Biology subjects

Vijayraghavan, S.

Publications and source records attributed to Vijayraghavan, S..

5 recordsLinked to original sources

bioRxiv2025

Second-Scale Neural Dynamics Shape Hormonal Outputs in Hypothalamic CRH Neurons

The elevation of glucocorticoids is a hallmark of stress, arising from the integration of rapid neuronal signals into sustained hormonal outputs. A key interface for this neuroendocrine signal translation is corticotropin releasing hormone (CRH) neurons in the paraventricular nucleus of the hypothalamus (PVN), which release CRH at the median eminence (ME). We recently discovered that CRHPVN neurons exhibit a characteristic shift in firing patterns from rhythmic short-bursts (low-activity state) to tonic firing (high-activity state) in response to stress. This raised a critical question: how are these distinct firing patterns are integrated into slower, sustained hormonal outputs at neuroendocrine terminals? Here, we implemented optical approaches to detect CRH release ex vivo and in vivo. Using newly developed sniffer cells for CRH, we measured CRH release at ME ex vivo, triggered by the distinct, in vivo-like firing patterns. Our results demonstrated that the primary determinant of neuroendocrine CRH release was the firing rate sustained over the timescale of seconds, with little contribution from specific firing patterns. These results collaborated with second-scale increase in firing rate triggered by stress stimuli. Additionally, we recorded the dynamics of CRH at the ME in the freely moving mice using genetically-encoded GPCR-activation based (GRAB) sensors for CRH. Foot shock stress triggered transient, time-locked increases in CRH release on the timescale of seconds. Importantly, these second-scale CRH pulses, when elicited during repeated foot shocks, were integrated over minutes to scale downstream hormone releases. Together, our data revealed critical roles of second-scale dynamics in CRHPVN neuron activity for the neuroendocrine translation of stress signals.

neuroscience↗

bioRxiv2025

Methylglyoxal mutagenizes single-stranded DNA via Rev1-associated slippage and mispairing

Methylglyoxal (MG) is a highly reactive aldehyde that is produced endogenously during metabolism and is derived from exogenous sources such as sugary food items and cigarette smoke. Unless detoxified by glyoxalases (Glo1 and Glo2), MG can readily react with all major biomolecules, including DNA and proteins, generating characteristic lesions and glycation-derived by- products. As a result, MG exposure has been linked to a variety of human diseases, including cancers. Prior studies show that MG can glycate DNA, preferentially on guanine residues, and cause DNA damage. However, the mutagenicity of MG is poorly understood in vivo. In the context of cancer, it is essential to comprehend the true contribution of MG to genome instability and global mutational burden. In the present study, we show that MG can robustly mutagenize induced single-stranded DNA (ssDNA) in yeast, within a guanine centered mutable motif. We demonstrate that genome-wide MG mutagenesis in ssDNA is greatly elevated throughout the genome in the absence of Glo1, and abrogated in the presence of the aldehyde quencher aminoguanidine. We uncovered strand slippage and mispairing as the predominant mechanism for generation of all MG-associated mutations, and demonstrate that the translesion polymerase Rev1 is necessary in this pathway. Finally, we find that the primary MG-associated mutation is enriched in a variety of sequenced tumor datasets. We discuss the genomic impact of methylglyoxal exposure in the context of mutagenesis, DNA damage, and carcinogenesis.

genetics↗

bioRxiv2024

Spike frequency adaptation in primate lateral prefrontal cortex neurons results from interplay between intrinsic properties and circuit dynamics

Recordings of cortical neurons isolated from brain slices and dissociated from their networks, display intrinsic spike frequency adaptation (I-SFA) to a constant current input. Interestingly, extracellular recordings in behaving subjects also show extrinsic-SFA (E-SFA) in response to sustained visual stimulation. Because neurons are isolated from brain networks in slice recordings, it is challenging to infer how I-SFA contributes to E-SFA in interconnected brains during behavior. To investigate this, we recorded responses of macaque lateral prefrontal cortex neurons in vivo during a visually guided saccade task and in acute brain slices in vitro. Broad spiking (BS) putative pyramidal cells and narrow spiking (NS) putative inhibitory interneurons exhibited E-SFA in vivo. In acute brain slices, both cell types displayed I-SFA though their magnitudes differed. To investigate how in vitro I-SFA contributes to in vivo E-SFA, we developed a data-driven hybrid circuit model in which local NS neurons are driven by BS input. We observed that model NS cell responses show longer SFA than observed in vivo. Introducing inhibition of NS cells to the model circuit removed this discrepancy. Our results indicate that both I-SFA and inhibitory circuit dynamics contribute to E-SFA in LPFC neurons. They highlight the contribution of single neuron and network dependent computations to neural activity underlying behavior.

neuroscience↗

bioRxiv2024

Multiple DNA repair pathways prevent acetaldehyde-induced mutagenesis in yeast

Acetaldehyde is the primary metabolite of alcohol and is present in many environmental sources including tobacco smoke. Acetaldehyde is genotoxic, whereby it can form DNA adducts and lead to mutagenesis. Individuals with defects in acetaldehyde clearance pathways have increased susceptibility to alcohol-associated cancers. Moreover, a mutation signature specific to acetaldehyde exposure is widespread in alcohol and smoking-associated cancers. However, the pathways that repair acetaldehyde-induced DNA damage and thus prevent mutagenesis are vaguely understood. Here, we used Saccharomyces cerevisiae to systematically delete genes in each of the major DNA repair pathways to identify those that alter acetaldehyde-induced mutagenesis. We found that deletion of the nucleotide excision repair (NER) genes, RAD1 or RAD14, led to an increase in mutagenesis upon acetaldehyde exposure. Acetaldehyde-induced mutations were dependent on translesion synthesis as well as DNA inter-strand crosslink (ICL) repair in{Delta} rad1 strains. Moreover, whole genome sequencing of the mutated isolates demonstrated an increase in C[->]A changes coupled with an enrichment of gCn[->]A changes in the acetaldehyde-treated{Delta} rad1 isolates. The gCn[->]A mutation signature has been shown to be diagnostic of acetaldehyde exposure in yeast and in human cancers. We also demonstrated that the deletion of the two DNA-protein crosslink (DPC) repair proteases, WSS1 and DDI1, also led to increased acetaldehyde-induced mutagenesis. Defects in base excision repair (BER) led to a mild increase in mutagenesis, while defects in mismatch repair (MMR), homologous recombination repair (HR) and post replicative repair pathways did not impact mutagenesis upon acetaldehyde exposure. Our results in yeast were further corroborated upon analysis of whole exome sequenced liver cancers, wherein, tumors with defects in ERCC1 and ERCC4 (NER), FANCD2 (ICL repair) or SPRTN (DPC repair) carried a higher gCn[->]A mutation load than tumors with no deleterious mutations in these genes. Our findings demonstrate that multiple DNA repair pathways protect against acetaldehyde-induced mutagenesis.

genetics↗

bioRxiv2022

Acetaldehyde makes a distinct mutation signature in single-stranded DNA

Acetaldehyde (AA), a by-product of ethanol metabolism, is acutely toxic due to its ability to react with various biological molecules including DNA and proteins, which can greatly impede key processes such as replication and transcription and lead to DNA damage. As such AA is classified as a group 1 carcinogen by the International Agency for Research on Cancer (IARC). Previous in vitro studies have shown that AA generates bulky adducts on DNA, with signature guanine-centered (GG[->]TT) mutations. However, due to its weak mutagenicity, short chemical half-life, and the absence of powerful genetic assays, there is considerable variability in reporting the genotoxic effects of AA in vivo. Here, we used an established yeast genetic reporter system and demonstrate that AA is highly mutagenic and makes strand-biased mutations on guanines (G[->]T) at a high frequency on single stranded DNA (ssDNA). We further demonstrate that AA-derived mutations occur through lesion bypass on ssDNA by the translesion polymerase Pol{zeta}. Finally, we describe a unique mutation signature for AA, which we then identify in several whole-genome and -exome sequenced cancers, particularly those associated with alcohol consumption.

genetics↗