Alternative polyadenylation quantitative trait methylation mapping in human cancers provides clues into the molecular mechanisms of APA

Genetic variants are involved in the orchestration of alternative polyadenylation (APA) events, while the role of DNA methylation in regulating APA remains unclear. We generated a comprehensive atlas of APA quantitative trait methylation sites (apaQTMs) across 21 different types of cancer (1,612 to 60,219 acting in cis and 4,448 to 142,349 in trans). Potential causal apaQTMs in non-cancer samples were also identified. Mechanistically, we observed a strong enrichment of cis-apaQTMs near polyadenylation sites (PASs) and both cis- and trans-apaQTMs in proximity to transcription factor (TF) binding regions. Through the integration of ChIP-signals and RNA-seq data from cell lines, we have identified several regulators of APA events, acting either directly or indirectly, implicating novel functions of some important genes, such as TCF7L2, which is known for its involvement in type 2 diabetes and cancers. Furthermore, we have identified a vast number of QTMs that share the same putative causal CpG sites with five different cancer types, underscoring the roles of QTMs, including apaQTMs, in the process of tumorigenesis. DNA methylation is extensively involved in the regulation of APA events in human cancers. In an attempt to elucidate the potential underlying molecular mechanisms of APA by DNA methylation, our study paves the way for subsequent experimental validations into the intricate biological functions of DNA methylation in APA regulation and the pathogenesis of human cancers. To present a comprehensive catalog of apaQTM patterns, we introduce the Pancan-apaQTM database, available at https://pancan-apaqtm-zju.shinyapps.io/pancanaQTM/.

Chromosome translocation affects multiple phenotypes, causes genome-wide dysregulation of gene expression, and remodels metabolome in hexaploid wheat

Chromosomal rearrangements (CRs) may occur in newly formed polyploids due to compromised meiotic fidelity. Moreover, CRs can be more readily tolerated in polyploids allowing their longer-term retention and hence potential spreading/fixation within a lineage. The direct functional consequences of CRs in plant polyploids remain unexplored. Here, we identified a heterozygous individual from a synthetic allohexaploid wheat in which the terminal parts of the long-arms of chromosomes 2D (approximately 193 Mb) and 4A (approximately 167 Mb) were reciprocally translocated. Five homogeneous translocation lines including both unbalanced and balanced types were developed by selfing fertilization of the founder mutant (RT [2DL; 4AL]-ter/1, reciprocal translocation). We investigated impacts of these translocations on phenotype, genome-wide gene expression and metabolome. We find that, compared with sibling wild-type, CRs in the form of both unbalanced and balanced translocations induced substantial changes of gene expression primarily via trans-regulation in the nascent allopolyploid wheat. The CRs also manifested clear phenotypic and metabolic consequences. In particular, the genetically balanced, stable reciprocal translocations lines showed immediate enhanced reproductive fitness relative to wild type. Our results underscore the profound impact of CRs on gene expression in nascent allopolyploids with wide-ranging phenotypic and metabolic consequences, suggesting CRs are an important source of genetic variation that can be exploited for crop breeding.

Non-additive genetic components contribute significantly to population-wide gene expression variation

Gene expression variation, an essential step between genomic variation and phenotypic landscape, is collectively controlled by local (cis) and distant (trans) regulatory changes. Nevertheless, how these regulatory elements differentially influence the heritability of expression traits remains unclear. Here, we bridge this gap by analyzing the transcriptomes of a large diallel panel consisting of 323 unique hybrids originated from genetically divergent yeast isolates. We estimated the broad- and narrow-sense heritability across 5,087 transcript abundance traits and showed that non-additive components account for 36% of the phenotypic variance on average. By comparing allelic expression ratios in the hybrid and the corresponding parental pair, we identified regulatory changes in 25% of all cases, with a majority acting in trans. We further showed that trans-regulation could underlie coordinated expression variation across highly connected genes, resulting in significantly higher non-additive variance and most likely in some of the missing heritability of gene expression traits.

Role of lncRNAs in cis- and trans-regulatory responses to salt in Populus trichocarpa

Long non-coding RNAs (lncRNAs) are emerging as versatile regulators in diverse biological processes. However, little is known about their cis- and trans-regulatory contributions in gene expression under salt stress. Using 27 RNA-seq data sets from Populus trichocarpa leaves, stems and roots, we identified 2988 high-confidence lncRNAs, including 1183 salt-induced differentially expressed lncRNAs. Among them, 301 lncRNAs have potential for positively affecting their neighboring genes, predominantly in a cis-regulatory manner rather than by co-transcription. Additionally, a co-expression network identified six striking salt-associated modules with a total of 5639 genes, including 426 lncRNAs, and in these lncRNA sequences, the DNA/RNA binding motifs are enriched. This suggests that lncRNAs might contribute to distant gene expression of the salt-associated modules in a trans-regulatory manner. Moreover, we found 30 lncRNAs that have potential to simultaneously cis- and trans-regulate salt-responsive homologous genes, and Ptlinc-NAC72, significantly induced under long-term salt stress, was selected for validating its regulation of the expression and functional roles of the homologs PtNAC72.A and PtNAC72.B (PtNAC72.A/B). The transient transformation of Ptlinc-NAC72 and a dual-luciferase assay of Ptlinc-NAC72 and PtNAC72.A/B promoters confirmed that Ptlinc-NAC72 can directly upregulate PtNAC72.A/B expression, and a presence/absence assay was further conducted to show that the regulation is probably mediated by Ptlinc-NAC72 recognizing the tandem elements (GAAAAA) in the PtNAC72.A/B 5' untranslated region (5'-UTR). Finally, the overexpression of Ptlinc-NAC72 produces a hypersensitive phenotype under salt stress. Altogether, our results shed light on the cis- and trans-regulation of gene expression by lncRNAs in Populus and provides an example of long-term salt-induced Ptlinc-NAC72 that could be used to mitigate growth costs by conferring plant resilience to salt stress.

Role of lncRNAs in cis- and trans-regulatory responses to salt in Populus trichocarpa

Long non-coding RNAs (lncRNAs) are emerging as versatile regulators in diverse biological processes. However, little is known about their cis- and trans-regulatory contributions in gene expression under salt stress. Using 27 RNA-seq data sets from Populus trichocarpa leaves, stems and roots, we identified 2988 high-confidence lncRNAs, including 1183 salt-induced differentially expressed lncRNAs. Among them, 301 lncRNAs have potential for positively affecting their neighboring genes, predominantly in a cis-regulatory manner rather than by co-transcription. Additionally, a co-expression network identified six striking salt-associated modules with a total of 5639 genes, including 426 lncRNAs, and in these lncRNA sequences, the DNA/RNA binding motifs are enriched. This suggests that lncRNAs might contribute to distant gene expression of the salt-associated modules in a trans-regulatory manner. Moreover, we found 30 lncRNAs that have potential to simultaneously cis- and trans-regulate salt-responsive homologous genes, and Ptlinc-NAC72, significantly induced under long-term salt stress, was selected for validating its regulation of the expression and functional roles of the homologs PtNAC72.A and PtNAC72.B (PtNAC72.A/B). The transient transformation of Ptlinc-NAC72 and a dual-luciferase assay of Ptlinc-NAC72 and PtNAC72.A/B promoters confirmed that Ptlinc-NAC72 can directly upregulate PtNAC72.A/B expression, and a presence/absence assay was further conducted to show that the regulation is probably mediated by Ptlinc-NAC72 recognizing the tandem elements (GAAAAA) in the PtNAC72.A/B 5' untranslated region (5'-UTR). Finally, the overexpression of Ptlinc-NAC72 produces a hypersensitive phenotype under salt stress. Altogether, our results shed light on the cis- and trans-regulation of gene expression by lncRNAs in Populus and provides an example of long-term salt-induced Ptlinc-NAC72 that could be used to mitigate growth costs by conferring plant resilience to salt stress.

Conservation and trans-regulation of histone modification in the A and B subgenomes of polyploid wheat during domestication and ploidy transition

BACKGROUND

Polyploidy has played a prominent role in the evolution of plants and many other eukaryotic lineages. However, how polyploid genomes adapt to the abrupt presence of two or more sets of chromosomes via genome regulation remains poorly understood. Here, we analyzed genome-wide histone modification and gene expression profiles in relation to domestication and ploidy transition in the A and B subgenomes of polyploid wheat.

RESULTS

We found that epigenetic modification patterns by two typical euchromatin histone markers, H3K4me3 and H3K27me3, for the great majority of homoeologous triad genes in A and B subgenomes were highly conserved between wild and domesticated tetraploid wheats and remained stable in the process of ploidy transitions from hexaploid to extracted tetraploid and then back to resynthesized hexaploid. However, a subset of genes was differentially modified during tetraploid and hexaploid wheat domestication and in response to ploidy transitions, and these genes were enriched for particular gene ontology (GO) terms. The extracted tetraploid wheat manifested higher overall histone modification levels than its hexaploid donor, and which were reversible and restored to normal levels in the resynthesized hexaploid. Further, while H3K4me3 marks were distally distributed along each chromosome and significantly correlated with subgenome expression as expected, H3K27me3 marks showed only a weak distal bias and did not show a significant correlation with gene expression.

CONCLUSIONS

Our results reveal overall high stability of histone modification patterns in the A and B subgenomes of polyploid wheat during domestication and in the process of ploidy transitions. However, modification levels of a subset of functionally relevant genes in the A and B genomes were trans-regulated by the D genome in hexaploid wheat.

Mechanistic insights into the evolution of the differential expression of tandemly arrayed cone opsin genes in zebrafish

The genome of many organisms contains several loci consisting of duplicated genes that are arrayed in tandem. The daughter genes produced by duplication typically exhibit differential expression patterns with each other or otherwise experience pseudogenization. Remarkably, opsin genes in fish are preserved after many duplications in different lineages. This fact indicates that fish opsin genes are characterized by a regulatory mechanism that could intrinsically facilitate the differentiation of the expression patterns. However, little is known about the mechanisms that underlie the differential expression patterns or how they were established during evolution. The loci of green (RH2)- and red (LWS)-sensitive cone opsin genes in zebrafish have been used as model systems to study the differential regulation of tandemly arrayed opsin genes. Over a decade of studies have uncovered several mechanistic features that might have assisted the differentiation and preservation of duplicated genes. Furthermore, recent progress in the understanding of the transcriptional process in general has added essential insights. In this article, the current understanding of the transcriptional regulation of differentially expressed tandemly arrayed cone opsin genes in zebrafish is summarized and a possible evolutionary scenario that could achieve this differentiation is discussed.

Multiple conformational states of the HPK1 kinase domain in complex with sunitinib reveal the structural changes accompanying HPK1 trans-regulation

Hematopoietic progenitor kinase 1 (HPK1 or MAP4K1) is a Ser/Thr kinase that operates via the c-Jun N-terminal kinase (JNK) and extracellular signal-regulated kinase (ERK) signaling pathways to dampen the T-cell response and antitumor immunity. Accordingly, selective HPK1 inhibition is considered a means to enhance antitumor immunity. Sunitinib, a multi-receptor tyrosine kinase (RTK) inhibitor approved for the management of gastrointestinal stromal tumors (GISTs), renal cell carcinoma (RCC), and pancreatic cancer, has been reported to inhibit HPK1 in vitro In this report, we describe the crystal structures of the native HPK1 kinase domain in both nonphosphorylated and doubly phosphorylated states, in addition to a double phosphomimetic mutant (T165E,S171E), each complexed with sunitinib at 2.17-3.00-Å resolutions. The native nonphosphorylated cocrystal structure revealed an inactive dimer in which the activation loop of each monomer partially occupies the ATP- and substrate-binding sites of the partner monomer. In contrast, the structure of the protein with a doubly phosphorylated activation loop exhibited an active kinase conformation with a greatly reduced monomer-monomer interface. Conversely, the phosphomimetic mutant cocrystal structure disclosed an alternative arrangement in which the activation loops are in an extended domain-swapped configuration. These structural results indicate that HPK1 is a highly dynamic kinase that undergoes trans-regulation via dimer formation and extensive intramolecular and intermolecular remodeling of the activation segment.

Gene Regulatory Variation in Drosophila melanogaster Renal Tissue

Genetic variation influencing levels of gene expression is abundant in natural populations, and may exert its effects through complex mechanisms that depend on an organism's genetic background and the tissue in which expression is measured. We investigated natural variation in gene expression in the Malpighian tubules of three inbred Drosophila melanogaster strains and their F₁ hybrids. One of the strains was from a population in the species' ancestral range (Zambia), while the other two were from a more recently derived population (Sweden). Although closely related, the two Swedish strains differed greatly in terms of their expression inheritance when hybridized with the Zambian strain, with one Swedish strain showing a large excess of genes with recessive expression inheritance, as well as a large number of genes with overdominant inheritance. Although most expression variation could be attributed to trans-regulation, there were ∼200 genes that showed allele-specific expression differences in each of the between-population hybrids, indicating that cis-regulation contributes as well. The cis-regulated genes were enriched with cytochrome P450 genes, and the upstream regions of six of these genes were incorporated into transgenic reporter gene constructs to test their effects on expression. Differential expression was observed for five of the six reporter genes in the Malpighian tubule, suggesting that a large proportion of cis-regulatory variation lies directly upstream of the affected gene. In most cases, the differential expression was specific to the Malpighian tubule or greater in this tissue than in the rest of the body, highlighting the importance of single-tissue studies of gene expression variation.

Dihydrotestosterone enhances growth and infectivity of Leishmania Mexicana

A strong sex-associated susceptibility towards Leishmania has been reported in males, yet little is known on the effect of hormones in Leishmania physiopathogenicity. Due to the enhanced susceptibility of males to Leishmania mexicana infections, we were interested in analysing the effect exerted by the main androgen produced in males (DHT) on L. mexicana promastigotes. Thus, the aim of this study was to assess the regulation exerted by dihydrotestosterone (DHT) on L. mexicana replication, infectivity, survival and development of tissue lesions. Experiments included growth curves of L. mexicana promastigotes incubated with different doses of DHT, their infection rate, intracellular survival and lesion development in BALB/c mice. Our data show that DHT significantly enhances parasite replication, infection rate and survival in bone marrow-derived macrophages (BMMФ). Promastigotes in the presence of DHT produced significantly larger lesions in BALB/c earlobes. These results suggest that DHT probably plays a critical role during L. mexicana infections, and the higher susceptibility of males possibly relates to benefits gained by the parasite from host-derived hormones. Our data shed new light on the physiopathology of Leishmania infections and are the first attempt to understand the direct interaction between Leishmania and androgens, particularly DHT. Understanding this trans-regulation process employed by parasites to exploit host molecules sheds new light on L. mexicana physiopathogenesis and opens a possible field for studies on drug development.

Vesiculated Long Non-Coding RNAs: Offshore Packages Deciphering Trans-Regulation between Cells, Cancer Progression and Resistance to Therapies

Extracellular vesicles (EVs) are nanosized vesicles secreted from virtually all cell types and are thought to transport proteins, lipids and nucleic acids including non-coding RNAs (ncRNAs) between cells. Since, ncRNAs are central to transcriptional regulation during developmental processes; eukaryotes might have evolved novel means of post-transcriptional regulation by trans-locating ncRNAs between cells. EV-mediated transportation of regulatory elements provides a novel source of trans-regulation between cells. In the last decade, studies were mainly focused on microRNAs; however, functions of long ncRNA (lncRNA) have been much less studied. Here, we review the regulatory roles of EV-linked ncRNAs, placing a particular focus on lncRNAs, how they can foster dictated patterns of trans-regulation in recipient cells. This refers to envisaging novel mechanisms of epigenetic regulation, cellular reprogramming and genomic instability elicited in recipient cells, ultimately permitting the generation of cancer initiating cell phenotypes, senescence and resistance to chemotherapies. Conversely, such trans-regulation may introduce RNA interference in recipient cancer cells causing the suppression of oncogenes and anti-apoptotic proteins; thus favoring tumor inhibition. Collectively, understanding these mechanisms could be of great value to EV-based RNA therapeutics achieved through gene manipulation within cancer cells, whereas the ncRNA content of EVs from cancer patients could serve as non-invasive source of diagnostic biomarkers and prognostic indicators in response to therapies.

Genome-wide patterns of regulatory divergence revealed by introgression lines

Understanding the genetic basis for changes in transcriptional regulation is an important aspect of understanding phenotypic evolution. Using interspecific introgression lines, we infer the mechanisms of divergence in genome-wide patterns of gene expression between the nightshades Solanum pennellii and S. lycopersicum (domesticated tomato). We find that cis- and trans-regulatory changes have had qualitatively similar contributions to divergence in this clade, unlike results from other systems. Additionally, expression data from four tissues (shoot apex, ripe fruit, pollen, and seed) suggest that introgressed regions in these hybrid lines tend to be downregulated, while background (nonintrogressed) genes tend to be upregulated. Finally, we find no evidence for an association between the magnitude of differential expression in NILs and previously determined sterility phenotypes. Our results contradict previous predictions of the predominant role of cis- over trans-regulatory divergence between species, and do not support a major role for gross genome-wide misregulation in reproductive isolation between these species.

Molecular Mechanisms and Evolutionary Processes Contributing to Accelerated Divergence of Gene Expression on the Drosophila X Chromosome

In species with a heterogametic sex, population genetics theory predicts that DNA sequences on the X chromosome can evolve faster than comparable sequences on autosomes. Both neutral and nonneutral evolutionary processes can generate this pattern. Complex traits like gene expression are not predicted to have accelerated evolution by these theories, yet a "faster-X" pattern of gene expression divergence has recently been reported for both Drosophila and mammals. Here, we test the hypothesis that accelerated adaptive evolution of cis-regulatory sequences on the X chromosome is responsible for this pattern by comparing the relative contributions of cis- and trans-regulatory changes to patterns of faster-X expression divergence observed between strains and species of Drosophila with a range of divergence times. We find support for this hypothesis, especially among male-biased genes, when comparing different species. However, we also find evidence that trans-regulatory differences contribute to a faster-X pattern of expression divergence both within and between species. This contribution is surprising because trans-acting regulators of X-linked genes are generally assumed to be randomly distributed throughout the genome. We found, however, that X-linked transcription factors appear to preferentially regulate expression of X-linked genes, providing a potential mechanistic explanation for this result. The contribution of trans-regulatory variation to faster-X expression divergence was larger within than between species, suggesting that it is more likely to result from neutral processes than positive selection. These data show how accelerated evolution of both coding and noncoding sequences on the X chromosome can lead to accelerated expression divergence on the X chromosome relative to autosomes.

Sex-specific effects of cis-regulatory variants in Drosophila melanogaster

Sexual dimorphism at the level of gene expression is common and well documented, but much less is known about how different cis-regulatory alleles interact with the different trans-regulatory environments present in males and females. Here we show that sex-specific effects of cis-regulatory variants are common in Drosophila.