Biology subjects

Sekar, V.

Publications and source records attributed to Sekar, V..

5 recordsLinked to original sources

bioRxiv2026

Human lymphatic organoids reconstruct convergent developmental routes to functional lymphatic vessels

The lymphatic vasculature maintains fluid balance, regulates immune surveillance, and supports tissue repair, yet how human lymphatic vessels arise and acquire specialized functions remains poorly understood. Here, guided by single-cell and spatial analyses of human embryos, we found that both lateral plate and paraxial mesoderm converge on venous endothelial intermediates with cardinal vein-like characteristics prior to lymphatic specification. Informed by these developmental trajectories, we generated three-dimensional lymphatic organoids from human pluripotent stem cells through two distinct mesodermal routes. The organoids formed capillary-like vascular networks with emerging button-like junctions and distinct endothelial and stromal programs. The lymphatic organoids were transcriptionally benchmarked to human fetal lymphatic endothelium. The organoids supported immune-cell interactions and antigen accumulation and, following transplantation, exhibited interstitial tracer uptake and transport. These findings establish a platform for investigating how distinct developmental origins shape human lymphatic specification, vascular organization, and function, with applications to lymphatic disease modeling and tissue repair.

developmental biology↗

bioRxiv2024

Landscape of microRNA and target expression variation and covariation in single mouse embryonic stem cells

MicroRNAs are small RNA molecules that can repress the expression of protein coding genes post-transcriptionally. Previous studies have shown that microRNAs can also have alternative functions including target noise buffering and co-expression, but these observations have been limited to a few microRNAs. Here we systematically study microRNA alternative functions in mouse embryonic stem cells, by genetically deleting Drosha - leading to global loss of microRNAs. We apply complementary single-cell RNA-seq methods to study the variation of the targets and the microRNAs themselves, and transcriptional inhibition to measure target half-lives. We find that microRNAs form four distinct co-expression groups across single cells. In particular the mir-290 and the mir-182 clusters are abundantly, variably and inversely expressed. Intriguingly, some cells have global biases towards specific miRNAs originating from either end of the hairpin precursor, suggesting the presence of unknown regulatory cofactors. We find that miRNAs generally increase variation and covariation of their targets at the RNA level, but we also find miRNAs such as miR-182 that appear to have opposite functions. In particular, miRNAs that are themselves variable in expression, such as miR-291a, are more likely to induce covariations. In summary, we apply genetic perturbation and multi-omics to give the first global picture of microRNA dynamics at the single cell level.

genomics↗

bioRxiv2022

agoTRIBE detects miRNA-target interactions transcriptome-wide in single cells

MicroRNAs are gene regulatory molecules that play important roles in numerous biological processes including human health. The function of a given microRNA is defined by its selection of target transcripts, yet current state-of-the-art experimental methods to identify microRNA targets are laborious and require millions of cells. We have overcome these limitations by fusing the microRNA effector protein Argonaute2 to the RNA editing domain of ADAR2, allowing for the first time the detection of microRNA targets transcriptome-wide in single cells. Our agoTRIBE method reports functional microRNA targets which are additionally supported by evolutionary sequence conservation. As a proof-of-principle, we study microRNA interactions in single cells, and find substantial differential targeting across the cell cycle. Lastly, agoTRIBE additionally provides transcriptome-wide measurements of RNA abundance and will allow the deconvolution of microRNA targeting in complex samples such as tissues at the single-cell level.

genomics↗

bioRxiv2022

Single-cell transcriptomics to define Plasmodium falciparum stage-transition in the mosquito midgut

Malaria inflicts the highest rate of morbidity and mortality among the vector-borne diseases. The dramatic bottleneck of parasite numbers that occurs in the gut of the obligatory vector mosquito provides a promising target for novel control strategies. Using single-cell transcriptomics, we analyzed Plasmodium falciparum development in the mosquito gut, from unfertilized female gametes through the first 20 hours post blood feeding, including the zygote and ookinete stages. This study revealed the transcriptional trajectories of the ApiAP2 family of transcription factors, and of parasite stress genes in response to the harsh environment of the mosquito midgut. Further, employing structure-based functional predictions we found several upregulated genes predicted to encode intrinsically disordered proteins (IDPs), a category of proteins known for their importance in regulation of transcription, translation and protein-protein interactions. IDPs are known for their antigenic properties and may serve as suitable targets for antibody or peptide-based transmission suppression strategies.

microbiology↗

bioRxiv2020

Gene regulation of the avian malaria parasite Plasmodium relictum, during the different stages within the mosquito vector

The malaria parasite Plasmodium relictum is one of the most widespread species of avian malaria. As is the case in its human counterparts, bird Plasmodium undergoes a complex life cycle infecting two hosts: the arthropod vector and the vertebrate host. In this study, we examine the transcriptome of P. relictum (SGS1) during crucial timepoints within its natural vector, Culex pipiens quinquefasciatus. Differential gene-expression analyses identified genes linked to the parasites life-stages at: i) a few minutes after the blood meal is ingested, ii) during peak oocyst production phase, iii) during peak sporozoite phase and iv) during the late-stages of the infection. A large amount of genes coding for functions linked to host-immune invasion and multifunctional genes was active throughout the infection cycle. One gene associated with a conserved Plasmodium membrane protein with unknown function was upregulated throughout the parasite development in the vector, suggesting an important role in the successful completion of the sporogonic cycle. Transcript annotation further revealed novel genes, which were significantly differentially expressed during the infection in the vector as well as upregulation of reticulocyte-binding proteins, which raises the possibility of the multifunctionality of these RBPs. We establish the existence of highly stage-specific pathways being overexpressed during the infection. This first study of gene-expression of a non-human Plasmodium species in its natural vector provides a comprehensive insight into the molecular mechanisms of the common avian malaria parasite P. relictum and provides essential information on the evolutionary diversity in gene regulation of the Plasmodiums vector stages.

evolutionary biology↗