Regional Distribution of Amyloid β‐Protein Precursor, Growth‐associated Phosphoprotein‐43 and Microtubule‐associated Protein 2 Messenger RNAs in the Nigrostriatal System of Normal and Weaver Mutant Mice and Effects of Ventral Mesencephalic Grafts

Using in situ hybridization histochemistry with [³²P]oligonucleotide probes, we studied the cellular localization of RNA transcripts for amyloid β‐protein precursor (βAPP), growth‐associated phosphoprotein‐43 (GAP‐43) and microtubule‐associated protein 2 (MAP2) in the mesostriatal system of normal (+/+) and weaver wv/wv mutant mice, which lose mesencephalic dopamine neurons. In addition, expression of the same messages was studied in ventral mesencephalic cell suspensions transplanted to the weaver striatum. Transcripts encoding GAP‐43, MAP2 and isoforms βAPP₆₉₅, βAPP₇₁₄ and βAPP₇₅₁ were present in normal substantia nigra and progressively reduced in weaver substantia nigra; such a reduction was correlated with dopamine neuron loss. The survival of dopamine neurons in unilateral intrastriatal grafts was documented by methamphetamine‐induced rotational asymmetry tests and by tyrosine hydroxylase immunocytochemistry. High hybridization signals were obtained for GAP‐43, MAP2, βAPP₆₉₅, βAPP₇₁₄ and βAPP₇₅₁ RNA transcripts in the grafted tissue; the βAPP₇₇₀ species‐normally seen in striatum and not substantia nigra‐was not expressed in the grafts, but it was present in the recipient striatum. Following immunocytochemical labelling with antibodies, GAP‐43 and MAP2 immunoreactivities were seen in cell processes in the grafts and surrounding tissue, whereas βAPP immunoreactivity was mainly found in grafted cell bodies. These results suggest that the transplanted mesencephalic cells mature very similarly to those in the normal substantia nigra, expressing different mRNAs that are normally present in the ventral midbrain and which are reduced in the weaver mutant as a consequence of dopamine neuron loss.