Fig 1. Cre-mediated recombination in the hindbrain activates lacZ expression from the ROSA reporter and abrogates Phospho-Smad immunostaining in conditional Bmpr double knockout mutants.

The Bcre-32 transgenic line induces the expression of lacZ throughout most of the neural tube at 10.5 dpc, except the ventral diencephalon (A, arrow). LacZ expression was detected in the pontine gray nucleus postnatally (B, arrow), and in the inferior olivary nuclei at P0 (C, arrow). In Panel D, a coronal section of 10.5 dpc caudal hindbrain demonstrates that lacZ expression is observed in the region of the dorsal hindbrain that expresses Atoh1, as shown by in situ hybridization in Panel E (compare arrow in E to arrow in D). Panel F demonstrates that phospho-Smad immunolabelled cells were found in the caudal rhombic lip at 11.5 dpc in the normal animals (arrow). However, no phospho-Smad-positive cells were detected in the same region and the same stage in the Bmpr double knockout animals (G, arrow). Panel H demonstrates the expression pattern of Msx2, whose expression is directly downstream of BMP signaling, in a normal 11.5 dpc embryo. In the mutant (Panel I), the expression of Msx2 was not detected in the neural tube. Scale bar: A, 250 μm; C (for B,C), 500 μm; E (for D-I), 50 μm.