Biology subjects

Jambhekar, A.

Publications and source records attributed to Jambhekar, A..

3 recordsLinked to original sources

bioRxiv2022

Signal integration by a bHLH circuit enables fate choice in neural stem cells

Stem cells integrate information from multiple signals in their environment to make fate decisions. It is unclear how signal integration is linked to the coordinated activation of a target fate program and simultaneous inactivation of competing fates. Here, we investigated this question in mouse neural stem cells, which differentiate synergistically into astrocytes in response to combined treatment with Bone Morphogenetic Protein (BMP) and Leukemia Inhibitory Factor (LIF) at the expense of alternative neuronal or oligodendrocyte fates. Analysis of the expression dynamics of Glial Fibrillary Acidic Protein (GFAP), an early astrocyte marker, showed that its synergistic activation in BMP and LIF reflects early activation by LIF which is sustained by a delayed contribution to its expression from BMP. In parallel, multiplexed RNA-FISH analysis of 14 basic helix-loop-helix (bHLH) transcription factors, known to regulate alternative fates, showed that LIF and BMP individually control different subsets of bHLHs, but together suppress all bHLHs known to promote alternative fates. Ectopic expression experiments showed that these bHLHs also inhibit GFAP induction, suggesting that suppression of alternative fates by BMP + LIF simultaneously relieves GFAP inhibition. In particular, BMP primarily affected inhibitory bHLHs indirectly, through induction of Id factors, explaining why it has a delayed contribution to GFAP transcription compared to LIF. These results show that a circuit of bHLH factors enables both synergistic astrocytic differentiation and suppression of alternative fates in NSCs. Signal integration by bHLH circuits for fate choice could be broadly relevant, given the widespread utilization of these and other bHLH factors across diverse developmental contexts.

systems biology↗

bioRxiv2022

Multi range ERK responses shape the proliferative trajectory of single cells following oncogene induced senescence

Oncogene-induced senescence (OIS) is a phenomenon in which aberrant oncogene expression causes non-transformed cells to enter a non-proliferative state. Cells undergoing OIS display phenotypic heterogeneity, with some cells senescing and others remaining proliferative. The causes of the heterogeneity remain poorly understood. We studied the sources of heterogeneity in the responses of human epithelial cells to oncogenic BRAFV600E expression. We found that a narrow expression range of BRAFV600E generated a wide range of activities of its downstream effector ERK. In population-level and single cell assays, ERK activity displayed a non-monotonic relationship to proliferation, with intermediate ERK activities leading to maximal proliferation. We profiled gene expression across a range of ERK activities over time and characterized four distinct ERK response classes, which we propose act in concert to generate the unique ERK-proliferation response. Altogether, our studies mapped the input-output relationships between ERK activity and proliferation providing important insights into how heterogeneity can be generated during OIS.

systems biology↗

bioRxiv2021

Chromatin state barriers enforce an irreversible mammalian cell fate decision

Stem and progenitor cells have the capacity to balance self-renewal and differentiation. Hematopoietic myeloid progenitors replenish more than 25 billion terminally differentiated neutrophils every day under homeostatic conditions and can increase this output in response to stress or infection. At what point along the spectrum of maturation do progenitors lose capacity for self-renewal and become irreversibly committed to differentiation? Using a system of conditional myeloid development that can be toggled between self-renewal and differentiation, we interrogated determinants of this point of no return in differentiation commitment. Irreversible commitment is due primarily to loss of open regulatory site access and disruption of a positive feedback transcription factor activation loop. Restoration of the transcription factor feedback loop extends the window of cell plasticity and alters the point of no return. These findings demonstrate how the chromatin state enforces and perpetuates cell fate and identifies potential avenues for manipulating cell identity. HighlightsO_LIThere exists a point of irreversible commitment in granulocytic differentiation C_LIO_LIChromatin state dynamics establish the transition from self-renewal to differentiation commitment C_LIO_LIReduced chromatin accessibility underlies an irreversible loss of regulatory site access C_LIO_LIRestoration of a transcription factor feedback loop alters the differentiation commitment point C_LI

molecular biology↗