Different congenital hydrocephalus-associated mutations in Trim71 impair stem cell differentiation via distinct gain-of-function mechanisms.

Congenital hydrocephalus (CH) is a common neurological disorder affecting many newborns. Imbalanced neurogenesis is a major cause of CH. Multiple CH-associated mutations are within the RNA-binding domain of Trim71, a conserved, stem cell-specific RNA-binding protein. How these mutations alter stem cell fate is unclear. Here, we show that the CH-associated mutations R595H and R783H in Trim71 accelerate differentiation and enhance neural lineage commitment in mouse embryonic stem cells (mESCs), and reduce binding to mRNAs targeted by wild-type Trim71, consistent with previous reports. Unexpectedly, however, each mutant binds an ectopic and distinct repertoire of target mRNAs. R595H-Trim71, but not R783H-Trim71 nor wild-type Trim71, binds the mRNA encoding β-catenin and represses its translation. Increasing β-catenin by overexpression or treatment with a Wnt agonist specifically restores differentiation of R595H-Trim71 mESCs. These results suggest that Trim71 mutations give rise to unique gain-of-function pathological mechanisms in CH. Further, our studies suggest that disruption of the Wnt/β-catenin signaling pathway can be used to stratify disease etiology and develop precision medicine approaches for CH.