Biology of released protein I: an experimental model murine muscular dystrophy

It has been previously shown that rapidly transported proteins are released from axons in vitro. A model developed to explain the probable function of released proteins states that the proteins released act as signals from the neurons to control Schwann cell activities. To test the validity of this hypothesis I chose to use Rej/129 dystrophic mice which clearly demonstrates that portions of the sciatic nerves display abnormal myelination patterns. For the purpose of this dissertation my objective was to establish if a difference existed between released proteins from nerves of normal mice and those of dystrophic mice, moreover to investigate these potential differencs.

Electrophoresis on Tris gels of protein released from nerves of several species including the mouse show consistent patterns of three bands having R(,f) values of 0.84, 0.89 and 0.98. Separation on tris gels of released proteins from dystrophic mice reveal that the 0.89 band is missing. To demonstrate that the 0.89 protein as well as the 0.84 and 0.98 proteins are transported from the cell body down the axon and therefore are neuronal in origin, spinal cords of mice were injected with {('3)H}leucine. Electrophoresis and scintillation counting of these radiolabelled proteins released from normal mice nerves reveals that these three proteins are present and labelled, therefore they are transported down the axon prior to release. Separation of the radiolabeled proteins released from dystrophic nerves indicated little radioactivity at R(,f) 0.89 which is consistent with desitometric scans of the electrophoretic gels. To further substantiate these results it was decided to utilize the more sensitive double label isotope technique. An unexpected result from the use of this procedure was the appearance of a substantial new peak at R(,f) 0.79. Upon re-examination of the densitometric tracings of stained gels containing released proteins from nerves of dystrophic mice a small peak was noted constituting 2-3% of the protein on the gel. Previously we considered this band insignificant and it did not match any protein bands found in normal animals.

In line with the original objective of this research these results show: (1) there is a consistent pattern of proteins released from nerves of all species investigated having R(,f) values of 0.84, 0.89 and 0.98, (2) the 0.89 band is missing in dystrophic mice, (3) all three bands are transported, and (4) although the dystrophic model demonstrated the loss of the 0.89 band there is an appearance of a new band at 0.79. From these results it is concluded that a difference exists between proteins released from the nerves of normal dystrophic mice. This difference is the loss of 0.89 protein and the appearance of the 0.79 band. Because both bands constitute the same relative proportions (2-3%) on densitometric scans of released protein it is suspected that the 0.89 protein has been altered such that it has an R(,f) value of 0.79 in the dystrophic model and therefore reflects a biochemical alteration in the mutant.