Selective developmental regulation of gene expression for insulin-like growth factor-binding proteins in mouse spinal cord

Study Design. Prospective, randomized experimental study in mice. Study Objective. To determine whether insulin-like growth factor binding proteins (IGFBPs) are present in mouse spinal cord and, if so, what role they play in its development. Summary of Background Data. Insulin-like growth factors are well recognized hormonal effectors of growth hormone and are expressed in the mammalian spinal cord. The IGFBPs are a group of six genetically distinct proteins that bind IGFs and modulate their bioactivity. They appear in the brain during development, localize to the neuromuscular junction, and promote motor neuron survival. The benefit of IGF-I in amyotrophic lateral sclerosis ALS and its potential use in preventing motor neuron apoptosis in spinal cord injury dictates that studies of the presence and response of IGFBPs in that tissue be performed. Methods. The IGFBPs in mouse spinal cord were analyzed by Western ligand blot, Western immunoblot, and reverse transcription- polymerase chain reaction at various time points from embryonic day 14 to postnatal day 30. Results. Three IGFBPs with molecular masses of 24, 28, and 32 kDa were found, the latter two being the most prominent. The data indicate that these are IGFBP-4, -5, and -2. Conclusion. Both IGFBP-2 and BP-5 are developmentally regulated in mouse spinal cord, with higher levels of those at early embryonic stages indicating their potential role in development of the mouse spinal cord.