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Inheritance and reprogramming of non-CG methylation at satellite DNA repeats

ABSTRACT: In vertebrates, DNA methylation predominantly occurs at CG dinucleotides however, widespread non-CG methylation (mCH) has been reported in mammalian embryonic stem cells and in the brain. In mammals, mCH is found at CAC trinucleotides in the nervous system, where it is associated with transcriptional repression, and at CAG trinucleotides in embryonic stem cells, where it positively correlates with transcription. Moreover, CAC methylation appears to be a conserved feature of adult vertebrate brains. Unlike any of those methylation signatures, here we describe a novel form of mCH that occurs in the TGCT context within zebrafish mosaic satellite repeats. TGCT methylation is inherited from both male and female gametes, remodelled during mid-blastula transition, and re-established during gastrulation in all embryonic layers. Moreover, we identify DNA methyltransferase 3ba (Dnmt3ba) as the primary enzyme responsible for the deposition of this mCH mark. Finally, we observe that TGCT-methylated repeats are specifically associated with H3K9me3-marked heterochromatin suggestive of a functional interplay between these two gene-regulatory marks. Altogether, this work provides insight into a novel form of vertebrate mCH and highlights the substrate diversity of vertebrate DNA methyltransferases.

ORGANISM(S): Danio rerio

PROVIDER: GSE149416 | GEO | 2020/05/26

REPOSITORIES: GEO

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Project description:Malignant (type II) testicular germ cell tumors (TGCT) are considered tumors of embryonic germ cell ancestry that diverge morphologically as seminoma (SE), and nonseminomas (NS), the latter including embryonal carcinoma (EC), teratoma (TE), yolk sac tumor (YS) and choriocarcinoma. We have analyzed the genomes and epigenomes of pure histological forms of TGCT (n=130) and 128 matched adjacent normal testicular tissues for TGCT core and subtype-specific DNA methylome profiles and somatic copy number aberrations (SCNA). Original data were compared with published data sets focused on differentiated and pluripotent states. First, we identified pan-TGCT recurrent erasure of maternal and paternal germline imprints and DPPA3 (STELLA), consistent with an embryonic germ cell ancestry. Beyond these conserved properties, we identified TGCT subtype-dependent epigenomic congruency with pluripotent versus somatic reference lineages, thereby establishing competency for lineage-conforming methylation reprogramming in the multi-potent common ancestor of TGCT. Notable subtype programming distinctions are as follows: the SE methylome reflects a ground-state of germ cell erasure; EC is found to harbor pervasive embryonic stem cell (ESC)-like CpH (non-CpG) methylation, absent in other TGCT and non-germ cell tumors and differentiated tissues. EC was further distinguished by ESC-like hypomethylation of NANOG, contrasting with NANOG methylation in TE, YS, and somatic tissues. Thus, EC methylomes present a novel mixed ESC/embryonic germ cell epigenomic state. TE global methylation was most convergent with somatic tissue; however, and unique among TGCT subtypes, TE manifested hypermethylation of the H19 paternal germline DMR. The YS methylome most closely resembled extra-embryonic trophoblast. The total set of findings provides evidence for a multi-potent TGCT stem cell whose progeny may harbor pluripotent, primordial germ/gonocyte, and somatic lineage-defining methylation marks. Despite such competency, no TGCT subtype restored erased parental germline imprints. TE is the exception, with H19 hypermethylation. Benign testis adjacent to TGCT exhibited a bimodal epigenotype distribution determined by spermatogenesis and significantly associated with high versus low Johnsen score. Overall, TGCT methylomes are trapped in a core embryonic germ cell-like state of DPPA3/STELLA and imprint erasure, while differential somatic and pluripotent reprogramming profiles are otherwise established.

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Inheritance and reprogramming of non-CG methylation at satellite DNA repeats

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