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 7

Hap1 deficiency decreases TrkB internalization and signaling.

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Hap1 deficiency decreases TrkB internalization and signaling. (A) Double...
(A) Double immunostaining of cultured brainstem cells (at 14 DIV) that had been infected with adenoviral GFP (top row) or adenoviral Hap1 siRNA with GFP (bottom row). Note that cells expressing Hap1 siRNA (green) show a decrease in the amount of internalized biotin-labeled BDNF compared with a noninfected cell or adenoviral GFP–infected cell. (B) Double immunostaining of cultured brainstem cells from WT (top row) and Hap1-KO (bottom row) pups also shows the decreased Hap1 and internalization of biotin-BDNF. The cells were stained with rabbit anti-Hap1 and mouse anti-biotin. Statistical results are described in the text. Scale bars in A and B: 5 μm. (C) Decreased phosphorylation of Erk and Akt in cultured brainstem cells infected by adenoviral Hap1 siRNA. The blots were probed with antibodies against Akt, Erk, and their phosphorylated forms. (D) The ratio (mean ± SEM; n = 3–4) of phosphorylated Erk or Akt to total Erk or Akt was quantified by densitometry. *P < 0.05, **P < 0.01.