Biology subjects

Song, L.

Publications and source records attributed to Song, L..

209 records · Page 12Linked to original sources

bioRxiv2018

Small RNAs gained during epididymal transit of sperm are essential for embryonic development in mice

The small RNA payload of mammalian sperm undergoes dramatic remodeling during development, as several waves of microRNAs and tRNA fragments are shipped to sperm during post-testicular maturation in the epididymis. Here, we take advantage of this developmental process to probe the function of the sperm RNA payload in preimplantation development. We generated zygotes via intracytoplasmic sperm injection (ICSI) using sperm obtained from the proximal (caput) vs. distal (cauda) epididymis, then characterized development of the resulting embryos. Embryos generated using caput sperm significantly overexpress multiple regulatory factors throughout preimplantation development, and subsequently implant inefficiently and fail soon after implantation. Remarkably, microinjection of purified cauda-specific small RNAs into caput-derived embryos not only completely rescued preimplantation molecular defects, but also suppressed the postimplantation embryonic lethality phenotype. These findings reveal an essential role for small RNA remodeling during post-testicular maturation of mammalian sperm, and identify a specific preimplantation gene expression program responsive to sperm-delivered microRNAs.

molecular biology↗

bioRxiv2018

Triggering the expression of a silent gene cluster from genetically intractable bacteria results in scleric acid discovery

Herein we report a strategy for the rapid and rational characterisation of novel microbial natural products from silent gene clusters. A conserved set of five regulatory genes was used as a query to search genomic databases and identify atypical biosynthetic gene clusters (BGCs). A 20-kb BGC from the genetically intractable Streptomyces sclerotialus bacterial strain was captured using yeast-based homologous recombination and introduced into validated heterologous hosts. CRISPR/Cas9-mediated genome editing was then employed to rationally inactivate the key transcriptional repressor and trigger production of an unprecedented class of hybrid natural products exemplified by (2-(benzoyloxy)acetyl)-L-proline, named scleric acid. Subsequent rounds of CRISPR/Cas9-mediated gene deletions afforded a selection of biosynthetic gene mutant strains which led to a plausible biosynthetic pathway for scleric acid assembly. Scleric acid and a key biosynthetic intermediate were also synthesised and used as authentic standards. The assembly of scleric acid involves two unique enzymatic condensation reactions that respectively link a proline and a benzoyl residue to each end of a rare hydroxyethyl-ACP intermediate. Scleric acid was then shown to exhibit moderate activity against Mycobacterium tuberculosis, as well as modest inhibition of the cancer-associated metabolic enzyme Nicotinamide N-methyltransferase (NNMT).

synthetic biology↗

bioRxiv2017

Hi-TOM: a platform for high-throughput tracking of mutations induced by CRISPR/Cas systems

The CRISPR/Cas system has been extensively applied to make precise genetic modifications in various organisms. Despite its importance and widespread use, large-scale mutation screening remains time-consuming, labour-intensive and costly. Here, we describe a cheap, practicable and high-throughput screening strategy that allows parallel screening of 96 x N (N denotes the number of targets) genome-modified sites. The strategy simplified and streamlined the process of next-generation sequencing (NGS) library construction by fixing the bridge sequences and barcoding primers. We also developed Hi-TOM (available at http://www.hi-tom.net/hi-tom/), an online tool to track the mutations with precise percentage. Analysis of the samples from rice, hexaploid wheat and human cells reveals that the Hi-TOM tool has high reliability and sensitivity in tracking various mutations, especially complex chimeric mutations that frequently induced by genome editing. Hi-TOM does not require specially design of barcode primers, cumbersome parameter configuration or additional data analysis. Thus, the streamlined NGS library construction and comprehensive result output make Hi-TOM particularly suitable for high-throughput identification of all types of mutations induced by CRISPR/Cas systems.

bioinformatics↗

bioRxiv2017

Glutamatergic drive along the septo-temporal axis of hippocampus boosts prelimbic oscillations in the neonatal mouse

The long-range coupling within prefrontal-hippocampal networks that account for cognitive performance emerges early in life. The discontinuous hippocampal theta bursts have been proposed to drive the generation of neonatal prefrontal oscillations, yet the cellular substrate of these early interactions is still unresolved. Here, we selectively target optogenetic manipulation of glutamatergic projection neurons in the CA1 area of either dorsal or intermediate/ventral hippocampus at neonatal age to elucidate their contribution to the emergence of prefrontal oscillatory entrainment. We show that despite stronger theta and ripples power in dorsal hippocampus, the prefrontal cortex is mainly coupled with intermediate/ventral hippocampus by phase-locking of neuronal firing via dense direct axonal projections. Theta band-confined activation by light of pyramidal neurons in intermediate/ventral but not dorsal CA1 that were transfected by in utero electroporation with high-efficiency channelrhodopsin boosts prefrontal oscillations. Our data causally elucidates the cellular origin of the long-range coupling in the developing brain.\n\nHighlightsO_LINeonatal theta bursts, sharp waves and ripples vary along septo-temporal axis\nC_LIO_LIHippocampal activity times prefrontal oscillations via direct axonal projections\nC_LIO_LISelective hippocampal targeting along septo-temporal axis causes precise firing\nC_LIO_LILight stimulation of hippocampal neurons at 8 Hz boosts prefrontal oscillations\nC_LI

neuroscience↗

bioRxiv2017

Identifying a TFIID interactome via integrated biochemical and high-throughput proteomic studies

The core promoter recognition TFIID complex acts as a central regulator for eukaryotic gene expression. To direct transcription initiation, TFIID binds the core promoter DNA and aids recruitment of the transcription machinery (e.g., RNA polymerase II) to the transcription start site. Many transcription factors target TFIID to control vital cellular processes. Current studies on finding TFIID interactors have predominantly focused on transcription factors. Yet, a comprehensive interactome of mammalian TFIID has not been established. Therefore, this study sought to reveal potential TFIID-nucleated networks by identifying likely co-regulatory factors that bind TFIID. By using intact native human TFIID complexes, we have exploited three independent approaches including a high-throughput Next Generation DNA sequencing coupled with proteomic analysis. Among these methods, we found some overlapping and new candidates in which we further assessed three putative interactors (i.e., Sox2, H2A and EMSY) by co-immunoprecipitation assays. Notably, in addition to known TFIID interactors, we identified a number of novel factors that participate either in co-regulatory pathways or non-transcription related functions of TFIID. Overal, these results indicate that, in addition to transcription initiation, mammalian TFIID may be involved in broader regulatory pathways than previous studies suggested.

biochemistry↗

bioRxiv2017

Incomplete MyoD-induced transdifferentiation is associated with chromatin remodeling deficiencies

Our current understanding of cellular transdifferentiation systems is limited. It is oftentimes unknown, at a genome-wide scale, how much transdifferentiated cells differ quantitatively from both the starting cells and the target cells. Focusing on transdifferentiation of primary human skin fibroblasts by forced expression of myogenic transcription factor MyoD, we performed quantitative analyses of gene expression and chromatin accessibility profiles of transdifferentiated cells compared to fibroblasts and myoblasts. In this system, we find that while many of the early muscle marker genes are reprogrammed, global gene expression and accessibility changes are still incomplete when compared to myoblasts. In addition, we find evidence of epigenetic memory in the transdifferentiated cells, with reminiscent features of fibroblasts being visible both in chromatin accessibility and gene expression. Quantitative analyses revealed a continuum of changes in chromatin accessibility induced by MyoD, and a strong correlation between chromatin-remodeling deficiencies and incomplete gene expression reprogramming. Classification analyses identified genetic and epigenetic features that distinguish reprogrammed from non-reprogrammed sites, and suggested ways to potentially improve transdifferentiation efficiency. Our approach for combining gene expression, DNA accessibility, and protein-DNA binding data to quantify and characterize the efficiency of cellular transdifferentiation on a genome-wide scale can be applied to any transdifferentiation system.

genomics↗

bioRxiv2017

Tandem histone-binding domains enhance the activity of a synthetic chromatin effector

Fusion proteins that specifically interact with biochemical marks on chromosomes represent a new class of synthetic transcriptional regulators that decode cell state information rather than DNA sequences. In multicellular organisms, information relevant to cell state, tissue identity, and oncogenesis is often encoded as biochemical modifications of histones, which are bound to DNA in eukaryotic nuclei and regulate gene expression states. We have previously reported the development and validation of the \"Polycomb-based transcription factor\" (PcTF), a fusion protein that recognizes histone modifications through a protein-protein interaction between its polycomb chromodomain (PCD) motif and trimethylated lysine 27 of histone H3 (H3K27me3) at genomic sites. We demonstrated that PcTF activates genes at methyl-histone-enriched loci in cancer-derived cell lines. However, PcTF induces modest activation of a methyl-histone associated reporter compared to a DNA-binding activator. Therefore, we modified PcTF to enhance its target affinity. Here, we demonstrate the activity of a modified regulator called Pc2TF, which has two tandem copies of the H3K27me3-binding PCD at the N-terminus. Pc2TF shows higher affinity for H3K27me3 in vitro and shows enhanced gene activation in HEK293 cells compared to PcTF. These results provide compelling evidence that the intrinsic histone-binding activity of the PCD motif can be used to tune the activity of synthetic histone-binding transcriptional regulators.

synthetic biology↗

bioRxiv2017

Evaluation Of Chromatin Accessibility In Prefrontal Cortex Of Schizophrenia Cases And Controls

Schizophrenia genome-wide association (GWA) studies have identified over 150 regions of the genome that are associated with disease risk, yet there is little evidence that coding mutations contribute to this disorder. To explore the mechanism of non-coding regulatory elements in schizophrenia, we performed ATAC-seq on adult prefrontal cortex brain samples from 135 individuals with schizophrenia and 137 controls, and identified 118,152 ATAC-seq peaks. These accessible chromatin regions in brain are highly enriched for SNP-heritability for schizophrenia (10.6 fold enrichment, P=2.4x10-4, second only to genomic regions conserved in Eutherian mammals) and replicated in an independent dataset (9.0 fold enrichment, P=2.7x10-4). This degree of enrichment of schizophrenia heritability was higher than in open chromatin found in 138 different cell and tissue types. Brain open chromatin regions that overlapped highly conserved regions exhibited an even higher degree of heritability enrichment, indicating that conservation can identify functional subsets within regulatory elements active in brain. However, we did not identify chromatin accessibility differences between schizophrenia cases and controls, nor did we find an interaction of chromatin QTLs with case-control status. This indicates that although causal variants map within regulatory elements, mechanisms other than differential chromatin may govern the contribution of regulatory element variation to schizophrenia risk. Our results strongly implicate gene regulatory processes involving open chromatin in the pathogenesis of schizophrenia, and suggest a strategy to understand the hundreds of common variants emerging from large genomic studies of complex brain diseases.

genomics↗

bioRxiv2017

Detection and quantification of viral RNA in human tumors using open source pipeline: viGEN

An estimated 17% of cancers worldwide are associated with infectious causes. The extent and biological significance of viral presence/infection in actual tumor samples is generally unknown but could be measured using human transcriptome (RNA-seq) data from tumor samples.\n\nWe present an open source bioinformatics pipeline viGEN, which combines existing well-known and novel RNA-seq tools for not only the detection and quantification of viral RNA, but also variants in the viral transcripts.\n\nThe pipeline includes 4 major modules: The first module allows to align and filter out human RNA sequences; the second module maps and count (remaining un-aligned) reads against reference genomes of all known and sequenced human viruses; the third module quantifies read counts at the individual viral genes level thus allowing for downstream differential expression analysis of viral genes between experimental and controls groups. The fourth module calls variants in these viruses. To the best of our knowledge, there are no publicly available pipelines or packages that would provide this type of complete analysis in one open source package.\n\nIn this paper, we applied the viGEN pipeline to two case studies. We first demonstrate the working of our pipeline on a large public dataset, the TCGA cervical cancer cohort. We also performed additional in-depth analyses on a small focused study of TCGA liver cancer patients. In this cohort, we perform viral-gene quantification, viral-variant extraction and survival analysis. This allowed us to find differentially expressed viral-transcripts and viral-variants between the groups of patients, and connect them to clinical outcome.\n\nFrom our analyses, we show that we were able to successfully detect the human papilloma virus among the TCGA cervical cancer patients. We compared the viGEN pipeline with two metagenomics tools and demonstrate similar sensitivity/specificity. We were also able to quantify viral-transcripts and extract viral-variants using the liver cancer dataset. The results presented corresponded with published literature in terms of rate of detection, viral gene expression patterns and impact of several known variants of HBV genome. Results also show novel information about distinct patterns of expression and co-expression in Hepatitis B and the Human Endogenous Retrovirus (HERV) K113 viruses.\n\nThis pipeline is generalizable, and can be used to provide novel biological insights into the significance of viral and other microbial infections in complex diseases, tumorigeneses and cancer immunology. The source code, with example data and tutorial is available at: https://github.com/ICBI/viGEN/.

bioinformatics↗

bioRxiv2016

Hnf4a mediates microbial control of intestinal gene expression and inflammation

Microbiota influence diverse aspects of intestinal epithelial physiology and disease in part by controlling tissue-specific transcription of host genes. However, host genomic mechanisms mediating microbial control of host gene expression are poorly understood. Using an unbiased screening strategy, we found that the zebrafish Hepatic nuclear factor 4 alpha (Hnf4a) transcription factor specifically binds and activates a microbiota-suppressed intestinal epithelial transcriptional enhancer. Genetic analysis disclosed that zebrafish hnf4a activates nearly half of the genes that are suppressed by microbiota, suggesting microbiota negatively regulate Hnf4a. In support, analysis of genomic architecture in mouse intestinal epithelial cells revealed that microbiota colonization leads to activation or inactivation of hundreds of enhancers along with drastic genome-wide reduction of Hnf4a and Hnf4g occupancy. Interspecies meta-analysis suggests Hnf4a may mediate microbial contributions to inflammatory bowel disease pathogenesis. These results indicate Hnf4a plays a critical conserved role in maintaining intestinal homeostasis in response to microbiota and inflammation.

genomics↗

bioRxiv2016

p53 dynamically directs TFIID assembly on target gene promoters

The p53 tumor suppressor protein is a central regulator that turns on vast gene networks to maintain cellular integrity upon various stimuli. p53 activates transcription initiation in part by aiding recruitment of TFIID to the promoter. However, the precise means by which p53 dynamically interacts with TFIID to facilitate assembly on target gene promoters remains elusive. To address this key question, we have undertaken an integrated approach involving single molecule fluorescence microscopy, single particle cryo-electron microscopy, and biochemistry. Our real-time single molecule imaging demonstrates that TFIID alone binds poorly to native p53 target promoters. p53 unlocks TFIIDs ability to bind DNA by increasing TFIID contacts with both the core promoter and a region surrounding p53s response element (RE). Analysis of single molecule dissociation kinetics reveals that TFIID interacts with promoters via transient and prolonged DNA binding modes that are each regulated by p53. Importantly, our structural work reveals that TFIIDs conversion from a canonical form to a rearranged DNA-binding conformation is enhanced in the presence of DNA and p53. Notably, TFIIDs interaction with DNA induces p53 to rapidly dissociate, effectively liberating the RE on the promoter. Collectively, these findings indicate that p53 dynamically escorts and loads the basal transcription machinery onto its target promoters.

biochemistry↗