492B Poster - 06. Regulation of gene expression
Friday April 08, 2:00 PM - 4:00 PM

Authors:
Hiep Tran; Badri Nath Singh; Joseph Kramer; Ruth Steward

Affiliation: Waksman Institute, Rutgers University

Keywords:
j. epigenetics; a. axon guidance

Tet (Ten-eleven translocation) is one of the most important epigenetic regulators. In vertebrates, TET1/2/3 control demethylation DNA to activate gene transcription. Both vertebrates and Drosophila Tet can also hydroxymethylate cytosine in mRNA (5hmrC). Our recent results show that Drosophila Tet is essential for viability and that the protein plays crucial roles in brain and muscle development. Further Tet binds to 2,500 genes and appears to deposit the 5hmrC modification to their mRNAs thereby enhancing their translation levels. In this study, we found that Tet is required for mushroom body axon outgrowth in the pupal brain. Lack of Tet resulted in β lobe axon crossing the brain midline. By comparing CRISPR/Cas9-induced point mutations in the Tet DNA binding domain (Tet^AXXC) and catalytic domains (Tet^YRA), we discovered that in the DNA binding domain mutant Tet^AXXC the β lobe axons crossed the brain midline. This phenotype was not observed in the catalytic domain mutant Tet^YRA. Surprisingly, in the DNA binding domain mutant, the expression of 1,597 genes in developing pupal brains were increased while the catalytic domain mutant only showed 28 genes up- and 16 genes down-regulated. Comparing these results with Tet ChIP-seq data from our recent study shows that 448 Tet-bound genes are upregulated in the DNA binding domain mutant. The RNA of 444 out of 448 genes do not show 5hmrC modification, indicating a distinct function of the Tet DNA binding and catalytic domains. The genes whose RNA level is increased in Tet^AXXC exhibit low levels or the absence of expression in wild-type brains demonstrating that Tet can suppress gene transcription via its DNA binding domain. Our study depicts a new function of Tet protein; it regulates axon outgrowth via an epigenetic mechanism in which Tet binds DNA and suppresses unwanted gene transcription in the brain, independent of cytosine methylation.