Abstract

Motor pools comprise a heterogeneous population of motor neurons that innervate distinct intramuscular targets. While the organization of motor neurons into motor pools has been well described, the time course and mechanism of motor pool diversification into functionally distinct classes remains unclear. γ-Motor neurons (γ-MNs) and α-motor neurons (α-MNs) differ in size, molecular identity, synaptic input and peripheral target. While α-MNs innervate extrafusal skeletal muscle fibers to mediate muscle contraction, γ-MNs innervate intrafusal fibers of the muscle spindle, and regulate sensitivity of the muscle spindle in response to stretch. In this study, we find that the secreted signaling molecule Wnt7a is selectively expressed in γ-MNs in the mouse spinal cord by embryonic day 17.5 and continues to molecularly distinguish γ-from α-MNs into the third postnatal week. Our data demonstrate that Wnt7a is the earliest known γ-MN marker, supporting a model of developmental divergence between α- and γ-MNs at embryonic stages. Furthermore, using Wnt7a expression as an early marker of γ-MN identity, we demonstrate a previously unknown dependence of γ-MNs on a muscle spindle-derived, GDNF-independent signal during the first postnatal week.

Links

Publisher Full Text

Authors

Ashrafi S, Lalancette-Hébert M, Friese A, Sigrist M, Arber S, Shneider NA, Kaltschmidt JA

Institution

Neuroscience Program, Weill Cornell Medical College, New York, New York 10065, USA.

Source

The Journal of neuroscience : the official journal of the Society for Neuroscience 32:25 2012 Jun 20 pg 8725-31

MeSH

Animals
Biological Markers
Cell Size
Cell Survival
Female
Glial Cell Line-Derived Neurotrophic Factor
Immunohistochemistry
Mice
Mice, Knockout
Motor Neurons, Gamma
Muscle Spindles
Pregnancy
Signal Transduction
Spinal Cord
Wnt Proteins

Pub Type(s)

Journal Article
Research Support, N.I.H., Extramural
Research Support, Non-U.S. Gov't

Language

eng

PubMed ID

22723712