Focusing on the mHb, the first step of the mHb axons is to grow dorsoventrally, presumably repulsed by semaphorins from the diencephalic alar plates (Funato et al., 2000; Sahay et al., 2003; Kantor et al., 2004) and then attracted by a netrin 1–deleted in colorectal cancer (Ntn1–Dcc) interaction from the ventral region (Funato et al., 2000). This evidence concerns the gene DCC and colorectal cancer.