Melanocyte lineage dynamics in development, growth and disease

Mgat4b-mediated selective N-glycosylation regulates melanocyte development and melanoma progression

Melanocyte development involves key pathways that are often recapitulated during melanoma initiation, highlighting the importance of understanding these regulatory processes. Our study identifies mgat4b, a glycosyl transferase involved in selective N-glycan branching enriched in pigment progenitors, as a regulator of directional cell migration and establishment of melanocyte stem cell (McSC) pool during early development. Single cell RNA (scRNA) sequencing analysis in zebrafish upon targeted disruption of mgat4b reveals, that migratory melanocyte progenitors marked by galectin expression fail to persist. Lectin affinity proteomic analysis reveals the glycosylation of key melanocyte proteins GPNMB, KIT, and TYRP1 to be under the control of MGAT4B in melanocytic cells. Additionally, mislocalization of Junctional plakoglobin (JUP) explains the observed defects in cell adhesion and migration to be regulated by MGAT4B but not its isozyme MGAT4A. Our meta-analysis further reveals that melanoma patients with both the BRAFV600E mutation and elevated MGAT4B levels have significantly worse survival outcomes compared to those with only the BRAFV600E mutation. By leveraging the zebrafish MAZERATI platform to model BRAFV600E driver mutation in vivo, we show that mgat4b mutant cells fail to aggregate and initiate tumors. RNA profiling of the transformed melanocytes revealed cell-cell junction, adhesion, and ECM binding to be probable contributing factors that resulted in the failure of tumor onset. Using a small-molecule inhibitor we demonstrate that complex N-glycosylation inhibits early-stage melanoma progression. Our study underscores the importance of selective N-glycan branching in both melanocyte development and melanoma initiation, suggesting MGAT4B as a promising therapeutic target for melanoma treatment.

Deciphering the Transcriptomic Complexity of Yak Skin Across Different Ages and Body Sites

Differences in skin and hair phenotypes between the scapular and ventral regions of yaks (Bos grunniens) are obvious and become more prominent with age. However, the genetic mechanism that causes differences in yak skin at different ages has not been reported. In this study, we investigated the transcriptomic profile of yak skin across different ages (0.5 years, 2.5 years, and 4.5 years) and body sites (scapular and ventral regions). Differential gene expression analysis was initially conducted to explore the transcriptomic differences in skin at different ages and different body sites. Subsequently, weighted gene co-expression network analysis (WGCNA) was employed to analyze the transcriptomic data comprehensively. The results showed that, among all comparison groups, the Y2.5_S vs. Y2.5_V group (regional comparison) exhibited the highest number of DEGs, with 491 genes (179 upregulated and 312 downregulated), followed by the Y2.5_V vs. Y0.5_V group (age comparison), which had 370 DEGs (103 upregulated and 267 downregulated). DEGs such as IGF2BP3, ADCY8, FOSL1, and S100A8 were found in all comparison groups of different ages, and multiple members of the HOX gene family including HOXC10, HOXA9, HOXA6, HOXB9, and HOXB6 were differentially expressed in comparison groups at different sites. Functional enrichment analysis showed that there were more obvious differences in immune function between different ages of skin and more obvious differences in endocrine function between different parts of skin. WGCNA revealed that genes related with immunity such as GLYATL2, ACSL5, and SPDEF were the core genes of the co-expression module associated with the scapula region, and multiple genes related to hair follicle development such as FOXN1, OVOL1, DLX3, HOXC13, and TCHH were found to be the hub genes of the co-expression module associated with the ventral region. Overall, our study provides valuable insights into the transcriptomic complexity of yak skin across different ages and body sites. The differential gene expression patterns and co-expression network modules identified in this study lay the foundation for further research on skin biology and adaptation mechanisms in yaks.

Dominant Negative Mitf Allele Impacts Melanophore and Xanthophore Development and Reveals Collaborative Interactions With Tfec in Zebrafish Chromatophore Lineages

Ectothermic vertebrates exhibit a diverse array of pigment cell types-chromatophores-that provide valuable opportunities to uncover mechanisms of fate specification and how they evolve. Like melanocytes of mammals, the melanophores of teleosts and other ectotherms depend on basic helix-loop-helix leucine zipper transcription factors encoded by orthologues of MITF. A different chromatophore, the iridescent iridophore, depends on the closely related transcription factor Tfec. Requirements for the specification of other chromatophore lineages remain largely uncertain. Here we identify a new allele of the zebrafish Mitf gene, mitfa, that results in a complete absence of not only melanophores but also yellow-orange xanthophores. Harboring a missense substitution in the DNA-binding domain identical to previously isolated alleles of mouse, we show that this new allele has defects in chromatophore precursor survival and xanthophore differentiation that extend beyond those of mitfa loss-of-function. Additional genetic analyses revealed interactions between Mitfa and Tfec as a likely basis for the observed phenotypes. Our findings point to collaborative roles for Mitfa and Tfec in promoting chromatophore development, particularly in xanthophore lineages, and provide new insights into evolutionary aspects of MITF functions across vertebrates.

Agouti and BMP signaling drive a naturally occurring fate conversion of melanophores to leucophores in zebrafish

The often-distinctive pigment patterns of vertebrates are varied in form and function and depend on several types of pigment cells derived from embryonic neural crest or latent stem cells of neural crest origin. These cells and the patterns they produce have been useful for uncovering features of differentiation and morphogenesis that underlie adult phenotypes, and they offer opportunities to discover how patterns and the cell types themselves have diversified. In zebrafish, a body pattern of stripes arises by self-organizing interactions among three types of pigment cells. Yet these fish also exhibit white ornamentation on their fins that depends on the transdifferentiation of black melanophores to white cells, "melanoleucophores." To identify mechanisms underlying this conversion we used ultrastructural, transcriptomic, mutational, and other approaches. We show that melanophore-melanoleucophore transition depends on regional BMP signals transduced through noncanonical receptors (Rgmb-Neo1a-Lrig2) as well as BMP-dependent signaling by Agouti genes, asip1 and asip2b. These signals lead to expression of transcription factor genes including foxd3 and runx3 that are necessary to induce loss of melanin, curtail new melanin production, and deploy a pathway for accumulating guanine crystals that, together, confer a white phenotype. These analyses uncover an important role for positional information in specifying ornamentation in zebrafish and show how tissue environmental cues and an altered gene regulatory program have allowed terminal addition of a distinct phenotype to a preexisting cell type.

Evodiamine inhibits programmed cell death ligand 1 expression via the PI3K/AKT signaling pathway to regulate antitumor immunity in melanoma

Malignant melanoma, a rare and aggressive skin cancer, arises from the transformation of cutaneous melanocytes and is associated with a poor prognosis. Evodiamine (EVO), a bioactive compound derived from traditional Chinese herbal medicine, has demonstrated significant inhibitory effects on various tumor cells. In this study, we aimed to investigate the potential of EVO in regulating melanoma immunity and elucidate its underlying mechanisms. Experimental results revealed that the IC50 value of EVO in B16-F10 cells for 24, 48, and 72 h were 11.73, 5.083, and 4.604 µM, respectively. EVO inhibited the proliferation, invasion, and metastasis of B16-F10 cells by more than 50%, while promoting apoptosis of higher concentration of EVO. EVO also significantly suppressed tumor growth by more than 80% and reduced spleen damage in tumor-bearing mice. Treatment with EVO led to a marked increase in T-cell subsets in the spleen, bone marrow, and tumors, with immunohistochemical (IHC) staining in particular showing about 50% higher. Furthermore, EVO inhibited the expression of programmed cell death ligand 1 (PD-L1) and the PI3K/AKT signaling pathway-related proteins in both B16-F10 cells and tumors. These findings suggest that EVO exerts antitumor effects by enhancing the tumor immune microenvironment and indicates its potential as a therapeutic agent for melanoma.

Somatic mutations distinguish melanocyte subpopulations in human skin

To better understand the homeostatic mechanisms governing melanocytes, we performed deep phenotyping of clonal expansions of single melanocytes from human skin. In total, we interrogated the mutational landscapes, gene expression profiles, and morphological features of 297 melanocytes from 31 donors. To our surprise, a population of melanocytes with low mutation burden was maintained in sun damaged skin. These melanocytes were more stem-like, smaller, less dendritic and displayed distinct gene expression profiles compared to their counterparts with high mutation burdens. We used single-cell spatial transcriptomics (10X Xenium) to reveal the spatial distribution of melanocytes inferred to have low and high mutation burdens (LowMut and HighMut cells), based on their gene expression profiles. LowMut melanocytes were found in hair follicles as well as in the interfollicular epidermis, whereas HighMut melanocytes resided almost exclusively in the interfollicular epidermis. We propose that melanocytes in the hair follicle occupy a privileged niche, protected from UV radiation, but periodically migrate out of the hair follicle to replenish the interfollicular epidermis after waves of photodamage. More broadly, our study illustrates the advantages of a cell atlas that includes mutational information, as cells can change their cellular states and positional coordinates over time, but mutations are like scars, providing a historical record of the homeostatic processes that were operative on each cell.

The Impact of Mutant EDNRB on the Two-End Black Coat Color Phenotype in Chinese Local Pigs

Endothelin Receptor Type B (EDNRB) is expressed in a variety of cells during embryonic stage, including melanocyte precursors cells. Our previous studies found that 11 bp deletion of EDNRB caused the two-end black (TEB) coat color in Chinese pigs. In this study, we aimed to explore the mutant EDNRB on the formation of TEB coat color in Chinese pigs. We constructed recombinant plasmid for wild and mutant EDNRB and EDN1, respectively, and transfected the recombinant plasmid into mouse B16 melanoma cells in groups. Real-time fluorescent quantitative PCR (RT-qPCR) was performed to detect expression of genes that participate in melanin pathway, including PLCγ, Raf, MITF. Comparing to the wild-type EDNRB cells, expression of the three genes in the cell line expressing mutant EDNRB cells was significantly reduced. We measured the melanin content produced by transfected recombinant granulocytes of wild and mutant EDNRB and found that the amount of melanin in mutant EDNRB cells was significantly lower than that of the wild. Wound-healing assay confirmed that the migration and mobility rate of mutant EDNRB cells were significantly lower than the wild. Co-immunoprecipitation further confirmed that mutant EDNRB could not interact with the EDN1 protein. In conclusion, this study revealed that the 11 bp deletion of EDNRB reduced the melanin production, which may be caused by inhibiting the expression of PLCγ, Raf, and MITF. The mutant EDNRB reduced melanocyte migration and could not interact with the EDN1 protein. We explored the effect of mutant EDNRB in Chinese pigs with TEB coat color, and the results provided a reference for exploring molecular mechanism of mutant EDNRB on the formation of TEB coat color pigs.

High frequency of melanoma in cdkn2b-/- /tp53-/- Xenopus tropicalis

Rationale: Melanoma, the deadliest form of skin cancer characterized by high therapy resistance, has undergone extensive investigation through the utilization of BRAFV600E-driven melanoma animal models. However, there exists a paucity of animal models for the rare hereditary melanoma resulting from germline CDKN2A mutations. Methods: Here, employing CRISPR/Cas9 technology, we generated cdkn2b-/-/tp53-/- Xenopus tropicalis on a tp53 knockout background to model human CDKN2A germline mutation-induced hereditary melanoma. Results: The findings unveiled that cdkn2b-/-/tp53-/- frogs spontaneously developed melanoma, pancreatic cancer, and other tumors. Specifically, these frogs exhibited a high penetrance of spontaneous melanoma, sharing characteristics with melanomas in human hereditary melanoma caused by germline CDKN2A mutations. During melanoma development in cdkn2b-/-/tp53-/- frogs, the occurrences of epithelial-to-mesenchymal transition, the reactivation of pigment cell progenitor cell transcriptional states, and the activation in the MAPK, NF-kB, PI3K-Akt, and TGF-β signaling pathways were noted. Conclusions: Overall, cdkn2b-/-/tp53-/- Xenopus tropicalis provides a vertebrate model for investigating the development of CDKN2A germline mutation-induced hereditary melanoma, contributing to the exploration of the pathogenesis of hereditary melanoma in humans.

Amelanotic Melanoma-Biochemical and Molecular Induction Pathways

Amelanotic melanoma (AM) is a subtype of hypomelanotic or completely amelanotic melanoma. AM is a rare subtype of melanoma that exhibits a higher recurrence rate and aggressiveness as well as worse surveillance than typical melanoma. AM shows a dysregulation of melanin production, cell cycle control, and apoptosis pathways. Knowing these pathways has an application in medicine due to targeted therapies based on the inhibiting elements of the abovementioned pathways. Therefore, we summarized and discussed AM biochemical and molecular induction pathways and personalized medicine approaches, clinical management, and future directions due to the fact that AM is relatively rare. AM is commonly misdiagnosed. Hence, the role of biomarkers is becoming significant. Nonetheless, there is a shortage of biomarkers specific to AM. BRAF, NRAS, and c-KIT genes are the main targets of therapy. However, the role of BRAF and KIT in AM varied among studies. BRAF inhibitors combined with MAK inhibitors demonstrate better results. Immune checkpoint inhibitors targeting CTLA-4 combined with a programmed death receptor 1 (PD-1) show better outcomes than separately. Fecal microbiota transplantation may overcome resistance to immune checkpoint therapy of AM. Immune-modulatory vaccines against indoleamine 2,3-dioxygenase (IDO) and PD ligand (PD-L1) combined with nivolumab may be efficient in melanoma treatment.