Modeling melanoblast development

The potential role of ubiquitination and deubiquitination in melanogenesis

Melanogenesis is a critical biochemical process in which melanocytes produce melanin, a crucial element involved in the formation of coat colour in mammals. According to several earlier studies, melanocytes' post-translational modifications of proteins primarily control melanogenesis. Among the many post-translational changes that can affect melanin production, ubiquitination and deubiquitination can keep melanin production going by changing how proteins that are related to melanin are broken down or kept stable. Ubiquitination and deubiquitination maintain ubiquitin homeostasis, which is a highly dynamic process in balance under the action of E3 ubiquitin ligase and deubiquitinating enzymes. However, the regulatory mechanisms underlying ubiquitination and deubiquitination in melanogenesis are yet to be thoroughly investigated. As a result, there has been a growing focus on exploring the potential correlation between melanogenesis, ubiquitination and deubiquitination. This study discusses the mechanisms of ubiquitination and deubiquitination in the context of melanogenesis, a crucial process for enhancing mammalian coat coloration and addressing pigment-related diseases.

Melanosome transport and regulation in development and disease

Melanosomes are specialized membrane-bound organelles that synthesize and organize melanin, ultimately providing color to the skin, hair, and eyes. Disorders in melanogenesis and melanosome transport are linked to pigmentary diseases, such as Hermansky-Pudlak syndrome, Chediak-Higashi syndrome, and Griscelli syndrome. Clinical cases of these pigmentary diseases shed light on the molecular mechanisms that control melanosome-related pathways. However, only an improved understanding of melanogenesis and melanosome transport will further the development of diagnostic and therapeutic approaches. Herein, we review the current literature surrounding melanosomes with particular emphasis on melanosome membrane transport and cytoskeleton-mediated melanosome transport. We also provide perspectives on melanosome regulatory mechanisms which include hormonal action, inflammation, autophagy, and organelle interactions.

ADAR1 mediated regulation of neural crest derived melanocytes and Schwann cell development

The neural crest gives rise to numerous cell types, dysfunction of which contributes to many disorders. Here, we report that adenosine deaminase acting on RNA (ADAR1), responsible for adenosine-to-inosine editing of RNA, is required for regulating the development of two neural crest derivatives: melanocytes and Schwann cells. Neural crest specific conditional deletion of Adar1 in mice leads to global depigmentation and absence of myelin from peripheral nerves, resulting from alterations in melanocyte survival and differentiation of Schwann cells, respectively. Upregulation of interferon stimulated genes precedes these defects, which are associated with the triggering of a signature resembling response to injury in peripheral nerves. Simultaneous extinction of MDA5, a key sensor of unedited RNA, rescues both melanocytes and myelin defects in vitro, suggesting that ADAR1 safeguards neural crest derivatives from aberrant MDA5-mediated interferon production. We thus extend the landscape of ADAR1 function to the fields of neural crest development and disease.

Modeling and analysis of melanoblast motion

Melanoblast migration is important for embryogenesis and is a key feature of melanoma metastasis. Many studies have characterized melanoblast movement, focusing on statistical properties and have highlighted basic mechanisms of melanoblast motility. We took a slightly different and complementary approach: we previously developed a mathematical model of melanoblast motion that enables the testing of biological assumptions about the displacement of melanoblasts and we created tests to analyze the geometric features of cell trajectories and the specific issue of trajectory interactions. Within this model, we performed simulations and compared the results with experimental data using geometric tests. In this paper, we developed the associated mathematical model and the main focus is to study the crossings between trajectories with new theoretical results about the variation of number of intersection points with respect to the crossing times. Using these results it is possible to study the random nature of displacements and the interactions between trajectories. This analysis has raised new questions, leading to the generation of strong arguments in favor of a trail left behind each moving melanoblast.

From neural crest cells to melanocytes: cellular plasticity during development and beyond

Here, we review melanocyte development and how the embryonic melanoblast, although specified to become a melanocyte, is prone to cellular plasticity and is not fully committed to the melanocyte lineage. Even fully differentiated and pigment-producing melanocytes do not always have a stable phenotype. The gradual lineage restriction of neural crest cells toward the melanocyte lineage is determined by both cell-intrinsic and extracellular signals in which differentiation and pathfinding ability reciprocally influence each other. These signals are leveraged by subtle differences in timing and axial positioning. The most extensively studied migration route is the dorsolateral path between the dermomyotome and the prospective epidermis, restricted to melanoblasts. In addition, the embryonic origin of the skin dermis through which neural crest derivatives migrate may also affect the segregation between melanogenic and neurogenic cells in embryos. It is widely accepted that, irrespective of the model organism studied, the immediate precursor of both melanoblast and neurogenic populations is a glial-melanogenic bipotent progenitor. Upon exposure to different conditions, melanoblasts may differentiate into other neural crest-derived lineages such as neuronal cells and vice versa. Key factors that regulate melanoblast migration and patterning will regulate melanocyte homeostasis during different stages of hair cycling in postnatal hair follicles.

Melanoblasts as Multipotent Cells in Murine Skin

Melanoblasts (MBs) are melanocyte precursors that are derived from neural crest cells (NCCs). We recently demonstrated the multipotency of MBs; they differentiate not only into pigmented melanocytes but also other NCC derivatives. We herein describe methods for the isolation of MBs from mouse skin by flow cytometry. Methods to culture isolated MBs that retain their multipotency and isolation methods for MBs using gene-modified mouse are also described.

Neural crest and the patterning of vertebrate craniofacial muscles

Patterning of craniofacial muscles overtly begins with the activation of lineage-specific markers at precise, evolutionarily conserved locations within prechordal, lateral, and both unsegmented and somitic paraxial mesoderm populations. Although these initial programming events occur without influence of neural crest cells, the subsequent movements and differentiation stages of most head muscles are neural crest-dependent. Incorporating both descriptive and experimental studies, this review examines each stage of myogenesis up through the formation of attachments to their skeletal partners. We present the similarities among developing muscle groups, including comparisons with trunk myogenesis, but emphasize the morphogenetic processes that are unique to each group and sometimes subsets of muscles within a group. These groups include branchial (pharyngeal) arches, which encompass both those with clear homologues in all vertebrate classes and those unique to one, for example, mammalian facial muscles, and also extraocular, laryngeal, tongue, and neck muscles. The presence of several distinct processes underlying neural crest:myoblast/myocyte interactions and behaviors is not surprising, given the wide range of both quantitative and qualitative variations in craniofacial muscle organization achieved during vertebrate evolution.

Sox10 regulates skin melanocyte proliferation by activating the DNA replication licensing factor MCM5

BACKGROUND

The control of cell proliferation is a fundamental aspect of tissue formation in development and regeneration. A cell type that illustrates this point particularly well is the neural crest-derived melanocyte, the pigment cell of vertebrates, as melanocytes can be followed easily during development and their pigment is directly visible in the integument of the adult. In mammals, melanocytes undergo physiological cycles of loss and proliferative regeneration during the hair cycle, and their proliferation is also critical during wound healing, repigmentation of depigmented lesions, and in melanoma formation and progression. Hence, a thorough analysis of the molecular parameters controlling melanocyte proliferation is crucial for our understanding of the physiology of this cell type both in health and disease.

OBJECTIVE

SOX10 is a critical regulator in melanocytes and melanoma cells, but its specific role in their proliferation is far from clear. In this study we analyze the role of SOX10 in regulating mammalian melanocyte proliferation in a mouse model.

METHODS

The role of SOX10 in melanoblast proliferation was analyzed in Sox10/+ mice by co-staining for melanocyte-specific markers and cell proliferation. In vitro, the role of SOX10 was studied by manipulating its levels using RNAi and analyzing the effects on DNA synthesis and cell growth and on gene expression at the RNA and protein levels.

RESULTS

Reduction of Sox10 gene dose led to a reduction in the number of melanoblasts. Knockdown of Sox10 in melanocytes led to inhibition of cell proliferation and a decrease in the expression of the minichromosome maintenance complex component 5 (MCM5). In fact, SOX10 directly activated MCM5 transcription by binding to conserved SOX10 consensus DNA sequences in the MCM5 promoter. Furthermore, the defect in cell proliferation could be rescued partially by overexpression of MCM5 in Sox10 knockdown melanocytes.

CONCLUSION

The results suggest that the SOX10-MCM5 axis plays an important role in controlling melanocyte proliferation. Our findings provide novel insights into the regulatory mechanisms of melanocyte proliferation and may have implications for our understanding of the roles of SOX10 and MCM5 in abnormal melanocyte proliferation disorders such as cutaneous melanoma.

Neuroendocrine Cells of the Prostate Derive from the Neural Crest

The histogenesis of prostatic neuroendocrine cells is controversial: a stem cell hypothesis with a urogenital sinus-derived progeny of all prostatic epithelial cells is opposed by a dual origin hypothesis, favoring the derivation of neuroendocrine cells from the neural crest, with the secretory and basal cells being of urogenital sinus origin. A computer-assisted 3D reconstruction was used to analyze the distribution of chromogranin A immunoreactive cells in serial sections of human fetal prostate specimens (gestation weeks 18 and 25). Immunohistochemical double labeling studies with YFP and serotonin antisera combined with electron microscopy were carried out on double-transgenic Wnt1-Cre/ROSA26-YFP mice showing stable YFP expression in all neural crest-derived cell populations despite loss of Wnt1 expression. 3D reconstruction of the distribution pattern of neuroendocrine cells in the human fetal prostate indicates a migration of paraganglionic cells passing the stroma and reaching the prostate ducts. Double-transgenic mice showed 55% double labeling of periurethral neuroendocrine cells expressing both serotonin and YFP, whereas single serotonin labeling was observed in 36% and exclusive YFP labeling in 9%. The results favor the assumption of a major fraction of neural crest-derived neuroendocrine cells in both the human and murine prostates.

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

BACKGROUND

Melanoblasts (MBs), derived from neural crest cells, only differentiate into melanocytes (Ms) in vivo. We previously showed that MBs isolated from mouse skin were multipotent, generating neurons (Ns) and glial cells (Gs) together with Ms. Using Sox10-IRES-Venus mice and mouse embryonic stem cells, we investigated how MBs expressed their multipotency.

RESULTS

MBs generated colonies containing Ns, Gs, and Ms in the presence of ST2 stromal cells, but they generated only M colonies when incubated with keratinocytes or ST2 culture supernatant, thus showing that MBs required contact with ST2 stromal cells for expression of their multipotency. Notch signaling was shown to be one of the important cues for the maintenance and differentiation of MBs through cell-cell contact. When Notch signaling was inhibited, MBs mainly generated colonies that contained just one type of cells, Ns, Gs, or Ms; the number of colonies containing two or three types of cells markedly decreased even on ST2 stromal cells, showing restriction of their differentiation potency. Whereas when Notch signaling was activated, the number of colonies containing two or three types of cells increased, indicating that their multipotency had been maintained.

CONCLUSIONS

Our results demonstrate that Notch signaling played novel roles in MB multipotency.

Microphthalmia-associated transcription factor/T-box factor-2 axis acts through Cyclin D1 to regulate melanocyte proliferation

OBJECTIVES

Control of cell proliferation is critical for accurate cell differentiation and tissue formation, during development and regeneration. Here, we have analysed the role of microphthalmia-associated transcription factor MITF and its direct target, T-box factor TBX2, in regulating proliferation of mammalian neural crest-derived melanocytes.

MATERIALS AND METHODS

Immunohistochemistry was used to examine spatial and temporal expression of TBX2 in melanocytes in vivo. RNAi and cell proliferation analysis were used to investigate functional roles of TBX2. Furthermore, quantitative RT-PCR, western blot analysis and flow cytometry were used to further scrutinize molecular mechanisms underlying TBX2-dependent cell proliferation.

RESULTS

TBX2 was found to be co-expressed with MITF in melanocytes of mouse hair follicles. Specific Tbx2 knockdown in primary neural crest cells led to inhibition MITF-positive melanoblast proliferation. Tbx2 knockdown in melan-a cells led to reduction in Cyclin D1 expression and G1-phase cell cycle arrest. TBX2 directly activated Ccnd1 transcription by binding to a specific sequence in the Ccnd1 promoter, and the defect in cell proliferation could be rescued partially by overexpression of Cyclin D1 in Tbx2 knockdown melanocytes.

CONCLUSIONS

Results suggest that the Mitf-Tbx2-Cyclin D1 pathway played an important role in regulation of melanocyte proliferation, and provided novel insights into the complex physiology of melanocytes.

The neural crest: a versatile organ system

The neural crest is the name given to the strip of cells at the junction between neural and epidermal ectoderm in neurula-stage vertebrate embryos, which is later brought to the dorsal neural tube as the neural folds elevate. The neural crest is a heterogeneous and multipotent progenitor cell population whose cells undergo EMT then extensively and accurately migrate throughout the embryo. Neural crest cells contribute to nearly every organ system in the body, with derivatives of neuronal, glial, neuroendocrine, pigment, and also mesodermal lineages. This breadth of developmental capacity has led to the neural crest being termed the fourth germ layer. The neural crest has occupied a prominent place in developmental biology, due to its exaggerated migratory morphogenesis and its remarkably wide developmental potential. As such, neural crest cells have become an attractive model for developmental biologists for studying these processes. Problems in neural crest development cause a number of human syndromes and birth defects known collectively as neurocristopathies; these include Treacher Collins syndrome, Hirschsprung disease, and 22q11.2 deletion syndromes. Tumors in the neural crest lineage are also of clinical importance, including the aggressive melanoma and neuroblastoma types. These clinical aspects have drawn attention to the selection or creation of neural crest progenitor cells, particularly of human origin, for studying pathologies of the neural crest at the cellular level, and also for possible cell therapeutics. The versatility of the neural crest lends itself to interlinked research, spanning basic developmental biology, birth defect research, oncology, and stem/progenitor cell biology and therapy.

Sun exposure, sunbeds and sunscreens and melanoma. What are the controversies?

The association between various measures of sun exposure and melanoma risk is quite complex to dissect as many case-control studies of melanoma included different subtypes of melanomas which are likely to be biologically different, so interpretation of the data is difficult. Screening bias in countries with high levels of sun exposure is also an issue. Now that progress is being made in the genetic subclassification of melanoma tumours, it is apparent that melanomas have different somatic changes according to body sites/histological subtypes and that UV exposure may be relevant for some but not all types of melanomas. Melanoma behaviour also points to non-sun-related risk factors, and complex gene-environment interactions are likely. As UV exposure is the only environmental factor ever linked to melanoma, it is still prudent to avoid excessive sun exposure and sunburn especially in poor tanners. However, the impact of strict sun avoidance, which should not be recommended, may take years to be apparent as vitamin D deficiency is a now a common health issue in Caucasian populations, with a significant impact on health in general.

Melanoma. Shall we move away from the sun and focus more on embryogenesis, body weight and longevity?

There are many observations regarding the behaviour of melanoma which points away from sunshine as the main cause of this tumour. Incidence data shows that the increase is mostly seen for thin melanomas which cannot be attributed to sun exposure but increasing screening over the last 20 years. Melanoma behaves in a similar fashion all over the world regarding age of onset, gender differences and histological subtypes. An excess of naevi is the strongest risk factor for melanoma and their appearance and involution throughout life, and the differences in naevus distribution according to gender is giving us a lot of clues about melanoma biology. Melanoma like all cancers is a complex disease with the involvement of many common and low penetrance genes many of them involved in pigmentation and naevogenesis but these only explain a very small portion of melanoma susceptibility. Genes involved in melanocyte differentiation early on in embryogenesis are also becoming relevant for melanoma initiation and progression. Reduced senescence and longevity as well as body weight and energy expenditure are also relevant for melanoma susceptibility. These observations with links between melanoma and non-sun related phenotypes as well as gene discoveries should help to assess the relative contribution of genetic and environmental factors in its causation.

Cellular and molecular mechanisms controlling the migration of melanocytes and melanoma cells

During embryonic development in vertebrates, the neural crest-derived melanoblasts migrate along the dorsolateral axis and cross the basal membrane separating the dermis from the epidermis to reach their final location in the interfollicular epidermis and epidermal hair follicles. Neoplastic transformation converts melanocytes into highly invasive and metastatic melanoma cells. In vitro, these cells extend various types of protrusions and adopt two interconvertible modes of migration, mesenchymal and amoeboid, driven by different signalling molecules. In this review, we describe the major contributions of natural mouse mutants, mouse models generated by genetic engineering and in vitro culture systems, to identification of the genes, signalling pathways and mechanisms regulating the migration of normal and pathological cells of the melanocyte lineage, at both the cellular and molecular levels.

The EJC component Magoh regulates proliferation and expansion of neural crest-derived melanocytes

Melanoblasts are a population of neural crest-derived cells that generate the pigment-producing cells of our body. Defective melanoblast development and function underlies many disorders including Waardenburg syndrome and melanoma. Understanding the genetic regulation of melanoblast development will help elucidate the etiology of these and other neurocristopathies. Here we demonstrate that Magoh, a component of the exon junction complex, is required for normal melanoblast development. Magoh haploinsufficient mice are hypopigmented and exhibit robust genetic interactions with the transcription factor, Sox10. These phenotypes are caused by a marked reduction in melanoblast number beginning at mid-embryogenesis. Strikingly, while Magoh haploinsufficiency severely reduces epidermal melanoblasts, it does not significantly affect the number of dermal melanoblasts. These data indicate Magoh impacts melanoblast development by disproportionately affecting expansion of epidermal melanoblast populations. We probed the cellular basis for melanoblast reduction and discovered that Magoh mutant melanoblasts do not undergo increased apoptosis, but instead are arrested in mitosis. Mitotic arrest is evident in both Magoh haploinsufficient embryos and in Magoh siRNA treated melanoma cell lines. Together our findings indicate that Magoh-regulated proliferation of melanoblasts in the dermis may be critical for production of epidermally-bound melanoblasts. Our results point to a central role for Magoh in melanocyte development.