Biology subjects

Pellegrini, M.

Publications and source records attributed to Pellegrini, M..

12 recordsLinked to original sources

bioRxiv2018

Human Epigenetic Aging is Logarithmic with Time Across the Entire Lifespan

It is well established that organisms undergo epigenetic changes both during development and aging. Developmental changes have been extensively studied to characterize the differentiation of stem cells into diverse lineages. Epigenetic changes during aging have been characterized by multiple epigenetic clocks, that allow the prediction of chronological age based on methylation status. Despite their accuracy and utility, epigenetic age biomarkers leave many questions about epigenetic aging unanswered. Specifically, they do not permit the unbiased characterization of non-linear epigenetic aging trends across entire life spans, a critical question underlying this field of research. Here we a provide an integrated framework to address this question. Our model, inspired from evolutionary models, is able to account for acceleration/deceleration in epigenetic changes by fitting an individuals model age, the epigenetic age, which is related to chronological age in a non-linear fashion. We have devised a two stage procedure leveraging these model ages to infer aging trends over the entire lifespan of a population. Application of this procedure to real data measured across broad age ranges, from before birth to old age, and from two tissue types, suggests a universal logarithmic trend characterizes epigenetic aging across entire lifespans. This observation may have important implications for the development and application of future, more accurate, aging biomarkers.

genomics↗

bioRxiv2018

Seed Genome Hypomethylated Regions Are Enriched In Transcription Factor Genes

The precise mechanisms that control gene activity during seed development remain largely unknown. Previously, we showed that several genes essential for seed development, including those encoding storage proteins, fatty acid biosynthesis enzymes, and transcriptional regulators, such as ABI3 and FUS3, are located within hypomethylated regions of the soybean genome. These hypomethylated regions are similar to the DNA methylation valleys (DMVs), or canyons, found in mammalian cells. Here, we address the question of the extent to which DMVs are present within seed genomes, and what role they might play in seed development. We scanned soybean and Arabidopsis seed genomes from post-fertilization through dormancy and germination for regions that contain < 5% or < 0.4% bulk methylation in CG-, CHG-, and CHH-contexts over all developmental stages. We found that DMVs represent extensive portions of seed genomes, range in size from 5 to 76 kb, are scattered throughout all chromosomes, and are hypomethylated throughout the plant life cycle. Significantly, DMVs are enriched greatly in transcription factor genes, and other developmental genes, that play critical roles in seed formation. Many DMV genes are regulated with respect to seed stage, region, and tissue - and contain H3K4me3, H3K27me3, or bivalent marks that fluctuate during development. Our results indicate that DMVs are a unique regulatory feature of both plant and animal genomes, and that a large number of seed genes are regulated in the absence of methylation changes during development - probably by the action of specific transcription factors and epigenetic events at the chromatin level.\n\nSignificanceWe scanned soybean and Arabidopsis seed genomes for hypomethylated regions, or DNA Methylation Valleys (DMVs), present in mammalian cells. A significant fraction of seed genomes contain DMV regions that have < 5% bulk DNA methylation, or, in many cases, no detectable DNA methylation. Methylation levels of seed DMVs do not vary detectably during seed development with respect to time, region, and tissue, and are present prior to fertilization. Seed DMVs are enriched in transcription factor genes and other genes critical for seed development, and are also decorated with histone marks that fluctuate with developmental stage, resembling in significant ways their animal counterparts. We conclude that many genes playing important roles in seed formation are regulated in the absence of detectable DNA methylation events, and suggest that selective action of transcriptional activators and repressors, as well as chromatin epigenetic events play important roles in making a seed - particularly embryo formation.

plant biology↗

bioRxiv2018

Dual RNAseq of human leprosy lesions identifies bacterial determinants linked to host immune response

To understand how the interaction between an intracellular bacterium and the host immune system contributes to outcome at the site of infection, we studied leprosy, a disease that forms a clinical spectrum, in which progressive infection by the intracellular bacterium Mycobacterium leprae is characterized by the production of type | IFNs and antibody production. We performed dual RNAseq on patient lesions, identifying a continuum of distinct bacterial states that are linked to the host immune response. The bacterial burden, represented by the fraction of bacterial transcripts, correlates with a host type | IFN gene signature, known to inhibit antimicrobial responses. Second, the bacterial transcriptional activity, defined by the bacterial mRNA/rRNA ratio, links bacterial heat shock proteins with the BAFF-BCMA host antibody response pathway. Our findings provide a platform for interrogation of host and pathogen transcriptomes at the site of infection, allowing insight into mechanisms of inflammation in human disease.

microbiology↗

bioRxiv2017

Dot2dot: Accurate Whole-Genome Tandem Repeats Discovery

The advent of sequencing technologies and the consequent computational analysis of genomes has confirmed the evidence that DNA sequences contain a relevant amount of repetitions. A particularly important category of repeating sequences is that of tandem repeats (TRs). TRs are short, almost identical sequences that lie adjacent to each other. The abundance of TRs in eukaryotic genomes has suggested that they play a role in many cellular processes and, indeed, are also involved in the onset and progress of several genetic disorders.\n\nBuilding upon the idea that similar sequences can be easily displayed using graphical methods, we formalized the structure that TRs induce in dot plot matrices where a sequence is compared with itself. We further observed that a compact representation of these matrices can be built and searched in linear time in the size of the input sequence. Exploiting this observation, we developed an algorithm fast enough to be suitable for whole-genome discovery of tandem repeats.\n\nWe compared our algorithm with seven state of the art methods using as a gold standard five collections of tandem repeats: pathology-linked, forensic, for population analysis, genealogic-oriented, and variable TRs in regulatory regions. In addition, we run our algorithm on seven reference genomes to test the suitability of our approach for whole-genome analysis. Experiments show that our method: is always more accurate than the other methods, and completes the analysis of the biggest available reference genome in about one day running at a rate of 0.98Gbp/h on a standard workstation.

genomics↗

bioRxiv2017

Comparison of reprogramming factor targets reveals both species-specific and conserved mechanisms in early iPS cells

Both human and mouse fibroblasts can be reprogrammed to pluripotency with Oct4, Sox2, Klf4, and c-Myc (OSKM) transcription factors. While both systems generate pluripotency, human reprogramming takes considerably longer than mouse. To assess additional similarities and differences, we sought to compare the binding of the reprogramming factors between the two systems. In human fibroblasts, the OSK factors initially target many more closed chromatin sites compared to mouse. Despite this difference, the intra- and intergenic distribution of target sites, target genes, primary binding motifs, and combinatorial binding patterns between the reprogramming factors are largely shared. However, while many OSKM binding events in early mouse cell reprogramming occur in syntenic regions, only a limited number is conserved in human. In summary, these findings suggest similar general effects of OSKM binding across these two species, even though the detailed regulatory networks have diverged significantly.

genomics↗

bioRxiv2017

A Phylogenomic Study Quantifies Competing Mechanisms for Pseudogenization in Prokaryotes

BackgroundPseudogenes are non-functional sequences in the genome with homologous sequences that are functional (i.e. genes). They are abundant in eukaryotes where they have been extensively investigated, while in prokaryotes they are significantly scarcer and less well studied. Here we conduct a comprehensive analysis of the evolution of pseudogenes in prokaryotes. For this analysis we consider a broad range of bacteria, but also focus on the leprosy pathogen Mycobacterium leprae, which contains an unusually large number of pseudogenes which comprise approximately 40% of its entire genome.\n\nResultsWe have developed an informatics-based approach to characterize the evolution of pseudogenes. This approach combines tools from phylogenomics, genomics, and transcriptomics. The results we obtain suggest the presence of two mechanisms for pseudogene formation: failed horizontal gene transfer events and disruption of native genes.\n\nConclusionsWe conclude that while in most bacteria the former is most likely responsible for the majority of pseudogenization events, in mycobacteria, and in particular in M. leprae with its exceptionally high pseudogene numbers, the latter predominates. We believe that our study sheds new light on the evolution of pseudogenes in bacteria, by utilizing new methodologies that are applied to the unusually abundant M. leprae pseudogenes and their orthologs. As such, we anticipate that it will be of broad interest to both evolutionary biologists as well as microbiologists.

evolutionary biology↗

bioRxiv2017

Epigenome-wide association in adipose tissue from the METSIM cohort identifies novel loci and the involvement of adipocytes and macrophages in diabetes traits

Most epigenome-wide association studies to date have been conducted in blood. However, metabolic syndrome is mediated by a dysregulation of adiposity and therefore it is critical to study adipose tissue in order to understand the effects of this syndrome on epigenomes. To determine if natural variation in DNA methylation was associated with metabolic syndrome traits, we profiled global methylation levels in subcutaneous abdominal adipose tissue. We measured association between 32 clinical traits related to diabetes and obesity in 201 people from the Metabolic Syndrome In Men cohort. We performed epigenome-wide association studies between DNA methylation levels and traits, and identified associations for 13 clinical traits in 21 loci. We prioritized candidate genes in these loci using eQTL, and identified 18 high confidence candidate genes, including known and novel genes associated with diabetes and obesity traits. Using methylation deconvolution, we examined which cell types may be mediating the associations, and concluded that most of the loci we identified were specific to adipocytes. We determined whether the abundance of cell types varies with metabolic traits, and found that macrophages increased in abundance with the severity of metabolic syndrome traits. Finally, we developed a DNA methylation based biomarker to assess type II diabetes risk in adipose tissue. In conclusion, our results demonstrate that profiling DNA methylation in adipose tissue is a powerful tool for understanding the molecular effects of metabolic syndrome on adipose tissue, and can be used in conjunction with traditional genetic analyses to further characterize this disorder.

genetics↗

bioRxiv2017

DNA methylation estimation using methylation-sensitive restriction enzyme bisulfite sequencing (MREBS)

Whole-genome bisulfite sequencing (WGBS) and reduced representation bisulfite sequencing (RRBS) are widely used for measuring DNA methylation levels on a genome-wide scale(1). Both methods have limitations: WGBS is expensive and prohibitive for most large-scale projects; RRBS only interrogates 6-12% of the CpGs in the human genome(16,19). Here, we introduce methylation-sensitive restriction enzyme bisulfite sequencing (MREBS) which has the reduced sequencing requirements of RRBS, but significantly expands the coverage of CpG sites in the genome. We built a multiple regression model that combines the two features of MREBS: the bisulfite conversion ratios of single cytosines (as in WGBS and RRBS) as well as the number of reads that cover each locus (as in MRE-seq(12)). This combined approach allowed us to estimate differential methylation across 60% of the genome using read count data alone, and where counts were sufficiently high in both samples (about 1.5% of the genome), our estimates were significantly improved by the single CpG conversion information. We show that differential DNA methylation values based on MREBS data correlate well with those based on WGBS and RRBS. This newly developed technique combines the sequencing cost of RRBS and DNA methylation estimates on a portion of the genome similar to WGBS, making it ideal for large-scale projects of mammalian genomes.

genomics↗

bioRxiv2017

A Novel Uropathogenic Escherichia Coli Genome (strain D3) and Comparative Analysis with Other Uropathogenic and Nonpathogenic Strains

BackgroundBacterial urinary tract infections are extremely prevalent, with half of women having at least one infection at some point in their lives. Most often the causative pathogen is the common gut microbe Escherichia coli. One such E. coli, strain D3, caused a bladder infection in a male adult, and was resistant to multiple antibiotics. We sequenced and assembled the genome of D3, and present it along with a comparative analysis against other pathogenic and nonpathogenic E. Coli strains.\n\nResultsBy comparing the predicted proteins of D3 with those from 5 uropathogenic and 7 nonpathogenic E. Coli strains, we generated a list of 38 genes present in most (4-5) pathogenic strains, but absent in all nonpathogenic strains. Among these were 9 proteins of the Pap fimbrial operon, which has previously been associated with cell adherence and the formation of biofilms. Lastly, we analyzed the list of predicted genes uniquely present in D3 compared to all other strains, and identified multiple transposable elements.\n\nConclusionsThe presence of fimbria in most pathogenic E. coli strains, and their absence in nonpathogenic ones, suggests that they play a role in pathogenicity, a notion supported by previous work. We also found that D3-specific genes are strongly enriched with transposases, recombinases, and integrase, suggesting that these mobile elements have been inserted or expanded in D3, relative to other strains in the study.

pathology↗

bioRxiv2017

The Peach RGF/GLV Signalling Peptide pCTG134 Is Involved In A Regulatory Circuit That Sustains Auxin And Ethylene Actions

Peach is a climacteric species whose ripening is regulated by the plant hormone ethylene. A crosstalk mechanism with auxin is necessary to support climacteric ethylene synthesis. The homeostasis control of auxin is regulated also by the activity of peptide hormones (PHs), acting both as short and long distant ligands. In this work, we investigated the role of CTG134, a peach gene encoding a GOLVEN-like PH isolated in mesocarp at the onset of ripening.\n\nIn peach fruit, CTG134 was expressed during the climacteric transition and its mRNA level was induced by auxin and 1-methylcyclopropene (1-MCP) treatments, whereas it was minimally affected by ethylene. To better elucidate its function, CTG134 was overexpressed in Arabidopsis and tobacco, which showed abnormal root hair growth, similar to wild-type plants treated with a synthetic form of the peptide. Molecular surveys demonstrated an impaired hormonal crosstalk, resulting in a re-modulated expression of a set of genes involved in both ethylene and auxin domains. In addition, the promoter of pCTG134 fused with GUS reporter highlighted gene activity in plant organs in which the auxin-ethylene interplay is known to occur. These data support the role of pCTG134 as mediator in an auxin-ethylene regulatory circuit.\n\nHighlightThe role of the peach RGF/GLV peptide during root hair formation in Arabidopsis and tobacco supports its involvement in a cross-hormonal auxin-ethylene regulatory circuit.

plant biology↗

bioRxiv2017

Loss of MECP2 leads to telomere dysfunction and neuronal stress

To determine the role for mutations of MECP2 in Rett Syndrome, we generated isogenic lines of human iPSCs (hiPSCs), neural progenitor cells (NPCs), and neurons from patient fibroblasts with and without MECP2 expression in an attempt to recapitulate disease phenotypes in vitro. Molecular profiling uncovered neuronal specific gene expression changes including induction of a Senescence Associated Secretory Phenotype (SASP) program. Patient derived Neurons made without MECP2 show signs of stress, including induction of p53, and senescence. The induction of p53 appeared to affect dendritic branching in Rett neurons, as p53 inhibition restored dendritic complexity. These disease-in-a-dish data suggest that loss of MECP2 can lead to dendritic defects due to an increase in aspects of neuronal aging.

developmental biology↗

bioRxiv2017

Addressing the digital divide in contemporary biology: Lessons from teaching UNIX

Researchers in the biomedical sciences increasingly rely on applications that lack a graphical interface and require inputting code that, such as UNIX. Scientists who are not trained in computer science face an enormous challenge in analyzing the high-throughput data their research groups generate. We present a training model for use of command-line tools when the learner has little to no prior knowledge of UNIX.

scientific communication and education↗