Biology subjects

Natarajan, V. T.

Publications and source records attributed to Natarajan, V. T..

5 recordsLinked to original sources

bioRxiv2024

Mgat4b mediated selective N-glycosylation regulates melanocyte development and melanoma progression

Melanocyte development involves key pathways that are often recapitulated during melanoma initiation, highlighting the importance of understanding the regulators that control these early processes and also contribute to cancer onset. Our study identifies mgat4b, a glycosyl transferase involved in selective N-glycan branching enriched in pigment progenitors, as a key regulator of directional melanocyte migration and establishment of melanocyte stem cell (McSC) pool during early development. Single cell RNA (scRNA) sequencing analysis in zebrafish upon targeted disruption of mgat4b reveals, that migratory melanocyte progenitors marked by galectin expression fail to persist. Lectin affinity proteomic analysis reveals the glycosylation of key melanocyte proteins GPNMB, KIT, and TYRP1 to be under the control of MGAT4B in melanocytic cells. Additionally, mislocalization of Junctional plakoglobin (JUP) explains the observed defects in cell adhesion and migration to be regulated by MGAT4B but not its isozyme MGAT4A. Our meta-analysis further reveals that melanoma patients with both the BRAFV600E mutation and elevated MGAT4B levels have significantly worse survival outcomes compared to those with only the BRAFV600E mutation. By leveraging the MAZERATI platform to model BRAFV600E driver mutation in vivo, we show that mgat4b mutant cells fail to aggregate and initiate tumors. RNA profiling of the transformed melanocytes revealed cell-cell junction, adhesion and ECM binding to be probable contributing factors that resulted in the failure of tumor onset. Using a small-molecule inhibitor we demonstrate the inhibitory role of this complex N-glycosylation in the progression of early-stage melanoma. Our study underscores the importance of selective N-glycan branching in both melanocyte development and melanoma initiation, suggesting MGAT4B as a promising therapeutic target for melanoma treatment.

cancer biology↗

bioRxiv2023

Melanocytes Exhibit Distinct Cell States Governed by A Gene Regulatory Network Under Stochastic Influence

Melanocytes serve as a protector of the skin against external stressors such as ultraviolet radiations. While melanocytes remain functional for nearly the entire lifespan of an individual, how they respond efficiently and survive such insults remain elusive. Here, we show the co-existence of multiple distinct states of normal human epidermal melanocytes (NHEMs). Using a progressive pigmentation model, we show that stochasticity in gene expression can lead to the co-existence of multiple melanocyte states. Using active enhancers and gene expression footprint, we identified state-specific transcription factors and constructed a gene regulatory network (GRN). The GRN couples pigmentation and cell cycle regulators and explains the co-existence and transitions of the melanocyte states. Finally, we show that NHEMs respond to external cues by altering the cell state dynamics. These results demonstrate that stochasticity in gene expression followed by epigenetic modification leads to the co-existence of multiple melanocyte states enabling an efficient response to environmental cues.

cell biology↗

bioRxiv2023

Migration and establishment of progenitor pool of melanocytes is governed by SEMA3E-PLXND1 signaling

Vertebrate pigmentation is an outcome of an interplay of several signaling pathways that result in immense diversity of pigment patterns observed across the animal kingdom. Transitory nature of these signaling events impedes deciphering pathways that control migration and establishment of melanocyte stem cells (McSC), necessary for pigment patterning. Using zebrafish and cultured mammalian melanocytes, we uncover a hitherto unknown role for Plexin D1 signaling. This pathway directs migration by F-actin modulation and further dictates subsequent functional states of melanocytes through a transcriptional response. In zebrafish, abrogation of PLXND1 derails melanocyte migration and reduces mid-line melanophores emerging from the regeneration competent McSC pool. In cultured melanocytes, activation of PLXND1 by the ligand semaphorin 3E reduces the velocity of migration, influences directional correlation, and promotes movement towards positive cues such as SCF. PLXND1 activation results in EGFR signaling necessary for McSC establishment, and induces GNAS, an effector of MC1R pathway involved in melanocyte maturation. Identification of this long-range secreted negative chemotactic signaling provides a missing player and enriches reaction diffusion model for pigment patterning.

developmental biology↗

bioRxiv2022

Whole exome-sequencing of vitiligo lesions indicate lower burden of somatic variations: implications in risk for non-melanoma skin cancers

Mapping of somatic variations has enabled understanding the progression of clonal variations from healthy skin to cutaneous malignancies. Highlighting, the adaptive nature of pigmentation, germline mutations in albinism amplify skin cancer susceptibility. However, lower incidence of non-melanoma skin cancer among subjects with acquired depigmenting skin disorder vitiligo is enigmatic and a matter of longstanding debate. To address this, we performed high-coverage exome sequencing of matched non-lesional and lesional vitiligo skin along with whole blood to account for germline variations. Our analysis suggests lower burden of somatic cancer-associated variations in exposed depigmented lesional skin compared to the non-lesional skin. A detailed investigation of vitiligo skin transcriptome reveals elevation of DNA repair and cell-proliferation pathways. Validation by comet-assay for DNA damage and cell cycle analysis of epidermal cells suggest undamaged DNA in vitiligo lesions that could be attributed to higher proliferation-coupled repair. Endorsing this, UV-signature variations are not prominent, instead SBS5 associated with endogenous mutational processes is conspicuous in both the vitiligo tissues. Our systematic pilot study indicates lower somatic mutation burden in vitiligo skin and supports the earlier demographic observation on lower risk of non-melanoma skin cancer in vitiligo subjects, providing an opportunity to learn strategies for cancer prevention from vitiligo. Brief SummaryVitiligo skin harbors decreased somatic variation burden in cancer-associated genes and a concomitant augmentation in DNA repair response, explaining the lower incidence of cutaneous malignancies.

genomics↗

bioRxiv2021

Adaptive convergent evolution of genome proofreading in SARS-CoV2: insights into the Eigen's paradox

Evolutionary history of coronaviruses holds the key to understand mutational behavior and prepare for possible future outbreaks. By performing comparative genome analysis of nidovirales that contain the family of coronaviruses, we traced the origin of proofreading, surprisingly to the eukaryotic antiviral component ZNFX1. This common recent ancestor contributes two zinc finger (ZnF) motifs that are unique to viral exonuclease, segregating them from DNA proof-readers. Phylogenetic analyses indicate that following acquisition, genomes of coronaviruses retained and further fine-tuned proofreading exonuclease, whereas related families harbor substitution of key residues in ZnF1 motif concomitant to a reduction in their genome sizes. Structural modelling followed by simulation suggests the role of ZnF in RNA binding. Key ZnF residues strongly coevolve with replicase, and the helicase involved in duplex RNA unwinding. Hence, fidelity of replication in coronaviruses is a result of convergent evolution, that enables maintenance of genome stability akin to cellular proofreading systems.

evolutionary biology↗