Biology subjects

Birchmeier, C.

Publications and source records attributed to Birchmeier, C..

10 recordsLinked to original sources

bioRxiv2026

c-MAF transduces motor neuron firing to sustain fast-glycolytic myofibers and neuromuscular junctions

This study examined how motoneuron activity influences transcription factor binding in mouse fast glycolytic Myh4+ muscle fibers. Single nucleus multiomics of innervated versus denervated tibialis anterior muscles revealed altered chromatin accessibility: SIX and c-MAF binding sites decreased while JUN, FOS, and RUNX1 sites increased in denervated Myh4+ myonuclei. c-MAF showed strong nuclear enrichment after 100 Hz stimulation and periods of increased motoneuron activity but was absent following denervation, establishing it as a primary readout of fast motoneuron firing. Genome-wide analysis demonstrated that c-MAF binding site spacing encodes functionally distinct muscle gene programs. Analysis of constitutive and inducible skeletal muscle-specific c-Maf mutants revealed that c-MAF loss caused region-specific MYH4+ fiber atrophy, MYH1/MYH2 fiber type shifts resembling ALS G93A mouse phenotypes, and progressive neuromuscular junction fragmentation with increased motoneuron terminal sprouting and ectopic reinnervation. These findings establish c-MAF as a critical mediator linking motoneuron activity to muscle gene regulation, fiber integrity, and neuromuscular junction maintenance in fast glycolytic fibers.

physiology↗

bioRxiv2025

Identification of V0g propriospinal neurons and their role in locomotor control

Propriospinal neurons relay sensory and motor information across the spinal cord and are critical components of the circuits coordinating body movements. Their diversity and roles in motor control are not clearly defined yet. In this study, by combining anatomical, molecular, and functional analyses in mice, we identified and characterized an ascending subtype of propriospinal neurons belonging to the Pitx2+ V0 family of spinal neurons. We found that Pitx2+ ascending neurons are integrated in spinal sensorimotor circuits and their function is important for the execution of precise limb movements required for effectively moving in challenging environments, like walking on a horizontal ladder or a balance beam. This work advances our understanding of the functional organization of propriospinal and V0 neurons, highlighting a previously unappreciated role in adjusting body movements to the more demanding needs of skilled locomotor tasks.

neuroscience↗

bioRxiv2022

The molecular foundation of proprioceptor muscle-type identity

The precise execution of coordinated movements depends on proprioception, the sense of body position in space. However, the molecular underpinnings of proprioceptive neuron subtype identities are not clear yet. In this study, we searched for molecular correlates of proprioceptor subtypes defined according to the identity of the muscle they innervate. We identified and validated signatures for subtypes monitoring the activity of back, abdominal, and hindlimb muscles. We found that proprioceptor muscle identity is acquired early in development and comprise programs controlling wiring specificity. Altogether this work paves the way for defining the mechanisms underlying the development of proprioceptor subtypes to the single muscle level and dissect their contributions to motor control.

neuroscience↗

bioRxiv2022

Prox2+ and Runx3+ neurons regulate esophageal motility

Sensory neurons of the vagus nerve monitor distention and stretch in the gastrointestinal tract. Major efforts are underway to assign physiological functions to the many distinct subtypes of vagal sensory neurons. Here, we used genetically guided anatomical tracing, optogenetics and electrophysiology to identify and characterize three vagal sensory neuronal subtypes expressing Prox2 and Runx3. We show that these neuronal subtypes innervate the esophagus and stomach where they display regionalized innervation patterns. Their electrophysiological analysis showed that they are all low threshold mechanoreceptors, but possess different adaptation properties. Lastly, genetic ablation of Prox2+ and Runx3+ neurons demonstrated their essential roles for esophageal peristalsis and swallowing in freely behaving animals. Our work reveals the identity and function of the vagal neurons that provide mechanosensory feedback from the esophagus to the brain, and could lead to better understanding and treatment of esophageal motility disorders.

neuroscience↗

bioRxiv2022

The IgCAM BT-IgSF (IgSF11) is essential for connexin43-mediated astrocyte-astrocyte and ependymal cell-cell coupling

The type I transmembrane protein BT-IgSF is predominantly localized in the brain and testes. It belongs to the CAR subgroup of Ig cell adhesion proteins, which have been hypothesized to regulate connexin expression or localization. Here, we studied the putative link between BT-IgSF and connexins in astrocytes, ependymal cells and neurons of the mouse. Global knockout of BT-IgSF caused an increase in the clustering of connexin43 (Gja1), but not of connexin30 (Gjb6), on astrocytes and ependymal cells. Additionally, knockout animals displayed reduced expression levels of connexin43 protein in the cortex and hippocampus. Importantly, analysis of biocytin spread in hippocampal or cortical slices from mature mice of either sex revealed a decrease in astrocytic cell-cell coupling in the absence of BT-IgSF. Blocking either protein biosynthesis or proteolysis showed that the lysosomal pathway increased connexin43 degradation. Localization of connexin43 in subcellular compartments was not impaired in the mutant. In contrast to connexin43 the localization and expression of connexin36 (Gjd2) on neurons was not affected by the absence of BT-IgSF. Overall, our data indicate that the IgCAM BT-IgSF is essential for correct gap junction-mediated astrocyte-to-astrocyte and ependymal cell-to-ependymal cell communication. Significance StatementAstrocytes regulate a variety of physiological processes in the developing and adult brain that are essential for proper brain function. Astrocytes form extensive networks in the brain and communicate via gap junctions. Disruptions of gap junction coupling are found in several diseases such as neurodegeneration or epilepsy. Here, we demonstrate that the cell adhesion protein BT-IgSF is essential for gap junction mediated coupling between astrocytes in the cortex and hippocampus.

cell biology↗

bioRxiv2021

SMER28 attenuates PI3K/mTOR signaling by direct inhibition of PI3K p110 delta

SMER28 (Small molecule enhancer of Rapamycin 28) is an autophagy-inducing compound functioning by a hitherto unknown mechanism. Here we confirm its autophagy-inducing effect by assessing classical autophagy-related parameters. Interestingly, we also discovered several additional effects of SMER28, including growth retardation and reduced G1 to S phase progression. Most strikingly, SMER28 treatment led to a complete arrest of receptor tyrosine kinase signaling, and consequently growth factor-induced cell scattering and dorsal ruffle formation. This coincided with a dramatic reduction of phosphorylation patterns of PI3K downstream effectors. Consistently, SMER28 directly inhibited PI3K{delta} and to a lesser extent p110{gamma}. The biological relevance of our observations was underscored by interference of SMER28 with InlB-mediated host cell entry of Listeria monocytogenes, which requires signaling through the prominent receptor typrosine kinase c-Met. This effect was signaling-specific, since entry of unrelated, gram-negative Salmonella Typhimurium was not inhibited.

cell biology↗

bioRxiv2021

An executive center for the intake of liquids

It has long been known that orofacial movements for feeding can be triggered, coordinated, and often rhythmically organized at the level of the brainstem, without input from higher centers. We uncover two nuclei that can organize the movements for ingesting fluids in mammals. These neuronal groups, defined by unique transcriptional codes and developmental origins, IRtPhox2b and Peri5Atoh1, are located, respectively, in the intermediate reticular formation of the medulla and around the motor nucleus of the trigeminal nerve. They are premotor to all jaw-opening and tongue muscles. Stimulation of either, in awake animals, opens the jaw, while IRtPhox2b alone also protracts the tongue. Moreover, stationary stimulation of IRtPhox2b entrains a rhythmic alternation of tongue protraction and retraction, synchronized with jaw opening and closing, that mimics lapping. Finally, fiber photometric recordings show that IRtPhox2b is active during volitional lapping. Our study identifies one of the long hypothesized subcortical nuclei underpinning a stereotyped feeding behavior.

neuroscience↗

bioRxiv2020

Fructose 1,6-bisphosphate sensing by pyruvate kinase isozymes M2 (PKM2) controls MyoD stability and myogenic differentiation

Glucose exerts beneficial effects on myogenesis and muscle physiology. However, the mechanisms by which glucose regulates myogenesis remain ill-defined or incompletely understood. Here, we show that low glycolysis destabilizes MyoD protein, a master myogenic transcription factor. Intriguingly, MyoD is not controlled by the cellular energy status per se, but by the level of fructose 1,6-bisphosphate, an intermediate metabolite of glycolysis. Fructose 1,6-bisphosphate is sensed by pyruvate kinase M2 (PKM2). In the presence of fructose 1,6-bisphosphate, PKM2 form tetramers that sequester the Huwe1 E3 ubiquitin ligase to the cytoplasm. Reduced fructose 1,6-bisphosphate levels dissociate the tetramer, releasing Huwe1 into the nucleus where it targets MyoD for degradation. Genetic or pharmacological modulation of PKM2-Huwe1 axis restores myogenic differentiation in glucose restricted conditions. Our results show that glucose metabolism directly regulates protein stability of a key myogenic factor and provide a rationale for enhancing myogenesis.

cell biology↗

bioRxiv2020

Single-nucleus transcriptomics reveals functional compartmentalization in syncytial skeletal muscle cells

Syncytial skeletal muscle cells contain hundreds of nuclei in a shared cytoplasm. We investigated nuclear heterogeneity and transcriptional dynamics in the uninjured and regenerating muscle using single-nucleus RNA-sequencing (snRNAseq) of isolated nuclei from muscle fibers. This revealed distinct nuclear subtypes unrelated to fiber type diversity, completely novel subtypes as well as the expected ones at the neuromuscular and myotendinous junctions. In fibers of the Mdx dystrophy mouse model, new subtypes emerged, among them nuclei expressing a repair signature that were also abundant in the muscle of dystrophy patients, and a nuclear population associated with necrotic fibers. Finally, modifications of our approach revealed the compartmentalization in the rare and specialized muscle spindle. Our data identifies new nuclear compartments of the myofiber and defines a molecular roadmap for their functional analyses; the data can be freely explored on the MyoExplorer server (https://shiny.mdc-berlin.net/MyoExplorer/).

developmental biology↗

bioRxiv2019

EHD2-mediated restriction of caveolar dynamics regulates cellular lipid uptake

Eps15-homology domain containing protein 2 (EHD2) is a dynamin-related ATPase located at the neck of caveolae, but its physiological function has remained unclear. We found that global genetic ablation of EHD2 in mice led to increased fat deposits in several organs. This organismic phenotype was paralleled at the cellular level by an increased lipid uptake via a CD36-dependent pathway, an elevated number of detached caveolae and higher caveolar mobility. Following a high fat diet, various enzymes involved in de novo fatty acid synthesis were down-regulated in EHD2 KO mice. Furthermore, EHD2 expression itself was down-regulated in the visceral fat of two obese mouse models and in diet-induced obesity. Thus, EHD2 controls a cell-autonomous, caveolae-dependent lipid uptake pathway, implicating a role of EHD2 in fat accumulation and obesity.

cell biology↗