1,720,978 research outputs found
Enhancing rapeseed drought resilience: transcriptomic insights from superabsorbent polymer seed coatings
No full textEF-hand protein Ca2+ buffers regulate Ca2+ influx and exocytosis in sensory hair cells
No full textEF-hand Ca2+-binding proteins are thought to shape the spatiotemporal properties of cellular Ca2+ signaling and are prominently expressed in sensory hair cells in the ear. Here, we combined genetic disruption of parvalbumin-α, calbindin-D28k, and calretinin in mice with patch-clamp recording, in vivo physiology, and mathematical modeling to study their role in Ca2+ signaling, exocytosis, and sound encoding at the synapses of inner hair cells (IHCs). IHCs lacking all three proteins showed excessive exocytosis during prolonged depolarizations, despite enhanced Ca2+-dependent inactivation of their Ca2+ current. Exocytosis of readily releasable vesicles remained unchanged, in accordance with the estimated tight spatial coupling of Ca2+ channels and release sites (effective “coupling distance” of 17 nm). Substitution experiments with synthetic Ca2+ chelators indicated the presence of endogenous Ca2+ buffers equivalent to 1 mM synthetic Ca2+-binding sites, approximately half of them with kinetics as fast as 1,2-Bis(2-aminophenoxy)ethane-N,N,N′,N′-tetraacetic acid (BAPTA). Synaptic sound encoding was largely unaltered, suggesting that excess exocytosis occurs extrasynaptically. We conclude that EF-hand Ca2+ buffers regulate presynaptic IHC function for metabolically efficient sound coding
Transcriptomic and physiological effects of superabsorbent polymer seed coating on maize under drought stress
No full textDrought stress severely impairs maize germination and early seedling growth, posing a significant threat to global food security. To address this, superabsorbent polymers (SAPs) are being explored as an effective seed-coating method to improve water availability during the crucial germination phase. However, their comparative efficacy and underlying molecular mechanisms remain insufficiently understood. In this study, we evaluated the effects of three distinct SAPs, two fossil-based (MERCK, SWT) and one natural-based (ABG), on maize germination and seedling development under controlled drought conditions. We integrated physiological (germination rate and NA + ), biochemical (total phenol content), and transcriptomic (mRNA-seq) analyses to provide a comprehensive multi-level assessment. Physiologically, among all SAPs, the MERCK was the most effective, resulting in the highest proportion of normal seedlings and the fewest abnormal seedlings. In contrast, the SWT treatment was detrimental, increasing the proportion of abnormal seedlings, suggesting phytotoxic effects. Biochemically, all SAP treatments resulted in elevated seedling sodium (Na + ) content, indicating potential secondary ionic stress. Transcriptomic analysis further elucidated these observations, revealing a set of differentially expressed genes, including those involved in stress response ( BADH , FACT , XCP2 ), SAP-specific response ( DRB5 , RAF35 , EDR1 ), and combined salt/drought stress ( WRKY47 , DTX20 ), as promising candidate biomarkers for stress assessment and breeding. Our research highlights the nuanced efficacy of SAPs; specifically, the MERCK SAP yielded more favorable outcomes, while other formulations occasionally caused unexpected phytotoxicity. The identified gene expression patterns not only mechanistically explain the observed physiological responses but also offer a valuable panel of molecular biomarkers. These markers can be used to screen novel SAP applications, such as seed coatings, and to breed stress-resilient maize cultivars
Molecular and structural investigation of assembly, maturation and heterogeneity of inner hair cell ribbon synapses
Full text linkAge-related hearing and balance impairments represent the most common sensory deficits in humans. Both senses rely on hair cell ribbon synapses, which are highly specialized to sustain continuous release of neurotransmitter filled synaptic vesicles mediating indefatigable signal transmission. Disruption of their complex structural features are associated with disorders. However, their developmental aspects including the time course of ribbon synapse assembly, ribbon material targeting to active zones and their morphological maturation remain elusive.
To address these questions, I first attempted to characterize the nanostructure of the auditory ribbon-type synapse by using electron microscopy and electron-tomography. The morphology of the inner hair cell (IHC) ribbon synapse was investigated in the mouse cochlea from late embryonic stages into adulthood. I could show that afferent synaptic contacts are established before floating spherical ribbon precursors arrive at immature active zones. Furthermore, pre-embedding immunogold labelings revealed two of the ribbon precursor constituents, namely RIBEYE and piccolino. The close proximity of floating ribbon precursors to cytoskeletal structures indicates active transport mechanisms to target them towards active zones. Moreover, ribbon fusion events around the onset of hearing serve as one key mechanism to transform multiple small ribbons per synaptic contact in IHCs of pre-hearing mice to a predominantly single and large synaptic ribbon in hearing animals. A similar structural confinement was found for the postsynaptic density. The employment of large 3D volume imaging techniques exhibited a morphological spatial gradient of active zones within individual IHCs, which is already established prior to hearing onset. Synapses of the modiolar side exhibited more frequently multiple ribbons per contact with generally larger sized ribbons, whereas pillar sides revealed a lower synapse density with contacts comprising a single and smaller ribbon.
In the second part of this thesis, I studied the loss of the ribbon specific protein RIBEYE and its impact on the ultrastructural organization of cochlear IHC active zones. Multiple conventional-like active zones were present at each ribbonless synaptic contact of IHCs in RIBEYE knockout mice, which implies a partial compensation. Exploring older mature animals excluded a developmental delay in these knockout mice.
In the third part, I compared my developmental results from auditory IHCs with the two different types of vestibular hair cells from the utricle. While developmental processes have been studied extensively in the auditory pathway, much less is reported for the vestibular system. Utricular hair cells can be divided into type I and type II cells. In contrast to cochlear IHCs, they do not exhibit a change in size or number of synaptic ribbons per synapse or in the number of synaptic vesicles upon maturation. Unexpectedly, floating ribbons were present even in 11 months old mice arguing against a pure precursor function as described for immature IHCs. The number of floating ribbons increased during development in type I cells forming clusters, but decreased in type II cells. I propose that the large number of floating ribbons in type I hair cell could be the result of a secondary detachment of synaptic ribbons, which indicates a distinct maturation compared to type II and cochlear HCs. Type II hair cells showed a sequence of maturational events, which was more comparable to cochlear IHCs.
In conclusion, mapping hair cell synapses during development resulted in the discovery of structural modifications, which correlate to functional maturation processes of the active zone. If also occurring in mature hair cells, the observed fusion or detachment events of ribbon material might represent a mechanism to modulate the ribbon size and number, which might influence the respective synaptic strength in cochlear and vestibular hair cells
Age-dependent structural reorganization of utricular ribbon synapses
No full textIn mammals, spatial orientation is synaptically-encoded by sensory hair cells of the vestibular labyrinth. Vestibular hair cells (VHCs) harbor synaptic ribbons at their presynaptic active zones (AZs), which play a critical role in molecular scaffolding and facilitate synaptic release and vesicular replenishment. With advancing age, the prevalence of vestibular deficits increases; yet, the underlying mechanisms are not well understood and the possible accompanying morphological changes in the VHC synapses have not yet been systematically examined. We investigated the effects of maturation and aging on the ultrastructure of the ribbon-type AZs in murine utricles using various electron microscopic techniques and combined them with confocal and super-resolution light microscopy as well as metabolic imaging up to 1 year of age. In older animals, we detected predominantly in type I VHCs the formation of floating ribbon clusters, mostly consisting of newly synthesized ribbon material. Our findings suggest that VHC ribbon-type AZs undergo dramatic structural alterations upon aging
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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