Spiral ganglion (SG) neurons of the cochlea convey all auditory inputs to the brain, yet the cellular and molecular complexity necessary to decode the various acoustic features in the SG has remained ...unresolved. Using single-cell RNA sequencing, we identify four types of SG neurons, including three novel subclasses of type I neurons and the type II neurons, and provide a comprehensive genetic framework that define their potential synaptic communication patterns. The connectivity patterns of the three subclasses of type I neurons with inner hair cells and their electrophysiological profiles suggest that they represent the intensity-coding properties of auditory afferents. Moreover, neuron type specification is already established at birth, indicating a neuronal diversification process independent of neuronal activity. Thus, this work provides a transcriptional catalog of neuron types in the cochlea, which serves as a valuable resource for dissecting cell-type-specific functions of dedicated afferents in auditory perception and in hearing disorders.
Branching morphogenesis governs the formation of many organs such as lung, kidney, and the neurovascular system. Many studies have explored system-specific molecular and cellular regulatory ...mechanisms, as well as self-organizing rules underlying branching morphogenesis. However, in addition to local cues, branched tissue growth can also be influenced by global guidance. Here, we develop a theoretical framework for a stochastic self-organized branching process in the presence of external cues. Combining analytical theory with numerical simulations, we predict differential signatures of global vs. local regulatory mechanisms on the branching pattern, such as angle distributions, domain size, and space-filling efficiency. We find that branch alignment follows a generic scaling law determined by the strength of global guidance, while local interactions influence the tissue density but not its overall territory. Finally, using zebrafish innervation as a model system, we test these key features of the model experimentally. Our work thus provides quantitative predictions to disentangle the role of different types of cues in shaping branched structures across scales.
Somatic sensation is defined by the existence of a diversity of primary sensory neurons with unique biological features and response profiles to external and internal stimuli. However, there is no ...coherent picture about how this diversity of cell states is transcriptionally generated. Here, we use deep single cell analysis to resolve fate splits and molecular biasing processes during sensory neurogenesis in mice. Our results identify a complex series of successive and specific transcriptional changes in post-mitotic neurons that delineate hierarchical regulatory states leading to the generation of the main sensory neuron classes. In addition, our analysis identifies previously undetected early gene modules expressed long before fate determination although being clearly associated with defined sensory subtypes. Overall, the early diversity of sensory neurons is generated through successive bi-potential intermediates in which synchronization of relevant gene modules and concurrent repression of competing fate programs precede cell fate stabilization and final commitment.
Abstract
Different types of spiral ganglion neurons (SGNs) are essential for auditory perception by transmitting complex auditory information from hair cells (HCs) to the brain. Here, we use deep, ...single cell transcriptomics to study the molecular mechanisms that govern their identity and organization in mice. We identify a core set of temporally patterned genes and gene regulatory networks that may contribute to the diversification of SGNs through sequential binary decisions and demonstrate a role for NEUROD1 in driving specification of a I
c
-SGN phenotype. We also find that each trajectory of the decision tree is defined by initial co-expression of alternative subtype molecular controls followed by gradual shifts toward cell fate resolution. Finally, analysis of both developing SGN and HC types reveals cell-cell signaling potentially playing a role in the differentiation of SGNs. Our results indicate that SGN identities are drafted prior to birth and reveal molecular principles that shape their differentiation and will facilitate studies of their development, physiology, and dysfunction.
Proprioceptive neurons (PNs) are essential for the proper execution of all our movements by providing muscle sensory feedback to the central motor network. Here, using deep single cell RNAseq of ...adult PNs coupled with virus and genetic tracings, we molecularly identify three main types of PNs (Ia, Ib and II) and find that they segregate into eight distinct subgroups. Our data unveil a highly sophisticated organization of PNs into discrete sensory input channels with distinct spatial distribution, innervation patterns and molecular profiles. Altogether, these features contribute to finely regulate proprioception during complex motor behavior. Moreover, while Ib- and II-PN subtypes are specified around birth, Ia-PN subtypes diversify later in life along with increased motor activity. We also show Ia-PNs plasticity following exercise training, suggesting Ia-PNs are important players in adaptive proprioceptive function in adult mice.
In humans, neurosecretory chromaffin cells control a number of important bodily functions, including those related to stress response. Chromaffin cells appear as a distinct cell type at the beginning ...of midgestation and are the main cellular source of adrenalin and noradrenalin released into the blood stream. In mammals, two different chromaffin organs emerge at a close distance to each other, the adrenal gland and Zuckerkandl organ (ZO). These two structures are found in close proximity to the kidneys and dorsal aorta, in a region where paraganglioma, pheochromocytoma and neuroblastoma originate in the majority of clinical cases. Recent studies showed that the chromaffin cells comprising the adrenal medulla are largely derived from nerve-associated multipotent Schwann cell precursors (SCPs) arriving at the adrenal anlage with the preganglionic nerve fibers, whereas the migratory neural crest cells provide only minor contribution. However, the embryonic origin of the ZO, which differs from the adrenal medulla in a number of aspects, has not been studied in detail. The ZO is composed of chromaffin cells in direct contact with the dorsal aorta and the intraperitoneal cavity and disappears through an autophagy-mediated mechanism after birth. In contrast, the adrenal medulla remains throughout the entire life and furthermore, is covered by the adrenal cortex. Using a combination of lineage tracing strategies with nerve- and cell type-specific ablations, we reveal that the ZO is largely SCP-derived and forms in synchrony with progressively increasing innervation. Moreover, the ZO develops hand-in-hand with the adjacent sympathetic ganglia that coalesce around the dorsal aorta. Finally, we were able to provide evidence for a SCP-contribution to a small but significant proportion of sympathetic neurons of the posterior paraganglia. Thus, this cellular source complements the neural crest, which acts as a main source of sympathetic neurons. Our discovery of a nerve-dependent origin of chromaffin cells and some sympathoblasts may help to understand the origin of pheochromocytoma, paraganglioma and neuroblastoma, all of which are currently thought to be derived from the neural crest or committed sympathoadrenal precursors.
Developmental cell death plays an important role in the construction of functional neural circuits. In vertebrates, the canonical view proposes a selection of the surviving neurons through stochastic ...competition for target-derived neurotrophic signals, implying an equal potential for neurons to compete. Here we show an alternative cell fitness selection of neurons that is defined by a specific neuronal heterogeneity code. Proprioceptive sensory neurons that will undergo cell death and those that will survive exhibit different molecular signatures that are regulated by retinoic acid and transcription factors, and are independent of the target and neurotrophins. These molecular features are genetically encoded, representing two distinct subgroups of neurons with contrasted functional maturation states and survival outcome. Thus, in this model, a heterogeneous code of intrinsic cell fitness in neighboring neurons provides differential competitive advantage resulting in the selection of cells with higher capacity to survive and functionally integrate into neural networks.
The formation of functional connectivity in the nervous system is governed by axon guidance that instructs nerve growth and branching during development, implying a similarity between neuronal ...subtypes in terms of nerve extension. We demonstrate the molecular mechanism of another layer of complexity in vertebrates by defining a transcriptional program underlying growth differences between positionally different neurons. The rate of axon extension of the early subset of embryonic dorsal root ganglion sensory neurons is encoded in neurons at different axial levels. This code is determined by a segmental pattern of axial levels of Runx family transcription factor Runx3. Runx3 in turn determines transcription levels of genes encoding cytoskeletal proteins involved in axon extension, including Rock1 and Rock2 which have ongoing activities determining axon growth in early sensory neurons and blocking Rock activity reverses axon extension deficits of Runx3−/− neurons. Thus, Runx3 acts to regulate positional differences in axon extension properties apparently without affecting nerve guidance and branching, a principle that could be relevant to other parts of the nervous system.
The transcription factor Runx3 controls intrinsic differences in axonal growth rates by regulating the expression of cytoskeletal proteins including Rock1 and 2.
Emergence of neuron types Faure, Louis; Techameena, Prach; Hadjab, Saida
Current opinion in cell biology,
12/2022, Letnik:
79
Journal Article
Recenzirano
Odprti dostop
Neuron types are the building blocks of the nervous system, and therefore, of functional circuits. Understanding the origin of neuronal diversity has always been an essential question in neuroscience ...and developmental biology. While knowledge on the molecular control of their diversification has largely increased during the last decades, it is now possible to reveal the dynamic mechanisms and the actual stepwise molecular changes occurring at single-cell level with the advent of single-cell omics technologies and analysis with high temporal resolution. Here, we focus on recent advances in the field and in technical and analytical tools that enable detailed insights into the emergence of neuron types in the central and peripheral nervous systems.
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•Single-cell transcriptome analysis and histochemistry reveals principles for step-wise embryonic diversification.•Transcriptomic investigations confirmed that both states: progenitor and neuron contribute to neuronal diversity.•Single-cell RNA sequencing identifies early diversity of neurons formed via bi-potential intermediates.•Single-cell RNA sequencing shows that branching of cell fate occurs via burst of competitive modules of synchronized genes.
Tinnitus is a phantom auditory perception, which can be induced via application of concentrated sodium salicylate, and is known to be associated with hearing loss and altered neuronal excitability in ...peripheral and central auditory neurons. The molecular features of this excitability, however, has been poorly characterized to date. Brain-derived neurotrophic factor (BDNF), the activity-dependent cytoskeletal protein (Arg3.1, also known as Arc), and c-Fos are known to be affected by changes in excitability and plasticity. Using reverse transcription-polymerase chain reaction, in situ hybridization, and immunohistochemistry, the expression of these genes was monitored in the rat auditory system after local (cochlear) and systemic application of salicylate. Induction of tinnitus and hearing loss was verified in a behavioral model. Regardless of the mode of salicylate application, a common pattern became evident: 1) BDNF mRNA expression was increased in the spiral ganglion neurons of the cochlea; and 2) Arg3.1 expression was significantly reduced in the auditory cortex. Local application of the GABA(A) receptor modulator midazolam resulted in the reversal not only of salicylate-induced changes in cochlear BDNF expression, but also in cortical Arg3.1 expression, indicating that the tinnitus-associated changes in cochlear BDNF expression trigger the decline of cortical Arg3.1 expression. Furthermore, local midazolam application reduced tinnitus perception in the animal model. These findings support Arg3.1 and BDNF as markers for activity changes in the auditory system and suggest a role of GABAergic inhibition of cochlear neurons in the modulation of Arg3.1 plasticity changes in the auditory cortex and tinnitus perception.
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