Analysis of the midbrain-hindbrain boundary cell fate using a boundary cell-specific Cre-mouse strain.

We describe here a transgenic mouse line MHB-Cre, which expresses Cre recombinase in a group of cells at the midbrain-hindbrain boundary. Using this mouse line, we studied the contribution of the boundary cells to distinct brain areas during development. Initially, the MHB-Cre expression coincides with that of Cdh22 and p21 around the Otx2 expression border in a narrow population of cells with reduced proliferative activity. Consistent with their location on both sides of the Otx2 expression border, the Cre expressing boundary cells contribute both to midbrain as well as hindbrain. However, the majority of recombinant cells remain close to the mid- and hindbrain border, suggesting very limited cell mixing within these brain compartments during development. Interestingly, dorsocaudally oriented fibers of the midbrain dopaminergic neurons follow the path marked by the boundary cells.