Biology subjects

Potok, M. E.

Publications and source records attributed to Potok, M. E..

3 recordsLinked to original sources

bioRxiv2021

Maternally-inherited anti-sense piRNAs antagonize transposon expression in teleost embryos

Transposable elements threaten genome stability, and the Piwi-piRNA system has evolved to silence transposons in the germline1-6. However, it remains largely unknown what mechanisms are utilized in early vertebrate embryos prior to germline establishment and ping-pong piRNA production. To address this, we first characterized small RNAs in early zebrafish embryos and detected abundant maternally-deposited, Ziwi-associated, antisense piRNAs that map largely to evolutionarily young long terminal repeat (LTR) retrotransposons. Notably, the focal establishment of the repressive modification H3K9me2/3 coincides with these young LTR elements, is deposited independent of transcription, and is required for LTR silencing. We find piRNAs highly enriched and maintained in primordial germ cells (PGCs), which display lower LTR expression than somatic cells. To examine the consequences of piRNA loss, we used reciprocal zebrafish-medaka hybrids, which display selective activation of LTRs that lack maternally-contributed targeting piRNAs. Thus, the Piwi-piRNA system actively antagonizes transposons in the soma and PGCs during early vertebrate embryogenesis.

developmental biology↗

bioRxiv2020

DNA polymerase epsilon is a central coordinator of heterochromatin structure and function in Arabidopsis

BackgroundChromatin organizes the DNA molecule and regulates its transcriptional activity through epigenetic modifications. Heterochromatic regions of the genome are generally transcriptionally silent while euchromatin is more prone to transcription. During DNA replication, both genetic information and chromatin modifications must be faithfully passed on to daughter strands. There is evidence that DNA polymerases play a role in transcriptional silencing, but the extent of their contribution and how it relates to heterochromatin maintenance is unclear. ResultsWe isolate a strong hypomorphic Arabidopsis thaliana mutant of the POL2A catalytic subunit of DNA polymerase epsilon and show that POL2A is required to stabilize heterochromatin silencing genome wide, likely by preventing replicative stress. We reveal that POL2A inhibits DNA methylation and histone H3 lysine 9 methylation. Hence, release of heterochromatin silencing in POL2A deficient mutants paradoxically occurs in a chromatin context of increased level of these two repressive epigenetic marks. At the nuclear level, POL2A defect is associated with fragmentation of heterochromatin. ConclusionThese results indicate that POL2A is critical to secure both heterochromatin structure and function. We also reveal that unhindered replisome progression is required for the faithful propagation of DNA methylation through the cell cycle.

genomics↗

bioRxiv2019

Arabidopsis SWR1-associated protein methyl-CpG-binding domain 9 is required for histone H2A.Z deposition.

Deposition of the histone variant H2A.Z by the SWI2/SNF2-Related 1 chromatin remodeling complex (SWR1-C) is important for gene regulation in eukaryotes, but the composition of the Arabidopsis SWR1-C has not been thoroughly characterized. Here identify interacting partners of a conserved Arabidopsis SWR1 subunit, ACTIN-RELATED PROTEIN 6 (ARP6). We isolated nine predicted components, and identified additional interactors implicated in histone acetylation and chromatin biology. One of the novel interacting partners, methyl-CpG-binding domain 9 (MBD9), also strongly interacted with the Imitation SWItch (ISWI) chromatin remodeling complex. MBD9 was required for deposition of H2A.Z at a distinct subset of ARP6-dependent loci. MBD9 was preferentially bound to nucleosome-depleted regions at the 5 ends of genes containing high levels of activating histone marks. These data suggest that MBD9 is a SWR1-C interacting protein required for H2A.Z deposition at a subset of actively transcribing genes.

molecular biology↗