Biology subjects

Govind, C. K.

Publications and source records attributed to Govind, C. K..

6 recordsLinked to original sources

bioRxiv2023

The association of the RSC remodeler complex with chromatin depends on prefoldin-like Bud27 and determines nucleosome positioning and polyadenylation sites usage in Saccharomyces cerevisiae

The tripartite interaction between the chromatin remodeler complex RSC, RNA polymerase subunit Rpb5 and prefoldin-like Bud27 is necessary for proper RNA pol II elongation. Indeed lack of Bud27 alters this association and affects transcription elongation. This work investigates the consequences of lack of Bud27 on the chromatin association of RSC and RNA pol II, and on nucleosome positioning. Our results demonstrate that RSC binds chromatin to gene bodies and lack of Bud27 alters this association, mainly around polyA sites. This alteration impacts chromatin organization and leads to the accumulation of RNA pol II molecules around polyA sites, likely to be arrested or slower. Our data suggest that RSC is necessary to maintain chromatin organization around those sites, and any alteration of this organization results in the widespread use of alternative polyA sites. Finally, we also find a similar molecular phenotype that occurs upon TOR inhibition with rapamycin, which suggests that alternative polyadenylation observed upon TOR inhibition is likely Bud27-dependent.

molecular biology↗

bioRxiv2022

The role of histone acetyltransferases Gcn5 and Esa1 in recruiting the RSC complex and maintaining nucleosome-depleted regions genome-wide in Saccharomyces cerevisiae

Chromatin remodelers are essential for the maintenance of chromatin structure and gene regulation. In this study, we examined the role of histone acetyltransferases (HATs) Gcn5 and Esa1 in regulating RSC and histone occupancies and their effects on transcription genome-wide. We identified contrasting roles of HATs in modulating RSC occupancies in promoters and ORFs. In HAT mutants, RSC accumulated in nucleosome depleted regions (NDRs) with "fragile nucleosomes (FNs)" more than those with stable -1 nucleosomes. Moreover, the accumulation was more significant in the Esa1 mutant than in the Gcn5 mutant. However, RSC NDR accumulation was not observed in cells lacking H3 or H4 tails. Furthermore, we observed marked increases in histone occupancies in NDRs in the HAT mutants genome-wide. Overall, these data suggest that FNs use hypoacetylated tails to recruit RSC to NDRs, and subsequent acetylation of the tails promote histone eviction. In contrast to the promoters, RSC occupancies were significantly reduced in transcribed ORFs in the HAT mutants. Additionally, the HAT mutants showed reduced TBP and Pol II binding at promoters. Thus, our data implicate HATs and RSC in maintaining NDRs, regulating chromatin structure, and promoting transcription.

genomics↗

bioRxiv2020

Transcriptomic analysis of naïve human embryonic stem cells cultured in three-dimensional PEG scaffolds

Derivation of primed and naive human embryonic stem cells (ESCs) have prompted an increased interest in devising culture conditions for maintaining their pluripotency and differential potential. Naive ESCs are characterized by improved viability, proliferation, and differentiation capacity in comparison to primed ESCs. However, traditional two-dimensional (2-D) cell culture techniques fail to mimic the three-dimensional (3-D) in vivo microenvironment, which results in altered morphological and molecular characteristics of ESCs. Here, we describe the use of 3-D self-assembling scaffolds that support growth and maintenance of the naive state characteristics of human ESC line, Elf1. Scaffolds were formed via a Michael addition reaction upon combination of two 8-arm polyethylene glycol (PEG) polymers functionalized with thiol (PEG-8-SH) and acrylate (PEG-8-Acr) end groups. 3-D scaffolds not only maintained the naive state, but also supported long-term growth for up to 3 weeks without requiring routine passaging and manipulation. 3-D grown cells exhibited upregulation of core (OCT4, NANOG, and SOX2) and naive (KLF17, KLF4, TFCP2L1, DPPA3, and DNMT3L) genes. These genes returned to normal levels when 3-D grown cells were propagated under 2-D culture conditions. Examination of RNA-sequencing demonstrated significant changes in gene expression profiles between 2-D and 3-D grown Elf1 cells. Gene Ontology analysis revealed upregulation of biological processes involved in the regulation of transcription and translation, as well as {beta}-catenin-TCF complex assembly, extracellular matrix organization, and chromatin remodeling in 3-D grown Elf1 cells. 3-D culture conditions also induced upregulation of genes associated with several signaling pathways including Wnt signaling and focal adhesion. However, p53 signaling pathway associated genes were downregulated under these culture conditions. Our findings provide insight into the possible mechanisms of prolonged self-renewal as well as upregulation of pluripotent genes stimulated by the transduction of mechanical signals from the 3-D microenvironment.

cell biology↗

bioRxiv2020

The RSC complex remodels nucleosomes in transcribed coding sequences and promotes transcription in Saccharomyces cerevisiae

RSC (Remodels the Structure of Chromatin) is a conserved ATP-dependent chromatin remodeling complex that regulates many biological processes, including transcription by RNA polymerase II (Pol II). We report that RSC contributes to generation of accessible nucleosomes in transcribed coding sequences (CDSs). RSC MNase ChIP-seq data revealed that RSC-bound nucleosome fragments were very heterogenous (~80 bp to 180 bp) compared to a sharper profile displayed by the MNase inputs (140 bp to 160 bp), supporting the idea that RSC promotes accessibility of nucleosomal DNA. Notably, RSC binding to +1 nucleosomes and CDSs, but not with -1 nucleosomes, strongly correlated with Pol II occupancies, suggesting that RSC enrichment in CDSs is linked to transcription. We also observed that Pol II associates with nucleosomes throughout transcribed CDSs, and similar to RSC, Pol II-protected fragments were highly heterogenous, consistent with the idea that Pol II interacts with remodeled nucleosome in CDSs. This idea is supported by the observation that the genes harboring high-levels of RSC in their CDSs were the most strongly affected by ablating RSC function. We also find that rapid nuclear depletion of Sth1 decreases nucleosome accessibility and results in accumulation of Pol II in highly transcribed CDSs. This is consistent with a slower clearance of elongating Pol II in cells with reduced RSC function, and is distinct from the effect of RSC depletion on PIC assembly. Altogether, our data provide evidence in support of the role of RSC in promoting Pol II elongation, in addition to its role in regulating transcription initiation.

genomics↗

bioRxiv2018

Acetylation-Dependent Recruitment of the FACT Complex and Its Role in Regulating Pol II Occupancy Genome-Wide in Saccharomyces cerevisiae.

Histone chaperones, chromatin remodelers, and histone modifying complexes play a critical role in alleviating the nucleosomal barrier for DNA-dependent processes. Here, we have examined the role of two highly conserved yeast (Saccharomyces cerevisiae) histone chaperones, FACT and Spt6, in regulating transcription. We show that the H3 tail contributes to the recruitment of FACT to coding sequences in a manner dependent on acetylation. We found that deleting a H3 HAT Gcn5 or mutating lysines on the H3 tail impairs FACT recruitment at ADH1 and ARG1 genes. However, deleting the H4 tail or mutating the H4 lysines failed to dampen FACT occupancy in coding regions. Additionally, we show that FACT-depletion reduces Pol II occupancy in the 5 ends genome-wide. In contrast, Spt6-depletion leads to reduction in Pol II occupancy towards the 3 end, in a manner dependent on the gene-length. Severe transcription and histone eviction defects were also observed in a strain that was impaired for Spt6 recruitment (spt6{Delta}202) and depleted of FACT. Importantly, the severity of the defect strongly correlated with WT Pol II occupancies at these genes, indicating critical roles of Spt6 and Spt16 in promoting high-level transcription. Collectively, our results show that both FACT and Spt6 are important for transcription globally and may participate during different stages of transcription.

genetics↗

bioRxiv2018

Saccharomyces cerevisiae histone Chaperones FACT and Spt6 modulate Pol II and histone occupancy genome-wide

Histone chaperones, chromatin remodelers, and histone modifying complexes play a critical role in alleviating the nucleosomal barrier. Here, we have examined the role of two highly conserved yeast (Saccharomyces cerevisiae) histone chaperones, FACT and Spt6, in regulating transcription and histone occupancy. We show that the H3 tail contributes to the recruitment of FACT to coding sequences in a manner dependent on acetylation. We found that deleting a H3 HAT Gcn5 or mutating lysines on the H3 tail impairs FACT recruitment at ADH1 and ARG1 genes. However, deleting the H4 tail or mutating the H4 lysines failed to dampen FACT occupancy in coding regions. Additionally, we show that FACT-depletion greatly reduces Pol II occupancy in the 5 ends genome-wide. By contrast, Spt6-depletion led to reduction in Pol II occupancy towards the 3 end, in a manner dependent on the gene-length. Severe transcription and histone eviction defects were also observed in a strain that was impaired for Spt6 recruitment (spt6{Delta}202) and depleted of FACT. Importantly, the severity of the defect strongly correlated with WT Pol II occupancies at these genes, indicating critical roles of Spt6 and Spt16 in promoting high-level transcription. Collectively, our study shows cooperation, as well as redundancy between chaperones, FACT and Spt6, in regulating transcription and chromatin in coding regions of transcribed genes.

genetics↗