A mouse model for tracking nigrostriatal dopamine neuron axon growth.

The midbrain dopaminergic system, which consists of neurons of the substantia nigra and the ventral tegmental area, is a subject of intense interest, since the loss of neurons from the substantia nigra results in motor disorders characteristic of Parkinson's disease. We have generated a knock-in reporter mouse line with the tau-lacZ fusion gene inserted into the Pitx3 locus via homologous recombination. This approach permitted the visualisation of midbrain specific dopaminergic axonal tracts from both the substantia nigra and the ventral tegmental area in phenotypically normal heterozygous Pitx3-taulacZ brain tissues, either in situ or following culture in vitro, by a simple and sensitive beta-galactosidase enzyme reaction. Thus the Pitx3-taulacZ mice could serve as a valuable tool for the identification of molecules regulating midbrain dopaminergic neuritogenesis, either in vivo in combination with genetic manipulation in mice, or in vitro using organ cultures.