Biology subjects

Haberl, M. G.

Publications and source records attributed to Haberl, M. G..

5 recordsLinked to original sources

bioRxiv2025

Deep mapping of the endomembrane system of cerebellar Purkinje neurons

Neuronal function relies on the precise spatial organization of intracellular membrane-bounded organelles involved in anabolism and Ca2+ sequestration, such as the Golgi apparatus, mitochondria and the endoplasmic reticulum (ER), along with structures involved in catabolism, such as lysosomes. Despite their known roles in energy supply, calcium homeostasis, and proteostasis, our understanding of how the anabolism-linked organelles are structurally arranged within neurons remains incomplete. Due to the tremendous complexity in the morphologies and fine structural features and interwoven nature of these intracellular organelles, particularly the ER, our understanding of their structural organization is limited, particularly, with regard to quantitative assessments of their sites of interaction and accurate measures of their volumetric proportions inside of a single large neuron. To approach this challenge, we used serial block-face scanning electron microscopy (SBEM) to generate large-scale 3D EM volumes and electron tomography on high-pressure frozen tissue of the rodent cerebellum, including the largest cells in the vertebrate brain, the cerebellar Purkinje neuron as well as the most abundant cell type in the vertebrate brain, the much smaller cerebellar granule neuron. We reconstructed the neuronal ultrastructure of these different cell types, focusing on the ER, mitochondria and membrane contact sites, to then characterize intracellular motifs and organization principles in detail, providing a first full map to quantitatively describe a neuronal endoarchitectome. At the gross level organization, we found that the intracellular composite of organelles are cell type specific features, with specific differences between Purkinje neurons and Granule cells. At the level of fine structure, we mapped ultrastructural domains within Purkinje neurons where ER and mitochondria associate directly. In addition to cell type specific differences, we observed significant subcellular regional variation, particularly within the axon initial segment (AIS) of Purkinje neurons, where we identified ultrastructural domains with sharply contrasting distributions of ER and mitochondria. These findings suggest a finely tuned spatial organization of organelles that may underpin the distinct functional demands along the axon. We expect that our subcellular map, along with the methods developed to obtain these maps, will facilitate future studies in health, aging and disease to characterize defined features, by developing a framework for quantitative analysis of the neuronal ultrastructure.

neuroscience↗

bioRxiv2024

cfos principal cells and interneurons are strongly reactivated by sharp wave ripples

Sharp wave ripples (SWRs) reactivate hippocampal activity patterns during memory consolidation, but whether they recruit cFos engram cells is unclear. We tagged CA1 neurons activated during sequential exploration of two spatial contexts and later identified them in vivo by optotagging. We found that the cfos engram population is composed of place cells, non-place principal cells and inhibitory interneurons. cFos-tagged place cells were reused across context exposures while maintaining context specific maps. During post-behavior rest, cFos-tagged place cells and interneurons showed stronger SWR recruitment than untagged cells, with cFos identity being more closely associated with SWR modulation than firing rate features. cFos-tagged interneurons were speed- and theta-modulated, preferentially coupled to cFos-tagged place cells during SWRs, and preferentially recruited from parvalbumin and somatostatin expressing classes. After exposure to contexts outside the original tagging experience, enhanced interneuron recruitment was attenuated, whereas tagged place cells retained elevated SWR coupling. Thus, SWRs engage excitatory and inhibitory components of a cFos-tagged spatial ensemble, linking cellular engram identity to hippocampal network dynamics during memory consolidation.

neuroscience↗

bioRxiv2022

Localized APP pathology in the hippocampus is sufficient to result in progressive disorganization of the timing of neuronal firing patterns

Deficits in spatial navigation are among the early symptoms in Alzheimers disease patients, consistent with the hippocampal formation as the site for spatial computations and disease onset. Although the correspondence between the early symptoms and brain regions that are affected early in the disease has been recognized, it is not clear whether progressive cognitive decline is solely caused by a spreading pathology or whether a focal pathology can by itself cause aberrant neuronal activity in a larger network. These possibilities cannot be distinguished in standard disease models which broadly express APP across brain regions. We therefore generated a mouse model in which the expression of mutant human APP was limited to hippocampal CA3 cells (CA3-APP mice). We first asked whether the limited pathology in CA3 can result in memory deficits and found impaired performance of CA3-APP mice in a hippocampus-dependent memory task. By then recording in the CA1 region, we asked to what extent neuronal activity patterns emerged in a brain region which received projections from APP-expressing CA3 cells, but did itself not show any primary pathology. While the spatial firing patterns of CA1 cells were preserved, we observed a reduced theta oscillation frequency in the local field potential and in a subpopulation of principal cells in CA1. Furthermore, CA1 interneurons showed decreased theta oscillation frequencies, and this effect was even more pronounced in CA3 interneurons, which also do not directly express APP. Pathology that is highly localized and limited to presynaptic cells is thus sufficient to cause aberrant firing patterns in postsynaptic neuronal networks, which indicates that disease progression is not only from a spreading molecular pathology but also mediated by progressive physiological dysfunction.

neuroscience↗

bioRxiv2020

A genetic probe for visualizing glutamatergic synapses and vesicles by 3D electron microscopy

Communication between neurons relies on the release of diverse neurotransmitters, which represent a key-defining feature of a neurons chemical and functional identity. Neurotransmitters are packaged into vesicles by specific vesicular transporters. However, tools for labeling and imaging synapses and synaptic vesicles based on their neurochemical identity remain limited. We developed a genetically encoded probe to identify glutamatergic synaptic vesicles at the levels of both light and electron microscopy (EM) by fusing the mini singlet oxygen generator (miniSOG) probe to an intra-lumenal loop of the vesicular glutamate transporter-2. We then used a 3D imaging method, serial block face scanning EM, combined with a deep learning approach for automatic segmentation of labeled synaptic vesicles to assess the subcellular distribution of transporter-defined vesicles at nanometer scale. These tools represent a new resource for accessing the subcellular structure and molecular machinery of neurotransmission and for transmitter-defined tracing of neuronal connectivity.

neuroscience↗

bioRxiv2020

CDeep3M-Preview: Online segmentation using the deep neural network model zoo

Sharing deep neural networks and testing the performance of trained networks typically involves a major initial commitment towards one algorithm, before knowing how the network will perform on a different dataset. Here we release a free online tool, CDeep3M-Preview, that allows end-users to rapidly test the performance of any of the pre-trained neural network models hosted on the CIL-CDeep3M modelzoo. This feature makes part of a set of complementary strategies we employ to facilitate sharing, increase reproducibility and enable quicker insights into biology. Namely we: (1) provide CDeep3M deep learning image segmentation software through cloud applications (Colab and AWS) and containerized installations (Docker and Singularity) (2) co-hosting trained deep neural networks with the relevant microscopy images and (3) providing a CDeep3M-Preview feature, enabling quick tests of trained networks on user provided test data or any of the publicly hosted large datasets. The CDeep3M-modelzoo and the cellimagelibrary.org are open for contributions of both, trained models as well as image datasets by the community and all services are free of charge.

neuroscience↗