Progenitors of the protochordate ocellus as an evolutionary origin of the neural crest

The neural crest represents a highly multipotent population of embryonic stem cells found only in vertebrate embryos. Acquisition of the neural crest during the evolution of vertebrates was a great advantage, providing Chordata animals with the first cellular cartilage, bone, dentition, advanced nervous system and other innovations. Today not much is known about the evolutionary origin of neural crest cells. Here we propose a novel scenario in which the neural crest originates from neuroectodermal progenitors of the pigmented ocelli in Amphioxus-like animals. We suggest that because of changes in photoreception needs, these multipotent progenitors of photoreceptors gained the ability to migrate outside of the central nervous system and subsequently started to give rise to neural, glial and pigmented progeny at the periphery

Heterogeneity and Developmental Connections between Cell Types Inhabiting Teeth

Every tissue is composed of multiple cell types that are developmentally, evolutionary and functionally integrated into the unit we call an organ. Teeth, our organs for biting and mastication, are complex and made of many different cell types connected or disconnected in terms of their ontogeny. In general, epithelial and mesenchymal compartments represent the major framework of tooth formation. Thus, they give rise to the two most important matrix–producing populations: ameloblasts generating enamel and odontoblasts producing dentin. However, the real picture is far from this quite simplified view. Diverse pulp cells, the immune system, the vascular system, the innervation and cells organizing the dental follicle all interact, and jointly participate in transforming lifeless matrix into a functional organ that can sense and protect itself. Here we outline the heterogeneity of cell types that inhabit the tooth, and also provide a life history of the major populations. The mouse model system has been indispensable not only for the studies of cell lineages and heterogeneity, but also for the investigation of dental stem cells and tooth patterning during development. Finally, we briefly discuss the evolutionary aspects of cell type diversity and dental tissue integration

X-ray microtomography–based atlas of mouse cranial development

X-ray microtomography (CT) has become an invaluable tool for non-destructive analysis of biological samples in the field of developmental biology. Mouse embryos are a typical model for investigation of human developmental diseases. By obtaining 3D high-resolution scans of the mouse embryo heads, we gain valuable morphological information about the structures prominent in the development of future face, brain, and sensory organs. The development of facial skeleton tracked in these CT data provides a valuable background for further studies of congenital craniofacial diseases and normal development. In this work, reusable tomographic data from 7 full 3D scans of mouse embryo heads are presented and made publicly available. The ages of these embryos range from E12.5 to E18.5. The samples were stained by phosphotungstic acid prior to scanning, which greatly enhanced the contrast of various tissues in the reconstructed images and enabled precise segmentation. The images were obtained on a laboratory-based CT system. Furthermore, we provide manually segmented masks of mesenchymal condensations (for E12.5 and E13.5) and cartilage present in the nasal capsule of the scanned embryos. We present a comprehensive dataset of X-ray 3D computed tomography images of the developing mouse head with high-quality manual segmentation masks of cartilaginous nasal capsules. The provided CT images can be used for studying any other major structure within the developing mouse heads. The high quality of the manually segmented models of nasal capsules may be instrumental to understanding the complex process of the development of the face in a mouse model

Theory of branching morphogenesis by local interactions and global guidance

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

An interactive and intuitive visualisation method for X-ray computed tomography data of biological samples in 3D Portable Document Format

3D imaging approaches based on X-ray microcomputed tomography (microCT) have become increasingly accessible with advancements in methods, instruments and expertise. The synergy of material and life sciences has impacted biomedical research by proposing new tools for investigation. However, data sharing remains challenging as microCT files are usually in the range of gigabytes and require specific and expensive software for rendering and interpretation. Here, we provide an advanced method for visualisation and interpretation of microCT data with small file formats, readable on all operating systems, using freely available Portable Document Format (PDF) software. Our method is based on the conversion of volumetric data into interactive 3D PDF, allowing rotation, movement, magnification and setting modifications of objects, thus providing an intuitive approach to analyse structures in a 3D context. We describe the complete pipeline from data acquisition, data processing and compression, to 3D PDF formatting on an example of craniofacial anatomical morphology in the mouse embryo. Our procedure is widely applicable in biological research and can be used as a framework to analyse volumetric data from any research field relying on 3D rendering and CT-biomedical imaging

Schwann Cell Precursors Generate the Majority of Chromaffin Cells in Zuckerkandl Organ and Some Sympathetic Neurons in Paraganglia

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

Striking parallels between carotid body glomus cell and adrenal chromaffin cell development

Carotid body glomus cells mediate essential reflex responses to arterial blood hypoxia. They are dopaminergic and secrete growth factors that support dopaminergic neurons, making the carotid body a potential source of patient-specific cells for Parkinson’s disease therapy. Like adrenal chromaffin cells, which are also hypoxia-sensitive, glomus cells are neural crest-derived and require the transcription factors Ascl1 and Phox2b; otherwise, their development is little understood at the molecular level. Here, analysis in chicken and mouse reveals further striking molecular parallels, though also some differences, between glomus and adrenal chromaffin cell development. Moreover, histology has long suggested that glomus cell precursors are ‘émigrés’ from neighbouring ganglia/nerves, while multipotent nerve-associated glial cells are now known to make a significant contribution to the adrenal chromaffin cell population in the mouse. We present conditional genetic lineage-tracing data from mice supporting the hypothesis that progenitors expressing the glial marker proteolipid protein 1, presumably located in adjacent ganglia/nerves, also contribute to glomus cells. Finally, we resolve a paradox for the ‘émigré’ hypothesis in the chicken - where the nearest ganglion to the carotid body is the nodose, in which the satellite glia are neural crest-derived, but the neurons are almost entirely placode-derived - by fate-mapping putative nodose neuronal 'émigrés' to the neural crest

Molecular differences between stromal cell populations from deciduous and permanent human teeth

Introduction: Deciduous and permanent human teeth represent an excellent model system to study aging of stromal populations. Aging is tightly connected to self-renewal and proliferation and thus, mapping potential molecular differences in these characteristics between populations constitutes an important task. Methods: Using specifically designed microarray panels, Real-Time Quantitative Polymerase Chain Reaction (RT q-PCR), Western blot, immunohistochemistry and siRNA-mediated knock down experiments, we have detected a number of molecules that were differentially expressed in dental pulp from deciduous and permanent teeth extracted from young children and adults, respectively. Results: Among the differentially regulated genes, high-mobility group AT-hook 2 (HMGA2), a stem cell-associated marker, stood out as a remarkable example with a robust expression in deciduous pulp cells. siRNA-mediated knock down of HMGA2 expression in cultured deciduous pulp cells caused a down-regulated expression of the pluripotency marker NANOG. This finding indicates that HMGA2 is a pulpal stem cell regulatory factor. In addition to this, we discovered that several proliferation-related genes, including CDC2A and CDK4, were up-regulated in deciduous pulp cells, while matrix genes COL1A1, fibronectin and several signaling molecules, such as VEGF, FGFr-1 and IGFr-1 were up-regulated in the pulp cells from permanent teeth. Conclusions: Taken together, our data suggest that deciduous pulp cells are more robust in self- renewal and proliferation, whereas adult dental pulp cells are more capable of signaling and matrix synthesis

Nerve-associated Schwann cell precursors contribute extracutaneous melanocytes to the heart, inner ear, supraorbital locations and brain meninges

Melanocytes are pigmented cells residing mostly in the skin and hair follicles of vertebrates, where they contribute to colouration and protection against UV-B radiation. However, the spectrum of their functions reaches far beyond that. For instance, these pigment-producing cells are found inside the inner ear, where they contribute to the hearing function, and in the heart, where they are involved in the electrical conductivity and support the stiffness of cardiac valves. The embryonic origin of such extracutaneous melanocytes is not clear. We took advantage of lineage-tracing experiments combined with 3D visualizations and gene knockout strategies to address this long-standing question. We revealed that Schwann cell precursors are recruited from the local innervation during embryonic development and give rise to extracutaneous melanocytes in the heart, brain meninges, inner ear, and other locations. In embryos with a knockout of the EdnrB receptor, a condition imitating Waardenburg syndrome, we observed only nerve-associated melanoblasts, which failed to detach from the nerves and to enter the inner ear. Finally, we looked into the evolutionary aspects of extracutaneous melanocytes and found that pigment cells are associated mainly with nerves and blood vessels in amphibians and fish. This new knowledge of the nerve-dependent origin of extracutaneous pigment cells might be directly relevant to the formation of extracutaneous melanoma in humans