The Abelson-helper integration site 1 ( AHI1 ) gene encodes for a ciliary transition zone localizing protein that when mutated causes the human ciliopathy, Joubert syndrome. We prepared and examined neuronal cultures derived from male and female embryonic Ahi1 +/+ and Ahi1 –/– mice (littermates) and found that the distribution of ciliary melanin-concentrating hormone receptor-1 (MchR1) was significantly reduced in Ahi1 –/– neurons; however, the total and surface expression of MchR1 on Ahi1 –/– neurons was similar to controls ( Ahi1 +/+). This indicates that a pathway for MchR1 trafficking to the surface plasma membrane is intact, but the process of targeting MchR1 into cilia is impaired in Ahi1-deficient mouse neurons, indicating a role for Ahi1 in localizing MchR1 to the cilium. Mouse Ahi1 –/– neurons that fail to accumulate MchR1 in the ciliary membrane have significant decreases in two downstream MchR1 signaling pathways [cAMP and extracellular signal-regulated kinase (Erk)] on MCH stimulation. These re...