Genome-wide histone modification profiling of inner cell mass and trophectoderm of bovine blastocysts by RAT-ChIP

Molecular cloning of PRD-like homeobox genes expressed in bovine oocytes and early IVF embryos

BACKGROUND

Embryonic genome activation (EGA) is a critical step in early embryonic development, as it marks the transition from relying on maternal factors to the initiation of transcription from embryo's own genome. The factors associated with EGA are not well understood and need further investigation. PRD-like (PRDL) homeodomain transcription factors (TFs) are considered to play crucial roles in this early event during development but these TFs have evolved differently, even within mammalian lineages. Different numbers of PRDL TFs have been predicted in bovine (Bos taurus); however, their divergent evolution requires species-specific confirmation and functional investigations.

RESULTS

In this study, we conducted molecular cloning of mRNAs for the PRDL TFs ARGFX, DUXA, LEUTX, NOBOX, TPRX1, TPRX2, and TPRX3 in bovine oocytes or in vitro fertilized (IVF) preimplantation embryos. Our results confirmed the expression of PRDL TF genes in early bovine development at the cDNA level and uncovered their structures. For each investigated PRDL TF gene, we isolated at least one homeodomain-encoding cDNA fragment, indicative of DNA binding and thus potential role in transcriptional regulation in developing bovine embryos. Additionally, our cDNA cloning approach allowed us to reveal breed-related differences in bovine, as evidenced by the identification of a high number of single nucleotide variants (SNVs) across the PRDL class homeobox genes. Subsequently, we observed the prediction of the 9aa transactivation domain (9aaTAD) motif in the putative protein sequence of TPRX3 leading us to conduct functional analysis of this gene. We demonstrated that the TPRX3 overexpression in bovine fibroblast induces not only protein-coding genes but also short noncoding RNAs involved in splicing and RNA editing. We supported this finding by identifying a shared set of genes between our and published bovine early embryo development datasets.

CONCLUSIONS

Providing full-length cDNA evidence for previously predicted homeobox genes that belong to PRDL class improves the annotation of the bovine genome. Updating the annotation with seven developmentally-important genes will enhance the accuracy of RNAseq analysis with datasets derived from bovine preimplantation embryos. In addition, the absence of TPRX3 in humans highlights the species-specific and TF-specific regulation of biological processes during early embryo development.

Molecular and cellular programs underlying the development of bovine pre-implantation embryos

Early embryonic mortality is a major cause of infertility in cattle, yet the underlying molecular causes remain a mystery. Over the past half century, assisted reproductive technologies such as in vitro fertilisation and somatic cell nuclear transfer have been used to improve cattle reproductive efficiency; however, reduced embryo developmental potential is seen compared to their in vivo counterparts. Recent years have seen exciting progress across bovine embryo research, including genomic profiling of embryogenesis, new methods for improving embryo competence, and experimenting on building bovine embryos from stem cell cultures. These advances are beginning to define bovine embryo molecular and cellular programs and could potentially lead to improved embryo health. Here, I highlight the current status of molecular determinants and cellular programs of bovine embryo development and new opportunities to improve the bovine embryo health.

Current status of genome-wide epigenetic profiling of mammalian preimplantation embryos

Background

Genome-wide information on epigenetic modifications in mammalian preimplantation embryos was an unexplored sanctuary of valuable research insights protected by the difficulty of its analysis. However, that is no longer the case, and many epigenome maps are now available for sightseeing there.

Methods

This review overviews the current status of genome-wide epigenetic profiling in terms of DNA methylome and histone modifications in mammalian preimplantation embryos.

Main findings

As the sensitivity of methods for analyzing epigenetic modifications increased, pioneering work began to explore the genome-wide epigenetic landscape in the mid-2010s, first for DNA methylation and then for histone modifications. Since then, a huge amount of data has accumulated, revealing typical epigenetic profiles in preimplantation development and, more recently, changes in response to environmental interventions.

Conclusions

These accumulating data may be used to improve the quality of preimplantation embryos, both in terms of their short-term developmental competence and their subsequent long-term health implications.

The Establishment of CDK9/ RNA PolII/H3K4me3/DNA Methylation Feedback Promotes HOTAIR Expression by RNA Elongation Enhancement in Cancer

Long non-coding RNA HOX Transcript Antisense RNA (HOTAIR) is overexpressed in multiple cancers with diverse genetic profiles. Importantly, since HOTAIR heavily contributes to cancer progression by promoting tumor growth and metastasis, HOTAIR becomes a potential target for cancer therapy. However, the underlying mechanism leading to HOTAIR deregulation is largely unexplored. Here, we performed a pan-cancer analysis using more than 4,200 samples and found that intragenic exon CpG island (Ex-CGI) was hypermethylated and was positively correlated to HOTAIR expression. Also, we revealed that Ex-CGI methylation promotes HOTAIR expression through enhancing the transcription elongation process. Furthermore, we linked up the aberrant intragenic tri-methylation on H3 at lysine 4 (H3K4me3) and Ex-CGI DNA methylation in promoting transcription elongation of HOTAIR. Targeting the oncogenic CDK7-CDK9-H3K4me3 axis downregulated HOTAIR expression and inhibited cell growth in many cancers. To our knowledge, this is the first time that a positive feedback loop that involved CDK9-mediated phosphorylation of RNA Polymerase II Serine 2 (RNA PolII Ser2), H3K4me3, and intragenic DNA methylation, which induced robust transcriptional elongation and heavily contributed to the upregulation of oncogenic lncRNA in cancer has been demonstrated. Targeting the oncogenic CDK7-CDK9-H3K4me3 axis could be a novel therapy in many cancers through inhibiting the HOTAIR expression.

RGD v2.0: a major update of the ruminant functional and evolutionary genomics database

Ruminant Genome Database (RGD; http://animal.nwsuaf.edu.cn/RGD) provides visualization and analysis tools for ruminant comparative genomics and functional annotations. As more high-quality ruminant genome assemblies have become available, we have redesigned the user interface, integrated and expanded multi-omics data, and developed novel features to improve the database. The new version, RGD v2.0, houses 78 ruminant genomes; 110-species synteny alignments for major livestock (including cattle, sheep, goat) and wild ungulates; 21 012 orthologous gene clusters with Gene Ontology and pathway annotation; ∼8 600 000 conserved elements; and ∼1 000 000 cis-regulatory elements by utilizing 1053 epigenomic data sets. The transcriptome data in RGD v2.0 has nearly doubled, currently with 1936 RNA-seq data sets, and 155 174 phenotypic data sets have been newly added. New and updated features include: (i) The UCSC Genome Browser, BLAT, BLAST and Table Browser tools were updated for six available ruminant livestock species. (ii) The LiftOver tool was newly introduced into our browser to allow coordinate conversion between different ruminant assemblies. And (iii) tissue specificity index, tau, was calculated to facilitate batch screening of specifically expressed genes. The enhanced genome annotations and improved functionality in RGD v2.0 will be useful for study of genome evolution, environmental adaption, livestock breeding and biomedicine.

Comparative analysis of histone H3K4me3 modifications between blastocysts and somatic tissues in cattle

Epigenetic changes induced in the early developmental stages by the surrounding environment can have not only short-term but also long-term consequences throughout life. This concept constitutes the “Developmental Origins of Health and Disease” (DOHaD) hypothesis and encompasses the possibility of controlling livestock health and diseases by epigenetic regulation during early development. As a preliminary step for examining changes of epigenetic modifications in early embryos and their long-lasting effects in fully differentiated somatic tissues, we aimed to obtain high-throughput genome-wide histone H3 lysine 4 trimethylation (H3K4me3) profiles of bovine blastocysts and to compare these data with those from adult somatic tissues in order to extract common and typical features between these tissues in terms of H3K4me3 modifications. Bovine blastocysts were produced in vitro and subjected to chromatin immunoprecipitation-sequencing analysis of H3K4me3. Comparative analysis of the blastocyst-derived H3K4me3 profile with publicly available data from adult liver and muscle tissues revealed that the blastocyst profile could be used as a “sieve” to extract somatic tissue-specific modifications in genes closely related to tissue-specific functions. Furthermore, principal component analysis of the level of common modifications between blastocysts and somatic tissues in meat production-related and imprinted genes well characterized inter- and intra-tissue differences. The results of this study produced a referential genome-wide H3K4me3 profile of bovine blastocysts within the limits of their in vitro source and revealed its common and typical features in relation to the profiles of adult tissues.

The Epigenetics of Gametes and Early Embryos and Potential Long-Range Consequences in Livestock Species-Filling in the Picture With Epigenomic Analyses

The epigenome is dynamic and forged by epigenetic mechanisms, such as DNA methylation, histone modifications, chromatin remodeling, and non-coding RNA species. Increasing lines of evidence support the concept that certain acquired traits are derived from environmental exposure during early embryonic and fetal development, i.e., fetal programming, and can even be "memorized" in the germline as epigenetic information and transmitted to future generations. Advances in technology are now driving the global profiling and precise editing of germline and embryonic epigenomes, thereby improving our understanding of epigenetic regulation and inheritance. These achievements open new avenues for the development of technologies or potential management interventions to counteract adverse conditions or improve performance in livestock species. In this article, we review the epigenetic analyses (DNA methylation, histone modification, chromatin remodeling, and non-coding RNAs) of germ cells and embryos in mammalian livestock species (cattle, sheep, goats, and pigs) and the epigenetic determinants of gamete and embryo viability. We also discuss the effects of parental environmental exposures on the epigenetics of gametes and the early embryo, and evidence for transgenerational inheritance in livestock.

Efficient low-cost chromatin profiling with CUT&Tag

We recently introduced Cleavage Under Targets & Tagmentation (CUT&Tag), an epigenomic profiling strategy in which antibodies are bound to chromatin proteins in situ in permeabilized nuclei. These antibodies are then used to tether the cut-and-paste transposase Tn5. Activation of the transposase simultaneously cleaves DNA and adds adapters ('tagmentation') for paired-end DNA sequencing. Here, we introduce a streamlined CUT&Tag protocol that suppresses DNA accessibility artefacts to ensure high-fidelity mapping of the antibody-targeted protein and improves the signal-to-noise ratio over current chromatin profiling methods. Streamlined CUT&Tag can be performed in a single PCR tube, from cells to amplified libraries, providing low-cost genome-wide chromatin maps. By simplifying library preparation CUT&Tag requires less than a day at the bench, from live cells to sequencing-ready barcoded libraries. As a result of low background levels, barcoded and pooled CUT&Tag libraries can be sequenced for as little as $25 per sample. This enables routine genome-wide profiling of chromatin proteins and modifications and requires no special skills or equipment.