Division of Developmental Biology at Cincinnati Children's.
Genetically altered mice lacking PlexA1 in corticospinal neurons develop and maintain the so-called cortico-motoneuronal (CM) connections into adulthood, it found.
In a test examining whether CM connections affect hand dexterity, PlexA1 mutant mice were found significantly more skilled and faster than normal mice at grabbing and eating food.
In early human development, expression of PlexA1 is weak in the layer of the brain responsible for the nerve connections, the researchers said, but not in mice during the equivalent period of postnatal growth.
First author Zirong Gu, postdoctoral research scientist at Columbia University, said, "In this paper, we uncover the developmental, cellular, and molecular pathways that give rise to CM connections, and show the impact of CM connections on hand dexterity.
"This data represents a major breakthrough in our understanding of how species-specific corticospinal circuits develop in different mammals.
"It is our hope that it will facilitate the development of future therapies to treat children struggling with fine motor deficits.”
Yoshida noted more research is needed to explore the evolution of the mammalian corticospinal system that leads to greater fine motor control in higher primates including people.
Yoshida said, "It's possible that some patients with motor disabilities have upregulated expression of PlexA1 or activated PlexA1 signaling that diminish cortico-motor-neuron connections and fine motor skills.
"Inhibition of PlexA1 signaling during childhood might be a way to restore these skills."