Brain-derived proteins that rescue spinal motoneurons from cell death in the chick embryo: comparisons with target-derived and recombinant factors.

Spinal motoneurons that normally die during early development can be rescued by a variety of purified growth or neurotrophic factors and target tissue extracts. There is also indirect evidence that brain or supraspinal afferent input may influence lumbar motoneuron survival during development and that this effect may be mediated by central nervous system-derived trophic agents. This report examines the biological and biochemical properties of motoneuron survival activity obtained from extracts of the embryonic chick brain. Treatment with an ammonium sulfate (25% to 75%) fraction of embryonic day 16 (E16) or E10 brain extracts rescued many spinal motoneurons that otherwise die during the normal period of cell death in vivo (E6 to E10). The same fractions also enhanced lumbar motoneuron survival following deafferentation. There were both similarities and differences between the active fractions derived from brain extracts (BEX) when compared with extracts derived from target muscles (MEX) or with purified neurotrophic factors. Survival activity from E10 BEX was as effective in promoting motoneuron survival as E10 MEX and more effective than astrocyte-conditioned media. Unlike MEX, the active fractions from BEX also rescued placode-derived nodose ganglion cells. In addition, unlike nerve growth factor and brain-derived neurotrophic factor, active BEX fractions did not rescue neural crest-derived dorsal root ganglion cells or sympathetic ganglion neurons. Interestingly, among many cranial motor and other brainstem nuclei examined, only the survival of motoneurons from the abducens nucleus was enhanced by BEX. Active proteins obtained from BEX were further separated by gel filtration chromatography and by preparative isoelectric focusing techniques. Activity was recovered in a basic (pI 8) and an acidic (pI 5) small molecular weight protein fraction (20 kD or less). The specific activity of the basic fraction was increased x66 when compared with the specific activity of crude BEX, and the basic fraction had a slightly higher specific activity than the acidic fraction. The biological and biochemical properties of these fractions are discussed in the context of known neurotrophic factors and their effects on normal and lesion-induced motoneuron death during development.