Biology subjects

Dedek, K.

Publications and source records attributed to Dedek, K..

9 recordsLinked to original sources

bioRxiv2026

Socially transmitted knowledge of hibernation sites in bats

In temperate regions around the world, bats travel long distances every winter to gather at hibernation sites. A longstanding hypothesis is that each new generation of bats learns about the locations of these sites (called hibernacula) from older individuals, yet clear and compelling evidence demonstrating social transmission of this knowledge has been lacking. Here, we compiled 30,882 observations from 1985 to 2023 of 13,852 Greater mouse-eared bats (Myotis myotis) that were banded and observed at summer roosts, winter hibernacula, or both. Our analyses revealed four lines of evidence that Greater mouse-eared bats find suitable hibernacula using social information acquired at summer roosts. First, naive yearlings were more likely to be seen sharing their first hibernacula with adults from their summer birth colony relative to a null model where bats moved independently. Second, adult bats were also more likely to co-switch together into the same hibernacula across winters than expected from independent movements. Third, bats that roosted together in the summer were more likely to share a different site as a hibernaculum during the winter: being observed together during a summer changed the probability of a pair being observed together during a winter from 5% to 12%. Finally, high-resolution tracking revealed an instance of tandem flights to hibernacula sites during the summer, demonstrating that yearlings can learn from experienced adult bats months before hibernation. Together, our findings show that maternity colonies serve as "information centers" where females acquire knowledge of suitable hibernation sites throughout their long lives.

animal behavior and cognition↗

bioRxiv2026

Expression patterns and interaction profiles of heterotrimeric transducin subunits in the retina of the European robin ( Erithacus rubecula )

The heterotrimeric G-protein transducin (Gt) is mediating phototransduction in rod and cone cells of the vertebrate retina, but its expression patterns in migratory songbirds is unknown. We characterised Gt expression in the European robin, a night-migratory songbird known for its light-dependent magnetoreception. One well-supported hypothesis of magnetoreception involves radical-pair formation in the blue light receptor cryptochrome type 4a. The - and {gamma}-subunits of cone specific transducin have been identified as possible interaction partners of cryptochrome 4a. Therefore, we analysed the expression patterns of various G-protein subunits in bird photoreceptors by combining single cell RNA sequencing and immunohistochemistry. Protein-protein interaction was tested by pulldown, co-immunoprecipitation, and NanoBiT luminescence assays. G-protein subunits Gt{beta}1 and Gt{beta}3 are predominantly expressed in rods and cones, and Gt{gamma}T2 was the principal isoform in cones, whereas Gt{gamma}11 was associated with rods. In contrast, we did not detect Gt{gamma}10 expression in either photoreceptor type. Interaction assays demonstrated that all three {beta}{gamma} combinations; {beta}{gamma}T2, {beta}{gamma}10, and {beta}{gamma}11, can associate in vitro. These findings indicate that {beta}{gamma} dimer formation in vivo is likely constrained by the photoreceptor-specific expression of the respective subunits. The absence of Gt{gamma}10 expression in rods and cones does not support a role in photoreceptor-based magnetoreception.

Molecular Biology↗

bioRxiv2025

Cryptochrome 4b protein is likely irrelevant for the radical pair based magnetoreception in the European robin

Avian cryptochrome 4 (Cry4) protein is a putative magnetosensitive molecule facilitating precise long-distance navigation in migratory birds. Two splice variants of Cry4 were reported in European robin (Erithacus rubecula), namely ErCry4a and ErCry4b. It is known that ErCry4a protein exhibits electron transfer between the flavin adenine dinucleotide (FAD) cofactor and tryptophan residues that generates magnetically sensitive radical pairs for magnetoreception. However, little is known about the ErCry4b isoform. We therefore characterized the properties of ErCry4b to see whether it fulfills prerequisites to be a radical pair magnetic sensor molecule. Our results show that ErCry4b protein does not bind FAD in vitro. Computational structure simulations revealed that the FAD non-binding in ErCry4b is likely due to protein structure dynamics. Furthermore, ErCry4b protein abundance in the robin retina, cerebellum and liver is below the detection limit of immunoprecipitation assays coupled with mass spectrometry. Meanwhile, transcript analyses show that ErCRY4b mRNA abundance is 10 times less than ErCRY4b in the retina. In conclusion, ErCry4b does not fulfill the prerequisites to be a radical pair based magnetic sensing molecule due to the lack of FAD binding, and it might not even be expressed as a functional protein in the European robin.

biochemistry↗

bioRxiv2025

Morphology and connectivity of retinal horizontal cells in two avian species

In the outer vertebrate retina, the visual signal is separated into intensity and wavelength information. In birds, seven types of photoreceptors (one rod, four single cones, and two members of the double cone) mediate signals to >20 types of second-order neurons, the bipolar cells and horizontal cells. Horizontal cells contribute to color and contrast processing by providing feedback signals to photoreceptors and feedforward signals to bipolar cells. In fish, reptiles, and amphibians they either encode intensity or show color-opponent responses. Yet, for the bird retina, the number of horizontal cell types is not fully resolved and even more importantly, the synapses between photoreceptors and horizontal cells have never been quantified for any bird species. With a combination of light microscopy and serial EM reconstructions, we found four different types of horizontal cells in two distantly related species, the domestic chicken and the European robin. In agreement with some earlier studies, we confirmed two highly abundant cell types (H1, H2) and two rare cell types (H3, H4), of which H1 is an axon-bearing cell, whereas H2-H4 are axonless. Horizontal cell contacts to photoreceptors were type-specific and similar to the turtle retina, which confirms the high degree of evolutionary conservation in the vertebrate outer retina. Our data further suggests that H1 and potentially H2 cells may encode intensity, whereas H3 and H4 may represent color opponent horizontal cells which may contribute to the birds superb color and/or high acuity vision.

neuroscience↗

bioRxiv2024

Uncovering the electrical synapse proteome in retinal neurons via in vivo proximity labeling

AbstractElectrical synapses containing Connexin 36 (Cx36) represent the main means for direct electrical communication among neurons in the mammalian nervous system. However, little is known about the protein complexes that constitute these synapses. In the present study, we applied different BioID strategies to screen the interactomes of Connexin 36 and its zebrafish orthologue Cx35b in retinal neurons. For in vivo proximity labeling in mice, we took advantage of the Cx36-EGFP strain and expressed a GFP-nanobody-TurboID fusion construct selectively in AII amacrine cells. For in vivo BioID in zebrafish, we generated a transgenic line expressing a Cx35b-TurboID fusion under control of the Cx35b promoter. Both strategies allowed us to capture a plethora of molecules that were associated with electrical synapses and showed a high degree of evolutionary conservation in the proteomes of both species. Besides known interactors of Cx36 such as ZO-1 and ZO-2 we have identified more than 50 new proteins, such as scaffold proteins, adhesion molecules and regulators of the cytoskeleton. Moreover, we determined the subcellular localization of these proteins in mouse retina and tested potential binding interactions with Cx36. Amongst these new interactors, we identified signal induced proliferation associated 1 like 3 (Sipa1l3), a protein that has been implicated in cell junction formation and cell polarity, as a new scaffold of electrical synapses. Interestingly, Sipa1l3 was able to interact with ZO-1, ZO-2 and Cx36, suggesting a pivotal role in electrical synapse function. In summary, our study provides the first detailed view of the electrical synapse proteome in retinal neurons, which is likely to apply to electrical synapses elsewhere.

neuroscience↗

bioRxiv2024

Full-length Cryptochrome 1 in the outer segments of the retinal blue cone photoreceptors in humans and great apes suggests a role beyond transcriptional repression

Mammalian cryptochrome 1 (CRY1) is a central player in the circadian transcription-translation feedback loop, crucial for maintaining a roughly 24-hour rhythm. CRY1 was suggested to also function as blue-light photoreceptor in humans and has been found to be expressed at the mRNA level in various cell types of the inner retina. However, attempts to detect CRY1 at the protein level in the human retina have remained unsuccessful so far. Using various C-terminal specific antibodies recognizing full-length CRY1 protein, we consistently detected selective labelling in the outer segments of short wavelength-sensitive (SWS1, "blue") cone photoreceptor cells across human, bonobo, and gorilla retinae. No other retinal cell types were stained, which is in contrast to what would be expected of a ubiquitous clock protein. Subcellular fractionation experiments in transfected HEK cells using a C-terminal specific antibody located full-length CRY1 in the cytosol and membrane fractions. Our findings indicate that human CRY1 has several different functions including at least one non-clock function. Our results also raise the likely possibility that several different versions of CRY1 exists in humans. We suggest that truncation of the C-terminal tail, maybe to different degrees, may affect the localization and function of human CRY1.

cell biology↗

bioRxiv2024

The first interneuron of the mouse visual system is tailored to the natural environment through morphology and electrical coupling

The topographic complexity of the mouse retina has long been underestimated, as obvious specializations, like a fovea or visual streak, are absent. However, anatomical and functional gradients exist. It was recently shown that receptive fields of retinal ganglion cells change their shape along the dorso-ventral retinal axis. These variations likely reflect the non-uniform statistics of the visual environment which vary dramatically from ground to sky. Horizontal cells are the first visual interneurons and dictate the synaptic signaling between photoreceptors and bipolar cells by lateral interactions, thereby shaping the receptive fields of down-stream neurons. Thus, we asked whether regional specializations are present at this earliest stage of synaptic circuitry, i.e. at the level of horizontal cells. We analyzed horizontal cell density distributions, morphological properties, localization of gap junction proteins, and the spatial extent of horizontal cell electrical coupling across complete retinas. All of these horizontal cell key features were asymmetrically organized along the dorso-ventral axis. Dorsal horizontal cells were less densely distributed, had larger dendritic trees, and electrical coupling was more extensive than in their ventral counterparts. The steepest change along this gradient occurred at the opsin transition zone of photoreceptors, i.e. the mouse visual horizon. Therefore, our results show that the cellular and synaptic organization of the mouse visual system are adapted to the visual environment at the earliest possible level, and that horizontal cells are well suited to form the cellular substrate for the global gradient previously described for the receptive field structures of retinal ganglion cells.

neuroscience↗

bioRxiv2022

Intralumenal docking of Cx36 channels in the ER isolates mis-trafficked protein

The intracellular domains of connexins are essential for the assembly of gap junctions. For connexin 36 (Cx36), the major neuronal connexin, it has been shown that a dysfunctional PDZ binding motif interferes with electrical synapse formation. However, it is still unknown how this motif coordinates the transport of Cx36. In the present study, we characterize a phenotype of Cx36 mutants that lack a functional PDZ binding motif using HEK293T cells as an expression system. We provide evidence that an intact PDZ binding motif is critical for proper ER export of Cx36. Removing the PDZ binding motif of Cx36 results in ER retention and the formation of multi-membrane vesicles containing gap junction-like connexin aggregates. Using a combination of site directed mutagenesis and electron micrographs we reveal that these vesicles consist of Cx36 channels that docked prematurely in the ER. Our data suggest a model in which ER-retained Cx36 channels reshape the ER membrane into concentric whorls that are released into the cytoplasm.

cell biology↗

bioRxiv2019

Retinal horizontal cells use different synaptic sites for global feedforward and local feedback signaling

In the outer plexiform layer (OPL) of the mouse retina, two types of cone photoreceptors (cones) provide input to more than a dozen types of cone bipolar cells (CBCs). This transmission is modulated by a single horizontal cell (HC) type, the only interneuron in the outer retina. Horizontal cells form feedback synapses with cones and feedforward synapses with CBCs. However, the exact computational role of HCs is still debated. Along with performing global signaling within their laterally coupled network, HCs also provide local, cone-specific feedback. Specifically, it has not been clear which synaptic structures HCs use to provide local feedback to cones and global forward signaling to CBCs.\n\nHere, we reconstructed in a serial block-face electron microscopy volume the dendritic trees of five HCs as well as cone axon terminals and CBC dendrites to quantitatively analyze their connectivity. In addition to the fine HC dendritic tips invaginating cone axon terminals, we also identified \"bulbs\", short segments of increased dendritic diameter on the primary dendrites of HCs. These bulbs are located well below the cone axon terminal base and make contact to other cells mostly identified as other HCs or CBCs. Using immunolabeling we show that HC bulbs express vesicular gamma-aminobutyric acid transporters and co-localize with GABA receptor {gamma}2 subunits. Together, this suggests the existence of two synaptic strata in the mouse OPL, spatially separating cone-specific feedback and feedforward signaling to CBCs. A biophysics-based computational model of a HC dendritic branch supports the hypothesis that the spatial arrangement of synaptic contacts allows simultaneous local feedback and global feedforward signaling.

neuroscience↗