Histone lysine methyltransferase Pr-set7/SETD8 promotes neural stem cell reactivation

The ability of neural stem cells (NSCs) to switch between quiescence and proliferation is crucial for brain development and homeostasis. Increasing evidence suggest that variants of histone lysine methyltransferases including KMT5A are associated with neurodevelopmental disorders. However, the function of KMT5A/Pr-set7/SETD8 in the central nervous system is not well established. Here, we show that Drosophila Pr-Set7 is a novel regulator of NSC reactivation. Loss-of-function of pr-set7 causes a delay in NSC reactivation and loss of H4K20 monomethylation in the brain. Through NSC-specific in vivo profiling, we demonstrate that Pr-set7 binds to the promoter region of cyclin dependent kinase 1 (cdk1) and Wnt pathway transcriptional co-activator earthbound1/jerky (ebd1). Further validation indicates that Pr-set7 is required for the expression of cdk1 and ebd1 in the brain. Similar to Pr-set7, Cdk1 and Ebd1 promote NSC reactivation. Moreover, Cdk1 upregulates the Ebd1 levels in NSCs, while Ebd1 appears to downregulate Cdk1 expression, suggesting a negative feedback regulation. Finally, overexpression of Cdk1 and Ebd1 significantly suppressed NSC reactivation defects observed in pr-set7-depleted brains. Therefore, Pr-set7, the sole H4K20 methyltransferase, promotes NSC reactivation through regulating Wnt signaling and cell-cycle progression. Given the conservation of Pr-set7, our findings may contribute to the understanding of mammalian KMT5A/PR-SET7/SETD8 in NSC proliferation and associated neurodevelopmental disorders. Overall design: Examination of gene regions targeted by Pr-set7 in NSCs. Two batches of experiments were conducted. In each batch, one control (UAS-Dam) and one gene-of-interest (UAS-Dam-Pr-set7) were included. UAS contructs were induced under NSC-specific driver, grh-Gal4. Dam-Pr-set7 then bound to DNA and methylated adenines (m6A) at the nearby GATC motifs. By examining the DNA methlyation status through next generation sequencing, Pr-set7 target regions could be identified.