Messenger RNAs from chick muscle encode a motoneuronal survival-promoting factor.

The survival of motoneurons requires a trophic factor derived from the target muscles, but the nature of this trophic factor is not known. We examined whether skeletal muscle expresses mRNAs encoding survival-promoting factors for motoneurons. Messenger RNAs were purified from hindlimbs of chick embryos and injected into Xenopus oocytes for translation. The media conditioned by incubation of the injected oocytes were applied to chick embryos during the natural cell death period of lumbar motoneurons. This procedure significantly reduced the magnitude of natural motoneuronal death. The conditioned media also promoted the survival of motoneurons cultured from chick embryos.