Covalent chemical modifications of cellular RNAs directly impact all biological processes. However, our mechanistic understanding of the enzymes catalyzing these modifications, their substrates and biological functions, remains vague. Amongst RNA modifications N 6-methyladenosine (m 6 A) is widespread and found in messenger (mRNA), ribosomal (rRNA), and noncoding RNAs. Here, we undertook a systematic screen to uncover new RNA methyltransferases. We demonstrate that the methyltransferase-like 5 (METTL5) protein catalyzes m 6 A in 18S rRNA at position A 1832. We report that absence of Mettl5 in mouse embryonic stem cells (mESCs) results in a decrease in global translation rate, spontaneous loss of pluripotency, and compromised differentiation potential. METTL5-deficient mice are born at non-Mendelian rates and develop morphological and behavioral abnormalities. Importantly, mice lacking METTL5 recapitulate symptoms of patients with DNA variants in METTL5, thereby providing a new mouse disease model. Overall, our biochemical, molecular, and in vivo characterization highlights the importance of m 6 A in rRNA in stemness, differentiation, development, and diseases.
SummaryThe RING E3 ubiquitin ligase UHRF1 controls DNA methylation through its ability to target the maintenance DNA methyltransferase DNMT1 to newly replicated chromatin. DNMT1 recruitment relies on ubiquitylation of histone H3 by UHRF1; however, how UHRF1 deposits ubiquitin onto the histone is unknown. Here, we demonstrate that the ubiquitin-like domain (UBL) of UHRF1 is essential for RING-mediated H3 ubiquitylation. Using chemical crosslinking and mass spectrometry, biochemical assays, and recombinant chromatin substrates, we show that the UBL participates in structural rearrangements of UHRF1 upon binding to chromatin and the E2 ubiquitin conjugating enzyme UbcH5a/UBE2D1. Similar to ubiquitin, the UBL exerts its effects through a hydrophobic patch that contacts a regulatory surface on the “backside” of the E2 to stabilize the E2-E3-chromatin complex. Our analysis of the enzymatic mechanism of UHRF1 uncovers an unexpected function of the UBL domain and defines a new role for this domain in DNMT1-dependent inheritance of DNA methylation.
Recently, covalent modifications of RNA, such as methylation, have emerged as key regulators of all aspects of RNA biology and have been implicated in numerous diseases, for instance, cancer. Here, we undertook a combination of in vitro and in vivo screens to test 78 potential methyltransferases for their roles in hepatocellular carcinoma (HCC) cell proliferation. We identified methyltransferase-like protein 6 (METTL6) as a crucial regulator of tumor cell growth. We show that METTL6 is a bona fide transfer RNA (tRNA) methyltransferase, catalyzing the formation of 3-methylcytidine at C32 of specific serine tRNA isoacceptors. Deletion of Mettl6 in mouse stem cells results in changes in ribosome occupancy and RNA levels, as well as impaired pluripotency. In mice, Mettl6 knockout results in reduced energy expenditure. We reveal a previously unknown pathway in the maintenance of translation efficiency with a role in maintaining stem cell self-renewal, as well as impacting tumor cell growth profoundly.
Abstract. STELLA is a robotic observatory with two fully automatic telescopes (STELLA-I and STELLA-II) located at the Teide Observatory in Tenerife, Spain. Not only the telescopes are automatic but also the entire observatory, no human presence is needed for observing -not even in remote control. STELLA-I supports a high-resolution, fiber-fed and benchmounted echelle spectrograph and a wide-field CCD imaging photometer while STELLA-II feeds a similar but wide-band imaging photometer and a testbed for prototype adaptive optics for robotic telescopes. The first telescope is scheduled for first light in
Genome-wide DNA demethylation is a unique feature of mammalian development and naïve pluripotent stem cells. Here, we describe a recently evolved pathway in which global hypomethylation is achieved by the coupling of active and passive demethylation. TET activity is required, albeit indirectly, for global demethylation, which mostly occurs at sites devoid of TET binding. Instead, TET-mediated active demethylation is locus-specific and necessary for activating a subset of genes, including the naïve pluripotency and germline marker Dppa3 (Stella, Pgc7). DPPA3 in turn drives large-scale passive demethylation by directly binding and displacing UHRF1 from chromatin, thereby inhibiting maintenance DNA methylation. Although unique to mammals, we show that DPPA3 alone is capable of inducing global DNA demethylation in non-mammalian species (Xenopus and medaka) despite their evolutionary divergence from mammals more than 300 million years ago. Our findings suggest that the evolution of Dppa3 facilitated the emergence of global DNA demethylation in mammals.
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