Sox proteins in melanocyte development and melanoma

Putative role of HIF transcriptional activity in melanocytes and melanoma biology

Hypoxia-inducible factor-1α (HIF-1α) is a highly oxygen sensitive bHLH protein that is part of the heterodimeric HIF-1 transcription factor. Under hypoxic stress, HIF-1 activity is induced to control expression of multiple downstream target genes, including vascular endothelial growth factor (VEGF). The normal epidermis exists in a constant mild hypoxic microenvironment and constitutively expresses HIF-1α and HIF-2α. Expression of HIF-1α and/or HIF-2α has been suggested to correlate with the increased malignant potential of melanocytes, therefore, failures of melanoma therapies may be partially linked to high HIF activity. Notably, melanomas that have the V600E BRAF mutation exhibit increased HIF-1α expression. We have utilized a bioinformatics approach to identify putative hypoxia response elements (HREs) in a set of genes known to participate in the process of melanogenesis (includingTRPM1, SLC45A2, HRAS, C-KIT, PMEL and CRH). While some of the mechanistic links between these genes and the HIF pathway have been previously explored, others await further investigation. Although agents targeting HIF activity have been proposed as novel treatment modalities for melanoma, there are currently no clinical trials in progress to test their efficacy in melanoma.

SOX10 promotes melanoma cell invasion by regulating melanoma inhibitory activity

The transcription factor SOX10 (SRY (sex determining region Y)-box 10) has a key role in the embryonic development of melanocytes. Recently, it has been suggested that SOX10 is highly relevant for melanoma development and survival. However, the distinct functions and downstream targets of SOX10 in melanoma remain widely unknown. In this study, we inhibited SOX10 via RNA interference in different human melanoma cell lines and found a significantly reduced invasion capacity in vitro and in the chick embryo model. At later time points, SOX10 inhibition reduced proliferation and induced cell death. We identified melanoma inhibitory activity (MIA) as a direct target gene of SOX10, which is an essential protein for melanoma cell migration and invasion. Expression levels of SOX10 and MIA strictly correlated in melanoma cell lines, and SOX10 inhibition reduced MIA expression and promoter activity. Direct binding of SOX10 to the MIA promoter was demonstrated by electrophoretic mobility shift assay and chromatin immunoprecipitation. Ectopic expression of MIA in SOX10-inhibited melanoma cells restored the invasion capacity, supporting the hypothesis that MIA is responsible for SOX10-mediated melanoma cell invasion. Our data provide evidence for a critical role of SOX10 in melanoma cell invasion through the regulation of MIA and highlight its role as a therapeutic target in melanoma.

Overexpression of meloe gene in melanomas is controlled both by specific transcription factors and hypomethylation

The melanoma antigens MELOE-1 and MELOE-2 are encoded by a messenger, called meloe, overexpressed in melanomas compared with other tumour cell types and healthy tissues. They are both able to elicit melanoma-specific T cell responses in melanoma patients, and MELOE-1-specific CD8 T cells have been involved in melanoma immunosurveillance. With the aim to develop immunotherapies targeting this antigen, we investigated the transcriptional mechanisms leading to the preferential expression of meloe messenger in the melanocytic lineage. We defined the minimal promoter region of meloe gene and identified binding motifs for a set of transcription factors. Using mutagenesis, co-transfection experiments and chromatin immunoprecipitation, we showed that transcription factors involved in meloe promoter activity in melanomas were the melanocytic specific SOX9 and SOX10 proteins together with the activated P-CREB protein. Furthermore, we showed that meloe promoter was hypomethylated in melanomas and melanocytes, and hypermethylated in colon cancer cell lines and mesotheliomas, thus explaining the absence of P-CREB binding in these cell lines. This was a second key to explain the overerexpression of meloe messenger in the melanocytic lineage. To our knowledge, such a dual transcriptional control conferring tissue-specificity has never been described for the expression of tumour antigens.

Pleiotropic function of SRY-related HMG box transcription factor 4 in regulation of tumorigenesis

In addition to their critical roles in embryonic development, cell fate decision, and differentiation, members of Sox (Sry-related high-mobility group box) family of transcription factors including Sox4 have been implicated in various cancers. Multiple studies have revealed an increased expression along with specific oncogenic function of Sox4 in tumors, while others observed a reduced expression of Sox4 in different types of malignancies and suppression of tumor initiation or progression by this protein. More interestingly, the prognostic value of Sox4 is debated due to obvious differences between various reports as well as inconsistencies within specific studies. This review summarizes our current understanding of Sox4 expression pattern and its transcription-dependent, as well as transcription-independent, functions in tumor initiation or progression and its correlation with patient survival. We also discuss the existing discrepancies between different reports and their possible explanations.

Riding the crest of the wave: parallels between the neural crest and cancer in epithelial-to-mesenchymal transition and migration

The neural crest (NC) is first induced as an epithelial population of cells at the neural plate border requiring complex signaling between bone morphogenetic protein, Wnt, and fibroblast growth factors to differentiate the neural and NC fate from the epidermis. Remarkably, following induction, these cells undergo an epithelial-to-mesenchymal transition (EMT), delaminate from the neural tube, and migrate through various tissue types and microenvironments before reaching their final destination where they undergo terminal differentiation. This process is mirrored in cancer metastasis, where a primary tumor will undergo an EMT before migrating and invading other cell populations to create a secondary tumor site. In recent years, as our understanding of NC EMT and migration has deepened, important new insights into tumorigenesis and metastasis have also been achieved. These discoveries have been driven by the observation that many cancers misregulate developmental genes to reacquire proliferative and migratory states. In this review, we examine how the NC provides an excellent model for studying EMT and migration. These data are discussed from the perspective of the gene regulatory networks that control both NC and cancer cell EMT and migration. Deciphering these processes in a comparative manner will expand our knowledge of the underlying etiology and pathogenesis of cancer and promote the development of novel targeted therapeutic strategies for cancer patients. © 2013 Wiley Periodicals, Inc.

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

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

A far-upstream (-70 kb) enhancer mediates Sox9 auto-regulation in somatic tissues during development and adult regeneration

SOX9 encodes a transcription factor that presides over the specification and differentiation of numerous progenitor and differentiated cell types, and although SOX9 haploinsufficiency and overexpression cause severe diseases in humans, including campomelic dysplasia, sex reversal and cancer, the mechanisms underlying SOX9 transcription remain largely unsolved. We identify here an evolutionarily conserved enhancer located 70-kb upstream of mouse Sox9 and call it SOM because it specifically activates a Sox9 promoter reporter in most Sox9-expressing somatic tissues in transgenic mice. Moreover, SOM-null fetuses and pups reduce Sox9 expression by 18–37% in the pancreas, lung, kidney, salivary gland, gut and liver. Weanlings exhibit half-size pancreatic islets and underproduce insulin and glucagon, and adults slowly recover from acute pancreatitis due to a 2-fold impairment in Sox9 upregulation. Molecular and genetic experiments reveal that Sox9 protein dimers bind to multiple recognition sites in the SOM sequence and are thereby both necessary and sufficient for enhancer activity. These findings thus uncover that Sox9 directly enhances its functions in somatic tissue development and adult regeneration through SOM-mediated positive auto-regulation. They provide thereby novel insights on molecular mechanisms controlling developmental and disease processes and suggest new strategies to improve disease treatments.

Interplay of microRNAs, transcription factors and target genes: linking dynamic expression changes to function

MicroRNAs (miRNAs) are ubiquitously expressed small non-coding RNAs that, in most cases, negatively regulate gene expression at the post-transcriptional level. miRNAs are involved in fine-tuning fundamental cellular processes such as proliferation, cell death and cell cycle control and are believed to confer robustness to biological responses. Here, we investigated simultaneously the transcriptional changes of miRNA and mRNA expression levels over time after activation of the Janus kinase/Signal transducer and activator of transcription (Jak/STAT) pathway by interferon-γ stimulation of melanoma cells. To examine global miRNA and mRNA expression patterns, time-series microarray data were analysed. We observed delayed responses of miRNAs (after 24-48 h) with respect to mRNAs (12-24 h) and identified biological functions involved at each step of the cellular response. Inference of the upstream regulators allowed for identification of transcriptional regulators involved in cellular reactions to interferon-γ stimulation. Linking expression profiles of transcriptional regulators and miRNAs with their annotated functions, we demonstrate the dynamic interplay of miRNAs and upstream regulators with biological functions. Finally, our data revealed network motifs in the form of feed-forward loops involving transcriptional regulators, mRNAs and miRNAs. Additional information obtained from integrating time-series mRNA and miRNA data may represent an important step towards understanding the regulatory principles of gene expression.

Development and developmental disorders of the enteric nervous system

The enteric nervous system (ENS) arises from neural crest-derived cells that migrate into and along the gut, leading to the formation of a complex network of neurons and glial cells that regulates motility, secretion and blood flow. This Review summarizes the progress made in the past 5 years in our understanding of ENS development, including the migratory pathways of neural crest-derived cells as they colonize the gut. The importance of interactions between neural crest-derived cells, between signalling pathways and between developmental processes (such as proliferation and migration) in ensuring the correct development of the ENS is also presented. The signalling pathways involved in ENS development that were determined using animal models are also described, as is the evidence for the involvement of the genes encoding these molecules in Hirschsprung disease-the best characterized paediatric enteric neuropathy. Finally, the aetiology and treatment of Hirschsprung disease in the clinic and the potential involvement of defects in ENS development in other paediatric motility disorders are outlined.

Identification of miR-145 as a key regulator of the pigmentary process

The current treatments for hyperpigmentation are often associated with a lack of efficacy and adverse side effects. We hypothesized that microRNA (miRNA)-based treatments may offer an attractive alternative by specifically targeting key genes in melanogenesis. The aim of this study was to identify miRNAs interfering with the pigmentary process and to assess their functional role. miRNA profiling was performed on mouse melanocytes after three consecutive treatments involving forskolin and solar-simulated UV (ssUV) irradiation. Sixteen miRNAs were identified as differentially expressed in treated melan-a cells versus untreated cells. Remarkably, a 15-fold downregulation of miR-145 was detected. Overexpression or downregulation of miR-145 in melan-a cells revealed reduced or increased expression of Sox9, Mitf, Tyr, Trp1, Myo5a, Rab27a, and Fscn1, respectively. Moreover, a luciferase reporter assay demonstrated direct targeting of Myo5a by miR-145 in mouse and human melanocytes. Immunofluorescence tagging of melanosomes in miR-145-transfected human melanocytes displayed perinuclear accumulation of melanosomes with additional hypopigmentation of harvested cell pellets. In conclusion, this study has established an miRNA signature associated with forskolin and ssUV treatment. The significant down- or upregulation of major pigmentation genes, after modulating miR-145 expression, suggests a key role for miR-145 in regulating melanogenesis.

Identification of the hypoxia-inducible factor 2α nuclear interactome in melanoma cells reveals master proteins involved in melanoma development

Hypoxia-inducible factors (HIFs) are heterodimeric transcription factors that play a key role in cellular adaptation to hypoxia. HIF proteins are composed of an α subunit regulated by oxygen pressure (essentially HIF1α or HIF2α) and a constitutively expressed β subunit. These proteins are often overexpressed in cancer cells, and HIF overexpression frequently correlates with poor prognosis, making HIF proteins promising therapeutic targets. HIF proteins are involved in melanoma initiation and progression; however, the specific function of HIF2 in melanoma has not yet been studied comprehensively. Identifying protein complexes is a valuable way to uncover protein function, and affinity purification coupled with mass spectrometry and label-free quantification is a reliable method for this approach. We therefore applied quantitative interaction proteomics to identify exhaustively the nuclear complexes containing HIF2α in a human melanoma cell line, 501mel. We report, for the first time, a high-throughput analysis of the interactome of an HIF subunit. Seventy proteins were identified that interact with HIF2α, including some well-known HIF partners and some new interactors. The new HIF2α partners microphthalmia-associated transcription factor, SOX10, and AP2α, which are master actors of melanoma development, were confirmed via co-immunoprecipitation experiments. Their ability to bind to HIF1α was also tested: microphthalmia-associated transcription factor and SOX10 were confirmed as HIF1α partners, but the transcription factor AP2α was not. AP2α expression correlates with low invasive capacities. Interestingly, we demonstrated that when HIF2α was overexpressed, only cells expressing large amounts of AP2α exhibited decreased invasive capacities in hypoxia relative to normoxia. The simultaneous presence of both transcription factors therefore reduces cells' invasive properties. Knowledge of the HIF2α interactome is thus a useful resource for investigating the general mechanisms of HIF function and regulation, and here we reveal unexpected, distinct roles for the HIF1 and HIF2 isoforms in melanoma progression.

Integration of ChIP-seq and machine learning reveals enhancers and a predictive regulatory sequence vocabulary in melanocytes

We take a comprehensive approach to the study of regulatory control of gene expression in melanocytes that proceeds from large-scale enhancer discovery facilitated by ChIP-seq; to rigorous validation in silico, in vitro, and in vivo; and finally to the use of machine learning to elucidate a regulatory vocabulary with genome-wide predictive power. We identify 2489 putative melanocyte enhancer loci in the mouse genome by ChIP-seq for EP300 and H3K4me1. We demonstrate that these putative enhancers are evolutionarily constrained, enriched for sequence motifs predicted to bind key melanocyte transcription factors, located near genes relevant to melanocyte biology, and capable of driving reporter gene expression in melanocytes in culture (86%; 43/50) and in transgenic zebrafish (70%; 7/10). Next, using the sequences of these putative enhancers as a training set for a supervised machine learning algorithm, we develop a vocabulary of 6-mers predictive of melanocyte enhancer function. Lastly, we demonstrate that this vocabulary has genome-wide predictive power in both the mouse and human genomes. This study provides deep insight into the regulation of gene expression in melanocytes and demonstrates a powerful approach to the investigation of regulatory sequences that can be applied to other cell types.

RhoJ regulates melanoma chemoresistance by suppressing pathways that sense DNA damage

Melanomas resist conventional chemotherapeutics, in part, through intrinsic disrespect of apoptotic checkpoint activation. In this study, using an unbiased genome-wide RNA interference screen, we identified RhoJ and its effector PAK1, as key modulators of melanoma cell sensitivity to DNA damage. We find that RhoJ activates PAK1 in response to drug-induced DNA damage, which then uncouples ATR from its downstream effectors, ultimately resulting in a blunted DNA damage response (DDR). In addition, ATR suppression leads to the decreased phosphorylation of ATF2 and consequent increased expression of the melanocyte survival gene Sox10 resulting in a higher DDR threshold required to engage melanoma cell death. In the setting of normal melanocyte behavior, this regulatory relationship may facilitate appropriate epidermal melanization in response to UV-induced DNA damage. However, pathologic pathway activation during oncogenic transformation produces a tumor that is intrinsically resistant to chemotherapy and has the propensity to accumulate additional mutations. These findings identify DNA damage agents and pharmacologic inhibitors of RhoJ/PAK1 as novel synergistic agents that can be used to treat melanomas that are resistant to conventional chemotherapies.

Screening of MITF and SOX10 regulatory regions in Waardenburg syndrome type 2

Waardenburg syndrome (WS) is a rare auditory-pigmentary disorder that exhibits varying combinations of sensorineural hearing loss and pigmentation defects. Four subtypes are clinically defined based on the presence or absence of additional symptoms. WS type 2 (WS2) can result from mutations within the MITF or SOX10 genes; however, 70% of WS2 cases remain unexplained at the molecular level, suggesting that other genes might be involved and/or that mutations within the known genes escaped previous screenings. The recent identification of a deletion encompassing three of the SOX10 regulatory elements in a patient presenting with another WS subtype, WS4, defined by its association with Hirschsprung disease, led us to search for deletions and point mutations within the MITF and SOX10 regulatory elements in 28 yet unexplained WS2 cases. Two nucleotide variations were identified: one in close proximity to the MITF distal enhancer (MDE) and one within the U1 SOX10 enhancer. Functional analyses argued against a pathogenic effect of these variations, suggesting that mutations within regulatory elements of WS genes are not a major cause of this neurocristopathy.

SOXs in human prostate cancer: implication as progression and prognosis factors

Background

SOX genes play an important role in a number of developmental processes. Potential roles of SOXs have been demonstrated in various neoplastic tissues as tumor suppressors or promoters depending on tumor status and types. The aim of this study was to investigate the involvement of SOXs in the progression and prognosis of human prostate cancer (PCa).

Methods

The gene expression changes of SOXs in human PCa tissues compared with non-cancerous prostate tissues was detected using gene expression microarray, and confirmed by real-time quantitative reverse transcriptase-polymerase chain reaction (QRT-PCR) analysis and immunohositochemistry. The roles of these genes in castration resistance were investigated in LNCaP xenograft model of PCa.

Results

The microarray analysis identified three genes (SOX7, SOX9 and SOX10) of SOX family that were significantly dis-regulated in common among four PCa specimens. Consistent with the results of the microarray, differential mRNA and protein levels of three selected genes were found in PCa tissues by QRT-PCR analysis and immunohistochemistry. Additionally, we found that the immunohistochemical staining scores of SOX7 in PCa tissues with higher serum PSA level (P = 0.02) and metastasis (P = 0.03) were significantly lower than those with lower serum PSA level and without metastasis; the increased SOX9 protein expression was frequently found in PCa tissues with higher Gleason score (P = 0.02) and higher clinical stage (P < 0.0001); the down-regulation of SOX10 tend to be found in PCa tissues with higher serum PSA levels (P = 0.03) and advanced pathological stage (P = 0.01). Moreover, both univariate and multivariate analyses showed that the down-regulation of SOX7 and the up-regulation of SOX9 were independent predictors of shorter biochemical recurrence-free survival. Furthermore, we discovered that SOX7 was significantly down-regulated and SOX9 was significantly up-regulated during the progression to castration resistance.

Conclusions

Our data offer the convince evidence that the dis-regulation of SOX7, SOX9 and SOX10 may be associated with the aggressive progression of PCa. SOX7 and SOX9 may be potential markers for prognosis in PCa patients. Interestingly, the down-regulation of SOX7 and the up-regulation of SOX9 may be important mechanisms for castration-resistant progression of PCa.

Hirschsprung disease: a developmental disorder of the enteric nervous system

Hirschsprung disease (HSCR), which is also called congenital megacolon or intestinal aganglionosis, is characterized by an absence of enteric (intrinsic) neurons from variable lengths of the most distal bowel. Because enteric neurons are essential for propulsive intestinal motility, infants with HSCR suffer from severe constipation and have a distended abdomen. Currently the only treatment is surgical removal of the affected bowel. HSCR has an incidence of around 1:5,000 live births, with a 4:1 male:female gender bias. Most enteric neurons arise from neural crest cells that emigrate from the caudal hindbrain and then migrate caudally along the entire gut. The absence of enteric neurons from variable lengths of the bowel in HSCR results from a failure of neural crest-derived cells to colonize the affected gut regions. HSCR is therefore regarded as a neurocristopathy. HSCR is a multigenic disorder and has become a paradigm for understanding complex factorial disorders. The major HSCR susceptibility gene is RET. The penetrance of several mutations in HSCR susceptibility genes is sex-dependent. HSCR can occur as an isolated disorder or as part of syndromes; for example, Type IV Waardenburg syndrome is characterized by deafness and pigmentation defects as well as intestinal aganglionosis. Studies using animal models have shown that HSCR genes regulate multiple processes including survival, proliferation, differentiation, and migration. Research into HSCR and the development of enteric neurons is an excellent example of the cross fertilization of ideas that can occur between human molecular geneticists and researchers using animal models. WIREs Dev Biol 2013, 2:113-129. doi: 10.1002/wdev.57 For further resources related to this article, please visit the WIREs website.

Sox10 is expressed in primary melanocytic neoplasms of various histologies but not in fibrohistiocytic proliferations and histiocytoses

BACKGROUND

Sox10 is a transcription factor associated with neural crest development. Its expression has been reported in melanocytes and peripheral nerve sheath cells and their associated tumors.

OBJECTIVE

To assess Sox10 sensitivity in benign and malignant melanocytic neoplasms of various histologic subtypes and to discern the specificity of Sox10 in distinguishing between melanocytic neoplasms and fibrohistiocytic and histiocytic mimickers.

METHODS

Sox10 expression was examined by immunohistochemistry in 145 cases of formalin-fixed paraffin-embedded tissue, including benign and malignant melanocytic lesions of various histologies and stages (n = 83), fibrohistiocytic and histiocytic lesions (n = 33), and peripheral nerve sheath tumors (n = 19), among others (n = 10).

RESULTS

Immunoreactivity with Sox10 was observed in 100% (83/83) of benign and malignant melanocytic lesions of various subtypes, as well as in 100% (19/19) of benign and malignant peripheral nerve sheath lesions. Among the fibrohistiocytic proliferations and histiocytoses examined, Sox10 was negative in all cases (0/33). Sox10 expression did not vary by histologic subtype in nevi or melanoma; however, both the percentage of tumor nuclei demonstrating Sox10 expression and the intensity of expression were inversely correlated with malignant potential (nevi, melanoma in situ, invasive and metastatic melanoma) (P < .001, P = .016, respectively). Malignant peripheral nerve sheath tumors also showed decreased mean Sox10 expression and decreased intensity of expression when compared with benign counterparts (P < .001, P = .021, respectively).

LIMITATIONS

This is a retrospective study with 145 cases included.

CONCLUSIONS

Sox10 is a highly sensitive marker for melanocytic proliferations and may be useful diagnostically when the differential diagnosis includes fibrohistiocytic and histiocytic proliferations demonstrating S100 expression.

Neural crest delamination and migration: from epithelium-to-mesenchyme transition to collective cell migration

After induction and specification in the ectoderm, at the border of the neural plate, the neural crest (NC) population leaves its original territory through a delamination process. Soon afterwards, the NC cells migrate throughout the embryo and colonize a myriad of tissues and organs where they settle and differentiate. The delamination involves a partial or complete epithelium-to-mesenchyme transition (EMT) regulated by a complex network of transcription factors including several proto-oncogenes. Studying the relationship between these genes at the time of emigration, and their individual or collective impact on cell behavior, provides valuable information about their role in EMT in other contexts such as cancer metastasis. During migration, NC cells are exposed to large number of positive and negative regulators that control where they go by generating permissive and restricted areas and by modulating their motility and directionality. In addition, as most NC cells migrate collectively, cell-cell interactions play a crucial role in polarizing the cells and interpreting external cues. Cell cooperation eventually generates an overall polarity to the population, leading to directional collective cell migration. This review will summarize our current knowledge on delamination, EMT and migration of NC cells using key examples from chicken, Xenopus, zebrafish and mouse embryos. Given the similarities between neural crest migration and cancer invasion, these cells may represent a useful model for understanding the mechanisms of metastasis.

Post-embryonic nerve-associated precursors to adult pigment cells: genetic requirements and dynamics of morphogenesis and differentiation

The pigment cells of vertebrates serve a variety of functions and generate a stunning variety of patterns. These cells are also implicated in human pathologies including melanoma. Whereas the events of pigment cell development have been studied extensively in the embryo, much less is known about morphogenesis and differentiation of these cells during post-embryonic stages. Previous studies of zebrafish revealed genetically distinct populations of embryonic and adult melanophores, the ectotherm homologue of amniote melanocytes. Here, we use molecular markers, vital labeling, time-lapse imaging, mutational analyses, and transgenesis to identify peripheral nerves as a niche for precursors to adult melanophores that subsequently migrate to the skin to form the adult pigment pattern. We further identify genetic requirements for establishing, maintaining, and recruiting precursors to the adult melanophore lineage and demonstrate novel compensatory behaviors during pattern regulation in mutant backgrounds. Finally, we show that distinct populations of latent precursors having differential regenerative capabilities persist into the adult. These findings provide a foundation for future studies of post-embryonic pigment cell precursors in development, evolution, and neoplasia.

Understanding the biology of post-embryonic stem and progenitor cells is of both basic and translational importance. To identify mechanisms by which stem and progenitor cells are established, maintained, and recruited to particular fates, we are using the zebrafish adult pigment pattern. Previous work showed that embryonic and adult pigment cells have different genetic requirements, but little is known about the molecular or proliferative phenotypes of precursors to adult pigment cells or where these precursors reside during post-embryonic development. We show here that post-embryonic pigment cell precursors are associated with peripheral nerves and that these cells migrate to the skin during the larval-to-adult transformation when the adult pigment pattern forms. We also define morphogenetic and differentiative roles for several genes in promoting these events. Finally, we demonstrate that latent precursor pools persist into the adult and that different pools have different capacities for supplying new pigment cells in the context of pattern regeneration. Our study sets the stage for future analyses to identify additional common and essential features of pigment stem cell biology.

SOX10 expression in superficial spreading and nodular malignant melanomas

SOX10 is a transcription factor expressed in nerve cells and melanocytes. The aim of this study was to investigate the protein expression pattern of SOX10 in malignant melanoma tumors and to analyze whether the results correlated with clinical parameters and the proliferation marker Ki-67. Furthermore, proliferation and migration were analyzed in three different cell lines employing SOX10 small interfering RNA-mediated silencing. Expression patterns were determined in 106 primary tumors and 39 metastases in addition to 16 normal skin samples and six benign nevi employing immunohistochemistry and tissue microarrays. The immunohistochemical staining was evaluated manually and with an automated algorithm. SOX10 was strongly expressed in the benign tissues, but for the malignant tumors superficial spreading melanomas stained stronger than nodular malignant melanomas (P=0.008). The staining intensity was also inversely correlated with T-stage (Spearman's ρ=-0.261, P=0.008). Overall survival and time to recurrence were significantly correlated with SOX10 intensity, but not in multivariate analysis including T-stage. With the automated algorithm there was an inverse correlation between the SOX10 staining intensity and the proliferation marker, Ki-67 (ρ=-0.173, P=0.02) and a significant difference in the intensity signal between the benign tissues, the primary tumors and the metastases where the metastases stained the weakest (P≤0.001). SOX10 downregulation resulted in variable effects on proliferation and migration rates in the melanoma cell lines. In conclusion, the SOX10 intensity level differed depending on the tissue studied and SOX10 might have a role in survival. No conclusion regarding the role of SOX10 for in-vitro proliferation and migration could be drawn.

The Dark brown plumage color in chickens is caused by an 8.3-kb deletion upstream of SOX10

The Dark brown (DB) mutation in chickens reduces expression of black eumelanin and enhances expression of red pheomelanin, but only in certain parts of the plumage. Here, we present genetic evidence that an 8.3-kb deletion upstream of the SOX10 transcription start site is the causal mutation underlying the DB phenotype. The SOX10 transcription factor has a well-established role in melanocyte biology and is essential for melanocyte migration and survival. Previous studies have demonstrated that the mouse homolog of a highly conserved element within the deleted region is a SOX10 enhancer. The mechanism of action of this mutation remains to be established, but one possible scenario is that the deletion leads to reduced SOX10 expression which in turn down-regulates expression of key enzymes in pigment synthesis such as tyrosinase. Lower tyrosinase activity leads to a shift toward a more pheomelanistic (reddish) plumage color, which is the characteristic feature of the DB phenotype.

A curated online resource for SOX10 and pigment cell molecular genetic pathways

We describe the creation of a specialized web-accessible database named the Pigment Cell Gene Resource, which contains information on the genetic pathways that regulate pigment cell development and function. This manually curated database is comprised of two sections, an annotated literature section and an interactive transcriptional network diagram. Initially, this database focuses on the transcription factor SOX10, which has essential roles in pigment cell development and function, but the database has been designed with the capacity to expand in the future, allowing inclusion of many more pigmentation genes. Database URL: http://research.nhgri.nih.gov/pigment_cell/