Vyacheslav Dyachuk

Glial origin of mesenchymal stem cells in a tooth model system

Mesenchymal stem cells occupy niches in stromal tissues where they provide sources of cells for specialized mesenchymal derivatives during growth and repair. The origins of mesenchymal stem cells have been the subject of considerable discussion, and current consensus holds that perivascular cells form mesenchymal stem cells in most tissues. The continuously growing mouse incisor tooth offers an excellent model to address the origin of mesenchymal stem cells. These stem cells dwell in a niche at the tooth apex where they produce a variety of differentiated derivatives. Cells constituting the tooth are mostly derived from two embryonic sources: neural crest ectomesenchyme and ectodermal epithelium. It has been thought for decades that the dental mesenchymal stem cells giving rise to pulp cells and odontoblasts derive from neural crest cells after their migration in the early head and formation of ectomesenchymal tissue. Here we show that a significant population of mesenchymal stem cells during development, self-renewal and repair of a tooth are derived from peripheral nerve-associated glia. Glial cells generate multipotent mesenchymal stem cells that produce pulp cells and odontoblasts. By combining a clonal colour-coding technique with tracing of peripheral glia, we provide new insights into the dynamics of tooth organogenesis and growth.

Parasympathetic neurons originate from nerve-associated peripheral glial progenitors

Exploiting nervous paths already traveled The parasympathetic nervous system helps regulate the functions of many tissues and organs, including the salivary glands and the esophagus. To do so, it needs to reach throughout the body, connecting central systems to peripheral ones. Dyachuk et al. and Espinosa-Medina et al. explored how these connections are established in mice (see the Perspective by Kalcheim and Rohrer). Progenitor cells that travel along with the developing nerves can give rise to both myelinforming Schwann cells and to parasympathetic neurons. That means the interacting nerves do not have to find each other. Instead, the beginnings of the connections are laid down as the nervous system develops. Science, this issue p. 82, p. 87; see also p. 32 Parasympathetic neurons are born from Schwann cell precursors located in the nerves that carry preganglionic fibers. [Also see Perspective by Kalcheim and Rohrer] The peripheral autonomic nervous system reaches far throughout the body and includes neurons of diverse functions, such as sympathetic and parasympathetic. We show that the parasympathetic system in mice—including trunk ganglia and the cranial ciliary, pterygopalatine, lingual, submandibular, and otic ganglia—arise from glial cells in nerves, not neural crest cells. The parasympathetic fate is induced in nerve-associated Schwann cell precursors at distal peripheral sites. We used multicolor Cre-reporter lineage tracing to show that most of these neurons arise from bi-potent progenitors that generate both glia and neurons. This nerve origin places cellular elements for generating parasympathetic neurons in diverse tissues and organs, which may enable wiring of the developing parasympathetic nervous system.

Multipotent peripheral glial cells generate neuroendocrine cells of the adrenal medulla

Following the yellow brick road The adrenal glands affect a variety of processes such as stress responses and metabolism. The mature adrenal gland is formed from multiple tissue sources, including cells of neural origin. Furlan et al. traced the origins of these cells. The cells first become Schwann cell precursors and follow along nerves to travel from the dorsal root ganglia of the spine to the adrenal gland. Once there, the cells differentiate into chromaffin cells. The authors used singlecell transcriptomics to reveal the shifts in functional programs during migration, development, and differentiation. Science, this issue p. eaal3753 The adrenal gland is built from cells that travel along highways of nerves. INTRODUCTION Circulating adrenaline can have profound effects on the body’s “inner world,” adjusting levels depending on demand to maintain organ and bodily homeostasis during daily living. In the more extreme fight-or-flight response, the surge of adrenaline is “energizing” through effects on organs and tissues, including increased heart rate and blood glucose levels, and redirecting oxygen and glucose to limb muscles. Chromaffin cells located in the adrenal medulla constitute the main hormonal component of the autonomic nervous system and are the principal source for release of catecholamines, including adrenaline, in the systemic circulation. Understanding the cellular origin and biological processes by which the adrenal medulla is formed during development is needed for mechanistic insights into how the hormonal component of the autonomic nervous system is formed and its relation to the rest of the autonomic nervous system. RATIONALE Adrenergic chromaffin cells in the adrenal medulla are thought to originate from a common sympathoadrenal lineage close to the dorsal aorta, where these cells split in a dorsoventral direction, forming the sympathetic chain and adrenal medulla, respectively. Revisiting this dogma, we examined the cell type origin of chromaffin cells, lineage segregation of sympathoblasts and chromaffin cells, the gene programs driving specification of chromaffin cells from progenitors, and the proliferative dynamics by which the adrenal medulla is formed. RESULTS We found that chromaffin cells of the adrenal medulla are formed from peripheral glia stem cells, termed Schwann cell precursors. Genetic cell lineage tracing revealed that most chromaffin cells arise from Schwann cell precursors, and consistently, genetic ablation of Schwann cell precursors results in marked depletion of chromaffin cells. Genetic ablation of the preganglionic nerve, on which Schwann cell precursors migrate, similarly leads to marked deficiencies of chromaffin cells, and fate-tracing cells unable to differentiate into chromaffin cells reveal an accumulation of glia cells in the region of the adrenal medulla. Experiments reveal that sympathetic and adrenergic lineages diverge at an unexpectedly early stage during embryonic development. Embryonic development of the adrenal medulla relies on recruitment of numerous Schwann cell precursors with limited cell expansion. Thus, the large majority of chromaffin cells arise from Schwann cell precursors migrating on preganglionic nerves innervating the adrenal medulla. Unexpectedly, single-cell RNA sequencing revealed a complex gene-regulatory mechanism during differentiation of Schwann cell precursors to chromaffin cells, whereby Schwann cell precursors enter into a gene expression program unique for a transient cellular state. Subsequently, this gene program and chromaffin cell gene networks suppress glial gene programs, advancing cells into the chromaffin cell identity. CONCLUSION By revisiting development of the adrenergic sympathetic system, we discovered a new cellular origin of this nervous system component. The adrenergic medulla is built from both neural crest cells and Schwann cell precursors, with a major contribution from Schwann cell precursors in rodents. A cellular origin from Schwann cell precursors highlights the importance of peripheral nerves as a stem cell niche and transportation routes for progenitors essential for neuroendocrine development. These results and mechanisms of differentiation through a transient intermediate cell type may also be helpful in advancing our knowledge on neuroblastoma and pheochromocytoma, because these most often arise from the adrenal gland region. Adrenal medulla largely originates from Schwann cell precursors. Overview of adrenal medulla development resulting from lineage tracing and nerve ablation experiments. SCP, Schwann cell precursor; AG, adrenal gland; NT, neural tube; n, notochord; DRG, dorsal root ganglion; IML, intermediolateral column; NCC, neural crest cells; NC, neural crest; DA, dorsal aorta; SRG, suprarenal sympathetic ganglion. Red encodes early NCCs and their derivatives. Blue encodes late neural crest and SCP-derived cell types. Adrenaline is a fundamental circulating hormone for bodily responses to internal and external stressors. Chromaffin cells of the adrenal medulla (AM) represent the main neuroendocrine adrenergic component and are believed to differentiate from neural crest cells. We demonstrate that large numbers of chromaffin cells arise from peripheral glial stem cells, termed Schwann cell precursors (SCPs). SCPs migrate along the visceral motor nerve to the vicinity of the forming adrenal gland, where they detach from the nerve and form postsynaptic neuroendocrine chromaffin cells. An intricate molecular logic drives two sequential phases of gene expression, one unique for a distinct transient cellular state and another for cell type specification. Subsequently, these programs down-regulate SCP-gene and up-regulate chromaffin cell–gene networks. The AM forms through limited cell expansion and requires the recruitment of numerous SCPs. Thus, peripheral nerves serve as a stem cell niche for neuroendocrine system development.

Superficial cells are self-renewing chondrocyte progenitors, which form the articular cartilage in juvenile mice.

Articular cartilage has little regenerative capacity. Recently, genetic lineage tracing experiments have revealed chondrocyte progenitors at the articular surface. We further characterized these progenitors by using in vivo genetic approaches. Histone H2B–green fluorescent protein retention revealed that superficial cells divide more slowly than underlying articular chondrocytes. Clonal genetic tracing combined with immunohistochemistry revealed that superficial cells renew their number by symmetric division, express mesenchymal stem cell markers, and generate chondrocytes via both asymmetric and symmetric differentiation. Quantitative analysis of cellular kinetics, in combination with phosphotungstic acid–enhanced micro–computed tomography, showed that superficial cells generate chondrocytes and contribute to the growth and reshaping of articular cartilage. Furthermore, we found that cartilage renewal occurs as the progeny of superficial cells fully replace fetal chondrocytes during early postnatal life. Thus, superficial cells are self‐renewing progenitors that are capable of maintaining their own population and fulfilling criteria of unipotent adult stem cells. Furthermore, the progeny of these cells reconstitute adult articular cartilage de novo, entirely substituting fetal chondrocytes.—Li, L., Newton, P. T., Bouderlique, T., Sejnohova, M., Zikmund, T., Kozhemyakina, E., Xie, M., Krivanek, J., Kaiser, J., Qian, H., Dyachuk, V., Lassar, A. B., Warman, M. L., Barenius, B., Adameyko, I., Chagin, A. S. Superficial cells are self‐renewing chondrocyte progenitors, which form the articular cartilage in juvenile mice. FASEB J. 31, 1067–1084 (2017). www.fasebj.org

Innervation of bivalve larval catch muscles by serotonergic and FMRFamidergic neurons.

Bivalve larvae use catch muscles for rapid shell closure and maintenance of the closed condition. We used specific antibodies against the muscle proteins together with phalloidin and neuronal markers, FMRFamide and serotonin (5-HT), to analyze mutual distribution of muscle and neuronal elements in larvae of the mussel, Mytilus trossulus, and the oyster, Crassostrea gigas. At trochophore and early veliger stages no anatomical connections between muscular and nervous system were detected. By the pediveliger stage the 5-HT innervation of the anterior adductor developed in oyster only, while rich FMRFa innervation of the adductor muscles developed in both species. Possible roles and mechanisms of FMRFamide and serotonin in the regulation of the catch state are discussed.

Oriented clonal cell dynamics enables accurate growth and shaping of vertebrate cartilage

Cartilaginous structures are at the core of embryo growth and shaping before the bone forms. Here we report a novel principle of vertebrate cartilage growth that is based on introducing transversally-oriented clones into pre-existing cartilage. This mechanism of growth uncouples the lateral expansion of curved cartilaginous sheets from the control of cartilage thickness, a process which might be the evolutionary mechanism underlying adaptations of facial shape. In rod-shaped cartilage structures (Meckel, ribs and skeletal elements in developing limbs), the transverse integration of clonal columns determines the well-defined diameter and resulting rod-like morphology. We were able to alter cartilage shape by experimentally manipulating clonal geometries. Using in silico modeling, we discovered that anisotropic proliferation might explain cartilage bending and groove formation at the macro-scale. DOI: http://dx.doi.org/10.7554/eLife.25902.001

Non-centrosomal Microtubule Organization in Differentiated Cells

The centrosome consists of a pair of centrioles surrounded by pericentriolar material. During the formation of the mitotic spindle, multi-protein complexes in the pericentriolar material are involved in the nucleation and anchorage of microtubules. In postmitotic cells of many tissues, proteins of the pericentriolar material lose their association with the centrosome and redistribute to various sites in the cytoplasm, to the cellular cortex, or to the nuclear surface. Consequently, the organization of the microtubule network is changed. Localization of centrosomal proteins and organization of microtubules follow cell type-specific patterns, to fulfill specialized functions. For example, in polarized epithelia, microtubules are involved in transcytosis and establishment of epithelial polarity, in neurons microtubules are necessary for axonal transport, or in muscle microtubules participate in the assembly of sarcomeres and in the positioning of nuclei. In this review, the principles of microtubule organization in different cell types will be described. The role of microtubules in muscle cells and the potential involvement of microtubule-dependent processes in muscular diseases will be documented in detail.

Modulation of Mytilus trossulus (Bivalvia: Mollusca) larval survival and growth in culture

Commercial importance and ability to live in a wide range of salinities have made the common mussel, Mytilus trossulus, a relevant model to study modulation of larval growth and development. We investigated the effects of various salinities combined with neomycin and ampicillin application on Mytilus larvae survival and growth. Both neomycin and ampicillin enhanced trochophore and veliger survival under condition of low salinity. The average veliger size was increasing in accordance with the increase of salinity. In case of neomycin treatment 3.6% of the larvae reached the pediveliger stage. No abnormalities of larval morphology of the FMRFamide and 5-HT systems occurred after 7 days of culturing with both antibiotics.

The conformation of bovine serum albumin adsorbed to the surface of single all-dielectric nanoparticles following light-induced heating

Interaction between nanoparticles and biomolecules leads to the formation of biocompatible or bioadverse complexes. Despite the rapid development of nanotechnologies for biology and medicine, relatively little is known about the structure of such complexes. Here, we report on the changes in conformation of a blood protein (bovine serum albumin) adsorbed on the surface of single all-dielectric nanoparticles (silicon and germanium) following light-induced heating to 640 K. This protein is considerably more resistant to heat when adsorbed on the nanoparticle than when in solution or in the solid state. Intriguingly, with germanium nanoparticles this heat resistance is more pronounced than with silicon. These observations will facilitate biocompatible usage of all-dielectric nanoparticles.

Nervous system development in the Pacific oyster, Crassostrea gigas (Mollusca: Bivalvia)

BackgroundBivalves comprise a large, highly diverse taxon of invertebrate species. Developmental studies of neurogenesis among species of Bivalvia are limited. Due to a lack of neurogenesis information, it is difficult to infer a ground pattern for Bivalvia. To provide more comprehensive morphogenetic data on bivalve molluscs and relationships among molluscan clades, we investigated neurogenesis in the Pacific oyster, Crassostrea gigas, from the appearance of the first sensory cells to the formation of the larval ganglionic nervous system by co-immunocytochemistry of the neuronal markers FMRFamide or 5-HT and vesicular acetylcholine transporter (VAChT).ResultsNeurogenesis begins with the emergence of the apical serotonin-immunoreactive (5-HT-ir) sensory cells and paired sensory posttrochal dorsal and ventral FMRFamide-immunoreactive (FMRFamide-ir) cells at the early trochophore stage. Later, at the early veliger stage, the apical organ (AO) includes 5-HT-ir, FMRFamide-ir, and VAChT-ir cells. At the same stage, VAChT-ir cells appear in the posterior region of larvae and send axons towards the AO. Thus, FMRFamide-ir neurites and VAChT-ir processes form scaffolds for longitudinal neurite bundles develop into the paired ventral nerve cords (VNC). Later-appearing axons from the AO/CG neurons join the neurite bundles comprising the VNC. All larval ganglia appear along the VNC as paired or fused (epiathroid) clusters in late veliger and pediveliger larvae. We observed the transformation of the AO into the cerebral ganglia, which abundantly innervated the velum, and the transformation of ventral neurons into the pedal ganglia, innervating the foot, gills, and anterior adductor muscle. The visceral ganglia appear last in the pediveliger oyster and innervate the visceral mass and posterior adductor of premetamorphic larvae. In addition, a local FMRFamide-ir network was detected in the digestive system of pediveliger larvae. We identified VAChT-ir nervous elements in oyster larvae, which have not been observed previously in molluscs. Finally, we performed a morphology-based comparative analysis of neuronal structures among bivalve, conchiferan, and aculiferan species.ConclusionsWe described the development of the nervous system during the larval development in Crassostrea gigas. These data greatly advance the currently limited understanding of neurodevelopment in bivalves and mollusks, which has hampered the generation of a ground pattern reconstruction of the last common ancestor of Mollusca. Our morphological data support phylogenomic data indicating a closer Bivalvia-Gastropoda sister group relationship than the Bivalvia-Scaphopoda (Diasoma) group relationship.