Biology subjects

Parasar, B.

Publications and source records attributed to Parasar, B..

5 recordsLinked to original sources

bioRxiv2026

A brain locus for viable gestation

The expectant mother's body is systemically remodeled by her hormones to weather the physiological vicissitudes of pregnancy. In contrast to other reproductive organs, how the expectant mother's brain promotes these system-wide changes is largely unexplored. Here we show that pregnancy induces profound changes in gene expression and identity of hormone-sensitive neurons and report a previously unknown class of such cells that is required for viable pregnancy. We performed RNA sequencing from late mid-gestation mice of four estrogen receptor alpha-expressing populations from hypothalamus and amygdala that regulate reproductive behaviors altered during gestation. Each of these populations undergoes such large, specific transcriptional shifts during pregnancy that these changes even exceed their transcriptional differences between the sexes. The gene expression changes during pregnancy also imbue particular transcriptomically-defined neuronal types within these four populations with new molecular identities. Targeted ablation of one such neuronal type, POANpy2r cells, precludes implantation and abrogates viable pregnancy. Taken together, we have uncovered an essential role of hormone-sensitive neurons in the brain in sustaining pregnancy. The etiology of spontaneous gestational loss, which afflicts ~15% of human pregnancies, remains idiopathic in many cases, and our findings suggest a brain-based mechanism that contributes to such events. More broadly, we provide a molecular and cellular foundation to study gestational processes in health and disease from the perspective of the pregnant brain-body axis.

neuroscience↗

bioRxiv2026

Whole-genome 3D architectural screen reveals modulators of brain DNA structure

Three-dimensional (3D) genome architecture is the foundation of gene regulation, and plays a critical role in normal physiology and disease. However, our understanding of its biochemical determinants has long been limited by technology: imaging-based screens only profile a small number of loci, while sequencing-based studies rarely exceed 100 samples or conditions. Here we present "in-plate chromosome conformation capture" (Plate-C), a high-throughput, cost-effective platform that profiles thousands of whole-genome architectures in a day. Plate-C enabled the first chemical screen for whole-genome structural changes--profiling 2,956 samples from 834 conditions across 5 neuronal and glial types, accompanied by 6,081 single cells using "easy diploid chromosome conformation capture" (Easy Dip-C) and 200,893 single-cell transcriptomes. We discovered that diverse, dose/time-dependent, and cell type/species-specific modes of DNA structural changes can be rapidly induced by manipulating epigenetic (HDAC, BET), metabolic (mTOR), proteostatic (UPR), developmental (GSK3/Wnt, Hedgehog), immune (cGAS/STING), and neurotransmission pathways. To validate our finding in vivo, we demonstrated in newborn mice that HDAC inhibition drives brain-wide genome rewiring within hours, highly correlated with changes in vitro and inducing a latent structural and transcriptional state orthogonal to normal differentiation. By enabling massively parallel profiling of whole-genome structures, Plate-C paves the way for systematic discovery of DNA folding principles to better understand and engineer the human genome in 3D.

genomics↗

bioRxiv2026

Genome expansions and regulatory contact entanglement help preserve ancestral metazoan synteny

Chromosomes constitute deeply conserved evolutionary units in many metazoan genomes, with chromosomal fusions and fissions, accompanied by sub-chromosomal rearrangements, rewiring three dimensional genome architecture. How chromatin loops and compartments that define distal regulatory interactions within chromosomes impose functional constraints that affect this long-term evolutionary process (and vice-versa) is an emerging research topic. Genome expansions, especially through transposable element (TE) activity, test these constraints by increasing the genomic distances over which regulatory interactions must function and were thus suggested to be the drivers of chromosomal rearrangements. To study dynamics and stability of such distal interactions in the light of genome expansions, we focus on the cnidarian Hydra vulgaris, which, based on its simple and well-understood biology as well as one of the largest genomes among cnidarians, is particularly suited to test how chromatin loop and genome architecture respond to genome expansion. We investigate genome architecture using Micro-C, single-cell Hi-C (Dip-C), and DNA FISH, and perform comparative analysis using available genomic and epigenomic data. Contrary to prior expectations, our analysis of whole-genome data and particular loci (e.g., Wnt) suggests a scenario where genome expansion did not only result in chromatin loops often reaching several megabases in hydra, but also led to regulatory contact mixing and entanglement, introducing additional constraints to maintain ancestral genomic architecture. Generalizing these findings across hundreds of metazoan genomes, we show a new mechanistic role for genome expansion in yielding entangled long-range regulatory configurations that, in turn, decelerate chromosomal rearrangements, thus maintaining (and not breaking) ancestral regulatory states and synteny. Significance statementSome of the largest and most repetitive animal genomes retain a surprisingly high level of deeply conserved metazoan synteny. As repetitive regions are often associated with chromosomal rearrangements, it has been enigmatic why syntenic retention is so frequently observed. In this study, using hydra as a model system for both stem cell biology and an evolutionary history rich in transposable-element driven genome expansion, a multi-level conformational landscape dissection reveals a multitude of long-range regulatory states. We show that mixing of multiple such regulatory links accompanied by genomic expansion is associated with maintained ancestral synteny, thus pointing to the counter-intuitive role of genome expansions as "fossilization" agents across metazoan genomes.

evolutionary biology↗

bioRxiv2023

Cerebellar Granule Cells Develop Non-neuronal 3D Genome Architecture over the Lifespan

The cerebellum contains most of the neurons in the human brain, and exhibits unique modes of development, malformation, and aging. For example, granule cells--the most abundant neuron type--develop unusually late and exhibit unique nuclear morphology. Here, by developing our high-resolution single-cell 3D genome assay Dip-C into population-scale (Pop-C) and virus-enriched (vDip-C) modes, we were able to resolve the first 3D genome structures of single cerebellar cells, create life-spanning 3D genome atlases for both human and mouse, and jointly measure transcriptome and chromatin accessibility during development. We found that while the transcriptome and chromatin accessibility of human granule cells exhibit a characteristic maturation pattern within the first year of postnatal life, 3D genome architecture gradually remodels throughout life into a non-neuronal state with ultra-long-range intra-chromosomal contacts and specific inter-chromosomal contacts. This 3D genome remodeling is conserved in mice, and robust to heterozygous deletion of chromatin remodeling disease-associated genes (Chd8 or Arid1b). Together these results reveal unexpected and evolutionarily-conserved molecular processes underlying the unique development and aging of the mammalian cerebellum.

neuroscience↗

bioRxiv2019

Engineered Th17 cell differentiation using a photo-activatable immune modulator

T helper 17 (Th17) cells, an important subset of CD4+ T cells, help to eliminate extracellular infectious pathogens that have invaded our tissues. Despite the critical roles of Th17 cells in immunity, how the immune system regulates the production and maintenance of this cell type remains poorly understood. In particular, the plasticity of these cells, or their dynamic ability to trans-differentiate into other CD4+ T cell subsets, remains mostly uncharacterized. Here, we report a synthetic immunology approach using a photo-activatable immune modulator (PIM) to increase Th17 cell differentiation on demand with spatial and temporal precision to help elucidate this important and dynamic process. In this chemical strategy, we developed a latent agonist that, upon photochemical activation, releases a small-molecule ligand that targets the aryl hydrocarbon receptor (AhR) and ultimately induces Th17 cell differentiation. We used this chemical tool to control AhR activation with spatiotemporal precision within cells and to modulate Th17 cell differentiation on demand by using UV light illumination. We envision that this approach will enable an understanding of the dynamic functions and behaviors of Th17 cells in vivo during immune responses and in mouse models of inflammatory disease.

biochemistry↗