Biology subjects

Seewald, A.

Publications and source records attributed to Seewald, A..

7 recordsLinked to original sources

bioRxiv2026

Mineralization kinetics during embryonic avian bone growth: a three-dimensional multiscale and cryogenic imaging approach

Bone formation during embryonic development requires the rapid and sustained delivery of large amounts of calcium to mineralizing tissue. In avian embryos, this process coincides with a unique physiological transition in calcium supply, shifting from limited yolk reserves to massive mobilization from the eggshell. To address the question of how calcium transport responds to the increasing mineral demand during this transition, we combine micro computed tomography with three-dimensional cryogenic FIB-SEM imaging at different embryonic stages in the developing quail femur. Over this developmental period, bone mineralized volume increases rapidly through periosteal expansion. We observe that bone forming cells consistently contain numerous membrane-bound carriers loaded with mineral precursors throughout all growth stages. By integrating measurements across length scales, we calculate the intracellular velocities required to sustain the observed mineral deposition in the successive developmental stages. Surprisingly, these velocities remain within a similar range across development, despite the significant difference of bone formation rates, and are consistent with active transport by molecular motors. The increasing mineral demand corresponds to the expansion of mineralizing surfaces, which leads to an increasing number of cells, while the transport capacity of individual cells remains similar. Our work reveals a perfect tuning between the calcium transport capacity and bone growth, even in a situation where the skeletal growth is accelerating in the quail embryo. Significance statementDespite the importance of bone mineralization for the integrity of the skeleton, surprisingly little is known about how calcium is transported across the organic matrix to the mineralization sites during embryonal development. Using an avian model, where the main source of calcium shifts from a limited contribution from the yolk to the massive reservoir in the eggshell, we quantify bone mineral deposition using tissue level characterization together with three-dimensional cryogenic nanoscale imaging. We discover that intracellular vesicles containing mineral precursors are transported at similar speed, although the overall mineral deposition rate is increasing six-fold from embryonal day 10 to 14. This shows that the acceleration in mineralization activity is due to an increased number of bone cells rather than to a larger workload for individual cells. These findings demonstrate that rapid bone development is regulated to synchronize growth rates and mineral transport.

physiology↗

bioRxiv2026

E. coli extracellular matrix: a tunable composite with hierarchical structure

Escherichia coli (E. coli) biofilms consist of bacteria, an extracellular matrix (ECM) mainly made of curli amyloid fibers, phosphoethanolamine-modified cellulose (pEtN-cellulose), and water. While curli amyloid fibers contribute to biofilm rigidity, pEtN-cellulose contributes to their cohesion. This work explores the interplay between these fibers, and how their interaction influence biofilm structure and mechanical properties. We performed a multiscale analysis on E. coli biofilms grown using strains producing curli and pEtN-cellulose, and only curli and only pEtN-cellulose in co-seeded ratios. Micro-indentation experiments, confocal microscopy, and cryo-FIBSEM 3D imaging revealed a composite-like behavior of the biofilm, where its mechanical properties depend on ECM composition and organization. Spectroscopic analysis of the extracted fibers showed that their biophysical properties are influenced by their pEtN-cellulose to curli ratio and assembly. We propose that pEtN-cellulose swelling is contrained by its interactions with rigid curli fibers. The reference E. coli strain maximizes this effect by assembling a curli/pEtN-cellulose hybrid material at the sub-micron scale, where its composition, interactions, and architecture can explain biofilm emergent properties. This knowledge on microbial ECM assembly opens new avenues for engineering living materials, especially for the use of bacterial biofilms as a source of bio-sourced materials.

biophysics↗

bioRxiv2025

Direct encoding of new visual concepts in early visual cortex

Neocortical memories are assumed to rely on slow systems consolidation through hippocampal offline reactivation. However, recent studies show rapid neocortical integration of new memories for information associated with prior knowledge. Testing the limits of rapid neocortical learning, we tracked memory formation across 24h with functional and diffusion-weighted MRI in subjects acquiring either conceptual or detailed knowledge of novel objects from identical visual stimulation. Concept learning-induced rapid, 24h-stable changes in strength and pattern of functional early visual cortex responses. These were co-localized with microstructural changes, correlated positively with categorization performance and negatively with context recognition. Detailed item-context learning elicited analogous changes in posterior parietal areas. Results show that the neocortex can rapidly learn without prior knowledge and that concept learning can occur in early sensory regions that process corresponding visual features. Thus, we substantiate the possibility of direct or parallel neocortical encoding without offline abstraction from individual episodes.

neuroscience↗

bioRxiv2023

Inhibitory fear memory engram in the mouse central lateral amygdala

Engrams are cellular substrates of memory traces that have been identified in various brain areas, including the amygdala. Most engrams identified so far are formed by excitatory, glutamatergic neurons. However, little attention has been paid to defining GABAergic inhibitory engrams. Here, we report an inhibitory engram in the central lateral amygdala (CeL), a crucial area for Pavlovian fear conditioning. This engram is primarily composed of GABAergic somatostatin-expressing (SST+) and to a lesser extent of protein kinase C-{delta}-expressing [PKC-{delta}(+)] neurons. Fear memory is accompanied by a preferential enhancement of mIPSC frequency onto PKC-{delta}(+) neurons as well as a general increment of amplitude. Moreover, non-engram cells exhibit higher mIPSC frequency than engram cells. The inhibition of the CeL GABAergic engram disinhibits the activity of engram-targeted areas and increases selectively the encoded fear expression. Our data defines the behavioral function of an engram formed exclusively by GABAergic inhibitory neurons in the mammalian CNS.

neuroscience↗

bioRxiv2023

Bone elongation in the embryo occurs without column formation in the growth plate

Chondrocyte columns, which are a hallmark of growth plate architecture, play a central role in bone elongation. Columns are formed by clonal expansion following rotation of the division plane, resulting in a stack of cells oriented parallel to the growth direction. However, despite decades of research, column structure has thus far been studied only in two dimensions. To fill this knowledge gap, we analyzed hundreds of Confetti multicolor clones in growth plates of mouse embryos using a pipeline comprising 3D imaging and algorithms for morphometric analysis. Surprisingly, analysis of the elevation angles between neighboring pairs of cells revealed that most cells did not display the typical stacking pattern associated with column formation, implying incomplete rotation of the division plane. Morphological analysis revealed that although embryonic clones were elongated, they formed clusters oriented perpendicular to the growth direction. Analysis of growth plates of postnatal mice revealed both complex columns, composed of both ordered and disordered cell stacks, and small, disorganized clusters located in the outer edges. Our finding that embryonic growth plates function without forming columns suggests that longitudinal bone growth is regulated by different cellular mechanisms during pre- and postnatal development. Moreover, the observed complex columnar and cluster arrangements may serve other, yet unknown morphogenetic functions. More broadly, our findings provide a new understanding of the cellular mechanisms underlying growth plate activity and bone elongation during development.

developmental biology↗

bioRxiv2023

Memory systems integration in sleep complements rapid systems consolidation in wakefulness

Sleep benefits memory performance by fostering systems consolidation, a process that embeds memories into neocortical networks and renders them independent of the hippocampus. Recent evidence shows that memory rehearsal during wakefulness likewise initiates systems consolidation and rapidly engenders neocortical engrams. Here, we investigate the effect of sleep-dependent consolidation for memories that have undergone rapid systems consolidation during wakefulness. After sleep compared to wakefulness, we find better memory retention and higher functional brain activity during memory retrieval in the medial parietal cortex, which hosts memory representations after rehearsal, and in the striatum and thalamus. Increased striatal and thalamic contributions were correlated with higher retrieval performance. Furthermore, all three regions decreased their functional connectivity to the hippocampus specifically after sleep. These findings show that besides continuing of systems consolidation initiated during wakefulness, sleep also acts to integrate different memory systems. Thus, rehearsal-induced and sleep-dependent consolidation seem to be complementary in nature.

neuroscience↗

bioRxiv2020

Midbrain dopaminergic inputs gate amygdala intercalated cell clusters by distinct and cooperative mechanisms

AO_SCPLOWBSTRACTC_SCPLOWDopaminergic signaling plays an important role in associative learning including fear and extinction learning. Dopaminergic midbrain neurons encode prediction error-like signals when threats differ from expectations. Within the amygdala, GABAergic intercalated cell (ITC) clusters receive the densest dopaminergic projections, but their physiological consequences are incompletely understood. ITCs are important for fear extinction, a function thought to be supported by activation of ventromedial cluster ITCs that inhibit central amygdala fear output. In mice, we reveal two distinct mechanisms how mesencephalic dopaminergic afferents control ITCs. Firstly, they co-release GABA to mediate rapid, direct inhibition. Secondly, dopamine suppresses inhibitory interactions between distinct ITC clusters via presynaptic D1-receptors. Early extinction training augments both, GABA co-release onto dorso-medial ITCs and dopamine-mediated suppression of dorso- to ventromedial inhibition between ITC clusters. These findings provide novel insights into dopaminergic mechanisms shaping the activity balance between distinct ITC clusters that could support their opposing roles in fear behavior.

neuroscience↗