Multipotency of melanoblasts isolated from murine skin depends on the Notch signal

Cell Fate Decisions in the Neural Crest, from Pigment Cell to Neural Development

The neural crest shows an astonishing multipotency, generating multiple neural derivatives, but also pigment cells, skeletogenic and other cell types. The question of how this process is controlled has been the subject of an ongoing debate for more than 35 years. Based upon new observations of zebrafish pigment cell development, we have recently proposed a novel, dynamic model that we believe goes some way to resolving the controversy. Here, we will firstly summarize the traditional models and the conflicts between them, before outlining our novel model. We will also examine our recent dynamic modelling studies, looking at how these reveal behaviors compatible with the biology proposed. We will then outline some of the implications of our model, looking at how it might modify our views of the processes of fate specification, differentiation, and commitment.

Exosomes from dental pulp cells attenuate bone loss in mouse experimental periodontitis

BACKGROUND AND OBJECTIVE

Exosomes are small vesicles secreted from many cell types. Their biological effects largely depend on their cellular origin and the physiological state of the originating cells. Exosomes secreted by mesenchymal stem cells exert therapeutic effects against multiple diseases and may serve as potential alternatives to stem cell therapies. We previously established and characterized human leukocyte antigen (HLA) haplotype homo (HHH) dental pulp cell (DPC) lines from human wisdom teeth. In this study, we aimed to investigate the effect of local administration of HHH-DPC exosomes in a mouse model of periodontitis.

METHODS

Exosomes purified from HHH-DPCs were subjected to particle size analysis, and expression of exosome markers was confirmed by western blotting. We also confirmed the effect of exosomes on the migration of both HHH-DPCs and mouse osteoblastic MC3T3-E1 cells. A mouse experimental periodontitis model was used to evaluate the effect of exosomes in vivo. The morphology of alveolar bone was assessed by micro-computed tomography (μCT) and histological analysis. The effect of exosomes on osteoclastogenesis was evaluated using a co-culture system.

RESULTS

The exosomes purified from HHH-DPCs were homogeneous and had a spherical membrane structure. HHH-DPC exosomes promoted the migration of both human DPCs and mouse osteoblastic cells. The MTT assay showed a positive effect on the proliferation of human DPCs, but not on mouse osteoblastic cells. Treatment with HHH-DPC exosomes did not alter the differentiation of osteoblastic cells. Imaging with µCT revealed that the exosomes suppressed alveolar bone resorption in the mouse model of periodontitis. Although no change was apparent in the dominance of TRAP-positive osteoclast-like cells in decalcified tissue sections upon exosome treatment, HHH-DPC exosomes significantly suppressed osteoclast formation in vitro.

CONCLUSIONS

HHH-DPC exosomes stimulated the migration of human DPCs and mouse osteoblastic cells and effectively attenuated bone loss due to periodontitis.

Cyclical fate restriction: a new view of neural crest cell fate specification

Neural crest cells are crucial in development, not least because of their remarkable multipotency. Early findings stimulated two hypotheses for how fate specification and commitment from fully multipotent neural crest cells might occur, progressive fate restriction (PFR) and direct fate restriction, differing in whether partially restricted intermediates were involved. Initially hotly debated, they remain unreconciled, although PFR has become favoured. However, testing of a PFR hypothesis of zebrafish pigment cell development refutes this view. We propose a novel 'cyclical fate restriction' hypothesis, based upon a more dynamic view of transcriptional states, reconciling the experimental evidence underpinning the traditional hypotheses.

Mechanisms of melanocyte polarity and differentiation: What can we learn from other neuroectoderm-derived lineages?

Melanocytes are neuroectoderm-derived pigment-producing cells with highly polarized dendritic morphology. They protect the skin against ultraviolet radiation by providing melanin to neighbouring keratinocytes. However, the mechanisms underlying melanocyte polarization and its relevance for diseases remain mostly elusive. Numerous studies have instead revealed roles for polarity regulators in other neuroectoderm-derived lineages including different neuronal cell types. Considering the shared ontogeny and morphological similarities, these lineages may be used as reference models for the exploration of melanocyte polarity, for example, regarding dendrite formation, spine morphogenesis and polarized organelle transport. In this review, we summarize and compare the latest progress in understanding polarity regulation in neuronal cells and melanocytes and project key open questions for future work.

Essential Role for Integrin-Linked Kinase in Melanoblast Colonization of the Skin

Melanocytes are pigment-producing cells found in the skin and other tissues. Alterations in the melanocyte lineage give rise to a plethora of human diseases, from neurocristopathies and pigmentation disorders to melanoma. During embryogenesis, neural crest cell subsets give rise to two waves of melanoblasts, which migrate dorsolaterally, hone to the skin, and differentiate into melanocytes. However, the mechanisms that govern colonization of the skin by the first wave of melanoblasts are poorly understood. Here we report that targeted inactivation of the integrin-linked kinase gene in first wave melanoblasts causes defects in the ability of these cells to form long pseudopods, to migrate, and to proliferate in vivo. As a result, integrin-linked kinase-deficient melanoblasts fail to populate normally the developing epidermis and hair follicles. We also show that defects in motility and dendricity occur upon integrin-linked kinase gene inactivation in mature melanocytes, causing abnormalities in cell responses to the extracellular matrix substrates collagen I and laminin 332. Significantly, the ability to form long protrusions in mutant cells in response to collagen is restored in the presence of constitutively active Rac1, suggesting that an integrin-linked kinase-Rac1 nexus is likely implicated in melanocytic cell establishment, dendricity, and functions in the skin.

Regulation of melanocyte stem cell behavior by the niche microenvironment

Somatic stem cells are regulated by their niches to maintain tissue homeostasis and repair throughout the lifetime of an organism. An excellent example to study stem cell/niche interactions is provided by the regeneration of melanocytes during the hair cycle and in response to various types of injury. These processes are regulated by neighboring stem cells and multiple signaling pathways, including WNT/β-catenin, KITL/KIT, EDNs/EDNRB, TGF-β/TGF-βR, α-MSH/MC1R, and Notch signaling. In this review, we highlight recent studies that have advanced our understanding of the molecular crosstalk between melanocyte stem cells and their neighboring cells, which collectively form the niche microenvironment, and we focus on the question of how McSCs/niche interactions shape the responses to genotoxic damages and mechanical injury.