Biology subjects

Saha, D.

Publications and source records attributed to Saha, D..

4 recordsLinked to original sources

bioRxiv2018

Encoding the expectation of a sensory stimulus

Most organisms possess an ability to differentiate unexpected or surprising sensory stimuli from those that are repeatedly encountered. How is this sensory computation performed? We examined this issue in the locust olfactory system. We found that odor-evoked responses in the antennal lobe (downstream to sensory neurons) systematically reduced upon repeated encounters of a temporally discontinuous stimulus. Rather than confounding information about stimulus identity and intensity, neural representations were optimized to encode equivalent stimulus-specific information with fewer spikes. Further, spontaneous activity of the antennal lobe network also changed systematically and became negatively correlated with the response elicited by the repetitive stimulus (i.e. a negative image). Notably, while response to the repetitive stimulus reduced, exposure to an unexpected/deviant cue generated undamped and even exaggerated spiking responses in several neurons. In sum, our results reveal how expectation regarding a stimulus is encoded in a neural circuit to allow response optimization and preferential filtering.

neuroscience↗

bioRxiv2018

RNA polymerase II pausing regulates a quiescence-dependent transcriptional program, priming cells for cell cycle reentry

Adult stem cells persist in mammalian tissues by entering a state of reversible arrest or quiescence associated with low transcription. Using cultured myoblasts and primary muscle stem cells, we show that RNA synthesis is strongly repressed in G0, returning within minutes of activation. We investigate the underlying mechanism and reveal a role for promoter-proximal RNAPol II pausing: by mapping global Pol II occupancy using ChIP-seq, in conjunction with RNA-seq to identify repressed transcriptional networks unique to G0. Strikingly, Pol II pausing is enhanced in G0 on genes encoding regulators of RNA biogenesis (Ncl, Rps24, Ctdp1), and release of pausing is critical for cell cycle re-entry. Finally, we uncover a novel, unexpected repressive role of the super-elongation complex component Aff4 in G0-specific stalling. We propose a model wherein Pol II pausing restrains transcription to maintain G0, preconfigures gene networks required for the G0-G1 transition, and sets the timing of their transcriptional activation.

developmental biology↗

bioRxiv2017

Dynamic contrast enhancement and flexible odor codes

Sensory stimuli evoke spiking activities patterned across neurons and time that are hypothesized to encode information about their identity. Since the same stimulus can be encountered in a multitude of ways, how stable or flexible are these stimulus-evoked responses? Here, we examined this issue in the locust olfactory system. In the antennal lobe, we found that both spatial and temporal features of odor-evoked responses varied in a stimulus-history dependent manner. The response variations were not random, but allowed the antennal lobe circuit to enhance the uniqueness of the current stimulus. Nevertheless, information about the odorant identity became confounded due to this contrast-enhancement computation. Notably, a linear logical classifier (OR-of-ANDs) that can decode information distributed in flexible subsets of neurons generated predictions that matched results from our behavioral experiments. In sum, our results reveal a simple computational logic for achieving the stability vs. flexibility tradeoff in sensory coding.

neuroscience↗

bioRxiv2017

Early warning signals regarding environmental suitability in the Drosophila antenna

HighlightsO_LIA novel geotaxis assay showed high intensity odorant exposures are harmful to flies\nC_LIO_LIRepulsion at high odor intensities can be a protective mechanism\nC_LIO_LIOlfactory receptor neuron (ORN) excitability abruptly changes with odor intensity\nC_LIO_LIA linear combination of ORN activities can robustly predict intensity-dependent behavioral repulsion\nC_LI\n\nSummaryThe olfactory system is uniquely positioned to warn an organism of environmental threats. Whether and how it encodes such information is not understood. Here, we examined this issue in the fruit fly Drosophila melanogaster. We found that intensity-dependent repulsion to chemicals safeguarded flies from harmful, high-intensity vapor exposures. To understand how sensory input changed as the odor valence switched from innocuous to threatening, we recorded from olfactory receptor neurons (ORNs) in the fly antenna. Primarily, we observed two response non-linearities: recruitment of non-active ORNs at higher intensities, and abrupt transitions in neural excitability from regular spiking to high-firing oscillatory regime. Although non-linearities observed in any single ORN was not a good indicator, a simple linear combination of firing events from multiple neurons provided robust recognition of threating/repulsive olfactory stimuli. In sum, our results reveal how information necessary to avoid environmental threats may also be encoded in the insect antenna.

neuroscience↗