Biology subjects

Viswanathan, V.

Publications and source records attributed to Viswanathan, V..

6 recordsLinked to original sources

bioRxiv2022

The Alternative Sigma Factor SigL Influences Clostridioides difficile Toxin Production, Sporulation, and Cell Surface Properties

The alternative sigma factor SigL (Sigma-54) facilitates bacterial adaptation to the extracellular environment by modulating the expression of defined gene subsets. A homolog of the gene encoding SigL is conserved in the diarrheagenic pathogen Clostridioides difficile. To explore the contribution of SigL to C. difficile biology, we generated sigL-disruption mutants (sigL::erm) in strains belonging to two phylogenetically distinct lineages - the human-relevant Ribotype 027 (strain BI-1) and the veterinary-relevant Ribotype 078 (strain CDC1). Comparative proteomics analyses of mutants and isogenic parental strains revealed lineage-specific SigL regulons. Concomitantly, loss of SigL resulted in pleotropic and distinct phenotypic alterations in the two strains. Sporulation kinetics, biofilm formation, and cell surface-associated phenotypes were altered in CDC1 sigL::erm relative to the isogenic parent strain, but remained unchanged in BI-1 sigL::erm. In contrast, secreted toxin levels were significantly elevated only in the BI-1 sigL::erm mutant relative to its isogenic parent. We also engineered SigL overexpressing strains and observed enhanced biofilm formation in the CDC1 background, and reduced spore titers as well as dampened sporulation kinetics in both strains. Thus, we contend that SigL is a key, pleiotropic regulator that dynamically influences C. difficiles virulence factor landscape, and thereby, its interactions with host tissues and co-resident microbes. Contribution to the FieldAlternative sigma factors modulate bacterial gene expression in response to environmental and metabolic cues. C. difficile encodes multiple alternative sigma factors which mediate critical cellular processes. A Sigma-54 ortholog, SigL, is conserved across all sequenced strains, yet its function remains to be elucidated. We demonstrate that SigL dynamically influences C. difficile biology in fundamental, but distinct, ways in two strains representing two clinically-relevant C. difficile phylogenetic lineages (ribotypes). Loss of SigL results in changes in sporulation kinetics, biofilm formation, alterations in cell surface properties, and secreted toxin levels in a strain-specific manner. SigL overexpression, however, uniformly impedes sporulation. Thus, SigL plays a fundamental role in regulating the expression of C. difficile virulence factors and likely profoundly impacts pathogenesis in a strain-specific manner.

microbiology↗

bioRxiv2021

Aldehyde dehydrogenase 3A1 deficiency leads to mitochondrial dysfunction and impacts salivary gland stem cell self-renewal, differentiation and survival

Adult salivary stem/progenitor cells (SSPC) have an intrinsic property to self-renew in order to maintain tissue architecture and homeostasis. Adult salivary glands have been documented to harbor SSPC, which have been shown to play a vital role in the regeneration of the glandular structures post radiation damage. We have previously demonstrated that activation of aldehyde dehydrogenase 3A1 (ALDH3A1) after radiation reduced aldehyde accumulation in SSPC, leading to less apoptosis and improved salivary function. We subsequently found that sustained pharmacological ALDH3A1 activation is critical to enhance regeneration of murine submandibular gland after radiation damage. Further investigation shows that ALDH3A1 function is crucial for SSPC self-renewal and differentiation even in the absence of radiation stress. Salivary glands from Aldh3a1-null mice have fewer acinar structures than wildtype mice. ALDH3A1 deletion or pharmacological inhibition in SSPC leads to a decrease in mitochondrial DNA copy number, lower expression of mitochondrial specific genes and proteins, structural abnormalities, lower membrane potential, and reduced cellular respiration. Loss or inhibition of ALDH3A1 also elevates ROS levels and accumulation of ALDH3A1 substrate 4-hydroxynonenal (4-HNE, a lipid peroxidation product), leading to decreased survival of murine SSPC that can be rescued by treatment with 4-HNE specific carbonyl scavengers. Our data indicate that ALDH3A1 activity protects mitochondrial function and is important for the development and regeneration activity of SSPC. This knowledge will help to guide our translational strategy of applying ALDH3A1 activators in the clinic to prevent radiation-related hyposalivation in head and neck cancer patients.

cell biology↗

bioRxiv2021

Speech categorization reveals the role of early-stage temporal-coherence processing in auditory scene analysis

Temporal coherence of sound fluctuations across spectral channels is thought to aid auditory grouping and scene segregation. Although prior studies on the neural bases of temporal-coherence processing focused mostly on cortical contributions, neurophysiological evidence suggests that temporal-coherence-based scene analysis may start as early as the cochlear nucleus (i.e., the first auditory region supporting cross-channel processing over a wide frequency range). Accordingly, we hypothesized that aspects of temporal-coherence processing that could be realized in early auditory areas may shape speech understanding in noise. We then explored whether physiologically plausible computational models could account for results from a behavioral experiment that measured consonant categorization in different masking conditions. We tested whether within-channel masking of target-speech modulations predicted consonant confusions across the different conditions, and whether predicted performance was improved by adding across-channel temporal-coherence processing mirroring the computations known to exist in the cochlear nucleus. Consonant confusions provide a rich characterization of error patterns in speech categorization, and are thus crucial for rigorously testing models of speech perception; however, to the best of our knowledge, they have not been utilized in prior studies of scene analysis. We find that within-channel modulation masking can reasonably account for category confusions, but that it fails when temporal fine structure (TFS) cues are unavailable. However, the addition of across-channel temporal-coherence processing significantly improves confusion predictions across all tested conditions. Our results suggest that temporal-coherence processing strongly shapes speech understanding in noise, and that physiological computations that exist early along the auditory pathway may contribute to this process.

neuroscience↗

bioRxiv2021

Temporal fine structure influences voicing confusions for consonant identification in multi-talker babble

To understand the mechanisms of speech perception in everyday listening environments, it is important to elucidate the relative contributions of different acoustic cues in transmitting phonetic content. Previous studies suggest that the envelope of speech in different frequency bands conveys most speech content, while the temporal fine structure (TFS) can aid in segregating target speech from background noise. However, the role of TFS in conveying phonetic content beyond what envelopes convey for intact speech in complex acoustic scenes is poorly understood. The present study addressed this question using online psychophysical experiments to measure the identification of consonants in multi-talker babble for intelligibility-matched intact and 64-channel envelope-vocoded stimuli. Consonant confusion patterns revealed that listeners had a greater tendency in the vocoded (versus intact) condition to be biased toward reporting that they heard an unvoiced consonant, despite envelope and place cues being largely preserved. This result was replicated when babble instances were varied across independent experiments, suggesting that TFS conveys voicing information beyond what is conveyed by envelopes for intact speech in babble. Given that multi-talker babble is a masker that is ubiquitous in everyday environments, this finding has implications for the design of assistive listening devices such as cochlear implants.

neuroscience↗

bioRxiv2021

Web-based Psychoacoustics: Hearing Screening, Infrastructure, and Validation

Anonymous web-based experiments are increasingly and successfully used in many domains of behavioral research. However, online studies of auditory perception, especially of psychoacoustic phenomena pertaining to low-level sensory processing, are challenging because of limited available control of the acoustics, and the unknown hearing status of participants. Here, we outline our approach to mitigate these challenges and validate our procedures by comparing web-based measurements to labbased data on a range of classic psychoacoustic tasks. Individual tasks were created using jsPsych, an open-source javascript front-end library. Dynamic sequences of psychoacoustic tasks were implemented using Django, an open-source library for web applications, and combined with consent pages, questionnaires, and debriefing pages. Subjects were recruited via Prolific, a web-based human-subject marketplace. Guided by a meta-analysis of normative data, we developed and validated a screening procedure to select participants for (putative) normal-hearing status; this procedure combined thresholding of scores in a suprathreshold cocktail-party task with filtering based on survey responses. Headphone use was standardized by supplementing procedures from prior literature with a binaural hearing task. Individuals meeting all criteria were re-invited to complete a range of classic psychoacoustic tasks. Performance trends observed in re-invited participants were in excellent agreement with lab-based data for fundamental frequency discrimination, gap detection, sensitivity to interaural time delay and level difference, comodulation masking release, word identification, and consonant confusions. Our results suggest that web-based psychoacoustics is a viable complement to lab-based research. Source code for our infrastructure is also provided.

neuroscience↗

bioRxiv2021

Modulation masking and fine structure shape neural envelope coding to predict speech intelligibility across diverse listening conditions

A fundamental question in the neuroscience of everyday communication is how scene acoustics shape the neural processing of attended speech sounds and in turn impact speech intelligibility. While it is well known that the temporal envelopes in target speech are important for intelligibility, how the neural encoding of target-speech envelopes is influenced by background sounds or other acoustic features of the scene is unknown. Here, we combine human electroencephalography with simultaneous intelligibility measurements to address this key gap. We find that the neural envelope-domain signal-to-noise ratio in target-speech encoding, which is shaped by masker modulations, predicts intelligibility over a range of strategically chosen realistic listening conditions unseen by the predictive model. This provides neurophysiological evidence for modulation masking. Moreover, using high-resolution vocoding to carefully control peripheral envelopes, we show that target-envelope coding fidelity in the brain depends not only on envelopes conveyed by the cochlea, but also on the temporal fine structure (TFS), which supports scene segregation. Our results are consistent with the notion that temporal coherence of sound elements across envelopes and/or TFS influences scene analysis and attentive selection of a target sound. Our findings also inform speech-intelligibility models and technologies attempting to improve real-world speech communication.

neuroscience↗