Tet Controls Axon Guidance in Early Brain Development through Glutamatergic Signaling

Abstract

AbstractMutations in human TET proteins have been found in individuals with neurodevelopmental disorders. Here we report a new function of Tet in regulatingDrosophilaearly brain development. We found that mutation in the Tet DNA-binding domain (TetAXXC) resulted in axon guidance defects in the mushroom body (MB). Tet is required in early brain development during the outgrowth of MB β axons. Transcriptomic study shows that glutamine synthetase 2 (Gs2), a key enzyme in glutamatergic signaling, is significantly downregulated in theTetAXXCmutant brains. CRISPR/Cas9 mutagenesis or RNAi knockdown of Gs2 recapitulates theTetAXXCmutant phenotype. Surprisingly, Tet and Gs2 act in the insulin-producing cells (IPCs) to control MB axon guidance, and overexpression of Gs2 in these cells rescues the axon guidance defects ofTetAXXC. TreatingTetAXXCwith the metabotropic glutamate receptor antagonist MPEP can rescue while treating with glutamate enhances the phenotype confirming Tet function in regulating glutamatergic signaling.TetAXXCand theDrosophilahomolog ofFragile X Messenger Ribonucleoprotein proteinmutant (Fmr13) have similar axon guidance defects and reduction in Gs2 mRNA levels. Interestingly, overexpression of Gs2 in the IPCs also rescues theFmr13phenotype, suggesting functional overlapping of the two genes. Our studies provide the first evidence that Tet can control the guidance of axons in the developing brain by modulating glutamatergic signaling and the function is mediated by its DNA-binding domain.