Huntingtin-associated protein 1 interacts with Ahi1 to regulate cerebellar and brainstem development in mice
Guoqing Sheng, … , Shi-Hua Li, Xiao-Jiang Li
Guoqing Sheng, … , Shi-Hua Li, Xiao-Jiang Li
Published July 17, 2008
Citation Information: J Clin Invest. 2008;118(8):2785-2795. https://doi.org/10.1172/JCI35339.
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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 3

Hap1 and Ahi1 stabilize each other.

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Hap1 and Ahi1 stabilize each other. (A) Western blots showing that a lac...
(A) Western blots showing that a lack of Hap1 reduces the level of Ahi1 in Hap1-KO mouse brain. (B) Immunostaining of the hypothalamus (Hyp) and amygdala (Amy) from WT and Hap1-KO mice also shows a decreased level of Ahi1 in the absence of Hap1. Original magnification, ×50. (C and D) Immunofluorescence images showing the lack of cytoplasmic Ahi1 puncta in neurons of the hypothalamus (C) and brainstem (D) in Hap1-KO mice. Scale bars: 5 μm. (E) Transfection of Hap1A or Hap1B into N2A cells increases the level of endogenous Ahi1. The relative levels (mean ± SEM; n = 4) of Ahi1 (the ratio of Ahi1 to tubulin on the same blot) are presented below the blots. **P < 0.01 compared with control. (F) Overexpression of different doses of Ahi1 in PC12 cells. Note that increasing Ahi1 expression also increases the level of endogenous Hap1. (G) The ratio (mean ± SEM; n = 3) of Hap1A or Hap1B to tubulin in cells transfected with different amounts (0.3–2.4 μg) of Ahi1 cDNA. *P < 0.05, **P < 0.01 compared with nontransfected cells (0 μg).