The fact that, despite reduced Cxcl12 signaling from the meninges in Foxc1hith/hith mice, we do not see any major disruption of CRC distribution might be best explained by the hypomorphic nature of the hith allele and incomplete loss of Cxcl12 signaling in the meninges early in development. The gene discussed is CXCL12; the disease is colorectal carcinoma.