Neural crest-directed gene transfer demonstrates Wnt1 role in melanocyte expansion and differentiation during mouse development

Examination of wnt signaling mediated melanin transport and shell color formation in Pacific oyster (Crassostrea gigas)

Mollusca exhibit remarkable diversity in shell coloration, attributed to the presence of melanin, a widely distributed pigment with various essential roles, such as mechanical strengthening, antioxidation and thermoregulation. However, the regulatory network governing melanogenesis and melanin transport in molluscs remains poorly understood. In this study, we conducted a systematic analysis of melanin distribution and transport in the Pacific oyster, utilizing light microscopy and high-resolution transmission electron microscopy. In addition, we characterized CgWnt1 and CgWnt2b-a in Crassostrea gigas, and analyzed Wnt signaling in melanocyte formation. Expression analysis revealed that these genes were predominantly expressed in the mantle of black-shelled individuals, particularly in the outer fold of the mantle. Furthermore, we employed RNA interference and inhibitors to specifically inhibit Wnt signaling in both in vivo and in vitro. The results revealed impaired melanogenesis and diminished tyrosinase activity upon Wnt signaling inhibition. These findings suggest the crucial role of Wnt ligands and downstream factors in melanogenesis. In summary, our study provides valuable insights into the regulatory mechanism of shell pigmentation in C. gigas. By demonstrating the promotion of melanogenesis through Wnt signaling modulation, we contribute to a better understanding of the complex processes underlying molluscan melanin production and shell coloration.

Supplementary Information

The online version contains supplementary material available at 10.1007/s42995-024-00221-5.

Transcriptome and exosome proteome analyses provide insights into the mantle exosome involved in nacre color formation of pearl oyster Pinctada fucata martensii

Color polymorphisms in molluscan shells play an important economic in the aquaculture industry. Among bivalves, shell color diversity can reflect properties such as growth rate and tolerance. In pearl oysters, the nacre color of the donor is closely related to the pearl color. Numerous genes and proteins involved in nacre color formation have been identified within the exosomes of the mantle. In this study, we analyzed the carotenoids present in the mantle of gold- and silver-lipped pearl oysters, identifying capsanthin and xanthophyll as crucial pigments contributing to coloration. Transcriptome analysis of the mantle revealed several differentially expressed genes (DEGs) involved in color formation, including ferric-chelate reductase, mantle genes, and larval shell matrix proteins. We also isolated and identified exosomes from the mantles of both gold- and silver-lipped strains of the pearl oyster Pinctada fucata martensii, revealing the extracellular transition mechanism of coloration-related proteins. From these exosomes, we obtained a total of 1223 proteins, with 126 differentially expressed proteins (DEPs) identified. These proteins include those associated with carotenoid metabolism and Fe(III) metabolism, such as apolipoproteins, scavenger receptor proteins, β,β-carotene-15,15'-dioxygenase, ferritin, and ferritin heavy chains. This study may provide a new perspective on the nacre color formation process and the pathways involved in deposition within the pearl oyster P. f. martensii.

Disrupting Hedgehog signaling in melanocytes by SUFU knockout leads to ocular melanocytosis and anterior segment malformation

Hedgehog (Hh) signaling is well known for its crucial role during development, but its specific role in individual cell lineages is less well characterized. Here, we disrupted Hh signaling specifically in melanocytes by using Cre-mediated cell-type-specific knockout of the Hh regulator suppressor of fused (Sufu). Interestingly, corresponding mice were fully pigmented and showed no developmental alterations in melanocyte numbers or distribution in skin and hair follicles. However, there were ectopic melanoblasts visible in the anterior chamber of the eye that eventually displayed severe malformation. Choroidal melanocytes remained unaltered. Surprisingly, the abnormal accumulation of anterior uveal melanoblasts was not the result of increased cell proliferation but of increased migration to ectopic locations such as the cornea. In melanoblasts in vitro, Sufu knockdown replicated the increase in cell migration without affecting proliferation and was mediated by an increased level of phosphorylated-ERK brought about by a reduction in the levels of the repressor form of GLI3. These results highlight the developmental divergence of distinct melanocyte subpopulations and may shed light on the pathogenesis of human ocular melanocytosis.

Overactive Wnt5a signaling disrupts hair follicle polarity during mouse skin development

The polarity of mouse hair follicles is controlled by the Frizzled (Fzd) receptors and other membrane planar cell polarity (PCP) proteins. Whether Wnt proteins can act as PCP ligands in the skin remains unknown. Here, we show that overexpression of Wnt5a in the posterior part of mouse embryos causes a local disruption of hair follicle orientation. The misoriented hair follicle phenotype in Wnt5a overexpressing mice can be rescued by a heterozygous loss of Fzd6, suggesting Wnt5a is likely to signal through Fzd6. Although the membrane distribution of PCP proteins seems unaffected by Wnt5a overexpression, transcriptional profiling analyses identify a set of genes as potential targets of the skin polarization program controlled by Wnt5a/Fzd6 signaling. Surprisingly, deletion of Wnt5a globally or in the posterior part of the mouse embryos does not affect hair follicle orientation. We show that many other Wnts are highly expressed in the developing skin. They can activate the Fzd6 signaling pathway in vitro and may act together with Wnt5a to regulate the Fzd6-mediated skin polarization. Our experiments demonstrate for the first time that Wnt5a can function as an orienting cue for mouse skin PCP.

Schwann cell precursors represent a neural crest-like state with biased multipotency

Schwann cell precursors (SCPs) are nerve-associated progenitors that can generate myelinating and non-myelinating Schwann cells but also are multipotent like the neural crest cells from which they originate. SCPs are omnipresent along outgrowing peripheral nerves throughout the body of vertebrate embryos. By using single-cell transcriptomics to generate a gene expression atlas of the entire neural crest lineage, we show that early SCPs and late migratory crest cells have similar transcriptional profiles characterised by a multipotent "hub" state containing cells biased towards traditional neural crest fates. SCPs keep diverging from the neural crest after being primed towards terminal Schwann cells and other fates, with different subtypes residing in distinct anatomical locations. Functional experiments using CRISPR-Cas9 loss-of-function further show that knockout of the common "hub" gene Sox8 causes defects in neural crest-derived cells along peripheral nerves by facilitating differentiation of SCPs towards sympathoadrenal fates. Finally, specific tumour populations found in melanoma, neurofibroma and neuroblastoma map to different stages of SCP/Schwann cell development. Overall, SCPs resemble migrating neural crest cells that maintain multipotency and become transcriptionally primed towards distinct lineages.

Genetic and Methylation Analysis of CTNNB1 in Benign and Malignant Melanocytic Lesions

Simple Summary

Recurrent CTNNB1 exon 3 mutations have been recognized in the distinct group of melanocytic tumors showing deep penetrating nevus-like morphology and in 1–2% of advanced melanoma. We performed a detailed genetic analysis of difficult-to-classify nevi and melanomas with CTNNB1 mutations and found that benign tumors (nevi) show characteristic morphological, genetic and epigenetic traits, which distinguish them from other nevi and melanoma. Malignant CTNNB1-mutant tumors (melanoma) demonstrated a different genetic profile, grouping clearly with other non-CTNNB1 melanomas in methylation assays. To further evaluate the role of CTNNB1 mutations in melanoma, we assessed a large cohort of clinically sequenced melanomas, identifying 38 tumors with CTNNB1 exon 3 mutations, including recurrent S45 (n = 13, 34%), G34 (n = 5, 13%), and S27 (n = 5, 13%) mutations. Locations and histological subtype of CTNNB1-mutated melanoma varied; none were reported as showing deep penetrating nevus-like morphology. The most frequent concurrent activating mutations were BRAF V600 (55%) and NRAS Q61 (34%).

Abstract

Melanocytic neoplasms have been genetically characterized in detail during the last decade. Recurrent CTNNB1 exon 3 mutations have been recognized in the distinct group of melanocytic tumors showing deep penetrating nevus-like morphology. In addition, they have been identified in 1–2% of advanced melanoma. Performing a detailed genetic analysis of difficult-to-classify nevi and melanomas with CTNNB1 mutations, we found that benign tumors (nevi) show characteristic morphological, genetic and epigenetic traits, which distinguish them from other nevi and melanoma. Malignant CTNNB1-mutant tumors (melanomas) demonstrated a different genetic profile, instead grouping clearly with other non-CTNNB1 melanomas in methylation assays. To further evaluate the role of CTNNB1 mutations in melanoma, we assessed a large cohort of clinically sequenced melanomas, identifying 38 tumors with CTNNB1 exon 3 mutations, including recurrent S45 (n = 13, 34%), G34 (n = 5, 13%), and S27 (n = 5, 13%) mutations. Locations and histological subtype of CTNNB1-mutated melanoma varied; none were reported as showing deep penetrating nevus-like morphology. The most frequent concurrent activating mutations were BRAF V600 (n = 21, 55%) and NRAS Q61 (n = 13, 34%). In our cohort, four of seven (58%) and one of nine (11%) patients treated with targeted therapy (BRAF and MEK Inhibitors) or immune-checkpoint therapy, respectively, showed disease control (partial response or stable disease). In summary, CTNNB1 mutations are associated with a unique melanocytic tumor type in benign tumors (nevi), which can be applied in a diagnostic setting. In advanced disease, no clear characteristics distinguishing CTNNB1-mutant from other melanomas were observed; however, studies of larger, optimally prospective, cohorts are warranted.

Research Progress on Targeted Antioxidant Therapy and Vitiligo

Vitiligo is a common acquired depigmenting disease characterized by the loss of functional melanocytes and epidermal melanin. Vitiligo has a long treatment cycle and slow results, which is one of the most difficult challenges for skin diseases. Oxidative stress plays an important role as an initiating and driving factor in the pathogenesis of vitiligo. Antioxidant therapy has recently become a research hotspot in vitiligo treatment. A series of antioxidants has been discovered and applied to the treatment of vitiligo, which has returned satisfactory results. This article briefly reviews the relationship between oxidative stress and vitiligo. We also describe the progress of targeted antioxidant therapy in vitiligo, with the aim of providing a reference for new drug development and treatment options for this condition.

Clinicopathologic and molecular characterization of melanomas mutated for CTNNB1 and MAPK

Wnt/β-catenin signaling plays crucial roles in melanocyte biology and may be implicated in melanoma progression. In this study, we retrospectively examined a real-life cohort of melanomas mutated for β-catenin (CTNNB1), in association or not with a MAPK mutation (of BRAF or NRAS), and analyzed their clinical, histopathological, and molecular characteristics. Our results indicate that, regardless of the presence of a concurrent MAPK mutation, CTNNB1mut cutaneous primary melanomas display more proliferative hallmarks (increased Breslow thickness, mitotic index, and ulceration) than their CTNNB1 wild-type counterparts. Accordingly, they often progress to the metastatic stage. Furthermore, concurrent CTNNB1 and MAPK mutations do not necessarily confer a deep penetrating nevi phenotype. Altogether, this study provides evidence that CTNNB1 mutations in melanomas are associated with specific clinical and pathological features.

Targeting GPCRs and Their Signaling as a Therapeutic Option in Melanoma

Simple Summary

Sixteen G-protein-coupled receptors (GPCRs) have been involved in melanogenesis or melanomagenesis. Here, we review these GPCRs, their associated signaling, and therapies.

Abstract

G-protein-coupled receptors (GPCRs) serve prominent roles in melanocyte lineage physiology, with an impact at all stages of development, as well as on mature melanocyte functions. GPCR ligands are present in the skin and regulate melanocyte homeostasis, including pigmentation. The role of GPCRs in the regulation of pigmentation and, consequently, protection against external aggression, such as ultraviolet radiation, has long been established. However, evidence of new functions of GPCRs directly in melanomagenesis has been highlighted in recent years. GPCRs are coupled, through their intracellular domains, to heterotrimeric G-proteins, which induce cellular signaling through various pathways. Such signaling modulates numerous essential cellular processes that occur during melanomagenesis, including proliferation and migration. GPCR-associated signaling in melanoma can be activated by the binding of paracrine factors to their receptors or directly by activating mutations. In this review, we present melanoma-associated alterations of GPCRs and their downstream signaling and discuss the various preclinical models used to evaluate new therapeutic approaches against GPCR activity in melanoma. Recent striking advances in our understanding of the structure, function, and regulation of GPCRs will undoubtedly broaden melanoma treatment options in the future.

Stabilization of β-catenin promotes melanocyte specification at the expense of the Schwann cell lineage

The canonical Wnt/β-catenin pathway governs a multitude of developmental processes in various cell lineages, including the melanocyte lineage. Indeed, β-catenin regulates transcription of Mitf-M, the master regulator of this lineage. The first wave of melanocytes to colonize the skin is directly derived from neural crest cells, whereas the second wave of melanocytes is derived from Schwann cell precursors (SCPs). We investigated the influence of β-catenin in the development of melanocytes of the first and second waves by generating mice expressing a constitutively active form of β-catenin in cells expressing tyrosinase. Constitutive activation of β-catenin did not affect the development of truncal melanoblasts but led to marked hyperpigmentation of the paws. By activating β-catenin at various stages of development (E8.5-E11.5), we showed that the activation of β-catenin in bipotent SCPs favored melanoblast specification at the expense of Schwann cells in the limbs within a specific temporal window. Furthermore, in vitro hyperactivation of the Wnt/β-catenin pathway, which is required for melanocyte development, induces activation of Mitf-M, in turn repressing FoxD3 expression. In conclusion, β-catenin overexpression promotes SCP cell fate decisions towards the melanocyte lineage.

Summary: Activation of β-catenin in bipotent Schwann cell precursors during a specific developmental window induces Mitf and represses FoxD3 to promote melanoblast cell fate at the expense of Schwann cells in limbs.

Novel generic models for differentiating stem cells reveal oscillatory mechanisms

Understanding cell fate selection remains a central challenge in developmental biology. We present a class of simple yet biologically motivated mathematical models for cell differentiation that generically generate oscillations and hence suggest alternatives to the standard framework based on Waddington's epigenetic landscape. The models allow us to suggest two generic dynamical scenarios that describe the differentiation process. In the first scenario, gradual variation of a single control parameter is responsible for both entering and exiting the oscillatory regime. In the second scenario, two control parameters vary: one responsible for entering, and the other for exiting the oscillatory regime. We analyse the standard repressilator and four variants of it and show the dynamical behaviours associated with each scenario. We present a thorough analysis of the associated bifurcations and argue that gene regulatory networks with these repressilator-like characteristics are promising candidates to describe cell fate selection through an oscillatory process.

Identification of shell-color-related microRNAs in the Manila clam Ruditapes philippinarum using high-throughput sequencing of small RNA transcriptomes

Shell-color polymorphism is a common phenomenon in several mollusk species and has been associated with thermal capacity, developmental stability, shell strength, and immunity. Shell-color polymorphism has been related to the differential expression of genes in several signal transduction pathways; however, the functions of micro-RNAs (miRNAs) in shell-color formation remain unclear. In the present study, we compared high-quality, small-RNA transcriptomes in three strains of the Manila clam Ruditapes philippinarum with specific shell-color patterns, artificially selected for six generations. Totals of 114 known and 208 novel miRNAs were identified by high-throughput sequencing, of which nine known and one novel miRNA were verified by stem-loop quantitative real time-polymerase chain reaction. Predicted miRNA targets were subjected to Gene Ontology and Kyoto Encyclopedia of Genes and Genomes pathway enrichment analyses. miR-137 and miR-216b and the Hedgehog signaling pathway and Wnt signaling pathway were identified as being potentially involved in pigment formation and regulation in R. philippinarum. These results may help to clarify the role of miRNAs in shell coloration and shed light on the mechanisms regulating color formation in bivalve shells.

Mesenteric Neural Crest Cells Are the Embryological Basis of Skip Segment Hirschsprung's Disease

BACKGROUND & AIMS

Defective rostrocaudal colonization of the gut by vagal neural crest cells (vNCCs) results in Hirschsprung's disease (HSCR), which is characterized by aganglionosis in variable lengths of the distal bowel. Skip segment Hirschsprung's disease (SSHD), referring to a ganglionated segment within an otherwise aganglionic intestine, contradicts HSCR pathogenesis and underscores a significant gap in our understanding of the development of the enteric nervous system. Here, we aimed to identify the embryonic origin of the ganglionic segments in SSHD.

METHODS

Intestinal biopsy specimens from HSCR patients were prepared via the Swiss-roll technique to search for SSHD cases. NCC migration from the neural tube to the gut was spatiotemporally traced using targeted cell lineages and gene manipulation in mice.

RESULTS

After invading the mesentery surrounding the foregut, vNCCs separated into 2 populations: mesenteric NCCs (mNCCs) proceeded to migrate along the mesentery, whereas enteric NCCs invaded the foregut to migrate along the gut. mNCCs not only produced neurons and glia within the gut mesentery, but also continuously complemented the enteric NCC pool. Two new cases of SSHD were identified from 183 HSCR patients, and Ednrb-mutant mice, but not Ret^-/- mice, showed a high incidence rate of SSHD-like phenotypes.

CONCLUSIONS

mNCCs, a subset of vNCCs that migrate into the gut via the gut mesentery to give rise to enteric neurons, could provide an embryologic explanation for SSHD. These findings lead to novel insights into the development of the enteric nervous system and the etiology of HSCR.

How faithfully does intramembranous bone regeneration recapitulate embryonic skeletal development?

Postnatal intramembranous bone regeneration plays an important role during a wide variety of musculoskeletal regeneration processes such as fracture healing, joint replacement and dental implant surgery, distraction osteogenesis, stress fracture healing, and repair of skeletal defects caused by trauma or resection of tumors. The molecular basis of intramembranous bone regeneration has been interrogated using rodent models of most of these conditions. These studies reveal that signaling pathways such as Wnt, TGFβ/BMP, FGF, VEGF, and Notch are invoked, reminiscent of embryonic development of membranous bone. Discoveries of several skeletal stem cell/progenitor populations using mouse genetic models also reveal the potential sources of postnatal intramembranous bone regeneration. The purpose of this review is to compare the underlying molecular signals and progenitor cells that characterize embryonic development of membranous bone and postnatal intramembranous bone regeneration.

SFRP5 inhibits melanin synthesis of melanocytes in vitiligo by suppressing the Wnt/β-catenin signaling

Secreted frizzled-related protein 5 (SFRP5) plays a pivotal role in regulating the development of many tissues and organs, however, as an inhibitor of Wnt signaling, the role of SFRP5 in vitiligo remains unknown. Hence, we speculated that SFRP5 might be associated with melanogenesis in melanocytes by regulating Wnt signaling in vitiligo. In this study, we found that SFRP5 was overexpressed in the skin lesions of patients with vitiligo. Compared with that in normal epidermal melanocytes (PIG1), the expression of SFRP5 was increased in vitiligo melanocytes (PIG3V). To investigate the effect of SFRP5 on melanin synthesis, PIG1 cells were infected with recombinant SFRP5 adenovirus (AdSFRP5), and PIG3V cells were infected with recombinant siSFRP5 adenovirus (AdsiSFRP5). The results showed that SFRP5 overexpression inhibited melanin synthesis in PIG1 cells through downregulation of microphthalmia-associated transcription factor (MITF) and its target proteins via suppression of the Wnt/β-catenin signaling pathway. Accordingly, SFRP5 silencing increased melanin synthesis and activated the Wnt signaling pathway in PIG3V cells. Moreover, SFRP5 overexpression also downregulated the transcriptional activity of T cell factor/lymphoid enhancer factor (TCF/LEF) in PIG1 cells. Furthermore, this inhibitory effect of SFRP5 on melanin synthesis was reversed by treatment with the β-catenin agonist, SKL2001. The inhibitory action of SFRP5 in pigmentation was further confirmed in vivo using a nude mouse model. Hence, our results indicate that SFRP5 can inhibit melanogenesis in melanocytes. Additionally, our findings showed that SFRP5 plays a vital role in the development of vitiligo, and thus may serve as a potential therapeutic target for vitiligo.

A kinase-deficient NTRK2 splice variant predominates in glioma and amplifies several oncogenic signaling pathways

Independent scientific achievements have led to the discovery of aberrant splicing patterns in oncogenesis, while more recent advances have uncovered novel gene fusions involving neurotrophic tyrosine receptor kinases (NTRKs) in gliomas. The exploration of NTRK splice variants in normal and neoplastic brain provides an intersection of these two rapidly evolving fields. Tropomyosin receptor kinase B (TrkB), encoded NTRK2, is known for critical roles in neuronal survival, differentiation, molecular properties associated with memory, and exhibits intricate splicing patterns and post-translational modifications. Here, we show a role for a truncated NTRK2 splice variant, TrkB.T1, in human glioma. TrkB.T1 enhances PDGF-driven gliomas in vivo, augments PDGF-induced Akt and STAT3 signaling in vitro, while next generation sequencing broadly implicates TrkB.T1 in the PI3K signaling cascades in a ligand-independent fashion. These TrkB.T1 findings highlight the importance of expanding upon whole gene and gene fusion analyses to include splice variants in basic and translational neuro-oncology research.

PD-L1 produced by HaCaT cells under polyinosinic-polycytidylic acid stimulation inhibits melanin production by B16F10 cells

Skin forms a physical barrier that protects the body against outside agents. The deepest layer of the skin, the stratum basale, contains two cell types: agent-sensing keratinocytes, and melanin-producing melanocytes. Keratinocytes can sense both harmless commensal organisms and harmful pathogens via Toll-like receptors (TLRs), and keratinocytes subsequently drive immune responses. Activation of TLR3 is required for barrier repair because it stimulates essential genes, including tight junction genes, and inflammatory cytokines. Within the basal layer of the skin, resident melanocytes use their dendritic processes to connect with approximately 30–40 neighboring keratinocytes. Most studies have focused on the transfer of melanin-synthesizing melanosomes from melanocytes to keratinocytes, but the potential regulation of melanogenesis by soluble factor(s) produced by keratinocytes remains to be explored. Studying such regulation in vivo is challenging because of the keratinocyte:melanocyte ratio in the epidermis and the location of the cells within the skin. Therefore, in this study, we investigated whether keratinocytes affected melanocyte melanogenesis in vitro under normal or inflammatory conditions. We found that polyinosinic-polycytidylic acid [poly(I:C)] stimulation induced PD-L1 secretion from HaCaT cells and that poly(I:C)-induced PD-L1 inhibited melanin production by B16F10 cells. These data provide key evidence that keratinocytes can alter melanocyte melanogenesis via the production of soluble factors under inflammatory conditions.

Histone variant dictates fate biasing of neural crest cells to melanocyte lineage

In the neural crest lineage, progressive fate restriction and stem cell assignment are crucial for both development and regeneration. Whereas fate commitment events have distinct transcriptional footprints, fate biasing is often transitory and metastable, and is thought to be moulded by epigenetic programmes. Therefore, the molecular basis of specification is difficult to define. In this study, we established a role for a histone variant, H2a.z.2, in specification of the melanocyte lineage from multipotent neural crest cells. H2a.z.2 silencing reduces the number of melanocyte precursors in developing zebrafish embryos and from mouse embryonic stem cells in vitro We demonstrate that this histone variant occupies nucleosomes in the promoter of the key melanocyte determinant mitf, and enhances its induction. CRISPR/Cas9-based targeted mutagenesis of this gene in zebrafish drastically reduces adult melanocytes, as well as their regeneration. Thereby, our study establishes the role of a histone variant upstream of the core gene regulatory network in the neural crest lineage. This epigenetic mark is a key determinant of cell fate and facilitates gene activation by external instructive signals, thereby establishing melanocyte fate identity.

Mammary Precancerous Stem and Non-Stem Cells Evolve into Cancers of Distinct Subtypes

There are distinct cell subpopulations in normal epithelial tissue, including stem cells, progenitor cells, and more differentiated cells, all of which have been extensively studied for their susceptibility to tumorigenesis. However, normal cells usually have to progress through a precancerous lesion state before becoming a full-blown tumor. Precancerous early lesions are heterogeneous, and the cell subset that is the primary source of the eventual tumor remains largely unknown. By using mouse models that are tailored to address this question, we identified a keratin 6a-expressing precancerous stem cell (PcSC) subset and a more differentiated whey acidic protein-positive (WAP+) cell subset in mammary precancerous lesions initiated by the Wnt1 oncogene. Both cell subsets rapidly progressed to cancer upon introduction of constitutively active versions of either HRAS or BRAF. However, the resulting tumors were dramatically different in protein profiles and histopathology: keratin 6a+ precancerous cells gave rise to adenocarcinoma, whereas WAP+ cells yielded metaplastic carcinoma with severe squamous differentiation and more robust activation of MEK/ERK signaling. Therefore, both stem and non-stem cells in mammary precancerous lesions can contribute to the eventual cancers, but their differentiation status determines the resulting cancer phenotype. This work identifies a previously unknown player in cancer heterogeneity and suggests that cancer prevention should target precancerous cells broadly and not be limited to PcSC. SIGNIFICANCE: This work uses a novel mouse mammary gland cancer model to show that tumors initiated from different precancerous mammary epithelial cells are distinct.

De Novo assembly and comparative transcriptome analyses of purple and green morphs of Apostichopus japonicus during body wall pigmentation process

Pigmentation processes provide a traceable and relevant trait for understanding key issues in evolutionary biology such as adaptation, speciation and the maintenance of balanced polymorphisms. The sea cucumber Apostichopus japonicus, which has nutritive and medical properties, is considered the most valuable commercial species in many parts of Asia. Compared with the green morph, the purple morph is rare and has great appeal to consumers. However, little is currently known about the molecular mechanism of body color formation in A. japonicus, even in echinoderm. Here, we employ illumina sequencing to examine expression patterns of the gene network underlying body wall development in purple and green morphs of A. japonicus. Overall, the number of down-regulated genes in the green morph was significantly more than in the purple morph during the pigmentation stage. We observed dynamic expression patterns of a large number of pigment, regulation and growth genes from the "Melanogenesis", "Melanoma", "Wnt signaling pathway", "Notch signaling pathway", "epithelium development", "epidermal growth factor receptor binding","growth factor activity" and "growth", including contrasting expression patterns of these genes in green and purple morph. This study provides comprehensive lists of differentially expressed genes during body wall development in the green and purple morphs, revealing potential candidate genes that may be involved in regulating body color formation and polymorphism. These data will provide valuable information for future genetic studies on sea cucumbers elucidating the molecular mechanisms underlying pigmentation, and may support the culture of desirable color morphs.

Non-Coding Transcriptome Maps across Twenty Tissues of the Korean Black Chicken, Yeonsan Ogye

Yeonsan Ogye is a rare Korean domestic chicken breed whose entire body, including feathers and skin, has a unique black coloring. Although some protein-coding genes related to this unique feature have been examined, non-coding elements have not been widely investigated. Thus, we evaluated coding and non-coding transcriptome expression and identified long non-coding RNAs functionally linked to protein-coding genes in Ogye. High-throughput RNA sequencing and DNA methylation sequencing were performed to profile the expression of 14,264 Ogye protein-coding and 6900 long non-coding RNA (lncRNA) genes and detect DNA methylation in 20 different tissues of an individual Ogye. Approximately 75% of Ogye lncRNAs and 45% of protein-coding genes showed tissue-specific expression. For some genes, tissue-specific expression levels were inversely correlated with DNA methylation levels in their promoters. Approximately 39% of tissue-specific lncRNAs displayed functional associations with proximal or distal protein-coding genes. Heat shock transcription factor 2-associated lncRNAs appeared to be functionally linked to protein-coding genes specifically expressed in black skin tissues, more syntenically conserved in mammals, and differentially expressed in black relative to in white tissues. Pending experimental validation, our findings increase the understanding of how the non-coding genome regulates unique phenotypes and can be used for future genomic breeding of chickens.

The b-HLH transcription factor Hes3 participates in neural plate border formation by interfering with Wnt/β-catenin signaling

Hes3 belongs to the Hes basic helix-loop-helix family of transcriptional repressors that play central roles in maintaining progenitor cells and regulating binary cell fate decisions in the embryo. During Xenopus laevis development, hes3 is expressed in the embryonic ectoderm in a horseshoe shape domain at the edge of the developing neural pate. Hes3 mis-expression at early neurula stage blocks neural crest (snai2, sox8, sox9 and sox10) and cranial placode (six1 and dmrta1) gene expression, and promotes neural plate (sox2 and sox3) fate. At tailbud stage, these embryos exhibited a massive up-regulation of both sox8 and sox10 expression, associated with an increase in genes important for melanocytes differentiation (mitf and dct). Using a hormone inducible construct we show that Hes3 does not induce a pigment cell differentiation program de novo, rather it maintains progenitor cells in an undifferentiated state, and as Hes3 expression subsides overtime these cells adopt a pigment cell fate. We demonstrate that mechanistically Hes3 mediates its activity through inhibition of Wnt/β-catenin signaling, a molecular pathway critical for neural crest specification and pigment cell lineage differentiation. We propose that Hes3 at the edge of the neural plate spatially restricts the response to mesoderm-derived Wnt ligands, thereby contributing to the establishment of sharp boundaries of gene expression at the neural plate border.

Identification and Characterization of Metastatic Factors by Gene Transfer into the Novel RIP-Tag; RIP-tva Murine Model

Metastatic cancer accounts for 90% of deaths in patients with solid tumors. There is an urgent need to better understand the drivers of cancer metastasis and to identify novel therapeutic targets. To investigate molecular events that drive the progression from primary cancer to metastasis, we have developed a bitransgenic mouse model, RIP-Tag; RIP-tva. In this mouse model, the rat insulin promoter (RIP) drives the expression of the SV40 T antigen (Tag) and the receptor for subgroup A avian leukosis virus (tva) in pancreatic β cells. The mice develop pancreatic neuroendocrine tumors with 100% penetrance through well-defined stages that are similar to human tumorigenesis, with stages including hyperplasia, angiogenesis, adenoma, and invasive carcinoma. Because RIP-Tag; RIP-tva mice do not develop metastatic disease, genetic alterations that promote metastasis can be identified easily. Somatic gene transfer into tva-expressing, proliferating pancreatic β premalignant lesions is achieved through intracardiac injection of avian retroviruses harboring the desired genetic alteration. A titer of >1 x 10⁸ infectious units per ml is considered appropriate for in vivo infection. In addition, avian retroviruses can infect cell lines derived from tumors in RIP-Tag; RIP-tva mice with high efficiency. The cell lines can also be used to characterize the metastatic factors. Here we demonstrate how to utilize this mouse model and cell lines to assess the functions of candidate genes in tumor metastasis.

Hypopigmenting Effects of Brown Algae-Derived Phytochemicals: A Review on Molecular Mechanisms

There is a rapid increase in the demand for natural hypopigmenting agents from marine sources for cosmeceutical and pharmaceutical applications. Currently, marine macroalgae are considered as a safe and effective source of diverse bioactive compounds. Many research groups are exploring marine macroalgae to discover and characterize novel compounds for cosmeceutical, nutraceutical, and pharmaceutical applications. Many types of bioactive secondary metabolites from marine algae, including phlorotannins, sulfated polysaccharides, carotenoids, and meroterpenoids, have already been documented for their potential applications in the pharmaceutical industry. Among these metabolites, phlorotannins from brown algae have been widely screened for their pharmaceutical and hypopigmenting effects. Unfortunately, the majority of these articles did not have detailed investigations on molecular targets, which is critical to fulfilling the criteria for their cosmeceutical and pharmaceutical use. Very recently, a few meroterpenoids have been discovered from Sargassum sp., with the examination of their anti-melanogenic properties and mechanisms. Despite the scarcity of in vivo and clinical investigations of molecular mechanistic events of marine algae-derived hypopigmenting agents, identifying the therapeutic targets and their validation in humans has been a major challenge for future studies. In this review, we focused on available data representing molecular mechanisms underlying hypopigmenting properties of potential marine brown alga-derived compounds.

Genetically engineered mouse models of melanoma

Melanoma is a complex disease that exhibits highly heterogeneous etiological, histopathological, and genetic features, as well as therapeutic responses. Genetically engineered mouse (GEM) models provide powerful tools to unravel the molecular mechanisms critical for melanoma development and drug resistance. Here, we expound briefly the basis of the mouse modeling design, the available technology for genetic engineering, and the aspects influencing the use of GEMs to model melanoma. Furthermore, we describe in detail the currently available GEM models of melanoma. Cancer 2017;123:2089-103. © 2017 American Cancer Society.

IBT-based quantitative proteomics identifies potential regulatory proteins involved in pigmentation of purple sea cucumber, Apostichopus japonicus

Sea cucumbers are an important economic species and exhibit high yield value among aquaculture animals. Purple sea cucumbers are very rare and beautiful and have stable hereditary patterns. In this study, isobaric tags (IBT) were first used to reveal the molecular mechanism of pigmentation in the body wall of the purple sea cucumber. We analyzed the proteomes of purple sea cucumber in early pigmentation stage (Pa), mid pigmentation stage (Pb) and late pigmentation stage (Pc), resulting in the identification of 5580 proteins, including 1099 differentially expressed proteins in Pb: Pa and 339 differentially expressed proteins in Pc: Pb. GO and KEGG analyses revealed possible differentially expressed proteins, including"melanogenesis", "melanosome", "melanoma", "pigment-biosynthetic process", "Epidermis development", "Ras-signaling pathway", "Wnt-signaling pathway", "response to UV light", and "tyrosine metabolism", involved in pigment synthesis and regulation in purple sea cucumbers. The large number of differentially expressed proteins identified here should be highly useful in further elucidating the mechanisms underlying pigmentation in sea cucumbers. Furthermore, these results may also provide the base for further identification of proteins involved in resistance mechanisms against melanoma, albinism, UV damage, and other diseases in sea cucumbers.

An ongoing role for Wnt signaling in differentiating melanocytes in vivo

A role for Wnt signaling in melanocyte specification from neural crest is conserved across vertebrates, but possible ongoing roles in melanocyte differentiation have received little attention. Using a systems biology approach to investigate the gene regulatory network underlying stable melanocyte differentiation in zebrafish highlighted a requirement for a positive-feedback loop involving the melanocyte master regulator Mitfa. Here, we test the hypothesis that Wnt signaling contributes to that positive feedback. We show firstly that Wnt signaling remains active in differentiating melanocytes and secondly that enhanced Wnt signaling drives elevated transcription of mitfa. We show that chemical activation of the Wnt signaling pathway at early stages of melanocyte development enhances melanocyte specification as expected, but importantly that at later (differentiation) stages, it results in altered melanocyte morphology, although melanisation is not obviously affected. Downregulation of Wnt signaling also results in altered melanocyte morphology and organization. We conclude that Wnt signaling plays a role in regulating ongoing aspects of melanocyte differentiation in zebrafish.

Wnt/β-catenin signaling inhibitor ICG-001 enhances pigmentation of cultured melanoma cells

BACKGROUND

Wnt/β-catenin signaling is important in development and differentiation of melanocytes.

OBJECTIVE

The object of this study was to evaluate the effects of several Wnt/β-catenin signaling inhibitors on pigmentation using melanoma cells.

METHODS

Melanoma cells were treated with Wnt/β-catenin signaling inhibitors, and then melanin content and tyrosinase activity were checked.

RESULTS

Although some inhibitors showed slight inhibition of pigmentation, we failed to observe potential inhibitory effect of those chemicals on pigmentation of HM3KO melanoma cells. Rather, one of powerful Wnt/β-catenin signaling inhibitors, ICG-001, increased the pigmentation of HM3KO melanoma cells. Pigmentation-enhancing effect of ICG-001 was reproducible in other melanoma cell line MNT-1. Consistent with these results. ICG-001 increased the expression of pigmentation-related genes, such as MITF, tyrosinase and TRP1. When ICG-001 was treated, the phosphorylation of CREB was significantly increased. In addition, ICG-001 treatment led to quick increase of intracellular cAMP level, suggesting that ICG-001 activated PKA signaling. The blockage of PKA signaling with pharmaceutical inhibitor H89 inhibited the ICG-001-induced pigmentation significantly.

CONCLUSIONS

These results suggest that PKA signaling is pivotal in pigmentation process itself, while the importance of Wnt/β-catenin signaling should be emphasized in the context of development and differentiation.

The WNT-less wonder: WNT-independent β-catenin signaling

β-catenin is known as an Armadillo protein that regulates gene expression following WNT pathway activation. However, WNT-independent pathways also activate β-catenin. During the establishment of the melanocyte lineage, β-catenin plays an important role. In the context of physiopathology, β-catenin is activated genetically or transiently in various cancers, including melanoma, where it can be found in the nucleus of tumors. In this review, we discuss alternative pathways that activate β-catenin independent of WNTs and highlight what is known regarding these pathways in melanoma. We also discuss the role of β-catenin as a transcriptional regulator in various cell types, with emphasis on the different transcription factors it associates with independent of WNT induction. Finally, the role of WNT-independent β-catenin in melanocyte development and melanomagenesis is also discussed.

Wnt/β-catenin signaling in melanoma: Preclinical rationale and novel therapeutic insights

WNT signaling regulates embryonic development and tissue homeostasis in the adult stage. Evolutionarily, activation of the WNT pathway is triggered by a large family of cytokines and activates a broad spectrum of downstream targets through two independent branches mediated by β-catenin (defined as canonical pathway) or PLC and small GTPase (defined as non-canonical pathway), respectively. Recent studies revealed the crucial role of WNT in the maintenance of cell metabolism and stemness as well as its deregulation in tumourigenesis and malignant transformation through oncogenic reprogramming, which contributes to cancer cell proliferation and differentiation, survival, stress response and resistance. In addition, multiple functional mutations discovered in human tumours have been reported to cause malignancy, indicating this pathway as a novel therapeutic target in oncology. Notably, emerging data highlights its involvement in the crosstalk between immune and cancer cells. However, contradictory effects have been also observed in different pre-clinical models when strategic(???) inhibitors are tested. In this review, we address the multifaceted regulatory mechanisms of WNT signaling in cancer, with a particular focus on current melanoma therapy, which has witnessed dramatic improvement in the last five years.

QTL Mapping of Endocochlear Potential Differences between C57BL/6J and BALB/cJ mice

We reported earlier that the endocochlear potential (EP) differs between C57BL/6J (B6) and BALB/cJ (BALB) mice, being lower in BALBs by about 10 mV (Ohlemiller et al. Hear Res 220: 10-26, 2006). This difference corresponds to strain differences with respect to the density of marginal cells in cochlear stria vascularis. After about 1 year of age, BALB mice also tend toward EP reduction that correlates with further marginal cell loss. We therefore suggested that early sub-clinical features of the BALB stria vascularis may predispose these mice to a condition modeling Schuknecht's strial presbycusis. We further reported (Ohlemiller et al. J Assoc Res Otolaryngol 12: 45-58, 2011) that the acute effects of a 2-h 110 dB SPL noise exposure differ between B6 and BALB mice, such that the EP remains unchanged in B6 mice, but is reduced by 40-50 mV in BALBs. In about 25 % of BALBs, the EP does not completely recover, so that permanent EP reduction may contribute to noise-induced permanent threshold shifts in BALBs. To identify genes and alleles that may promote natural EP variation as well as noise-related EP reduction in BALB mice, we have mapped related quantitative trait loci (QTLs) using 12 recombinant inbred (RI) strains formed from B6 and BALB (CxB1-CxB12). EP and strial marginal cell density were measured in B6 mice, BALB mice, their F1 hybrids, and RI mice without noise exposure, and 1-3 h after broadband noise (4-45 kHz, 110 dB SPL, 2 h). For unexposed mice, the strain distribution patterns for EP and marginal cell density were used to generate preliminary QTL maps for both EP and marginal cell density. Six QTL regions were at least statistically suggestive, including a significant QTL for marginal cell density on chromosome 12 that overlapped a weak QTL for EP variation. This region, termed Maced (Marginal cell density QTL) supports the notion of marginal cell density as a genetically influenced contributor to natural EP variation. Candidate genes for Maced notably include Foxg1, Foxa1, Akap6, Nkx2-1, and Pax9. Noise exposure produced significant EP reductions in two RI strains as well as significant EP increases in two RI strains. QTL mapping of the EP in noise-exposed RI mice yielded four suggestive regions. Two of these overlapped with QTL regions we previously identified for noise-related EP reduction in CBA/J mice (Ohlemiller et al. Hear Res 260: 47-53, 2010) on chromosomes 5 and 18 (Nirep). The present map may narrow the Nirep interval to a ~10-Mb region of proximal Chr. 18 that includes Zeb1, Arhgap12, Mpp7, and Gjd4. This study marks the first exploration of natural gene variants that modulate the EP. Their orthologs may underlie some human hearing loss that originates in the lateral wall.

LEF-1 Regulates Tyrosinase Gene Transcription In Vitro

TYR, DCT and MITF are three important genes involved in maintaining the mature phenotype and producing melanin; they therefore participate in neural crest cell development into melanocytes. Previous studies have revealed that the Wnt signaling factor lymphoid enhancer-binding factor (LEF-1) can enhance DCT and MITF gene expression. However, whether LEF-1 also affects TYR gene expression remains unclear. In the present study, we found that LEF-1 regulated TYR transcription in vitro. LEF-1 overexpression increased TYR gene promoter activity, whereas LEF-1 knockdown by RNA interference significantly decreased TYR expression. Moreover, the core GTTTGAT sequence (-56 to -50) within the TYR promoter is essential for the effect of LEF-1 on TYR expression, and chromatin immunoprecipitation (ChIP) assay indicated that endogenous LEF-1 interacts with the TYR promoter. In addition, we observed a synergistic transactivation of the TYR promoter by LEF-1 and MITF. These data suggest that Wnt signaling plays an important role in regulating melanocyte development and differentiation.

Acute Inhibition of MEK Suppresses Congenital Melanocytic Nevus Syndrome in a Murine Model Driven by Activated NRAS and Wnt Signaling

Congenital melanocytic nevus (CMN) syndrome is the association of pigmented melanocytic nevi with extra-cutaneous features, classically melanotic cells within the central nervous system, most frequently caused by a mutation of NRAS codon 61. This condition is currently untreatable and carries a significant risk of melanoma within the skin, brain, or leptomeninges. We have previously proposed a key role for Wnt signaling in the formation of melanocytic nevi, suggesting that activated Wnt signaling may be synergistic with activated NRAS in the pathogenesis of CMN syndrome. Some familial pre-disposition suggests a germ-line contribution to CMN syndrome, as does variability of neurological phenotypes in individuals with similar cutaneous phenotypes. Accordingly, we performed exome sequencing of germ-line DNA from patients with CMN to reveal rare or undescribed Wnt-signaling alterations. A murine model harboring activated NRAS(Q61K) and Wnt signaling in melanocytes exhibited striking features of CMN syndrome, in particular neurological involvement. In the first model of treatment for this condition, these congenital, and previously assumed permanent, features were profoundly suppressed by acute post-natal treatment with a MEK inhibitor. These data suggest that activated NRAS and aberrant Wnt signaling conspire to drive CMN syndrome. Post-natal MEK inhibition is a potential candidate therapy for patients with this debilitating condition.

Poised Regeneration of Zebrafish Melanocytes Involves Direct Differentiation and Concurrent Replenishment of Tissue-Resident Progenitor Cells

Efficient regeneration following injury is critical for maintaining tissue function and enabling organismal survival. Cells reconstituting damaged tissue are often generated from resident stem or progenitor cells or from cells that have dedifferentiated and become proliferative. While lineage-tracing studies have defined cellular sources of regeneration in many tissues, the process by which these cells execute the regenerative process is largely obscure. Here, we have identified tissue-resident progenitor cells that mediate regeneration of zebrafish stripe melanocytes and defined how these cells reconstitute pigmentation. Nearly all regeneration melanocytes arise through direct differentiation of progenitor cells. Wnt signaling is activated prior to differentiation, and inhibition of Wnt signaling impairs regeneration. Additional progenitors divide symmetrically to sustain the pool of progenitor cells. Combining direct differentiation with symmetric progenitor divisions may serve as a means to rapidly repair injured tissue while preserving the capacity to regenerate.

Distinct functionality of dishevelled isoforms on Ca2+/calmodulin-dependent protein kinase 2 (CamKII) in Xenopus gastrulation

CamKII is a novel binding partner of Arrb2/Dvl2 protein complexes and is required for convergent extension movements in Xenopus. CamKII physically and functionally interacts with Dvl2, whereas CamKII activity is antagonistically modulated by Dvl1 and Dvl3.

Wnt ligands trigger the activation of a variety of β-catenin–dependent and β-catenin–independent intracellular signaling cascades. Despite the variations in intracellular signaling, Wnt pathways share the effector proteins frizzled, dishevelled, and β-arrestin. It is unclear how the specific activation of individual branches and the integration of multiple signals are achieved. We hypothesized that the composition of dishevelled–β-arrestin protein complexes contributes to signal specificity and identified CamKII as an interaction partner of the dishevelled–β-arrestin protein complex by quantitative functional proteomics. Specifically, we found that CamKII isoforms interact differentially with the three vertebrate dishevelled proteins. Dvl1 is required for the activation of CamKII and PKC in the Wnt/Ca²⁺ pathway. However, CamKII interacts with Dvl2 but not with Dvl1, and Dvl2 is necessary to mediate CamKII function downstream of Dvl1 in convergent extension movements in Xenopus gastrulation. Our findings indicate that the different Dvl proteins and the composition of dishevelled–β-arrestin protein complexes contribute to the specific activation of individual branches of Wnt signaling.

Using the RCAS-TVA system to model human cancer in mice

For successful infection, avian sarcoma leukosis virus subgroup A (ASLV-A) requires its receptor, tumor virus A (TVA), to be present on the surface of target cells. This is the basis of the RCAS-TVA gene delivery system: Mammalian cells lack the gene encoding TVA and are normally resistant to infection by ASLV; however, transgenic targeting of TVA to specific cell types or tissues in the mouse renders these cells uniquely susceptible to infection by ASLV-A-based RCAS viruses. The RCAS-TVA system is a powerful tool for effectively modeling human tumors, including pancreatic, ovarian, and breast cancers, gliomas, and melanomas. RCAS viruses can deliver cDNAs (≤2.8 kb), as well as short hairpin RNAs (shRNAs), microRNAs (miRNAs), and other noncoding RNAs. Compared with traditional transgenic and knockout mice, the RCAS-TVA system has several strengths. First, virus delivery is generally performed postnatally and results in a relatively low infection rate of target cells; the sporadic postnatal expression of the gene of interest mimics the situation in developing human tumors. Second, a single transgenic mouse line can be used to compare the consequences of specific genes on tumor development, with viruses encoding oncogenes or shRNAs targeting specific tumor suppressor genes. TVA mouse strains can also be easily combined with transgenic, knock-in, and knockout mouse models to study cooperating genetic events.

Most human non-GCIMP glioblastoma subtypes evolve from a common proneural-like precursor glioma

To understand the relationships between the non-GCIMP glioblastoma (GBM) subgroups, we performed mathematical modeling to predict the temporal sequence of driver events during tumorigenesis. The most common order of evolutionary events is 1) chromosome (chr) 7 gain and chr10 loss, followed by 2) CDKN2A loss and/or TP53 mutation, and 3) alterations canonical for specific subtypes. We then developed a computational methodology to identify drivers of broad copy number changes, identifying PDGFA (chr7) and PTEN (chr10) as driving initial nondisjunction events. These predictions were validated using mouse modeling, showing that PDGFA is sufficient to induce proneural-like gliomas and that additional NF1 loss converts proneural to the mesenchymal subtype. Our findings suggest that most non-GCIMP mesenchymal GBMs arise as, and evolve from, a proneural-like precursor.

Developmental pathways activated in melanocytes and melanoma

Cutaneous malignant melanomas originate primarily within epidermal melanocytic cells. Melanoma cells share many characteristics with melanocyte precursors, suggesting that melanoma cells utilize the developmental programs of their normal counterpart for their own progression. The pigmentation system provides an advantageous model to assess survival pathway interactions in the melanocytic lineage, as genetic alterations controlling melanocyte development can be easily detectable by coat color phenotype that do not affect the viability of an animal. By integrating combinatorial gene knockout approaches, cell-based assays and immunohistochemical observations, recent studies have illustrated several genes and pathways that play important roles both in melanocyte specification and maintenance and in melanoma formation and progression. We are reviewing those genes and pathways to understand the connection between normal and cancerous development and to reveal therapeutic potential of targeting developmental pathways for melanoma therapy.

The neural stem cell lineage reveals novel relationships among spermatogonial germ stem cells and other pluripotent stem cells

The embryonic stem cell (ESC) derived from the inner cell mass is viewed as the core pluripotent cell (PC) type from which all other cell types emanate. This familiar perspective derives from an embryological time line in which PCs are ordered according to their time of appearance. However, this schema does not take into account their potential for interconversion, thereby excluding this critical quality of PCs. The persistence of bona fide pluripotent adult stem cells has garnered increasing attention in recent years. Adult pluripotent spermatogonial germ stem cells (aSGSCs) arise from primordial germ cells (pGCs) that emerge from the epiblast during gastrulation. Adult definitive neural stem cells (dNSCs) arise clonally from pluripotent embryonic primitive neural stem cells (pNSCs), which can also be derived clonally from ESCs. To test for stem cell-type convertibility, we employed differentiation in the clonal lineage from ESCs to pNSCs to dNSCs, and revealed the relationships and lineage positioning among various PC populations, including spermatogonial germ cells (aSGSCs), epiblast-derived stem cells (Epi-SCs) and the bFGF, Activin, and BIO-derived stem cell (FAB-SC). Adult, murine aSGSCs assumed a 'pseudo-ESC' state in vitro, and then differentiated into dNSCs, but not pNSCs. Similarly, Epi-SCs and FAB-SCs only gave rise to dNSCs and not to pNSCs. The results of these experiments suggest a new pluripotency lineage model describing the relationship(s) among PCs that better reflects the transitions between these cell types in vitro.

Mechanism and preclinical prevention of increased breast cancer risk caused by pregnancy

While a first pregnancy before age 22 lowers breast cancer risk, a pregnancy after age 35 significantly increases life-long breast cancer risk. Pregnancy causes several changes to the normal breast that raise barriers to transformation, but how pregnancy can also increase cancer risk remains unclear. We show in mice that pregnancy has different effects on the few early lesions that have already developed in the otherwise normal breast—it causes apoptosis evasion and accelerated progression to cancer. The apoptosis evasion is due to the normally tightly controlled STAT5 signaling going astray—these precancerous cells activate STAT5 in response to pregnancy/lactation hormones and maintain STAT5 activation even during involution, thus preventing the apoptosis normally initiated by oncoprotein and involution. Short-term anti-STAT5 treatment of lactation-completed mice bearing early lesions eliminates the increased risk after a pregnancy. This chemoprevention strategy has important implications for preventing increased human breast cancer risk caused by pregnancy.

DOI:http://dx.doi.org/10.7554/eLife.00996.001

Pregnancy changes the probability that a woman will later develop breast cancer. If a woman’s first pregnancy occurs before her 22^nd birthday, the chances of developing breast cancer are reduced. However, if the first pregnancy occurs after her 35^th birthday, there is an increased risk of breast cancer. It is not clear why this age-related difference exists, but as more women wait until their 30s to start a family, there is greater urgency to understand this difference.

Breasts undergo extensive changes during pregnancy. This remodeling makes their cells less likely to multiply, and also less likely to develop tumors, which could explain the protective effect of pregnancy for younger women. But why would older women not reap the same benefits? One hypothesis is that older first-time mothers are more likely than younger first-time mothers to already have breast tissue with cells carrying cancer-causing mutations, or to have clusters of abnormal precancerous cells.

Now, Haricharan et al. have tested this hypothesis by inserting two cancer-causing genes into female mice. Half of the mice were then made pregnant and allowed to nurse their young, whilst the other half were never mated. Although, both groups of mice later developed tumors, the mice that had been pregnant developed more tumors and did so faster.

The increased cancer levels in the mice that had been pregnant were not due to them having more precancerous cells at the early stages of pregnancy than the unmated mice of the same age. Further, the precancerous cells in the impregnated mice did not proliferate faster than those in the mice that were never pregnant. Instead, pregnancy weakened the protective process that culls pre-existing precancerous cells. These cells evaded destruction by activating a signaling pathway called the STAT5 pathway in response to pregnancy hormones.

Haricharan et al. also examined tissue samples from women with a very early form of breast cancer and found elevated levels of STAT5 in tumors from women who had been pregnant compared to those who had not been pregnant.

The good news is that precancerous cells do not always become cancerous. However, for those women with a high risk of developing breast cancer, Haricharan et al. suggest that temporarily reducing STAT5 activity after pregnancy with medication might reduce this risk. Treating mice with anti-STAT5 drugs for a few weeks after they finished nursing their young lessened the elevated cancer risk, and so the next challenge is to see if this approach will also be effective in human clinical trials.

DOI:http://dx.doi.org/10.7554/eLife.00996.002

Molecular and cellular pathogenesis of melanoma initiation and progression

Melanoma is a malignant tumor of melanocytes that can spread to other organs of the body, resulting in severe and/or lethal malignancies. Melanocytes are pigment-producing cells found in the deep layer of the epidermis and are originated from melanocytes stem cells through a cellular process called melanogenesis. Several genes and epigenetic and micro-environmental factors are involved in this process via the regulation and maintenance of the balance between melanocytes stem cells proliferation and their differentiation into melanocytes. Dysregulation of this balance through gain or loss of function of key genes implicated in the control and regulation of cell cycle progression and/or differentiation results in melanoma initiation and progression. This review aims to provide a comprehensive overview about the origin of melanocytes, the oncogenic events involved in melanocytes stem cells transformation, and the mechanisms implicated in the perpetuation of melanoma malignant phenotype.

Wnt signaling potentiates nevogenesis

Cellular senescence is a stable proliferation arrest associated with an altered secretory pathway (senescence-associated secretory phenotype). Cellular senescence is also a tumor suppressor mechanism, to which both proliferation arrest and senescence-associated secretory phenotype are thought to contribute. The melanocytes within benign human nevi are a paradigm for tumor-suppressive senescent cells in a premalignant neoplasm. Here a comparison of proliferating and senescent melanocytes and melanoma cell lines by RNA sequencing emphasizes the importance of senescence-associated proliferation arrest in suppression of transformation. Previous studies showed that activation of the Wnt signaling pathway can delay or bypass senescence. Consistent with this, we present evidence that repression of Wnt signaling contributes to melanocyte senescence in vitro. Surprisingly, Wnt signaling is active in many senescent human melanocytes in nevi, and this is linked to histological indicators of higher proliferative and malignant potential. In a mouse, activated Wnt signaling delays senescence-associated proliferation arrest to expand the population of senescent oncogene-expressing melanocytes. These results suggest that Wnt signaling can potentiate nevogenesis in vivo by delaying senescence. Further, we suggest that activated Wnt signaling in human nevi undermines senescence-mediated tumor suppression and enhances the probability of malignancy.

Modeling neural crest induction, melanocyte specification, and disease-related pigmentation defects in hESCs and patient-specific iPSCs

Melanocytes are pigment-producing cells of neural crest (NC) origin that are responsible for protecting the skin against UV irradiation. Pluripotent stem cell (PSC) technology offers a promising approach for studying human melanocyte development and disease. Here, we report that timed exposure to activators of WNT, BMP, and EDN3 signaling triggers the sequential induction of NC and melanocyte precursor fates under dual-SMAD-inhibition conditions. Using a SOX10::GFP human embryonic stem cell (hESC) reporter line, we demonstrate that the temporal onset of WNT activation is particularly critical for human NC induction. Subsequent maturation of hESC-derived melanocytes yields pure populations that match the molecular and functional properties of adult melanocytes. Melanocytes from Hermansky-Pudlak syndrome and Chediak-Higashi syndrome patient-specific induced PSCs (iPSCs) faithfully reproduce the ultrastructural features of disease-associated pigmentation defects. Our data define a highly specific requirement for WNT signaling during NC induction and enable the generation of pure populations of human iPSC-derived melanocytes for faithful modeling of pigmentation disorders.

A Wnt-er migration: the confusing role of β-catenin in melanoma metastasis

Wnt signaling in melanoma is complex, requiring the coordinate expression of multiple players. Depending on the context of receptors and co-receptors that are present, Wnt proteins may signal through either canonical or noncanonical pathways. The role of β-catenin in melanoma metastasis remains unclear; however, a new study points to the roles of Wnt5A and ARF6 in driving β-catenin expression and melanoma metastasis. Here, we discuss this finding and how it may help us define different subpopulations of melanoma cells that could have different outcomes, as well as different responses to therapy.

Wnt signaling in skin development, homeostasis, and disease

The skin and its appendages constitute the largest organ of the body. Its stratified epithelia offer protection from environmental stresses such as dehydration, irradiation, mechanical trauma, and pathogenic infection, whereas its appendages, like hair and sebaceous glands, help regulate body temperature as well as influence animal interaction and social behavior through camouflage and sexual signaling. To respond to and function effectively in a dynamic external environment, the skin and its appendages possess a remarkable ability to regenerate in a carefully controlled fashion. When this finely tuned homeostatic process is disrupted, skin diseases such as cancers may result. At present, the molecular signals that orchestrate cell proliferation, differentiation, and patterning in the skin remain incompletely understood. It is increasingly apparent that many morphogenetic pathways with key roles in development are also important in regulating skin biology. Of these, Wnt signaling has emerged as the dominant pathway controlling the patterning of skin and influencing the decisions of embryonic and adult stem cells to adopt the various cell lineages of the skin and its appendages, as well as subsequently controlling the function of differentiated skin cells. Here we will review established concepts and present recent advances in our understanding of the diverse roles that Wnt signaling plays in skin development, homeostasis, and disease.