Huntingtin-associated protein 1 interacts with Ahi1 to regulate cerebellar and brainstem development in mice
Guoqing Sheng, Xingshun Xu, Yung-Feng Lin, Chuan-En Wang, Juan Rong, Dongmei Cheng, Junmin Peng, Xiaoyan Jiang, Shi-Hua Li, Xiao-Jiang Li
Guoqing Sheng, Xingshun Xu, Yung-Feng Lin, Chuan-En Wang, Juan Rong, Dongmei Cheng, Junmin Peng, Xiaoyan Jiang, Shi-Hua Li, Xiao-Jiang Li
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Huntingtin-associated protein 1 interacts with Ahi1 to regulate cerebellar and brainstem development in mice

Abstract

Joubert syndrome is an autosomal recessive disorder characterized by congenital malformation of the cerebellum and brainstem, with abnormal decussation in the brain. Mutations in the Abelson helper integration site 1 gene, which encodes the protein AHI1, have been shown to cause Joubert syndrome. In this study, we found that mouse Ahi1 formed a stable complex with huntingtin-associated protein 1 (Hap1), which is critical for neonatal development and involved in intracellular trafficking. Hap1-knockout mice showed significantly reduced Ahi1 levels, defective cerebellar development, and abnormal axonal decussation. Suppression of Ahi1 also decreased the level of Hap1; and truncated Ahi1, which corresponds to the mutations in Joubert syndrome, inhibited neurite outgrowth in neuronal culture. Reducing Hap1 expression suppressed the level and internalization of TrkB, a neurotrophic factor receptor that mediates neurogenesis and neuronal differentiation, which led to decreased TrkB signaling. These findings provide insight into the pathogenesis of Joubert syndrome and demonstrate the critical role of the Ahi1-Hap1 complex in early brain development.

Authors

Guoqing Sheng, Xingshun Xu, Yung-Feng Lin, Chuan-En Wang, Juan Rong, Dongmei Cheng, Junmin Peng, Xiaoyan Jiang, Shi-Hua Li, Xiao-Jiang Li

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Figure 6

Hap1 deficiency decreases the level of TrkB.

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Hap1 deficiency decreases the level of TrkB. (A) Western blot analysis o...
(A) Western blot analysis of cerebellar tissues from WT and Hap1-KO mice showing the decreased level of TrkB. Western blotting also shows decreased Ahi1 and TrkB in the absence of Hap1 in brainstem tissue. (B) Densitometry of the ratio of TrkB to tubulin in WT and KO cerebellum or brainstem. *P < 0.05. (C) Inhibition of Ahi1 in cultured cerebellar neurons by adenoviral siRNA (109 and 1011 PFU/ml at final concentration) reduced the levels of Hap1 and TrkB. Control was adenoviral GFP infection. (D) Western blotting of biotinylated membrane and internalized fractions in cultured brainstem cells showing the decreased level of TrkB when Hap1 expression is suppressed by Hap1 siRNA. Control is adenoviral GFP–infected cells. The blots were probed with an antibody against tubulin to normalize the protein amount loaded in the gel. (E) The ratios (mean ± SEM; n = 4) of internalized TrkB to tubulin or membrane TrkB in neurons infected with control or Hap1 siRNA virus. *P < 0.05, **P < 0.01 compared with control.