Biology subjects

Sharma, U.

Publications and source records attributed to Sharma, U..

23 records · Page 2Linked to original sources

bioRxiv2020

Integrated genomic view of SARS-CoV-2 in India

India first detected SARS-CoV-2, causal agent of COVID-19 in late January-2020, imported from Wuhan, China. March-2020 onwards; importation of cases from rest of the countries followed by seeding of local transmission triggered further outbreaks in India. We used ARTIC protocol based tiling amplicon sequencing of SARS-CoV-2 (n=104) from different states of India using a combination of MinION and MinIT from Oxford Nanopore Technology to understand introduction and local transmission. The analyses revealed multiple introductions of SARS-CoV-2 from Europe and Asia following local transmission. The most prevalent genomes with patterns of variance (confined in a cluster) remain unclassified, here, proposed as A4-clade based on its divergence within A-cluster. The viral haplotypes may link their persistence to geo-climatic conditions and host response. Despite the effectiveness of non-therapeutic interventions in India, multipronged strategies including molecular surveillance based on real-time viral genomic data is of paramount importance for a timely management of the pandemic.

microbiology↗

bioRxiv2020

High-speed adaptive optics line-scan OCT for cellular-resolution optoretinography

Optoretinography - the non-invasive, optical imaging of light-induced functional activity in the retina - stands to provide a critical biomarker for testing the safety and efficacy of new therapies as well as their rapid translation to the clinic. Optical phase change in response to light, as readily accessible in phase-resolved OCT, offers a path towards all-optical imaging of retinal function. However, typical human eye motion adversely affects phase stability and precludes the recording of fast light-induced retinal events. Here we introduce a high-speed line-scan spectral domain OCT with adaptive optics (AO), aimed at volumetric imaging and phase-resolved acquisition of retinal responses to light. By virtue of parallel acquisition of an entire retinal cross-section (B-scan) in a single high-speed camera frame, depth-resolved tomograms at speeds up to 16 kHz were achieved with high sensitivity and phase stability. To optimize spectral and spatial resolution, an anamorphic detection paradigm was introduced enabling improved light collection efficiency and signal roll-off compared to traditional methods. The benefits in speed, resolution and sensitivity were exemplified in imaging nanometer-millisecond scale light-induced optical path length changes in cone photoreceptor outer segments. With 660 nm stimuli, individual cone responses readily segregated into three clusters, corresponding to long, middle and short-wavelength cones. Recording such optoretinograms on spatial scales ranging from individual cones, to 100 m-wide retinal patches offers a robust and sensitive biomarker for cone function in health and disease. Furthermore, incorporating this capability into an easy-to-use and ubiquitous diagnostic platform of OCT enables its widespread application to patient care and drug development.

bioengineering↗

bioRxiv2020

An atlas of cell types in the mammalian epididymis and vas deferens

Following spermatogenesis in the testis, mammalian sperm continue to mature over the course of approximately 10 days as they transit a long epithelial tube known as the epididymis. The epididymis is comprised of multiple segments/compartments that, in addition to concentrating sperm and preventing their premature activation, play key roles in remodeling the protein, lipid, and RNA composition of maturing sperm. In order to understand the complex roles for the epididymis in reproductive biology, we generated a single cell atlas of gene expression from the murine epididymis and vas deferens. We recovered all the key cell types of the epididymal epithelium, including principal cells, clear cells, and basal cells, along with associated support cells that include fibroblasts, smooth muscle, macrophages and other immune cells. Moreover, our data illuminate extensive regional specialization of principal cell populations across the length of the epididymis, with a substantial fraction of segment-specific genes localized in genomic clusters of functionally-related genes. In addition to the extensive region-specific specialization of principal cells, we find evidence for functionally-specialized subpopulations of stromal cells, and, most notably, two distinct populations of clear cells. Analysis of ligand/receptor expression reveals a network of potential cellular signaling connections, with several predicted interactions between cell types that may play roles in immune cell recruitment and other aspects of epididymal function. Our dataset extends on existing knowledge of epididymal biology, and provides a wealth of information on potential regulatory and signaling factors that bear future investigation.

developmental biology↗

bioRxiv2017

Small RNAs are trafficked from the epididymis to developing mammalian sperm

RNAs present in mature mammalian sperm are delivered to the zygote at fertilization, where they have the potential to affect early development. The biogenesis of the small RNA payload of mature sperm is therefore of great interest, as it may be a target of signaling pathways linking paternal conditions to offspring phenotype. Recent studies have suggested the surprising hypothesis that the small RNA payload carried by mature sperm may include RNAs that were not synthesized during testicular spermatogenesis, but that are instead delivered to sperm during the process of post-testicular maturation in the epididymis. To further test this hypothesis, we characterized small RNA dynamics during testicular and post-testicular germ cell maturation in mice. We show that purified testicular germ cell populations, including mature testicular spermatozoa, carry extremely low levels of tRNA fragments (tRFs), and that tRFs become highly abundant only after sperm have entered the epididiymis. The process of small RNA delivery to sperm can be recapitulated in vitro, as caput epididymosomes deliver small RNAs including tRFs and microRNAs to mature testicular spermatozoa. Finally, to definitively identify the tissue of origin for small RNAs in sperm, we carried out tissue-specific metabolic labeling of RNAs in intact mice, finding that mature sperm carry small RNAs that were originally synthesized in the somatic cells of the epididymis. Taken together, our data demonstrates that soma-germline small RNA transfer occurs in male mammals, most likely via vesicular transport from the epididymis to maturing sperm.

developmental biology↗

bioRxiv2017

A synthetic biology approach to probing nucleosome symmetry

The repeating subunit of chromatin, the nucleosome, includes two copies of each of the four core histones, and several recent studies have reported that asymmetrically-modified nucleosomes occur at regulatory elements in vivo. To probe the mechanisms by which histone modifications are read out, we designed an obligate pair of H3 heterodimers, termed H3X and H3Y, which we extensively validated genetically and biochemically. Comparing the effects of asymmetric histone tail point mutants with those of symmetric double mutants revealed that a single methylated H3K36 per nucleosome was sufficient to silence cryptic transcription in vivo. We also demonstrate the utility of this system for analysis of histone modification crosstalk, using mass spectrometry to separately identify modifications on each H3 molecule within asymmetric nucleosomes. The ability to generate asymmetric nucleosomes in vivo and in vitro provides a powerful and generalizable tool to probe the mechanisms by which H3 tails are read out by effector proteins in the cell.

molecular biology↗