PAX3 expression in normal skin melanocytes and melanocytic lesions (naevi and melanomas)

CD146, a therapeutic target involved in cell plasticity

Since its identification as a marker for advanced melanoma in the 1980s, CD146 has been found to have multiple functions in both physiological and pathological processes, including embryonic development, tissue repair and regeneration, tumor progression, fibrosis disease, and inflammations. Subsequent research has revealed that CD146 is involved in various signaling pathways as a receptor or co-receptor in these processes. This correlation between CD146 and multiple diseases has sparked interest in its potential applications in diagnosis, prognosis, and targeted therapy. To better comprehend the versatile roles of CD146, we have summarized its research history and synthesized findings from numerous reports, proposing that cell plasticity serves as the underlying mechanism through which CD146 contributes to development, regeneration, and various diseases. Targeting CD146 would consequently halt cell state shifting during the onset and progression of these related diseases. Therefore, the development of therapy targeting CD146 holds significant practical value.

Exosomes Derived from Hypertrophic Scar Fibroblasts Suppress Melanogenesis in Normal Human Epidermal Melanocytes

Post-burn hypertrophic scars often exhibit abnormal pigmentation. Exosomes play important roles in maintaining normal physiological homeostasis and in the pathological development of diseases. This study investigated the effects of the exosomes derived from hypertrophic scar fibroblasts (HTSFs) on melanocytes, which are pigment-producing cells. Normal fibroblasts (NFs) and HTSFs were isolated and cultured from normal skin and hypertrophic scar (HTS) tissue. Both the NF- and HTSF-exosomes were isolated from a cell culture medium and purified using a column-based technique. The normal human epidermal melanocytes were treated with both exosomes at a concentration of 100 μg/mL at different times. The cell proliferation, melanin content in the medium, apoptotic factors, transcription factors, melanin synthesis enzymes, signaling, signal transduction pathways, and activators of transcription factors (STAT) 1, 3, 5, and 6 were investigated. Compared with the Dulbecco's phosphate-buffered saline (DPBS)-treated controls and NF-exosomes, the HTSF-exosomes decreased the melanocyte proliferation and melanin secretion. The molecular patterns of apoptosis, proliferation, melanin synthesis, Smad and non-Smad signaling, and STATs were altered by the treatment with the HTSF-exosomes. No significant differences were observed between the DPBS-treated control and NF-exosome-treated cells. HTSF-derived exosomes may play a role in the pathological epidermal hypopigmentation observed in patients with HTS.

Gene expression profiles of skin from cyclin dependent kinases 5-knockdown mice

OBJECTIVE

This study aimed to identify genes regulated by cyclin dependent kinases 5 (CDK5) that participate in hair pigmentation in mice.

METHODS

The mRNA expression profiles of skin samples from CDK5-knockdown mice were constructed using high-throughput RNA sequencing and compared with those of wild-type mice.

RESULTS

In total, 8,002 known genes were differentially expressed between CDK5-knockdown and wild-type mice. Of these, 3,658 were upregulated and 4,344 were downregulated in the skin of CDK5-knockdown mice. An additional 318 previously unknown genes were also differentially expressed, with 171 downregulated and 147 upregulated genes in the skin of CDK5-knockdown mice. Of the known genes expressed in mouse skin, 80 were associated with hair color, with 61 showing lower expression and 19 exhibiting higher expression in skin of CDK5-knockdown mice. Importantly, the expression of the tyrosinase-related protein 1 (TYRP1) and the calcium signaling pathway were also found to be regulated by CDK5, suggesting that pigmentation is regulated by CDK5 via the calcium signaling pathway and TYRP1.

CONCLUSION

The transcriptome profiles obtained from the skin of CDK5-knockdown mice compared to wild-type mice provide a valuable resource to help understand the mechanism by which CDK5 regulates melanogenesis in mice and other animals.

Characterization and functional analysis of pax3 in body color transition of polychromatic Midas cichlids (Amphilophus citrinellus)

As the representative genetic and economic trait of ornamental fish, skin color has a strong impact on speciation and adaptation. However, the genetic basis of skin color pigmentation, differentiation and change is still not understood. The Midas cichlid fish with three typical body color transition stages of "black-gray‑gold" is an ideal model system for investigating the formation and change of fish body color. In this study, to investigate the regulatory role of the pair box 3 (pax3) gene in the early body color fading process of Midas cichlids, the complete cDNA sequence (3513 bp) of pax3 was successfully isolated from Midas cichlids (Amphilophus Citrinellus), and found to encode polypeptides of 491 amino acids. Expression patterns of the pax3 gene in tissues of Midas cichlids during different periods, including embryonic development and body color fading stages were detected by quantitative real-time PCR. The qRT-PCR analysis showed that pax3 was expressed in all tissues of adult fish, with a higher expression level in muscle and skin. The highest expression level in muscle tissue was significantly higher than that in other tissues (P < 0.05). During embryonic development, the expression tendency of pax3 was first increased and then decreased. In the three typical stages of early skin color fading from black to gold, pax3 expression in skin, caudal fin and scales all showed a downward trend. The expression level in the black stage was significantly higher than that in other stages (P < 0.05). Positive signal of pax3 protein was detected in the three typical skin color conversion stages, and the highest positive signal intensity was detected in the black stage, which was consistent with qRT-PCR results. After pax3 RNA interference, pax3 and the downstream genes mitf and tyr all decreased, while dct mRNA expression increased in the skin of fish. Western blotting also showed a decrease in pax3 protein concentration. Those results suggest that pax3 plays an important role in skin color formation, distribution and change in Midas cichlids through the melanogenesis pathway.

Human cutaneous interfollicular melanocytes differentiate temporarily under genotoxic stress

DNA-damage response of cutaneous interfollicular melanocytes to fractionated radiotherapy was investigated by immunostaining of tissue sections from punch biopsies collected before, during, and after the treatment of patients for breast cancer. Our clinical assay with sterilized hair follicles, excluded the migration of immature melanocytes from the bulge, and highlighted interfollicular melanocytes as an autonomous self-renewing population. About thirty percent are immature. Surrounding keratinocytes induced and maintained melanocyte differentiation as long as treatment was ongoing. Concomitant with differentiation, melanocytes were protected from apoptosis by transient upregulation of Bcl-2 and CXCR2. CXCR2 upregulation also indicated the instigation of premature senescence, preventing proliferation. The stem cell factor BMI1 was constitutively expressed exclusively in interfollicular melanocytes and further upregulated upon irradiation. BMI1 prevents apoptosis, terminal differentiation, and premature senescence, allowing dedifferentiation post-treatment, by suppressing the p53/p21-and p16-mediated response and upregulating CXCR2 to genotoxic damage. The pre-treatment immature subset of interfollicular melanocytes was restored after the exposure ended.

Downregulation of the paired box gene 3 inhibits the progression of skin cutaneous melanoma by inhibiting c-MET tyrosine kinase : PAX3 downregulation inhibits melanoma progression

BACKGROUND

The PAX3 (paired box gene 3) gene is highly expressed in several cancer types. However, its underlying mechanism of action in skin cutaneous melanoma (SKCM) remains unknown.

METHODS

In this study, we used the GEPIA database and western blotting to analyze the expression of PAX3. We performed the Kaplan-Meier survival analysis to evaluate the prognostic value of PAX3 in SKCM. Next, the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis was performed to evaluate the function of PAX3-related co-expressed genes. Additionally, the function and potential mechanism of action of PAX3 in SKCM were studied through functional experiments. Western blotting was used to detect the changes in the levels of epithelial-mesenchymal transition (EMT)-related and MET (c-MET tyrosine kinase) proteins following PAX3 knockdown. Finally, we assessed the correlation between PAX3 expression and the infiltration of CD4⁺/CD8⁺ T cells using the TISIDB database.

RESULTS

We found that PAX3 was overexpressed in the SKCM tissues and that these levels were indicative of a poor prognosis of SKCM. The KEGG pathway enrichment analysis showed that PAX3-related co-expressed genes were mainly associated with the oncogenic pathways. Knocking down PAX3 significantly inhibited the proliferation, invasion, and migration of SK-MEL-28 cells. The PAX3 expression was related significantly to the immune infiltration level of CD4⁺/CD8⁺ T cells.

CONCLUSIONS

Our findings demonstrated that PAX3 knockdown could reverse the EMT of tumor cells, inhibit the growth, and progression of SKCM cells. Therefore, PAX3 may have implications as a potential therapeutic target and promising prognostic biomarker for SKCM.

Molecular characterization of Pax7 and its role in melanin synthesis in Crassostrea gigas

The paired-box 7 (Pax7) is a transcription factor crucial for skin color polymorphism. However, the mechanism underlying the pigmentation associated with Pax7 in mollusks have yet to be elucidated. In this study, the cDNA sequence of Pax7 in the Pacific oyster Crassostrea gigas (CgPax7) was characterized. Phylogenetically, the identity of deduced amino acid sequence was similar to that of other mollusks and contained 463 amino acids, with conserved features of paired domain (PRD), homeobox domain (HD) and octapeptide. Gene expression analysis revealed that CgPax7 was markedly increased at D-shaped larvae stage and ubiquitously expressed in six examined tissues in adult oyster. The result of whole-mount in situ hybridization (WMISH) showed a restricted pattern of CgPax7 expression on margins of shell valves at D-shaped and umbo larvae stages. Additionally, although CgPax7 silencing had no significant effect on CgMitf expression, it significantly inhibited the expressions of CgPax7, CgTyr, CgTyrp1, CgTyrp2 and CgCdk2, genes involved in Tyr-mediated melanin synthesis. Furthermore, CgPax7 knockdown obviously decreased the tyrosinase activity. Less brown-granules at mantle edge was detected by micrographic examination and melanosomes defect was observed by transmission electron microscopy. It was demonstrated that CgPax7 play a key role in melanin synthesis by regulating Tyr-pathway in C. gigas. These findings indicated the potential framework by which mollusks pigmentation.

Adding Perplexity to Rarity: Diffuse S100-Protein and SOX10 Expression in a Molecularly Confirmed PAX7-Positive Primary Cutaneous Ewing Sarcoma

ABSTRACT

Primary cutaneous Ewing sarcoma (EWS) is a very rare neoplasm that shares similar morphologic, immunohistochemical, and molecular features with its osseous counterpart. Herein, we present an extraordinarily rare case of PAX7-positive cutaneous EWS in a 9-year-old girl that was also diffusely positive for SOX10 and S100-protein. Next generation sequencing detected the EWSR1-FLI1 fusion supporting the diagnosis, which was further validated by break-apart EWSR1 fluorescence in situ hybridization. Diffuse S100-protein and SOX10 expression has been reported only in a handful of cases of EWS and may pose significant diagnostic challenges for dermatopathologists. PAX7 is a recently introduced marker, which is highly sensitive for EWS and can potentially have discriminatory power in the differential diagnosis of cutaneous undifferentiated round blue cell tumors.

Detection and prognostic role of heterogeneous populations of melanoma circulating tumour cells

BACKGROUND

Circulating tumour cells (CTCs) can be assessed through a minimally invasive blood sample with potential utility as a predictive, prognostic and pharmacodynamic biomarker. The large heterogeneity of melanoma CTCs has hindered their detection and clinical application.

METHODS

Here we compared two microfluidic devices for the recovery of circulating melanoma cells. The presence of CTCs in 43 blood samples from patients with metastatic melanoma was evaluated using a combination of immunocytochemistry and transcript analyses of five genes by RT-PCR and 19 genes by droplet digital PCR (ddPCR), whereby a CTC score was calculated. Circulating tumour DNA (ctDNA) from the same patient blood sample, was assessed by ddPCR targeting tumour-specific mutations.

RESULTS

Our analysis revealed an extraordinary heterogeneity amongst melanoma CTCs, with multiple non-overlapping subpopulations. CTC detection using our multimarker approach was associated with shorter overall and progression-free survival. Finally, we found that CTC scores correlated with plasma ctDNA concentrations and had similar pharmacodynamic changes upon treatment initiation.

CONCLUSIONS

Despite the high phenotypic and molecular heterogeneity of melanoma CTCs, multimarker derived CTC scores could serve as viable tools for prognostication and treatment response monitoring in patients with metastatic melanoma.

Cell cycle regulatory markers in melanoma: New strategies in diagnosis and treatment

Background: Melanoma has been known as an aggressive type of skin cancer in recent years. Reports have distributed the spread rate of melanoma among white skin populations. Also, many studies have mentioned several causes of melanoma. Ultraviolet radiation was represented to be the most important reason for occurrence of melanoma. However, recent studies have found that a combination of factors, such as environmental and genetic factors, can contribute to occurrence of various cancers, specifically melanoma.

Methods: Different studies have been conducted on the efficacy of genetic disorders in melanoma. These surveys marked the key role of specific biomarkers in molecular and cellular processes, and investigations have found the expression of several genes in these processes. In addition, aberrant expression of these genes due to mutation and methylation can affect the whole process.

Results: The expression process of these genes is regulated by microRNAs. These new biomolecules have been considered as negative regulators because of managing molecular and cellular processes. MicroRNAs are small conserved regulators attached to their targets leading to rearrangement of gene expression. Adherence of these noncoding RNAs can cause mRNA degradation or inhibit its translation.

Conclusion: Recently, the application of specific genes in melanoma has been studied. In this review, the way melanoma is regulated because of these biomarkers and their demand through cell cycle in diagnosis, prognosis, and therapeutic periods was considered. Keywords: Melanoma, Biomarkers, Cell cycle, Biomolecules

Cardiomyocyte dedifferentiation and remodeling in 3D scaffolds to generate the cellular diversity of engineering cardiac tissues

The use of engineered cardiac tissues (ECTs) is a new strategy for the repair and replacement of cardiac tissues in patients with myocardial infarction, particularly at late stages. However, the mechanisms underlying the development of ECTs, including cell-scaffold interactions, are not fully understood, although they are closely related to their therapeutic effect. In the present study, we aimed to determine the cellular fate of cardiomyocytes in a 3D scaffold microenvironment, as well as their role in generating the cellular diversity of ECTs by single-cell sequencing analysis. Consistent with the observed plasticity of cardiomyocytes during cardiac regeneration, cardiomyocytes in 3D scaffolds appeared to dedifferentiate, showing an initial loss of normal cytoskeleton organization in the adaptive response to the new scaffold microenvironment. Cardiomyocytes undergoing this process regained their proliferation potential and gradually developed into myocardial cells at different developmental stages, generating heterogeneous regenerative ECTs. To better characterize the remodeled ECTs, high-throughput single-cell sequencing was performed. The ECTs contained a wide diversity of cells related to endogenous classes in the heart, including myocardial cells at different developmental stages and different kinds of interstitial cells. Non-cardiac cells seemed to play important roles in cardiac reconstruction, especially Cajal-like interstitial cells and macrophages. Altogether, our results showed for the first time that cells underwent adaptive dedifferentiation for survival in a 3D scaffold microenvironment to generate heterogeneous tissues. These findings provide an important basis for an improved understanding of the development and assembly of engineered tissues.

MITF-the first 25 years

In this review, Goding and Arnheiter present the current understanding of MITF's role and regulation in development and disease and highlight key areas where our knowledge of MITF regulation and function is limited.

All transcription factors are equal, but some are more equal than others. In the 25 yr since the gene encoding the microphthalmia-associated transcription factor (MITF) was first isolated, MITF has emerged as a key coordinator of many aspects of melanocyte and melanoma biology. Like all transcription factors, MITF binds to specific DNA sequences and up-regulates or down-regulates its target genes. What marks MITF as being remarkable among its peers is the sheer range of biological processes that it appears to coordinate. These include cell survival, differentiation, proliferation, invasion, senescence, metabolism, and DNA damage repair. In this article we present our current understanding of MITF's role and regulation in development and disease, as well as those of the MITF-related factors TFEB and TFE3, and highlight key areas where our knowledge of MITF regulation and function is limited.

PAX3 is a biomarker and prognostic factor in melanoma: Database mining

Paired box 3 (PAX3) is a transcription factor and critical regulator of pigment cell development during embryonic development. However, while there have been several studies on PAX3, its expression patterns and precise role remain to be clarified. The present study is an in-depth computational study of tumor-associated gene information, with specific emphasis on the expression of PAX3 in melanoma, using Oncomine along with an investigation of corresponding expression profiles in an array of cancer cell lines through Cancer Cell Line Encyclopedia analysis. Based on Kaplan-Meier analysis, the prognostic value of high PAX3 expression in tissues from patients with melanoma compared with normal tissues was assessed. PAX3 was more highly expressed in male patients with melanoma compared with female patients with melanoma. Using Oncomine and Coexpedia analysis, it was demonstrated that PAX3 expression was clearly associated with SRY-box 10 expression. The survival analysis results revealed that high PAX3 mRNA expression was associated with worse survival rates in patients with melanoma. These results suggested that PAX3 may be a biomarker and essential prognostic factor for melanoma, and provided an important theoretical basis for the development of melanoma treatments.

Identification of a Robust Methylation Classifier for Cutaneous Melanoma Diagnosis

Early diagnosis improves melanoma survival, yet the histopathological diagnosis of cutaneous primary melanoma can be challenging, even for expert dermatopathologists. Analysis of epigenetic alterations, such as DNA methylation, that occur in melanoma can aid in its early diagnosis. Using a genome-wide methylation screening, we assessed CpG methylation in a diverse set of 89 primary invasive melanomas, 73 nevi, and 41 melanocytic proliferations of uncertain malignant potential, classified based on interobserver review by dermatopathologists. Melanomas and nevi were split into training and validation sets. Predictive modeling in the training set using ElasticNet identified a 40-CpG classifier distinguishing 60 melanomas from 48 nevi. High diagnostic accuracy (area under the receiver operator characteristic curve = 0.996, sensitivity = 96.6%, and specificity = 100.0%) was independently confirmed in the validation set (29 melanomas, 25 nevi) and other published sample sets. The 40-CpG melanoma classifier included homeobox transcription factors and genes with roles in stem cell pluripotency or the nervous system. Application of the 40-CpG melanoma classifier to the diagnostically uncertain samples assigned melanoma or nevus status, potentially offering a diagnostic tool to assist dermatopathologists. In summary, the robust, accurate 40-CpG melanoma classifier offers a promising assay for improving primary melanoma diagnosis.

Pax3 Gene Regulated Melanin Synthesis by Tyrosinase Pathway in Pteria penguin

The paired-box 3 (Pax3) is a transcription factor and it plays an important part in melanin synthesis. In this study, a new Pax3 gene was identified from Pteria penguin (Röding, 1798) (P. penguin) by RACE-PCR (rapid-amplification of cDNA ends-polymerase chain reaction) and its effect on melanin synthesis was deliberated by RNA interference (RNAi). The cDNA of PpPax3 was 2250 bp long, containing an open reading fragment of 1365 bp encoding 455 amino acids. Amino acid alignment and phylogenetic tree showed PpPax3 shared the highest (69.2%) identity with Pax3 of Mizuhopecten yessoensis. Tissue expression profile showed that PpPax3 had the highest expression in mantle, a nacre-formation related tissue. The PpPax3 silencing significantly inhibited the expression of PpPax3, PpMitf, PpTyr and PpCdk2, genes involved in Tyr-mediated melanin synthesis, but had no effect on PpCreb2 and an increase effect on PpBcl2. Furthermore, the PpPax3 knockdown obviously decreased the tyrosinase activity, the total content of eumelanin and the proportion of PDCA (pyrrole-2,3-dicarboxylic acid) in eumelanin, consistent with influence of tyrosinase (Tyr) knockdown. These data indicated that PpPax3 played an important regulating role in melanin synthesis by Tyr pathway in P. penguin.

UV-Radiation Response Proteins Reveal Undifferentiated Cutaneous Interfollicular Melanocytes with Hyperradiosensitivity to Differentiation at 0.05 Gy Radiotherapy Dose Fractions

To date, the response activated in melanocytes by repeated genotoxic insults from radiotherapy has not been explored. We hypothesized that the molecular pathways involved in the response of melanocytes to ionizing radiation and ultraviolet radiation (UVR) are similar. Skin punch biopsies, not sun-exposed, were collected from prostate cancer patients before, as well as at 1 and 6.5 weeks after daily doses of 0.05-1.1 Gy. Interfollicular melanocytes were identified by ΔNp63- and eosin-periodic acid Schiff staining. Immunohistochemistry and immunofluorescence were performed to detect molecular markers of the melanocyte lineage. Melanocytes were negative for ΔNp63, and the number remained unchanged over the treatment period. At radiation doses as low as 0.05 Gy, melanocytes express higher protein levels of microphthalmia-associated transcription factor (MITF) and Bcl-2. Subsets of MITF- and Bcl-2-negative melanocytes were identified among interfollicular melanocytes in unexposed skin; the cell number in both subsets was reduced after irradiation in a way that indicates low-dose hyperradiosensitivity. A corresponding increase in MITF- and Bcl-2-positive cells was observed. PAX3 and SOX10 co-localized to some extent with MITF in unexposed skin, more so with radiation exposure. Low doses of ionizing radiation also intensified c-KIT and DCT staining. Nuclear p53 and p21 were undetectable in melanocytes. Apoptosis and proliferation could not be observed. In conclusion, undifferentiated interfollicular melanocytes were identified, and responded with differentiation in a hypersensitive manner at 0.05 Gy doses. Radioresistance regarding cell death was maintained up to fractionated doses of 1.1 Gy, applied for 7 weeks. The results suggest that the initial steps of melanin synthesis are common to ionizing radiation and UVR, and underline the importance of keratinocyte-melanocyte interaction behind hyperpigmentation and depigmentation to radiotherapy.

Downregulation of α-Melanocyte-Stimulating Hormone-Induced Activation of the Pax3-MITF-Tyrosinase Axis by Sorghum Ethanolic Extract in B16F10 Melanoma Cells

Ultraviolet irradiation-induced hyperpigmentation of the skin is associated with excessive melanin production in melanocytes. Tyrosinase (TYR) is a key enzyme catalyzing the rate-limiting step in melanogenesis. TYR expression is controlled by microphthalmia-associated transcription factor (MITF) expression. Sorghum is a cereal crop widely used in a variety of foods worldwide. Sorghum contains many bioactive compounds and is beneficial to human health. However, the effects of sorghum in anti-melanogenesis have not been well characterized. In this study, the biological activity of sorghum ethanolic extract (SEE) on α-melanocyte-stimulating hormone (α-MSH)-induced TYR expression was evaluated in B16F10 melanoma cells. SEE attenuated α-MSH-induced TYR gene promoter activity through the downregulation of the transcription factor MITF. We found that paired box gene 3 (Pax3) contributes to the maximal induction of MITF gene promoter activity. Further analysis demonstrated that SEE inhibited α-MSH-induced Pax3 expression. The collective results indicate that SEE attenuates α-MSH-induced TYR expression through the suppression of Pax3-mediated MITF gene promoter activity. Targeting the Pax3-MITF axis pathway could be considered a potential strategy to increase the efficacy of anti-melanogenesis.

Isolation and detection of circulating tumour cells from metastatic melanoma patients using a slanted spiral microfluidic device

Circulating Tumour Cells (CTCs) are promising cancer biomarkers. Several methods have been developed to isolate CTCs from blood samples. However, the isolation of melanoma CTCs is very challenging as a result of their extraordinary heterogeneity, which has hindered their biological and clinical study. Thus, methods that isolate CTCs based on their physical properties, rather than surface marker expression, such as microfluidic devices, are greatly needed in melanoma. Here, we assessed the ability of the slanted spiral microfluidic device to isolate melanoma CTCs via label-free enrichment. We demonstrated that this device yields recovery rates of spiked melanoma cells of over 80% and 55%, after one or two rounds of enrichment, respectively. Concurrently, a two to three log reduction of white blood cells was achieved with one or two rounds of enrichment, respectively. We characterised the isolated CTCs using multimarker flow cytometry, immunocytochemistry and gene expression. The results demonstrated that CTCs from metastatic melanoma patients were highly heterogeneous and commonly expressed stem-like markers such as PAX3 and ABCB5. The implementation of the slanted microfluidic device for melanoma CTC isolation enables further understanding of the biology of melanoma metastasis for biomarker development and to inform future treatment approaches.

Targeting protein kinase-b3 (akt3) signaling in melanoma

INTRODUCTION

Deregulated Akt activity leading to apoptosis inhibition, enhanced proliferation and drug resistance has been shown to be responsible for 35-70% of advanced metastatic melanomas. Of the three isoforms, the majority of melanomas have elevated Akt3 expression and activity. Hence, potent inhibitors targeting Akt are urgently required, which is possible only if (a) the factors responsible for the failure of Akt inhibitors in clinical trials is known; and (b) the information pertaining to synergistically acting targeted therapeutics is available. Areas covered: This review provides a brief introduction of the PI3K-Akt signaling pathway and its role in melanoma development. In addition, the functional role of key Akt pathway members such as PRAS40, GSK3 kinases, WEE1 kinase in melanoma development are discussed together with strategies to modulate these targets. Efficacy and safety of Akt inhibitors is also discussed. Finally, the mechanism(s) through which Akt leads to drug resistance is discussed in this expert opinion review. Expert opinion: Even though Akt play key roles in melanoma tumor progression, cell survival and drug resistance, many gaps still exist that require further understanding of Akt functions, especially in the (a) metastatic spread; (b) circulating melanoma cells survival; and

Trends in Regenerative Medicine: Repigmentation in Vitiligo Through Melanocyte Stem Cell Mobilization

Vitiligo is the most frequent human pigmentary disorder, characterized by progressive autoimmune destruction of mature epidermal melanocytes. Of the current treatments offering partial and temporary relief, ultraviolet (UV) light is the most effective, coordinating an intricate network of keratinocyte and melanocyte factors that control numerous cellular and molecular signaling pathways. This UV-activated process is a classic example of regenerative medicine, inducing functional melanocyte stem cell populations in the hair follicle to divide, migrate, and differentiate into mature melanocytes that regenerate the epidermis through a complex process involving melanocytes and other cell lineages in the skin. Using an in-depth correlative analysis of multiple experimental and clinical data sets, we generated a modern molecular research platform that can be used as a working model for further research of vitiligo repigmentation. Our analysis emphasizes the active participation of defined molecular pathways that regulate the balance between stemness and differentiation states of melanocytes and keratinocytes: p53 and its downstream effectors controlling melanogenesis; Wnt/β-catenin with proliferative, migratory, and differentiation roles in different pigmentation systems; integrins, cadherins, tetraspanins, and metalloproteinases, with promigratory effects on melanocytes; TGF-β and its effector PAX3, which control differentiation. Our long-term goal is to design pharmacological compounds that can specifically activate melanocyte precursors in the hair follicle in order to obtain faster, better, and durable repigmentation.

Single-Cell Resolution of Temporal Gene Expression during Heart Development

Activation of complex molecular programs in specific cell lineages governs mammalian heart development, from a primordial linear tube to a four-chamber organ. To characterize lineage-specific, spatiotemporal developmental programs, we performed single-cell RNA sequencing of >1,200 murine cells isolated at seven time points spanning embryonic day 9.5 (primordial heart tube) to postnatal day 21 (mature heart). Using unbiased transcriptional data, we classified cardiomyocytes, endothelial cells, and fibroblast-enriched cells, thus identifying markers for temporal and chamber-specific developmental programs. By harnessing these datasets, we defined developmental ages of human and mouse pluripotent stem-cell-derived cardiomyocytes and characterized lineage-specific maturation defects in hearts of mice with heterozygous mutations in Nkx2.5 that cause human heart malformations. This spatiotemporal transcriptome analysis of heart development reveals lineage-specific gene programs underlying normal cardiac development and congenital heart disease.

Non-coding RNAs in skin cancers: An update

Skin cancers are the most common form of cancer in humans. They can largely be categorized into Melanoma and Non-melanoma skin cancers. The latter mainly includes Squamous Cell Carcinoma (SCC) and Basal Cell Carcinoma (BCC), and have a higher incidence than melanomas. There has been a recent emergence of interest in the role of non-coding RNA's in pathogenesis of skin cancers. The transcripts which lack any protein coding capacity are called non-coding RNA. These non-coding RNA are further classified based on their length; small non-coding RNA (<200 nucleotides) and long non-coding RNA (>200 nucleotides). ncRNA They are involved at multiple transcriptional, post transcriptional and epigenetic levels, modulating cell proliferation, angiogenesis, senescence and apoptosis. Their expression pattern has also been linked to metastases, drug resistance and long term prognosis. They have both diagnostic and prognostic significance for skin cancers, and can also be a target for future therapies for cutaneous malignancies. More research is needed to further utilize their potential as therapeutic targets.

Biphenotypic sinonasal sarcoma: an expanded immunoprofile including consistent nuclear β-catenin positivity and absence of SOX10 expression

Biphenotypic sinonasal sarcoma (BSNS) is a recently recognized low-grade sarcoma that exhibits both neural and myogenic differentiation. This unique dual phenotype stems from recurrent rearrangements in PAX3, a transcription factor that promotes commitment along both lineages. While identification of PAX3 rearrangements by fluorescence in situ hybridization (FISH) can confirm a BSNS diagnosis, this assay is not widely available. This study evaluates whether an expanded immunohistochemical panel can facilitate recognition of BSNS without molecular analysis. Eleven cases of BSNS were identified from the surgical pathology archives of two academic medical centers. In 8 cases, the diagnosis was confirmed by FISH using custom probes for PAX3. In 3 cases, FISH failed but histologic and immunophenotypic findings were diagnostic for BSNS. All 11 BSNS (100%) were at least focally positive for S100 as well as calponin and/or smooth muscle actin. In addition, 10 (91%) of 11 expressed nuclear β-catenin, 8 (80%) of 10 expressed factor XIIIa, 4 (36%) of 11 expressed desmin, and 3 (30%) of 10 expressed myogenin. All 11 tumors were negative for SOX10. While no single marker resolves immunohistochemical overlap between BSNS and its histologic mimickers such as nerve sheath tumors, an extended immunohistochemical panel that includes β-catenin and SOX10 helps to support the diagnosis of BSNS without the need for gene rearrangement studies.

Mechanisms contributing to differential regulation of PAX3 downstream target genes in normal human epidermal melanocytes versus melanoma cells

Melanoma is a highly aggressive and drug resistant form of skin cancer. It arises from melanocytes, the pigment producing cells of the skin. The formation of these melanocytes is driven by the transcription factor PAX3 early during embryonic development. As a result of alternative splicing, the PAX3 gene gives rise to eight different transcripts which encode isoforms that have different structures and activate different downstream target genes involved in pathways of cell proliferation, migration, differentiation and survival. Furthermore, post-translational modifications have also been shown to alter the functions of PAX3. We previously identified PAX3 downstream target genes in melanocytes and melanoma cells. Here we assessed the effects of PAX3 down-regulation on this panel of target genes in primary melanocytes versus melanoma cells. We show that PAX3 differentially regulates various downstream target genes involved in cell proliferation in melanoma cells compared to melanocytes. To determine mechanisms behind this differential downstream target gene regulation, we performed immunoprecipitation to assess post-translational modifications of the PAX3 protein as well as RNAseq to determine PAX3 transcript expression profiles in melanocytes compared to melanoma cells. Although PAX3 was found to be post-translationally modified, there was no qualitative difference in phosphorylation and ubiquitination between melanocytes and melanoma cells, while acetylation of PAX3 was reduced in melanoma cells. Additionally, there were differences in PAX3 transcript expression profiles between melanocytes and melanoma cells. In particular the PAX3E transcript, responsible for reducing melanocyte proliferation and increasing apoptosis, was found to be down-regulated in melanoma cells compared to melanocytes. These results suggest that alternate transcript expression profiles activate different downstream target genes leading to the melanoma phenotype.

Narrow Band Ultraviolet B Treatment for Human Vitiligo Is Associated with Proliferation, Migration, and Differentiation of Melanocyte Precursors

In vitiligo, the autoimmune destruction of epidermal melanocytes produces white spots that can be repigmented by melanocyte precursors from the hair follicles, following stimulation with UV light. We examined by immunofluorescence the distribution of melanocyte markers (C-KIT, DCT, PAX3, and TYR) coupled with markers of proliferation (KI-67) and migration (MCAM) in precursors and mature melanocytes from the hair follicle and the epidermis of untreated and narrow band UVB (NBUVB)-treated human vitiligo skin. NBUVB was associated with a significant increase in the number of melanocytes in the infundibulum and with restoration of the normal melanocyte population in the epidermis, which was lacking in the untreated vitiligo. We identified several precursor populations (melanocyte stem cells, melanoblasts, and other immature phenotypes), and progressively differentiating melanocytes, some with putative migratory and/or proliferative abilities. The primary melanocyte germ was present in the untreated and treated hair follicle bulge, whereas a possible secondary melanocyte germ composed of C-KIT+ melanocytes was found in the infundibulum and interfollicular epidermis of UV-treated vitiligo. This is an exceptional model for studying the mobilization of melanocyte stem cells in human skin. Improved understanding of this process is essential for designing better treatments for vitiligo, ultimately based on melanocyte stem cell activation and mobilization.

PAX3 and ETS1 synergistically activate MET expression in melanoma cells

Melanoma is a highly aggressive disease that is difficult to treat due to rapid tumor growth, apoptotic resistance, and high metastatic potential. The MET tyrosine kinase receptor promotes many of these cellular processes, and while MET is often overexpressed in melanoma, the mechanism driving this overexpression is unknown. Since the MET gene is rarely mutated or amplified in melanoma, MET overexpression may be driven by to increased activation through promoter elements. In this report, we find that transcription factors PAX3 and ETS1 directly interact to synergistically activate MET expression. Inhibition of PAX3 and ETS1 expression in melanoma cells leads to a significant reduction of MET receptor levels. The 300 bp 5′ proximal MET promoter contains a PAX3 response element and two ETS1 consensus motifs. While ETS1 can moderately activate both of these sites without cofactors, robust MET promoter activation of the first site is PAX-dependent and requires the presence of PAX3, while the second site is PAX-independent. The induction of MET by ETS1 via this second site is enhanced by HGF-dependent ETS1 activation, thereby MET indirectly promotes its own expression. We further find that expression of a dominant negative ETS1 reduces the ability of melanoma cells to grow both in culture and in vivo. Thus, we discover a pathway where ETS1 advances melanoma through the expression of MET via PAX-dependent and independent mechanisms.

The role of microRNAs and long non-coding RNAs in the pathology, diagnosis, and management of melanoma

Melanoma is frequently lethal and its global incidence is steadily increasing. Despite the rapid development of different modes of targeted treatment, durable clinical responses remain elusive. A complete understanding of the molecular mechanisms that drive melanomagenesis is required, both genetic and epigenetic, in order to improve prevention, diagnosis, and treatment. There is increased appreciation of the role of microRNAs (miRNAs) in melanoma biology, including in proliferation, cell cycle, migration, invasion, and immune evasion. Data are also emerging on the role of long non-coding RNAs (lncRNAs), such as SPRY4-IT1, BANCR, and HOTAIR, in melanomagenesis. Here we review the data on the miRNAs and lncRNAs implicated in melanoma biology. An overview of these studies will be useful for providing insights into mechanisms of melanoma development and the miRNAs and lncRNAs that might be useful biomarkers or future therapeutic targets.

Human melanocytes form a PAX3-expressing melanocyte cluster on Matrigel by the cell migration process

BACKGROUND

The interactions between human epidermal melanocytes and their cellular microenvironment are important in the regulation of human melanocyte functions or in their malignant transformation into melanoma. Although the basement membrane extracellular matrix (BM-ECM) is one of major melanocyte microenvironments, the effects of BM-ECM on the human melanocyte functions are not fully explained at a molecular level.

OBJECTIVE

This study was aimed to characterize the molecular and cellular interactions between normal human melanocytes (NHMs) and BM-ECM.

METHODS

We investigated cell culture models of normal human melanocytes or melanoma cells on three-dimensional (3D) Matrigel to understand the roles of the basement membrane microenvironment in human melanocyte functions. Melanogenesis and melanobast biomarker expression in both primary human melanocytes and melanoma cells on 3D Matrigel were evaluated.

RESULTS

We found that NHMs migrated and formed reversible paired box 3 (PAX3) expressing cell clusters on three-dimensional (3D) Matrigel. The melanogenesis was significantly decreased in the PAX3 expressing cell cluster. The expression profile of PAX3, SOX10, and MITF in the melanocyte cluster on 3D Matrigel was similar to that of melanoblasts. Interestingly, PAX3 and SOX10 showed an inverse expression profile in NHMs, whereas the inverse expression pattern of PAX3 and SOX10 was disrupted in melanoma MNT1 and WM266-4 cells.

CONCLUSION

The human melanocyte culture on 3D Matrigel provides an alternative model system to study functions of human melanoblasts. In addition, this system will contribute to the elucidation of PAX3-related tumorigenic mechanisms to understand human melanoma.

Vitiligo: characterization of melanocytes in repigmented skin after punch grafting

BACKGROUND

Punch grafting is a surgical technique mainly applied in therapy-resistant, stable and circumscribed vitiligo.

OBJECTIVE

(i) To characterize in detail the features of the repigmented skin among punch grafts; and (ii) to correlate the ex vivo results with clinical data and punch grafting outcome.

METHODS

We evaluated by immunohistochemistry and image analysis the expression of a panel of specific melanocyte markers including HMB45, MITF, c-kit, MART-1 and TRP1, the proliferation marker Ki67 and the cell-cell adhesion molecule E-cadherin in tissue samples collected from nine patients after punch grafting.

RESULTS

Cells positive for MITF, c-kit, MART-1 and TRP1 were detected in the repigmented skin of all biopsies, whereas no reactivity was observed for HMB45. Melanocytes were identified along the entire length of the sections, and their mature state was assessed by the immuno-reactivity for the differentiation marker MART-1, the absence of cells positively stained for Ki67 and by the co-expression of c-kit and TRP1, a marker of a differentiated and pigmented state. Clinically, smaller punch grafts aimed at repigmenting lesional areas on the face gave the faster clinical results with no side-effects. Patients subjected to bigger punch grafts on the knee exhibited a longer repigmentation time and presented cobble stoning.

CONCLUSION

Our results suggest that the repigmentation observed in the areas between the grafts is due to the activation of the melanocytes located in the donor sites. These cells start to horizontally migrate towards the lesional skin thanks to successively the enlargement of intercellular spaces in relation to a decrease of E-cadherin reactivity and the up-modulation of pro-melanogenic mediators. Production and transfer of melanin in the surrounding keratinocytes and their persistence were assessed by the reactivity for MITF, c-kit, MART-1 and TRP1 but not for the pre-melanosome marker (HMB45).

Pax genes: regulators of lineage specification and progenitor cell maintenance

Pax genes encode a family of transcription factors that orchestrate complex processes of lineage determination in the developing embryo. Their key role is to specify and maintain progenitor cells through use of complex molecular mechanisms such as alternate RNA splice forms and gene activation or inhibition in conjunction with protein co-factors. The significance of Pax genes in development is highlighted by abnormalities that arise from the expression of mutant Pax genes. Here, we review the molecular functions of Pax genes during development and detail the regulatory mechanisms by which they specify and maintain progenitor cells across various tissue lineages. We also discuss mechanistic insights into the roles of Pax genes in regeneration and in adult diseases, including cancer.

Acid sphingomyelinase determines melanoma progression and metastatic behaviour via the microphtalmia-associated transcription factor signalling pathway

Melanoma is a rapidly growing and highly metastatic cancer with high mortality rates, for which a resolutive treatment is lacking. Identification of novel therapeutic strategies and biomarkers of tumour stage is thus of particular relevance. We report here on a novel biomarker and possible candidate therapeutic target, the sphingolipid metabolising enzyme acid sphingomyelinase (A-SMase). A-SMase expression correlates inversely with tumour stage in human melanoma biopsies. Studies in a mouse model of melanoma and on cell lines derived from mouse and human melanomas demonstrated that A-SMase levels of expression actually determine the malignant phenotype of melanoma cells in terms of pigmentation, tumour progression, invasiveness and metastatic ability. The action of A-SMase is mediated by the activation of the extracellular signal-regulated kinase, the subsequent proteasomal degradation of the Microphtalmia-associated transcription factor (Mitf) and inhibition of cyclin-dependent kinase 2, Bcl-2 and c-Met, downstream targets of Mitf involved in tumour cell proliferation, survival and metastatisation.

Immunohistochemical analyses point to epidermal origin of human Merkel cells

Merkel cells, the neurosecretory cells of skin, are essential for light-touch responses and may probably fulfill additional functions. Whether these cells derive from an epidermal or a neural lineage has been a matter of dispute for a long time. In mice, recent studies have clearly demonstrated an epidermal origin of Merkel cells. Given the differences in Merkel cell distribution between human and murine skin, it is, however, unclear whether the same holds true for human Merkel cells. We therefore attempted to gain insight into the human Merkel cell lineage by co-immunodetection of the Merkel cell marker protein cytokeratin 20 (CK20) with various proteins known to be expressed either in epidermal or in neural stem cells of the skin. Neither Sox10 nor Pax3, both established markers of the neural crest lineage, exhibited any cell co-labeling with CK20. By contrast, β1 integrin, known to be enriched in epidermal stem cells, was found in nearly 70 % of interfollicular epidermal and 25 % of follicular Merkel cells. Moreover, LRIG1, also enriched in epidermal stem cells, displayed significant co-immunolabeling with CK20 as well (approximately 20 % in the interfollicular epidermis and 7 % in the hair follicle, respectively). Further epidermal markers were detected in sporadic Merkel cells. Cells co-expressing CK20 with epidermal markers may represent a transitory state between stem cells and differentiated cells. β1 integrin is probably also synthesized by a large subset of mature Merkel cells. Summarizing, our data suggest that human Merkel cells may originate from epidermal rather than neural progenitors.

Melanoma biomolecules: independently identified but functionally intertwined

The majority of patients diagnosed with melanoma present with thin lesions and generally these patients have a good prognosis. However, 5% of patients with early melanoma (<1 mm thick) will have recurrence and die within 10 years, despite no evidence of local or metastatic spread at the time of diagnosis. Thus, there is a need for additional prognostic markers to help identify those patients that may be at risk of recurrent disease. Many studies and several meta-analyses have compared gene and protein expression in melanocytes, naevi, primary, and metastatic melanoma in an attempt to find informative prognostic markers for these patients. However, although a large number of putative biomarkers have been described, few of these molecules are informative when used in isolation. The best approach is likely to involve a combination of molecules. We believe one approach could be to analyze the expression of a group of interacting proteins that regulate different aspects of the metastatic pathway. This is because a primary lesion expressing proteins involved in multiple stages of metastasis may be more likely to lead to secondary disease than one that does not. This review focuses on five putative biomarkers – melanoma cell adhesion molecule (MCAM), galectin-3 (gal-3), matrix metalloproteinase 2 (MMP-2), chondroitin sulfate proteoglycan 4 (CSPG4), and paired box 3 (PAX3). The goal is to provide context around what is known about the contribution of these biomarkers to melanoma biology and metastasis. Although each of these molecules have been independently identified as likely biomarkers, it is clear from our analyses that each are closely linked with each other, with intertwined roles in melanoma biology.

The characterisation of Pax3 expressant cells in adult peripheral nerve

Pax3 has numerous integral functions in embryonic tissue morphogenesis and knowledge of its complex function in cells of adult tissue continues to unfold. Across a variety of adult tissue lineages, the role of Pax3 is principally linked to maintenance of the tissue’s resident stem/progenitor cell population. In adult peripheral nerves, Pax3 is reported to be expressed in nonmyelinating Schwann cells, however, little is known about the purpose of this expression. Based on the evidence of the role of Pax3 in other adult tissue stem and progenitor cells, it was hypothesised that the cells in adult peripheral nerve that express Pax3 may be peripheral glioblasts. Here, methods have been developed for identification and visualisation of Pax3 expressant cells in normal 60 day old mouse peripheral nerve that allowed morphological and phenotypic distinctions to be made between Pax3 expressing cells and other nonmyelinating Schwann cells. The distinctions described provide compelling support for a resident glioblast population in adult mouse peripheral nerve.

Identification of novel cholesteatoma-related gene expression signatures using full-genome microarrays

Background

Cholesteatoma is a gradually expanding destructive epithelial lesion within the middle ear. It can cause extensive local tissue destruction in the temporal bone and can initially lead to the development of conductive hearing loss via ossicular erosion. As the disease progresses, sensorineural hearing loss, vertigo or facial palsy may occur. Cholesteatoma may promote the spread of infection through the tegmen of the middle ear and cause meningitis or intracranial infections with abscess formation. It must, therefore, be considered as a potentially life-threatening middle ear disease.

Methods and Findings

In this study, we investigated differentially expressed genes in human cholesteatomas in comparison to regular auditory canal skin using Whole Human Genome Microarrays containing 19,596 human genes. In addition to already described up-regulated mRNAs in cholesteatoma, such as MMP9, DEFB2 and KRT19, we identified 3558 new cholesteatoma-related transcripts. 811 genes appear to be significantly differentially up-regulated in cholesteatoma. 334 genes were down-regulated more than 2-fold. Significantly regulated genes with protein metabolism activity include matrix metalloproteinases as well as PI3, SERPINB3 and SERPINB4. Genes like SPP1, KRT6B, PRPH, SPRR1B and LAMC2 are known as genes with cell growth and/or maintenance activity. Transport activity genes and signal transduction genes are LCN2, GJB2 and CEACAM6. Three cell communication genes were identified; one CDH19 and two from the S100 family.

Conclusions

This study demonstrates that the expression profile of cholesteatoma is similar to a metastatic tumour and chronically inflamed tissue. Based on the investigated profiles we present novel protein-protein interaction and signal transduction networks, which include cholesteatoma-regulated transcripts and may be of great value for drug targeting and therapy development.

Markers of circulating tumour cells in the peripheral blood of patients with melanoma correlate with disease recurrence and progression

BACKGROUND

Multimarker quantitative real-time polymerase chain reaction (qRT-PCR) represents an effective method for detecting circulating tumour cells in the peripheral blood of patients with melanoma.

OBJECTIVES

To investigate whether the phenotype of circulating melanoma cells represents a useful indicator of disease stage, recurrence and treatment efficacy.

METHODS

  Peripheral blood was collected from 230 patients with melanoma and 152 healthy controls over a period of 3years and 9months. Clinical data and blood samples were collected from patients with primary melanoma (early stages, 0-II, n=154) and metastatic melanoma (late stages, III-IV, n=76). Each specimen was examined by qRT-PCR analysis for the expression of five markers: MLANA, ABCB5, TGFβ2, PAX3d and MCAM.

RESULTS

 In total, 212 of the patients with melanoma (92%) expressed markers in their peripheral blood. Two markers, MLANA and ABCB5, had the greatest prognostic value, and were identified as statistically significant among patients who experienced disease recurrence within our study period, being expressed in 45% (MLANA) and 49% (ABCB5) of patients with recurrence (P=0·001 and P=0·031, respectively). For patients administered nonsurgical treatments, MCAM expression correlated with poor treatment outcome.

CONCLUSIONS

Circulating tumour cells were detectable at all stages of disease and long after surgical treatment, even when patients were considered disease free. Specifically, expression of ABCB5 and MLANA had significant prognostic value in inferring disease recurrence, while MCAM expression was associated with poor patient outcome after treatment, confirming multimarker qRT-PCR as a potential technique for monitoring disease status.

Evaluation of a multi-marker immunomagnetic enrichment assay for the quantification of circulating melanoma cells

Background

Circulating melanoma cells (CMCs) are thought to be valuable in improving measures of prognosis in melanoma patients and may be a useful marker of residual disease to identify non-metastatic patients requiring adjuvant therapy. We investigated whether immunomagnetic enrichment targeting multiple markers allows more efficient enrichment of CMCs from patient peripheral blood than targeting a single marker. Furthermore, we aimed to determine whether the number of CMCs in patient blood was associated with disease stage.

Methods

We captured CMCs by targeting the melanoma associated markers MCSP and MCAM as well as the melanoma stem cell markers ABCB5 and CD271, both individually and in combination, by immunomagnetic enrichment. CMCs were enriched and quantified from the peripheral blood of 10 non-metastatic and 13 metastatic melanoma patients.

Results

Targeting all markers in combination resulted in the enrichment of more CMCs than when any individual marker was targeted (p < 0.001-0.028). Furthermore, when a combination of markers was targeted, a greater number of CMCs were enriched in metastatic patients compared with non-metastatic patients (p = 0.007).

Conclusions

Our results demonstrated that a combination of markers should be targeted for optimal isolation of CMCs. In addition, there are significantly more CMCs in metastatic patients compared with non-metastatic patients and therefore quantification of CMCs may prove to be a useful marker of disease progression.

Extrafollicular dermal melanocyte stem cells and melanoma

Recent studies suggest that extrafollicular dermal melanocyte stem cells (MSCs) persist after birth in the superficial nerve sheath of peripheral nerves and give rise to migratory melanocyte precursors when replacements for epidermal melanocytes are needed on the basal epidermal layer of the skin. If a damaged MSC or melanocyte precursor can be shown to be the primary origin of melanoma, targeted identification and eradication of it by antibody-based therapies will be the best method to treat melanoma and a very effective way to prevent its recurrence. Transcription factors and signaling pathways involved in MSC self-renewal, expansion and differentiation are reviewed. A model is presented to show how the detrimental effects of long-term UVA/UVB radiation on DNA and repair mechanisms in MSCs convert them to melanoma stem cells. Zebrafish have many advantages for investigating the role of MSCs in the development of melanoma. The signaling pathways regulating the development of MSCs in zebrafish are very similar to those found in humans and mice. The ability to easily manipulate the MSC population makes zebrafish an excellent model for studying how damage to MSCs may lead to melanoma.

PAX Genes in Cancer; Friends or Foes?

PAX genes have been shown to be critically required for the development of specific tissues and organs during embryogenesis. In addition, PAX genes are expressed in a handful of adult tissues where they are thought to play important roles, usually different from those in embryogenesis. A common theme in adult tissues is a requirement for PAX gene expression in adult stem cell maintenance or tissue regeneration. The connections between adult stem cell PAX gene expression and cancer are intriguing, and the literature is replete with examples of PAX gene expression in either situation. Here we systematically review the literature and present an overview of postnatal PAX gene expression in normal and cancerous tissue. We discuss the potential link between PAX gene expression in adult tissue and cancer. In addition, we discuss whether persistent PAX gene expression in cancer is favorable or unfavorable.

The melanomas: a synthesis of epidemiological, clinical, histopathological, genetic, and biological aspects, supporting distinct subtypes, causal pathways, and cells of origin

Converging lines of evidence from varied scientific disciplines suggest that cutaneous melanomas comprise biologically distinct subtypes that arise through multiple causal pathways. Understanding the respective relationships of each subtype with etiologic factors such as UV radiation and constitutional factors is the first necessary step toward developing refined prevention strategies for the specific forms of melanoma. Furthermore, classifying this disease precisely into biologically distinct subtypes is the key to developing mechanism-based treatments, as highlighted by recent discoveries. In this review, we outline the historical developments that underpin our understanding of melanoma heterogeneity, and we do this from the perspectives of clinical presentation, histopathology, epidemiology, molecular genetics, and developmental biology. We integrate the evidence from these separate trajectories to catalog the emerging major categories of melanomas and conclude with important unanswered questions relating to the development of melanoma and its cells of origin.

Differential PAX3 functions in normal skin melanocytes and melanoma cells

The PAX3 transcription factor is the key regulator of melanocyte development during embryogenesis and is also frequently found in melanoma cells. While PAX3 is known to regulate melanocyte differentiation, survival, proliferation and migration during development, it is not clear if its function is maintained in adult melanocytes and melanoma cells. To clarify this we have assessed which genes are targeted by PAX3 in these cells. We show here that similar to its roles in development, PAX3 regulates complex differentiation networks in both melanoma cells and melanocytes, in order to maintain cells as "stem" cell-like (via NES and SOX9). We show also that mediators of migration (MCAM and CSPG4) are common to both cell types but more so in melanoma cells. By contrast, PAX3-mediated regulation of melanoma cell proliferation (through TPD52) and survival (via BCL2L1 and PTEN) differs from that in melanocytes. These results suggest that by controlling cell proliferation, survival and migration as well as maintaining a less differentiated "stem" cell like phenotype, PAX3 may contribute to melanoma development and progression.

Insights into the Role of PAX-3 in the Development of Melanocytes and Melanoma

Melanoma is the deadliest form of skin cancer in the United States with an increasing prevalence. However, the development of melanoma from a melanocyte precursor is still poorly defined. Understanding the molecules responsible for melanoma progression may lead to improved targeted therapy. One potential molecule is the paired box-3 (PAX-3) protein, which has been implicated in the development of melanocytes and malignant melanoma. In melanoma, the expression of PAX-3 is believed to be differentially regulated, and has been linked with malignancies and staging of the disease. The loss of PAX-3 regulation has also been associated with the loss of transforming growth factor-beta (TGF-β) activity, but its effect on PAX-3 in differentiated melanocytes as well as metastatic melanoma remains unclear. Understanding PAX-3 regulation could potentially shift melanoma to a less aggressive and less metastatic disease. This review summarizes our current knowledge on PAX-3 during melanocyte development, its regulation, and its implications in the development of novel chemo-immunotherapeutics against metastatic melanoma.

Differential roles of the pRb and Arf/p53 pathways in murine naevus and melanoma genesis

We report on a systematic analysis of genotype-specific melanocyte (MC) UVR responses in transgenic mouse melanoma models along with tumour penetrance and comparative histopathology. pRb or p53 pathway mutations cooperated with Nras(Q61K) to transform MCs. We previously reported that MCs migrate from the follicular outer root sheath into the epidermis after neonatal UVR. Here, we found that Arf or p53 loss markedly diminished this response. Despite this, mice carrying these mutations developed melanoma with very early age of onset after neonatal UVR. Cdk4(R24C) did not affect the MC migration. Instead, independent of UVR exposure, interfollicular dermal MCs were more prevalent in Cdk4(R24C) mice. Subsequently, in adulthood, these mutants developed dermal MC proliferations reminiscent of superficial congenital naevi. Two types of melanoma were observed in this model. The location and growth pattern of the first was consistent with derivation from the naevi, while the second appeared to be of deep dermal origin. In animals carrying the Arf or p53 defects, no naevi were detected, with all tumours ostensibly skipping the benign precursor stage in progression.