Biology subjects

Bass, H. W.

Publications and source records attributed to Bass, H. W..

13 recordsLinked to original sources

bioRxiv2026

KNOB K180 CONSTITUTIVE HETEROCHROMATIN OF MAIZE EXHIBIT TISSUE-SPECIFIC CHROMATIN SENSTITIVE PROFILES DISTINCT FROM OTHER TYPES OF HETEROCHROMATINS

BackgroundMaize knobs are regions of constitutive heterochromatin that are readily identified in both meiotic and somatic chromosomes. These structures have been characterized as stable throughout the cell cycle, exhibiting late replication during the S-phase, and are composed of two specific families of highly repetitive DNA sequences: K180 and TR-1. Although widely used as cytogenetic markers due to their variability in number and chromosomal position across inbred lines, hybrids, and landraces, little is known about their chromatin structure and dynamics. In this study, we analyzed chromatin accessibility of knobs using DNS-seq data across four maize tissues representing distinct developmental stages. ResultsOur results reveal that K180 knobs exhibit tissue-specific variation in chromatin accessibility, transitioning between open and closed states during development. In contrast, the TR-1 knob of chromosome 4 remained consistently inaccessible across all tissues analyzed. A knob composed of both K180, and TR-1 further supported this observation, with only the K180 region showing dynamic accessibility. To validate these findings, we also analyzed other repetitive regions such as centromeres, which showed a uniformly closed chromatin structure similar to TR-1. These results suggest a unique developmental modulation of chromatin accessibility associated with K180 repeats. While the chromatin accessibility of knobs does not reach the levels observed at Transcription Start Sites (TSS), the comparison among different classes of repetitive DNA within maize constitutive heterochromatin provides compelling evidence for sequence-specific and tissue-specific chromatin dynamics. ConclusionsOur findings uncover a previously unrecognized property of maize knobs and establish a reference for future studies on chromatin organization and epigenetic regulation of repetitive DNA in plant genomes.

genetics↗

bioRxiv2025

Analysis of alternative splicing uncovers a vastly expanded transcriptomic response to hypoxia in human vascular endothelial cells

Hypoxia is a fundamental pathophysiological stimulus that plays important roles in multiple cardiopulmonary diseases. During hypoxic stress, cells adapt by undergoing widespread transcriptional reprogramming. The conventional approach to investigating this response has largely involved RNA-seq analysis which typically quantifies transcriptional output at the level of individual genes. However, as most mammalian genes encode multiple transcripts that are divergently regulated by alternative splicing, consolidating these discrete features to the gene level can obscure critical changes within the transcriptome that are largely unappreciated. To more accurately define the role of individual transcript usage during hypoxia, herein we employed three different analytical strategies that collectively identified thousands of instances of alternative splicing in human endothelial cells undergoing hypoxic stress. Notably, the set of differentially utilized transcripts displayed minimal overlap with the genes identified to be differentially expressed by conventional RNA-seq analysis, indicating divergent usage of individual transcripts does not reliably culminate in a detectable change in overall expression. This outcome is particularly clear at the earliest time-point of hypoxia where we found the transcriptional response was mediated almost exclusively by alternative splicing. A subset of these acutely responsive genes was variably detected as differentially expressed or alternatively spliced at later time points, demonstrating hypoxic transcription is highly dynamic and temporally complex. Further, the number of genes in pathways incriminated in the hypoxic response was also expanded considerably when alternatively spliced transcripts were included in the analysis, suggesting distinct attributes of the hypoxic transcriptome are unveiled by transcript level assays that would otherwise be obfuscated by standard RNA-seq analyses that summarize expression to the gene level. Collectively, these results strongly point to alternative splicing being a significant, albeit understudied, component of the transcriptional response to hypoxic stress which is vastly more complicated than previously thought.

genomics↗

bioRxiv2025

Replication Timing Uncovers a Two-Compartment Nuclear Architecture of Interphase Euchromatin in Maize

Genome replication is temporally regulated during S phase, with specific genomic regions replicating at defined times in a process that is known as replication timing (RT). Based on 3D cytology in replicating nuclei, we previously proposed a "mini-domain chromatin fiber RT model" for maize euchromatin that suggested it is subdivided into early-S and middle-S compartments distinguished by chromatin condensation and RT. However, whether this compartmentalization reflects a general nuclear architecture that persists throughout the cell cycle was unclear. To test this model, we conducted two orthogonal assays - Hi-C for genome-wide interaction data and 3D FISH for direct visualization of chromatin organization. Hi-C eigenvalues and insulation scores revealed distinct patterns of early-S regions having negative insulation scores with long-range contacts while middle-S regions showed the opposite. Early-S regions correlated more strongly with epigenomic signatures of open, transcriptionally active chromatin than middle-S regions. 3D oligo FISH painting confirmed that early-S and middle-S regions occupy adjacent but largely non-overlapping nucleoplasmic spaces during all interphase stages, including G1. Our findings redefine the maize euchromatin "A" compartment as having two distinct, closely interspersed subcompartments, early-S and middle-S, underscoring the importance of replication timing (RT) as a defining feature of chromatin architecture and genome organization.

genetics↗

bioRxiv2025

The Cistrome Response to Hypoxia in Human Umbilical Vein Endothelial Cells

Hypoxic stress triggers transcriptional signaling mainly through hypoxia-inducible transcription factors (HIFs), which bind hypoxia response elements (HREs) in gene regulatory regions. However, only a small proportion ([~]1%) of known HREs are occupied by HIFs during hypoxia, suggesting the involvement of additional hypoxia-responsive factors. To address this gap, we utilized MNase-defined cistrome Occupancy Analysis sequencing (MOA-seq), with the term cistrome referring to all genomic regions where transcription factors and other trans-acting regulators are bound to cis-acting elements across the genome for a particular cell type or treatment. This MNase-based assay enables genome-wide, high-resolution (<30 bp) identification of transcription factor (TF) occupancy footprints embedded within larger regions, most of which were previously annotated as open or accessible chromatin. Applying this in situ cistrome mapping to fixed nuclei from endothelial cells under normoxia or hypoxia (1, 3, or 24 hours) revealed thousands of hypoxia-responsive genomic sites with dynamic TF footprints. The affected genes were enriched in canonical hypoxia-induced pathways, such as angiogenesis. Motif analysis identified over 100 candidate TFs potentially mediating these multifaceted genomic responses. By grouping hypoxia-modified occupancy signals across the hypoxia exposure times, we clustered differentially occupied MOA sites into defined 10 distinct TF kinetic clusters, half of which were associated with HIF1A. HIF1A-proximal binding sites suggested co-activators, while non-HIF1A clusters pointed to additional TFs that may have HIF1A-independent roles. This analysis provides insight into how multiple TF networks coordinate hypoxia responses and highlights the power of cistrome profiling to deepen our understanding of the complex genomic response to low oxygen conditions. KEY POINTSO_LIMOA-seq mapped TF occupancy at 21,765 sites in normoxia, including 7,444 beyond the known ENCODE cCREs. C_LIO_LIHypoxia for 1, 3, and 24h changes the cistrome occupancy at thousands of genes. C_LIO_LIClustering analysis of hypoxia-responsive footprints consolidated cistrome kinetics into HIF1A-associated and HIF1A-independent TFs. C_LI

genomics↗

bioRxiv2025

Transient alterations in nucleosome distribution and sensitivity to nuclease define the THP-1 monocyte to macrophage transition

The monocyte to macrophage transition is marked by alterations to both the structure and function of the genome, including changes in histone post-translational modifications, DNA methylation, 3D nuclear architecture, and expression of lineage specific genes. The nucleosome is the fundamental organizational unit of the eukaryotic genome and underpins both genome structure and function. However, nucleosome dynamics at promoters, which are essential for transcriptional regulation, are understudied in cellular differentiation. We conducted high-resolution chromatin structure profiling at promoters in the THP-1 cell line at eight different time points spanning PMA-induced monocyte to macrophage differentiation. We found that fewer than 10% of nucleosomes within promoters were redistributed during differentiation and only a subset of these were associated with immediate transcriptional alterations. Nucleosomes within the promoters of PMA-responsive genes were strongly positioned prior to differentiation and experienced minimal alterations during differentiation thus implying the existence of a pre-differentiation primed chromatin state. Additionally, we observed pronounced alterations in nucleosome sensitivity to MNase digestion within one hour of PMA-induced differentiation and the emergence of a highly resistant phenotype in fully differentiated cells. We found that resistance is correlated with active chromatin marks, transcription factor binding, gene expression, and higher order chromatin structure demonstrating that it is a useful measure of both genome structure and function. Together this suggests that, unlike more stable nucleosome distribution, transient sensitivity alterations may underpin new genomic functions in differentiating cells. Our results offer a framework for understanding how chromatin structural alterations potentiate cellular differentiation in a monocyte model and use methodology that is widely applicable to other systems. Summary sentenceNucleosome distribution is largely static during PMA induced monocyte differentiation while nucleosome sensitivity is highly dynamic and is associated with gene expression, active chromatin marks, transcription factor binding, and higher order chromatin structure.

genomics↗

bioRxiv2025

Dynamic nucleosome redistribution and increases innucleosome sensitivity underpin THP-1 macrophage response to LPS

Macrophages detect lipopolysaccharide (LPS) through toll-like receptor 4 (TLR-4) on the cell surface which initiates a signaling cascade resulting in the recruitment of regulatory factors to chromatin and subsequent expression of chemokine and cytokine genes. Primary response genes, marked by poised promoters and enhancers, are rapidly expressed after LPS stimulation, and their gene products activate secondary response genes via paracrine and autocrine signaling pathways. While the signaling cascades following macrophage activation are well understood, the dynamics of nucleosome architecture and regulatory factor binding in promoter regions during early and late LPS responses remain unclear. Here, we stimulated THP-1 derived macrophages with LPS and assessed nucleosome distribution and MNase sensitivity across promoters at eight time points spanning primary and secondary responses. We found that while nucleosome distribution was static over most promoters, LPS stimulation resulted in transient remodeling of a subset of immune and DNA repair gene promoters. We also observed distinct MNase sensitivity alterations in two phases which aligned with early and late gene expression patterns. Notably, while most Pol II promoters showed altered chromatin sensitivity, only a subset exhibited transcriptional changes, suggesting that widespread alterations in nucleosome distribution and sensitivity occur at promoters with or without alterations in gene expression. These findings provide new temporal insights into the transient and long-term effects of immune stimulation on promoter architecture and offer a methodological framework for additional time-resolved studies of chromatin remodeling in other systems. Summary sentenceFollowing LPS stimulation, a subset of nucleosomes in macrophage immune promoters undergo transient redistribution, whereas the majority of nucleosomes show changes in MNase sensitivity that are largely uncoupled from gene expression. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=163 SRC="FIGDIR/small/637695v1_ufig1.gif" ALT="Figure 1"> View larger version (46K): org.highwire.dtl.DTLVardef@198f47org.highwire.dtl.DTLVardef@dab80org.highwire.dtl.DTLVardef@1769d0corg.highwire.dtl.DTLVardef@40be27_HPS_FORMAT_FIGEXP M_FIG O_FLOATNOGraphical abstract.C_FLOATNO LPS stimulation of THP-1 derived macrophages leads to altered nucleosome occupancy and positioning within a subset of promoters which are enriched for LPS response genes. Altered distribution patterns permit regulatory factor binding and gene expression. The majority of promoters have altered nucleosome sensitivity with a trend towards increased sensitivity after LPS stimulation. Altered sensitivity results in regulatory factor binding and expression of LPS response genes. C_FIG

genomics↗

bioRxiv2023

Phenotypic variation in maize can be largely explained by genetic variation at transcription factor binding sites

Comprehensive maps of functional variation at transcription factor (TF) binding sites (cis-elements) are crucial for elucidating how genotype shapes phenotype. Here we report the construction of a pan-cistrome of the maize leaf under well-watered and drought conditions. We quantified haplotype-specific TF footprints across a pan-genome of 25 maize hybrids and mapped over two-hundred thousand genetic variants (termed binding-QTL) linked to cis-element occupancy. Three lines of evidence support the functional significance of binding-QTL: i) they coincide with numerous known causative loci that regulate traits, including VGT1, Trehalase1, and the MITE transposon near ZmNAC111 under drought; ii) their footprint bias is mirrored between inbred parents and by ChIP-seq; iii) partitioning genetic variation across genomic regions demonstrates that binding-QTL capture the majority of heritable trait variation across [~]70% of 143 phenotypes. Our study provides a promising approach to make previously hidden cis-variation more accessible for genetic studies and multi-target engineering of complex traits.

genomics↗

bioRxiv2022

SCsnvcna: Integrating SNVs and CNAs on a phylogenetic tree from single-cell DNA sequencing data

Single-cell DNA sequencing enables the construction of evolutionary trees that can reveal how tumors gain mutations and grow. Different whole genome amplification (WGA) procedures render genomic materials of different characteristics, often suitable for the detection of either single nucleotide variation (SNV) or for copy number aberration (CNA), but not for both, hindering the placement of both SNVs and CNAs on the same phylogenetic tree for the study of interplay of SNVs and CNAs. SCARLET places SNVs on a CNA tree, a tree derived based on the copy number profiles, while considering SNV loss due to copy number losses. However, SCARLET requires that the SNVs and CNAs are detected from the same sets of cells, which is technically challenging due to the sequencing errors or the low sequencing coverage associated with a particular WGA procedure. Here we presented a novel computational tool, SCsnvcna, that aims at placing SNVs on a CNA tree whereas the sets of cells rendering the SNVs and CNAs are independent, thus is more practical in terms of the technical challenge from single cell WGA process. SCsnvcna is a Bayesian probabilistic model that utilizes both the genotype constraints on the tree and the cellular prevalence (CP) to search the solution that has the highest joint probability. Both simulated and real datasets show that SCsnvcna is highly accurate in predicting the placement of SNVs and SNV cells. In addition, SCsnvcna has a precise prediction of SNV losses due to copy number loss.

bioinformatics↗

bioRxiv2020

Maize (Zea mays L.) nucleoskeletal proteins regulate nuclear envelope remodeling and function in stomatal complex development and pollen viability.

In eukaryotes, the nuclear envelope (NE) encloses chromatin and separates it from the rest of the cell. The Linker of Nucleoskeleton and Cytoskeleton (LINC) complex physically bridges across the NE, linking nuclear and cytoplasmic components. In plants, these LINC complexes are beginning to be ascribed roles in cellular and nuclear functions, including chromatin organization, regulation of nuclei shape and movement, and cell division. Homologs of core LINC components, KASH and SUN proteins, have previously been identified in maize. Here, we characterized the presumed LINC-associated maize nucleoskeletal proteins NCH1 and NCH2, homologs of members of the plant NMCP/CRWN family, and MKAKU41, homologous to AtKAKU4. All three proteins localized to the nuclear periphery when transiently and heterologously expressed as fluorescent protein fusions in Nicotiana benthamiana. Overexpression of MKAKU41 caused dramatic changes in the organization of the nuclear periphery, including nuclear invaginations that stained positive for non-nucleoplasmic markers of the inner and outer NE, and the ER. The severity of these invaginations was altered by changes in LINC connections and the actin cytoskeleton. In maize, MKAKU41 appeared to share genetic functions with other LINC components, including control of nuclei shape, stomatal complex development, and pollen viability. Overall, our data show that NCH1, NCH2, and MKAKU41 have characteristic properties of LINC-associated plant nucleoskeletal proteins, including interactions with NE components suggestive of functions at the nuclear periphery that impact the overall nuclear architecture.

cell biology↗

bioRxiv2020

New Tools for Hop Cytogenomics: Identification of Tandem Repeat Families from Long-Read Sequences of Humulus lupulus

Hop (Humulus lupulus L.) is known for its use as a bittering agent in beer and has a rich history of cultivation, beginning in Europe and now spanning the globe. There are five wild varieties worldwide, which may have been introgressed with cultivated varieties. As a dioecious species, its obligate outcrossing, non-Mendelian inheritance, and genomic structural variability have confounded directed breeding efforts. Consequently, understanding genome evolution in Humulus represents a considerable challenge, requiring additional resources, including integrated genome maps. In order to facilitate cytogenetic investigations into the transmission genetics of hop, we report here the identification and characterization of 17 new and distinct tandem repeat sequence families. A tandem repeat discovery pipeline was developed using k-mer filtering and dot plot analysis of PacBio long-read sequences from the hop cultivar Apollo. We produced oligonucleotide FISH probes from conserved regions of HuluTR120 and HulTR225 and demonstrated their utility to stain meiotic chromosomes from wild hop, var. neomexicanus. The HuluTR225 FISH probe hybridized to several loci per nucleus and exhibited irregular, non-Mendelian transmission in male meiocytes of wild hop. Collectively, these tandem repeat sequence families not only represent unique and valuable new cytogenetic reagents but also have the capacity to inform genome assembly efforts and support comparative genomic analyses.

plant biology↗

bioRxiv2019

The regulatory landscape of early maize inflorescence development

BackgroundThe functional genome of agronomically important plant species remains largely unexplored, yet presents a virtually untapped resource for targeted crop improvement. Functional elements of regulatory DNA revealed through profiles of chromatin accessibility can be harnessed for fine-tuning gene expression to optimal phenotypes in specific environments. ResultHere, we investigate the non-coding regulatory space in the maize (Zea mays) genome during early reproductive development of pollen- and grain-bearing inflorescences. Using an assay for differential sensitivity of chromatin to micrococcal nuclease (MNase) digestion, we profile accessible chromatin and nucleosome occupancy in these largely undifferentiated tissues and classify at least 1.6 percent of the genome as accessible, with the majority of MNase hypersensitive sites marking proximal promoters, but also 3 ends of maize genes. This approach maps regulatory elements to footprint-level resolution. Integration of complementary transcriptome profiles and transcription factor occupancy data are used to annotate regulatory factors, such as combinatorial transcription factor binding motifs and long non-coding RNAs, that potentially contribute to organogenesis, including tissue-specific regulation between male and female inflorescence structures. Finally, genome-wide association studies for inflorescence architecture traits based solely on functional regions delineated by MNase hypersensitivity reveals new SNP-trait associations in known regulators of inflorescence development as well as new candidates. ConclusionsThese analyses provide a comprehensive look into the cis-regulatory landscape during inflorescence differentiation in a major cereal crop, which ultimately shapes architecture and influences yield potential.

plant biology↗

bioRxiv2019

The Maize LINC KASH AtSINE-like2 (MLKS2) gene encodes an ARM domain protein that tethers the nucleus to F-actin and is required for normal development and meiotic chromosome segregation

The linker of nucleoskeleton and cytoskeleton (LINC) complex is an essential multi-protein structure spanning the eukaryotic nuclear envelope. The LINC complex functions to maintain nuclear architecture, positioning, and mobility, along with specialized functions in meiotic prophase and chromosome segregation. Members of the LINC complex were recently identified in maize, an important scientific and agricultural grass species. Here we characterized Maize LINC KASH AtSINE-like2, MLKS2, which encodes a highly conserved SINE-group plant KASH protein with characteristic N-terminal armadillo repeats (ARM). Using a heterologous expression system, we showed that actively expressed GFP-MLKS2 is targeted to the nuclear periphery and colocalizes with F-actin and the endoplasmic reticulum, but not microtubules in the cell cortex. Expression of GFP-MLKS2, but not GFP-MLKS2{Delta}ARM, resulted in nuclear anchoring. Genetic analysis of transposon-insertion mutations, mlks2-1 and mlks2-2, showed that the mutant phenotypes were pleiotropic, affecting root hair nuclear morphology, stomatal complex development, multiple aspects of meiosis, and pollen viability. In male meiosis, the mutants showed defects for bouquet-stage telomere clustering, nuclear repositioning, perinuclear actin accumulation, dispersal of late prophase bivalents, and meiotic chromosome segregation. These findings support a model in which the nucleus is connected to cytoskeletal F-actin through the ARM-domain, predicted alpha solenoid structure of MLKS2. Functional conservation of MLKS2 was demonstrated through genetic rescue of the misshapen nuclear phenotype of an Arabidopsis (triple-WIP) KASH mutant. This study establishes a role for the SINE-type KASH proteins in affecting the dynamic nuclear phenomena required for normal plant growth and fertility.

cell biology↗

bioRxiv2018

Identification and characterization of conserved and divergent genes encoding the nuclear envelope LINC complex in maize (Zea mays L.).

The LINC (Linker of Nucleoskeleton to Cytoskeleton) complex is an essential multi-protein structure spanning the nuclear envelope. It connects the cytoplasm to the nucleoplasm, functions to maintain nuclear shape and architecture, and regulates chromosome dynamics during cell division. Knowledge of LINC complex composition and function in the plant kingdom is primarily limited to Arabidopsis, but critically missing from the evolutionarily distant monocots which include grasses, the most important agronomic crops worldwide. To fill this knowledge gap, we identified and characterized 22 maize genes, including a new grass-specific KASH gene family. Using bioinformatic, biochemical, and cell biological approaches, we provide evidence that representative KASH candidates localize to the nuclear periphery and interact with ZmSUN2 in vivo. FRAP experiments using domain-deletion constructs verified that this SUN-KASH interaction was dependent on the SUN but not the coiled-coil domain of ZmSUN2. A summary working model is proposed for the entire maize LINC complex encoded by conserved and divergent gene families. These findings expand our knowledge of the plant nuclear envelope in a model grass species, with implications for both basic and applied cellular research.\n\nSUMMARY STATEMENTGenes encoding maize candidates for the core LINC and associated complex proteins have been comprehensively identified with functional validation by one or more assays for several of the KASH genes.

cell biology↗