Weiser, N.E. et al. (2017) International Worm Meeting "MORC-1 integrates nuclear RNAi and transgenerational chromatin architecture to promote germline immortality."

Brown, K.C., Gu, S.G., Yang, D.X., Snyder, M.J., Csankovszki, G., Kalinava, N., Weiser, N.E., Jacobsen, S.E., Kim, J.K., Chan, R.C., Montgomery, T.A., Khanikar, J., Feng, S., Freeberg, M.A.

[International Worm Meeting, 2017]

Germline-expressed endogenous siRNAs (endo-siRNAs) transmit multigenerational epigenetic information to ensure fertility in subsequent generations. In C. elegans, nuclear RNAi ensures robust inheritance of endo-siRNAs and deposition of H3K9me3 marks at target loci. The progressive loss of heterochromatin at endo-siRNA targets in nuclear RNAi mutants is thought to contribute to their mortal germline (Mrt) phenotype. However, the specific mechanisms by which nuclear RNAi mediates heterochromatin deposition and germline maintenance remain to be clarified. We have identified MORC-1, a highly-conserved zinc-finger protein, as a novel factor which links the nuclear RNAi pathway to heterochromatin formation and germline mortality. MORC-1 is essential for transgenerational fertility and acts as an effector of endo-siRNAs. Unexpectedly, MORC-1 is dispensable for siRNA inheritance but required for target silencing and maintenance of siRNA-dependent chromatin organization. To further elucidate the mechanism underlying the Mrt phenotype of morc-1(-) and nuclear RNAi mutants, we performed a forward genetic screen to identify mutations that suppress morc-1(-) Mrt. We identified four mutations in the gene encoding the H3K36 histone methyltransferase MET-1 as potent suppressors of morc-1(-) Mrt. Our finding that morc-1(-) and nuclear RNAi mutants exhibit progressive, MET-1-mediated gain of H3K36 methylation suggests that MORC-1 and nuclear RNAi play an important role in protecting their genomic targets from encroachment of H3K36me3.

Weiser NE et al. (2017) Dev Cell "MORC-1 Integrates Nuclear RNAi and Transgenerational Chromatin Architecture to Promote Germline Immortality."

Khanikar J, Weiser NE, Chan RC, Brown KC, Freeberg MA, Kim JK, Feng S, Jacobsen SE, Montgomery TA, Yang DX, Kalinava N, Csankovszki G, Gu SG, Snyder MJ

[Dev Cell, 2017]

Germline-expressed endogenous small interfering RNAs (endo-siRNAs) transmit multigenerational epigenetic information to ensure fertility in subsequent generations. In Caenorhabditis elegans, nuclear RNAi ensures robust inheritance of endo-siRNAs and deposition of repressive H3K9me3 marks at target loci. How target silencing is maintained in subsequent generations is poorly understood. We discovered that morc-1 is essential for transgenerational fertility and acts as an effector of endo-siRNAs. Unexpectedly, morc-1 is dispensable for siRNA inheritance but is required for targetsilencing and maintenance of siRNA-dependent chromatin organization. A forward genetic screen identified mutations in met-1, which encodes an H3K36 methyltransferase, as potent suppressors of morc-1(-) and nuclear RNAi mutant phenotypes. Further analysis of nuclear RNAi and morc-1(-) mutants revealed a progressive, met-1-dependent enrichment of H3K36me3, suggesting that robust fertility requires repression of MET-1 activity at nuclear RNAi targets. Without MORC-1 and nuclear RNAi, MET-1-mediated encroachment of euchromatin leads to detrimental decondensation of germline chromatin and germline mortality.

Weiser NE et al. (2019) Annu Rev Genet "Multigenerational Regulation of the Caenorhabditis elegans Chromatin Landscape by Germline Small RNAs."

Kim JK, Weiser NE

[Annu Rev Genet, 2019]

In animals, small noncoding RNAs that are expressed in the germline and transmitted to progeny control gene expression to promote fertility. Germline-expressed small RNAs, including endogenous small interfering RNAs (endo-siRNAs) and Piwi-interacting RNAs (piRNAs), drive the repression of deleterious transcripts such as transposons, repetitive elements, and pseudogenes. Recent studies have highlighted an important role for small RNAs in transgenerational epigenetic inheritance via regulation of heritable chromatin marks; therefore, small RNAs are thought to convey an epigenetic memory of genomic self and nonself elements. Small RNA pathways are highly conserved in metazoans and have been best described for the model organism <i>Caenorhabditis elegans</i>. In this review, we describe the biogenesis, regulation, and function of <i>C. elegans</i> endo-siRNAs and piRNAs, along with recent insights into how these distinct pathways are integrated to collectively regulate germline gene expression, transgenerational epigenetic inheritance, and ultimately, animal fertility. Expected final online publication date for the <i>Annual Review of Genetics</i> Volume 53 is November 25, 2019. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Kirshner, J.A. et al. (2019) International Worm Meeting "Investigating a role for MORC-1 in the CSR-1 gene licensing pathway."

Mehta, N., Weiser, N.E., Kirshner, J.A., Kim, J.K., Inoki, K.

[International Worm Meeting, 2019]

In C. elegans, germline gene expression is regulated in part by endogenous small RNA (endo-siRNA) pathways. In particular, nuclear endo-siRNA pathways function to silence pseudogenes, transposons and protein-coding genes not intended for germline expression by inducing heterochromatin formation. An opposing small RNA-mediated pathway also exists to promotegermline gene expression. This pathway is governed by a distinct subset of endo-siRNAs that interact with the essential Argonaute, CSR-1, to promote transcription of target genes. This atypical "gene licensing" RNAi pathway is mechanistically poorly understood. We identified a role for the conserved Zinc-finger ATPase, MORC-1, in maintaining silencing downstream of nuclear RNAi. Unexpectedly, we uncovered a novel role for MORC-1 in the CSR-1 germline gene licensing pathway. MORC-1 physically interacts with CSR-1 and regulates CSR-1 target genes. Furthermore, morc-1 and csr-1 mutants genetically suppress each other. While morc-1(-) mutants display a germline mortal (Mrt) phenotype, in which the worms get progressively less fertile from one generation to the next,morc-1(-) mutants on csr-1 RNAi maintain fertility for many more generations than either single mutant alone. This rescue is accompanied by a restoration of gross germline morphology. We are currently using ChIP-seq to identify the chromatin targets of MORC-1 in purified germline nuclei. Taken together, we propose a mechanism by which the chromatin factor, MORC-1, regulates germline gene expression in both gene silencing and licensing pathways by preserving the proper local chromatin environment.

Julia Grabitzki et al. (2006) European Worm Meeting "Identification of O-linked N-acetylglucosamine Modified Proteins in Caenorhabditis elegans"

Gunter Lochnit, Rudolf Geyer, Michael Ahrend, Brigitte Schmitz, Julia Grabitzki

[European Worm Meeting, 2006]

Julia Grabitzki1, Michael Ahrend2, Brigitte Schmitz2, Rudolf Geyer1 and Gnter Lochnit1. The posttranslational modification N-acetylglucosamine O-glycosidically linked (O-GlcNAc) to serine and threonine residues of proteins has been shown to be ubiquitous amongst eukaryotic proteins of the nucleus, cytoskeleton, cytoplasm, and has also been detected on cytosolic tails of membrane proteins [1]. O-GlcNAcylated proteins can form reversible multimeric complexes with other polypeptides or structures. The modification is often accompanied by phosphorylation/ dephosphorylation. O-GlcNAc can act either simultaneously or in a reciprocal fashion with phosphorylation. According to the Yin-Yang hypothesis, the phosphorylation/ dephosphorylation regulates O-GlcNAc-modified protein function (z.B. signal transduction and protein-protein interaction) in concert with phosphorylation [2-4]. The addition of O-GlcNAc to and the removal from the protein backbone is dynamic with rapid cycling in response to cellular signals or cellular stages.. Despite the fact, that Caenorhabiditis elegans is the best studied model organism, there have been no studies on O-GlcNAcylation in this organism so far. Therefore, to elucidate the role of O-GlcNAcylation, we investigated the proteome of a C. elegans mixed-stage population by two-dimensional gelelectrophoresis and subsequent western-blotting with the O-GlcNAc-specific antibody CTD 110.6 for the occurrence of this modification and identified the modified proteins by mass-spectrometry. We detected and identify several O-GlcNAc-modified proteins in C. elegans. Most of the identified proteins are involved in metabolic pathways. The prediction of the cellular localisation of the identified proteins revealed a predominant cytosolic occurrence of the O-GlcNAc modification.. References:. [1]. Rex-Mathes, M., J. Koch, Werner, S., Griffith, L. S and B. Schmitz. 2002. Methods Mol Biol 194: 73-87.. [2] Zachara, N.E. and G.W. Hart, Chem Rev, 2002. 102(2): p.431-8.. [3]. Griffith, L. S. and B. Schmitz. 1999. Eur J Biochem 262(3): 824-31.. [4] Wells, L. and G. W. Hart. 2003. FEBS Lett 546(1): 154-8.