Biology subjects

Gayen, S.

Publications and source records attributed to Gayen, S..

6 recordsLinked to original sources

bioRxiv2021

Single cell analysis reveals X chromosome upregulation is not global and primarily belongs to ancestral genes in pre-gastrulation embryos

Evolution of sex chromosome dosage compensation in mammals remains poorly understood. Ohnos hypothesis state that evolution of dosage compensation occurred through two steps: first, to compensate the dosage imbalance created due to the degradation of Y chromosome in male, upregulation of X-chromosome happened. Subsequently, transmission of X-chromosome upregulation (XCU) in female led to the evolution of X-chromosome inactivation (XCI) to counteract extra dosage of X-linked genes in female cells. Here, we have profiled gene-wise dynamics of XCU in pre-gastrulation mouse embryos at single cell level and found that XCU is dynamically linked with XCI, however, XCU is not global or chromosome-wide like XCI. Therefore, our result raises question whether XCU driven the evolution of XCI. If so, then why XCI is chromosome wide while XCU is not. We propose that XCI might have evolved independent of XCU and therefore refining the current model is necessary. Separately, we show that higher occupancy of different activating factors at upregulated X-linked genes leads to enhanced transcriptional burst frequency and thereby leads to upregulation. On the other hand, our analysis indicates that extent of upregulation, enrichment of different activating marks differs between ancestral and newly acquired X-linked genes. Altogether, our study provides significant insight into the dynamics and mechanistic basis of evolution of sex chromosome dosage compensation. O_FIG_DISPLAY_L [Figure 1] M_FIG_DISPLAY C_FIG_DISPLAY

genetics↗

bioRxiv2021

Paraxial mesoderm organoids model development of human somites

During the development of the vertebrate embryo, segmented structures called somites are periodically formed from the presomitic mesoderm (PSM), and give rise to the vertebral column. While somite formation has been studied in several animal models, it is less clear how well this process is conserved in humans. Recent progress has made it possible to study aspects of human paraxial mesoderm development such as the human segmentation clock in vitro using human pluripotent stem cells (hPSCs), however, somite formation has not been observed in these monolayer cultures. Here, we describe the generation of human paraxial mesoderm (PM) organoids from hPSCs (termed Somitoids), which recapitulate the molecular, morphological and functional features of paraxial mesoderm development, including formation of somite-like structures in vitro. Using a quantitative image-based screen, we identify critical parameters such as initial cell number and signaling modulations that reproducibly yielded somite formation in our organoid system. In addition, using single-cell RNA sequencing and 3D imaging, we show that PM organoids both transcriptionally and morphologically resemble their in vivo counterparts and can be differentiated into somite derivatives. Our organoid system is reproducible and scalable, allowing for the systematic and quantitative analysis of human spinal cord development and disease in vitro.

developmental biology↗

bioRxiv2020

Dynamic erasure of X chromosome upregulation during iPSC reprogramming and in the inner cell mass

In mammals, sex chromosome dosage is compensated through X-chromosome inactivation and active-X upregulation. It is believed that during early development, X-chromosome inactivation and active X upregulation happen in a highly coordinated fashion. However, such coordination between two X-chromosomes in other developmental contexts remains unexplored. Here, we have profiled the coordination between two X-chromosomes in female cells in different developmental contexts and cell types: pre-implantation embryos, embryonic epiblast cells, iPSC reprogramming, germ cell reprogramming, B-cell, and extra-embryonic endoderm stem (XEN) cells. Interestingly, we found that two X-chromosomes in female cells are not always coordinated; instead, it happens in a lineage-specific manner. Specially, while embryonic mouse epiblast cells, iPSC undergo erasure of X-upregulation upon reactivation of the inactive X, germ cells do not. Importantly, we show that the erasure of X-upregulation in epiblast or iPSC is potentially mediated via undifferentiated embryonic transcription Factor 1 (UTF1), which is absent or lowly expressed in late germ cells and therefore, germ cells are unable to erase upregulation. Moreover, we found that partial reactivation of the inactive X is insufficient to drive the erasure of upregulation globally, nor from their counterparts on the active X in XEN and B-cells. Finally, through a phenomenological mathematical model, we show that cross-inhibition between two X-chromosomes can reproduce the dynamics of reactivation and erasure of upregulation. Altogether, our study provides insight into the coordination between two X-chromosomes in female cells in different developmental contexts and related mechanistic aspects. O_FIG O_LINKSMALLFIG WIDTH=117 HEIGHT=200 SRC="FIGDIR/small/424181v2_ufig1.gif" ALT="Figure 1"> View larger version (38K): org.highwire.dtl.DTLVardef@1f01b7borg.highwire.dtl.DTLVardef@9c586borg.highwire.dtl.DTLVardef@70f8eaorg.highwire.dtl.DTLVardef@e5d000_HPS_FORMAT_FIGEXP M_FIG C_FIG

genetics↗

bioRxiv2019

Single Cell Analysis Reveals Partial Reactivation of X-chromosome Instead of chromosome wide dampening in Naive Human Pluripotent Stem Cells

Recently, a unique form of X-chromosome dosage compensation has been demonstrated in human preimplantation embryos, which happens through the dampening of X-linked gene expression from both X-chromosomes. Subsequently, X-chromosome dampening has also been demonstrated in female human pluripotent stem cells (hPSCs) during the transition from primed to naive state. However, the existence of dampened X-chromosomes remains controversial in both embryos and hPSCs. Specifically, in preimplantation embryos it has been shown that there is inactivation of X-chromosome instead of dampening. Here, we have performed allelic analysis of X-linked genes at the single cell level in hPSCs and found that there is partial reactivation of the inactive X-chromosome instead of chromosome-wide dampening upon conversion from primed to naive state. In addition, our analysis suggests that the reduced X-linked gene expression in naive hPSCs might be the consequence of erasure of active X-chromosome upregulation.

genetics↗

bioRxiv2019

Ligand dependent gene regulation by transient ER clustered enhancers

Unliganded nuclear receptors have been implicated in ligand-dependent gene regulation. However, the underlying mechanisms are not fully understood. Here we demonstrate that unliganded ER binds to specific sites in the genome thereby pre-marking them as future functional enhancers. Upon ligand exposure, ER binds to several EREs relatively proximal to the pre-marked, or persistent, ER-bound sites. Interestingly, the persistent sites interact extensively, via chromatin looping, with the proximal transiently bound sites forming ER clustered enhancers in 3D. CRISPR-based deletion of TFF1 persistent site disrupts the formation of its clustered enhancer resulting in the loss of E2-dependent induced expression of TFF1 and its neighboring genes within the same cluster. The clustered enhancers overlap with nuclear ER puncta that coalesce in a ligand-dependent manner. Furthermore, formation of clustered enhancers, as well as puncta, coincide with the active phase of signaling and their later disappearance results in the loss of gene expression even though persistent sites remain bound by ER. Our results establish the role of persistent unliganded ER binding in priming enhancer clusters in 3D that drive transient, but robust, gene expression in a ligand-dependent fashion.

molecular biology↗

bioRxiv2017

Induction of X-chromosome Inactivation by the Histone Demethylase SMCX/KDM5C

XY male and XX female mammals equalize X-linked gene expression through the mitotically-stable transcriptional inactivation of an X-chromosome in females. Although most genes are silent on the inactive-X, some escape silencing and are expressed at higher levels in females vs. males. Here, we show that the escapee Smcx/Kdm5c, encoding a histone H3K4me2/3 demethylase, underlies the female-specific induction of X-inactivation. Mouse embryonic epiblast cells and differentiating embryonic stem cells (ESCs) lacking SMCX show reduced expression of Xist RNA, which is required for X-inactivation. Smcx-heterozygous epiblast cells do not silence X-linked genes efficiently, despite robust Xist expression. Overexpression of mouse or human SMCX, but not a catalytically-inactive SMCX or the Y-chromosome homolog SMCY, is sufficient to induce Xist and, separately, to silence X-linked genes in male ESCs. Finally, SMCX dose is inversely correlated with H3K4me2 at X-linked loci. Thus, X-inactivation initiates through the evolutionarily conserved, dose-dependent function of the histone demethylase SMCX.

genetics↗