Biology subjects

Tanwar, J.

Publications and source records attributed to Tanwar, J..

3 recordsLinked to original sources

bioRxiv2026

SERCA2b loss of function drives pigmentation by inducing adaptive ER stress and enhancing mitochondrial calcium uptake: significance in pathological hyperpigmentation associated with Darier’s Disease

Pigmentation is a critical protective mechanism that safeguards the skin against UV-induced damage, whereas dysregulated pigmentation predisposes to pigmentary disorders and skin malignancies. Although calcium signaling has emerged as an important regulator of melanogenesis, the identity of the calcium-handling proteins and the molecular mechanisms linking calcium dynamics to pigmentation remain poorly understood. Here, we identify the ER calcium pump SERCA2b as a negative regulator of pigmentation through modulation of ER stress and mitochondrial calcium uptake. We demonstrate that SERCA2b expression inversely correlates with pigmentation levels, and gain- and loss-of-function studies establish SERCA2b as a suppressor of melanogenesis. Mechanistically, SERCA2b depletion induces adaptive ER stress, enhances ER-mitochondrial proximity, and promotes mitochondrial calcium uptake. Notably, mutations in SERCA2b are associated with Darier disease, a condition characterized by hyperpigmented skin lesions, although the underlying mechanism remains unknown. To address this, we generated SERCA2b mutants corresponding to variants identified in Indian Dariers disease patients and examined their effects on pigmentation, ER stress, and mitochondrial calcium dynamics. The mutant phenotypes closely recapitulated SERCA2b loss-of-function effects, demonstrating that adaptive ER stress and enhanced mitochondrial calcium signaling underlie hyperpigmentation associated with Dariers disease. Importantly, treatment with 4-phenylbutyrate (4-PBA), an FDA-approved ER stress alleviator, rescued mutant-induced hyperpigmentation, reduced ER stress, and normalized mitochondrial calcium uptake. Collectively, our findings uncover a previously unrecognized role of SERCA2b in skin pigmentation, establish a mechanistic link between SERCA2b mutations and hyperpigmentation, and identify adaptive ER stress pathways as potential therapeutic target for pigmentary disorders.

Cell Biology↗

bioRxiv2023

Mitochondrial calcium signaling mediated transcriptional regulation of keratin filaments is a critical determinant of melanogenesis

Mitochondria are versatile organelles that regulate several physiological functions. Many mitochondria-controlled processes are driven by mitochondrial Ca2+ signaling. However, role of mitochondrial Ca2+ signaling in melanosome biology remains unknown. Here, we show that pigmentation requires mitochondrial Ca2+ uptake. In vitro gain and loss of function studies demonstrated that Mitochondrial Ca2+ Uniporter (MCU) is crucial for melanogenesis while the MCU rheostats, MCUb and MICU1 negatively control melanogenesis. Zebrafish and mouse models showed that MCU plays a vital role in pigmentation in vivo. Mechanistically, MCU controls activation of transcription factor NFAT2 to induce expression of three keratins (keratin 5, 7 and 8), which we report as positive regulators of melanogenesis. Interestingly, keratin 5 in turn modulates mitochondrial Ca2+ uptake thereby this signaling module acts as a negative feedback loop that fine-tunes both mitochondrial Ca2+ signaling and melanogenesis. Mitoxantrone, an FDA approved drug that inhibits MCU, decreases physiological melanogenesis. Collectively, our data demonstrates a critical role for mitochondrial Ca2+ signaling in vertebrate pigmentation and reveal the therapeutic potential of targeting MCU for clinical management of pigmentary disorders. Given the centrality of mitochondrial Ca2+ signaling and keratin filaments in cellular physiology, this feedback loop may be functional in a variety of other pathophysiological conditions. HighlightsO_LIMCU complex mediated mitochondrial Ca2+ uptake is a novel regulator of vertebrate pigmentation C_LIO_LIKeratin filaments bridge mitochondrial Ca2+ signaling to melanosome biogenesis and maturation C_LIO_LITranscription factor NFAT2 connects mitochondrial Ca2+ dynamics to keratins expression C_LIO_LIMCU-NFAT2-Keratin 5 signaling module generates a negative feedback loop to maintain mitochondrial Ca2+ homeostasis and to ensure optimal melanogenesis C_LIO_LIInhibiting MCU with mitoxantrone, an FDA approved drug, leads to reduction in physiological pigmentation C_LI

cell biology↗

bioRxiv2019

Histone code dictates fate biasing of neural crest cells to melanocyte lineage

In the neural crest lineage, progressive fate-restriction and stem cell assignment are critical for both development and regeneration. While the fate-commitment events have distinct transcriptional footprints, fate-biasing is often transitory and metastable, and is thought to be moulded by epigenetic programs. Hence molecular basis of specification is difficult to define. In this study, we establish a role of a histone variant H2a.z.2 in specification of melanocyte lineage from multipotent neural crest cells. Silencing of H2a.z.2 reduces the number of melanocyte precursors in developing zebrafish embryos, and from mouse embryonic stem cells in vitro. We demonstrate that this histone variant occupies nucleosomes in the promoter of key melanocyte determinant Mitf, and enhances its induction. CRISPR-Cas9 based targeted mutagenesis of this gene in zebrafish drastically reduces adult melanocytes, as well as their regeneration. Thereby our study establishes a histone based specification code upstream to the core gene regulatory network in the neural crest lineage of melanocytes. This epigenetic code renders a poised state to the promoter of key determinant and enhances activation by external instructive signals thereby establishing melanocyte fate identity.

developmental biology↗