Biology subjects

Bajracharya, A.

Publications and source records attributed to Bajracharya, A..

3 recordsLinked to original sources

bioRxiv2022

PIF4/HEMERA-mediated daytime thermosensory growth requires the Mediator subunit MED14

While moderately elevated ambient temperatures do not trigger stress responses in plants, they do significantly stimulate the growth of specific organs through a process known as thermomorphogenesis. The basic helix-loop-helix transcription factor PHYTOCHROME-INTERACTING FACTOR 4 (PIF4) plays a central role in regulating thermomorphogenetic hypocotyl elongation in various plant species, including Arabidopsis thaliana. Although it is well known that PIF4 promotes plant thermosensory growth by activating genes involved in the biosynthesis and signaling of the phytohormone auxin, the detailed molecular mechanism of such transcriptional activation is not clear. Our previous studies demonstrated that HEMERA (HMR), a transcriptional co-activator of PIF4, promotes the thermo-induced expression of PIF4 target genes through its nine-amino-acid transactivation domain (9aaTAD). In this report, we investigate the role of the Mediator complex in the PIF4/HMR-mediated thermoresponsive gene expression. Through the characterization of various mutants of the Mediator complex, a tail subunit named MED14 is identified as an essential factor for thermomorphogenetic hypocotyl growth. MED14 is required for the thermal induction of PIF4 target genes but has a marginal effect on the levels of PIF4 and HMR. Further transcriptomic analyses confirm that the expression of numerous PIF4/HMR-dependent, auxin-related genes requires MED14 at warm temperatures. Moreover, PIF4 and HMR physically interact with MED14 and both are indispensable for the association of MED14 with the promoters of these thermoresponsive genes. Taken together, these results unveil an important thermomorphogenetic mechanism, in which PIF4 and HMR recruit the Mediator complex to activate auxin-related growth-promoting genes when plants sense moderate increases in ambient temperature. One-sentence summaryThe Mediator subunit MED14 promotes thermomorphogenesis by interacting with PHYTOCHROME-INTERACTING FACTOR 4 and HEMERA to induce the expression of growth-promoting genes at elevated temperatures.

plant biology↗

bioRxiv2021

Dorsolateral prefrontal cortex supports speech perception in listeners with cochlear implants

Cochlear implants are neuroprosthetic devices that can restore hearing in people with severe to profound hearing loss by electrically stimulating the auditory nerve. Because of physical limitations on the precision of this stimulation, the acoustic information delivered by a cochlear implant does not convey the same level of acoustic detail as that conveyed by normal hearing. As a result, speech understanding in listeners with cochlear implants is typically poorer and more effortful than in listeners with normal hearing. The brain networks supporting speech understanding in listeners with cochlear implants are not well understood, partly due to difficulties obtaining functional neuroimaging data in this population. In the current study, we assessed the brain regions supporting spoken word understanding in adult listeners with right unilateral cochlear implants (n=20) and matched controls (n=18) using high-density diffuse optical tomography (HD-DOT), a quiet and non-invasive imaging modality with spatial resolution comparable to that of functional MRI. We found that while listening to spoken words in quiet, listeners with cochlear implants showed greater activity in left prefrontal cortex than listeners with normal hearing, specifically in a region engaged in a separate spatial working memory task. These results suggest that listeners with cochlear implants require greater cognitive processing during speech understanding than listeners with normal hearing, supported by compensatory recruitment of left prefrontal cortex.

neuroscience↗

bioRxiv2021

A multi-dataset evaluation of frame censoring for task-based fMRI

Subject motion during fMRI can affect our ability to accurately measure signals of interest. In recent years, frame censoring--that is, statistically excluding motion-contaminated data within the general linear model using nuisance regressors--has appeared in several task-based fMRI studies as a mitigation strategy. However, there have been few systematic investigations quantifying its efficacy. In the present study, we compared the performance of frame censoring to several other common motion correction approaches for task-based fMRI using open data and reproducible workflows. We analyzed eight publicly-available datasets representing eleven distinct tasks in child, adolescent, and adult participants. Performance was quantified using maximum t-values in group analyses, and ROI-based mean activation and split-half reliability in single subjects. We compared frame censoring across several thresholds to the use of 6 and 24 canonical motion regressors, wavelet despiking, robust weighted least squares, and untrained ICA-based denoising, for a total of 240 separate analyses. Thresholds used to identify censored frames were based on both motion estimates (FD) and image intensity changes (DVARS). Relative to standard motion regressors, we found consistent improvements for modest amounts of frame censoring (e.g., 1-2% data loss), although these gains were frequently comparable to what could be achieved using other techniques. Importantly, no single approach consistently outperformed the others across all datasets and tasks. These findings suggest that the choice of a motion mitigation strategy depends on both the dataset and the outcome metric of interest.

neuroscience↗