Daniel Gyllborg

Oligodendrocyte heterogeneity in the mouse juvenile and adult central nervous system

One size does not fit all Oligodendrocytes are best known for their ability to myelinate brain neurons, thus increasing the speed of signal transmission. Marques et al. surveyed oligodendrocytes of developing mice and found unexpected heterogeneity. Transcriptional analysis identified 12 populations, ranging from precursors to mature oligodendrocytes. Transcriptional profiles diverged as the oligodendrocytes matured, building distinct populations. One population was responsive to motor learning, and another, with a different transcriptome, traveled along blood vessels. Science, this issue p. 1326 Brain oligodendrocytes express transcriptional heterogeneity between brain regions and age of development. Oligodendrocytes have been considered as a functionally homogeneous population in the central nervous system (CNS). We performed single-cell RNA sequencing on 5072 cells of the oligodendrocyte lineage from 10 regions of the mouse juvenile and adult CNS. Thirteen distinct populations were identified, 12 of which represent a continuum from Pdgfra+ oligodendrocyte precursor cells (OPCs) to distinct mature oligodendrocytes. Initial stages of differentiation were similar across the juvenile CNS, whereas subsets of mature oligodendrocytes were enriched in specific regions in the adult brain. Newly formed oligodendrocytes were detected in the adult CNS and were responsive to complex motor learning. A second Pdgfra+ population, distinct from OPCs, was found along vessels. Our study reveals the dynamics of oligodendrocyte differentiation and maturation, uncoupling them at a transcriptional level and highlighting oligodendrocyte heterogeneity in the CNS.

Molecular Diversity of Midbrain Development in Mouse, Human, and Stem Cells

Summary Understanding human embryonic ventral midbrain is of major interest for Parkinson’s disease. However, the cell types, their gene expression dynamics, and their relationship to commonly used rodent models remain to be defined. We performed single-cell RNA sequencing to examine ventral midbrain development in human and mouse. We found 25 molecularly defined human cell types, including five subtypes of radial glia-like cells and four progenitors. In the mouse, two mature fetal dopaminergic neuron subtypes diversified into five adult classes during postnatal development. Cell types and gene expression were generally conserved across species, but with clear differences in cell proliferation, developmental timing, and dopaminergic neuron development. Additionally, we developed a method to quantitatively assess the fidelity of dopaminergic neurons derived from human pluripotent stem cells, at a single-cell level. Thus, our study provides insight into the molecular programs controlling human midbrain development and provides a foundation for the development of cell replacement therapies.

A PBX1 transcriptional network controls dopaminergic neuron development and is impaired in Parkinson's disease

Pre‐B‐cell leukemia homeobox (PBX) transcription factors are known to regulate organogenesis, but their molecular targets and function in midbrain dopaminergic neurons (mDAn) as well as their role in neurodegenerative diseases are unknown. Here, we show that PBX1 controls a novel transcriptional network required for mDAn specification and survival, which is sufficient to generate mDAn from human stem cells. Mechanistically, PBX1 plays a dual role in transcription by directly repressing or activating genes, such as Onecut2 to inhibit lateral fates during embryogenesis, Pitx3 to promote mDAn development, and Nfe2l1 to protect from oxidative stress. Notably, PBX1 and NFE2L1 levels are severely reduced in dopaminergic neurons of the substantia nigra of Parkinsons disease (PD) patients and decreased NFE2L1 levels increases damage by oxidative stress in human midbrain cells. Thus, our results reveal novel roles for PBX1 and its transcriptional network in mDAn development and PD, opening the door for new therapeutic interventions.

Analysis of neural crest–derived clones reveals novel aspects of facial development

Facial shaping results from oriented divisions and crowd movements of ectomesenchymal cells during morphogenetic events. Cranial neural crest cells populate the future facial region and produce ectomesenchyme-derived tissues, such as cartilage, bone, dermis, smooth muscle, adipocytes, and many others. However, the contribution of individual neural crest cells to certain facial locations and the general spatial clonal organization of the ectomesenchyme have not been determined. We investigated how neural crest cells give rise to clonally organized ectomesenchyme and how this early ectomesenchyme behaves during the developmental processes that shape the face. Using a combination of mouse and zebrafish models, we analyzed individual migration, cell crowd movement, oriented cell division, clonal spatial overlapping, and multilineage differentiation. The early face appears to be built from multiple spatially defined overlapping ectomesenchymal clones. During early face development, these clones remain oligopotent and generate various tissues in a given location. By combining clonal analysis, computer simulations, mouse mutants, and live imaging, we show that facial shaping results from an array of local cellular activities in the ectomesenchyme. These activities mostly involve oriented divisions and crowd movements of cells during morphogenetic events. Cellular behavior that can be recognized as individual cell migration is very limited and short-ranged and likely results from cellular mixing due to the proliferation activity of the tissue. These cellular mechanisms resemble the strategy behind limb bud morphogenesis, suggesting the possibility of common principles and deep homology between facial and limb outgrowth.

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

Translation of WNT developmental programs into stem cell replacement strategies for the treatment of Parkinson's disease

Wnt signalling is a highly conserved pathway across species that is critical for normal development and is deregulated in multiple disorders including cancer and neurodegenerative diseases. Wnt signalling is critically required for midbrain dopaminergic (mDA) neuron development and maintenance. Understanding the molecular processes controlled by Wnt signalling may thus hold the key to understand the physiopathology and to develop novel therapies aimed at preventing the loss of mDA neurons in Parkinsons disease (PD). Pharmacological tools to activate Wnt signalling have been used to translate in vivo developmental processes into protocols for the generation of bona fide mDA neurons from human pluripotent stem cells. Moreover, these protocols are currently being fine‐tuned to generate mDA neurons for clinical trials in PD. At the same time, a vast amount of molecular details of Wnt signalling continues to emerge and remains to be implemented into new protocols. We hereby review novel pharmacological tools to activate Wnt signalling and how single‐cell RNA‐sequencing is contributing to unravel the complexity of this pathway in the developing human ventral midbrain, generating novel hypotheses and identifying new players and opportunities to further improve cell replacement therapy for PD.

Niche-derived laminin-511 promotes midbrain dopaminergic neuron survival and differentiation through YAP

Activation of the transcription factor YAP by an extracellular laminin promotes the differentiation and survival of dopaminergic neurons. YAP supports dopaminergic neurons Parkinson’s disease (PD) is a neurodegenerative disorder marked by progressive loss of dopaminergic neurons and motor control. Various factors promote or inhibit neuronal survival. Zhang et al. found that a prosurvival signal was mediated by the transcription cofactor YAP. YAP was activated in midbrain dopaminergic neurons in culture and in mice through an interaction between an integrin and the extracellular matrix protein laminin-511. YAP then transcriptionally activated dopaminergic neuron differentiation factors and a microRNA that decreased the synthesis of the apoptotic protein PTEN. The findings uncover a new role for YAP in neurons and a pathway that might be explored for the purpose of promoting dopaminergic neuron survival in PD patients. Parkinson’s disease (PD) is a neurodegenerative disorder in which the loss of dopaminergic neurons in the midbrain (mDA neurons) causes progressive loss of motor control and function. Using embryonic and mDA neurons, midbrain tissue from mice, and differentiated human neural stem cells, we investigated the mechanisms controlling the survival of mDA neurons. We found that the extracellular matrix protein laminin-511 (LM511) promoted the survival and differentiation of mDA neurons. LM511 bound to integrin α3β1 and activated the transcriptional cofactor YAP. LM511-YAP signaling enhanced cell survival by inducing the expression of the microRNA miR-130a, which suppressed the synthesis of the cell death–associated protein PTEN. In addition, LM511-YAP signaling increased the expression of transcription factors critical for mDA identity, such as LMX1A and PITX3, and prevented the loss of mDA neurons in response to oxidative stress, a finding that warrants further investigation to assess therapeutic potential for PD patients. We propose that by enhancing LM511-YAP signaling, it may be possible to prevent mDA neuron degeneration in PD or enhance the survival of mDA neurons in cell replacement therapies.

Molecular analysis of the midbrain dopaminergic niche during neurogenesis

Midbrain dopaminergic (mDA) neurons degenerate in Parkinson’s disease and are one of the main targets for cell replacement therapies. However, a comprehensive view of the signals and cell types contributing to mDA neurogenesis is not yet available. By analyzing the transcriptome of the mouse ventral midbrain at a tissue and single-cell level during mDA neurogenesis we found that three recently identified radial glia types 1-3 (Rgl1-3) contribute to different key aspects of mDA neurogenesis. While Rgl3 expressed most extracellular matrix components and multiple ligands for various pathways controlling mDA neuron development, such as Wnt and Shh, Rgl1-2 expressed most receptors. Moreover, we found that specific transcription factor networks explain the transcriptome and suggest a function for each individual radial glia. A network controlling neurogenesis was found in Rgl1, progenitor maintenance in Rgl2 and the secretion of factors forming the mDA niche by Rgl3. Our results thus uncover a broad repertoire of developmental signals expressed by each midbrain cell type during mDA neurogenesis. Cells identified for their emerging importance are Rgl3, a niche cell type, and Rgl1, a neurogenic progenitor that expresses ARNTL, a transcription factor that we find is required for mDA neurogenesis.

The Matricellular Protein R-Spondin 2 Promotes Midbrain Dopaminergic Neurogenesis and Differentiation

Summary The development of midbrain dopaminergic (mDA) neurons is controlled by multiple morphogens and transcription factors. However, little is known about the role of extracellular matrix proteins in this process. Here we examined the function of roof plate-specific spondins (RSPO1-4) and the floor plate-specific, spondin 1 (SPON1). Only RSPO2 and SPON1 were expressed at high levels during mDA neurogenesis, and the receptor LGR5 was expressed by midbrain floor plate progenitors. Surprisingly, RSPO2, but not SPON1, specifically promoted the differentiation of mDA neuroblasts into mDA neurons in mouse primary cultures and embryonic stem cells (ESCs). In addition, RSPO2 was found to promote not only mDA differentiation, but also mDA neurogenesis in human ESCs. Our results thus uncover an unexpected function of the matricellular protein RSPO2 and suggest an application to improve mDA neurogenesis and differentiation in human stem cell preparations destined to cell replacement therapy or drug discovery for Parkinson disease.