Biochemical control of melanogenesis and melanosomal organization

Antimelanogenic effect of fermented licorice water extract on murine melanoma B16F10 cells

This study investigated the skin-whitening effect of fermented licorice water extract (FLWE) on B16F10 melanocytes. Bioconversion mediated by Issatchenkia orientalis MFST-based fermentation altered licorice's bioactive components. FLWE significantly increased polyphenol and flavonoid content compared with non-fermented licorice water extract (LWE). FLWE more effectively inhibited melanocyte-stimulating hormone-induced melanin production and tyrosinase activity than LWE. RT-PCR and Western blotting revealed that FLWE inhibits the expression of microphthalmia-associated transcription factor (MITF), the transcription factor for TRP-1, TRP-2, and tyrosinase. On analyzing FLWE's inhibitory activity against preexisting tyrosinase within melanocytes, FLWE did not directly inhibit tyrosinase itself, suggesting that FLWE exerts its whitening effect by inhibiting MITF activation. TLC and HPLC indicated that FLWE's superior whitening effect emanates from increased levels of aglycone compounds (isoliquiritigenin, glycyrrhizic acid, licochalcone A, and glabridin) after licorice fermentation. Overall, FLWE is a potentially effective skin-whitening material without side effects (vitiligo) commonly associated with direct tyrosinase inhibition.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10068-025-01878-z.

Advancements in hyperpigmentation management: exploring conventional methods, phytoconstituents, novel approaches, and instrumental techniques

Hyperpigmentation is a common dermatological condition characterized by the darkening of patches of skin compared to the surrounding areas. It can occur in individuals of all skin types and ethnicities, and is caused by an overproduction or accumulation of melanin, the pigment responsible for the color of our skin, hair, and eyes. This comprehensive overview aims to delve into the various types, causes, risk factors, clinical manifestations, diagnosis, and treatment options for hyperpigmentation. Additionally, it explores the global and national prevalence of hyperpigmentation, its etiology, pathophysiology and diagnosis and treatment strategies. Furthermore, examines the formulations and dosage forms used to treat hyperpigmentation, including their side effects. It also discusses combination drugs and their associated side effects, as well as novel drug delivery systems and nanocarriers employed in the treatment of hyperpigmentation, providing insight into future prospects in this field.

Isolation, characterization and evaluation of oxypeucedanin and osthol from local endemic Prangos aricakensis Behçet and Yapar root as antioxidant, enzyme inhibitory, antibacterial and DNA protection: molecular docking and DFT approaches

Prangos species were previously used against many disorders due to their chemical component. Prangos aricakensis Behçet & Yapar is a newly discovered local endemic species in Turkey's eastern region, and there is no research on P. aricakensis in the literature. In this work, oxypeucedanin and osthol molecules have been isolated from the root part of P. aricakensis for the first time. Oxypeucedanin and osthol structures were elucidated by 1D and 2D NMR analysis. For the bioactivities determination, antioxidant (DPPH· and ABTS·+ scavenging), enzyme inhibition (AChE, BChE, tyrosinase, and urease), antibacterial and DNA protection activity studies were applied for both molecules and compared with standard drug molecules, after applying enzyme kinetic assays and in silico approaches to clarify the mechanism of action for both molecules with enzymes, using molecular docking and density functional theory (DFT). Oxypeucedanin (2.19 ± 0.38 µg/mL) and osthol (4.57 ± 1.28 µg/mL) exhibited better activity than standards in DPPH∙ scavenging activity. Osthol (11.76 ± 0.59 µg/mL) showed a better tyrosinase inhibition effect than kojic acid (12.82 ± 0.91 µg/mL), and oxypeucedanin (3.03 ± 0.01 µg/mL) showed better urease inhibition effect than thiourea (5.37 ± 1.86 µg/mL). Our results showed that the osthol molecule was an excellent skin protective agent while the oxypeucedanin molecule could be a remarkable antiulcer agent. Therefore, although this study is the first in its field, it remained in the in vitro and in silico stages and is thought to pave the way for in vivo studies in the future.Communicated by Ramaswamy H. Sarma.

Ssc-mir-221-3p regulates melanin production in Xiang pigs melanocytes by targeting the TYRP1 gene

BACKGROUND

MicroRNAs (miRNAs) are small endogenous non-coding RNAs that regulate gene expression by down-regulating it. Several studies have suggested that miRNAs plays a crucial role in mammalian skin color production. The TYRP1 gene, a member of the tyrosine family, is an important candidate gene that affects melanogenesis. This study aimed to identify genes and miRNAs that affect melanin production in Xiang pigs by transcriptome sequencing, and to validate their targeted regulatory relationships.

RESULTS

17 miRNAs and 1,230 genes were significantly differentially expressed (P < 0.05) in the black and white skin tissues of Jianbai Xiang pigs. miRNA-221-3p was identified as a candidate miRNA for melanin formation and its target gene, TYRP1, was selected. The TYRP1 gene is a member of the TYR gene family, which evolved from the TYR gene through chromosome segmental duplication. The function of the gene was highly conserved throughout the evolutionary process. overexpression of TYRP1 gene significantly increased the expression of TYR, TYRP1, and DCT genes P < 0.01, which led to an increase in the relative content of melanin. Silencing of TYRP1 through the use of TYRP1-siRNA significantly reduced the expression of TYR, TYRP1, and DCT genes in Jianbai Xiang pig melanocytes P < 0.01, which in turn decreased the relative melanin content. The targeted binding relationship between ssc-miR-221-3p and TYRP1 gene was validated. After transfection of porcine melanocytes with ssc-miR-221-3p mimic, the expression of ssc-miR-221-3p was significantly up-regulated (P < 0.01). Furthermore, the mRNA and protein levels of TYR, TYRP1, and DCT genes were significantly down-regulated (P < 0.01), and melanin content in cells was significantly reduced (P < 0.01).

CONCLUSION

The TYRP1 gene affects melanogenesis in melanocytes of Jianbai Xiang pigs, and ssc-miR-221-3p targets the TYRP1 gene to regulate melanogenesis in melanocytes of Jianbai Xiang pigs.

Evaluation of the Reduction of Skin Hyperpigmentation Changes under the Influence of a Preparation Containing Kojic Acid Using Hyperspectral Imaging—Preliminary Study

Aim: The aim of this study was to demonstrate the effects of using a preparation containing kojic acid on skin hyperpigmentation using hyperspectral imaging, which enables a quantitative assessment of the effect of the preparation used on the reduction of skin discoloration. Materials and methods: Preliminary studies were carried out on 12 patients with post-acne skin. A hyperspectral camera with a spectral range of 400–1000 nm was used to image skin hyperpigmentation before and after the application of 3% kojic acid. Hyperspectral profiles were analyzed, and image analysis and processing methods were applied. Results: Studies performed using a hyperspectral camera have shown that kojic acid reduces skin discoloration by increasing skin brightness in 75% of patients tested, reducing skin contrast in approximately 83% and increasing skin homogeneity in approximately 67% of patients.

A Comprehensive Review of Mammalian Pigmentation: Paving the Way for Innovative Hair Colour-Changing Cosmetics

The natural colour of hair shafts is formed at the bulb of hair follicles, and it is coupled to the hair growth cycle. Three critical processes must happen for efficient pigmentation: (1) melanosome biogenesis in neural crest-derived melanocytes, (2) the biochemical synthesis of melanins (melanogenesis) inside melanosomes, and (3) the transfer of melanin granules to surrounding pre-cortical keratinocytes for their incorporation into nascent hair fibres. All these steps are under complex genetic control. The array of natural hair colour shades are ascribed to polymorphisms in several pigmentary genes. A myriad of factors acting via autocrine, paracrine, and endocrine mechanisms also contributes for hair colour diversity. Given the enormous social and cosmetic importance attributed to hair colour, hair dyeing is today a common practice. Nonetheless, the adverse effects of the long-term usage of such cosmetic procedures demand the development of new methods for colour change. In this context, case reports of hair lightening, darkening and repigmentation as a side-effect of the therapeutic usage of many drugs substantiate the possibility to tune hair colour by interfering with the biology of follicular pigmentary units. By scrutinizing mammalian pigmentation, this review pinpoints key targetable processes for the development of innovative cosmetics that can safely change the hair colour from the inside out.

Investigating the morphology and genetics of scalp and facial hair characteristics for phenotype prediction

Microscopic traits and ultrastructure of hair such as cross-sectional shape, pigmentation, curvature, and internal structure help determine the level of variations between and across human populations. Apart from cosmetics and anthropological applications, such as determining species, somatic origin (body area), and biogeographic ancestry, the evidential value of hair has increased with rapid progression in the area of forensic DNA phenotyping (FDP). Individuals differ in the features of their scalp hair (greying, shape, colour, balding, thickness, and density) and facial hair (eyebrow thickness, monobrow, and beard thickness) features. Scalp and facial hair characteristics are genetically controlled and lead to visible inter-individual variations within and among populations of various ethnic origins. Hence, these characteristics can be exploited and made more inclusive in FDP, thereby leading to more comprehensive, accurate, and robust prediction models for forensic purposes. The present article focuses on understanding the genetics of scalp and facial hair characteristics with the goal to develop a more inclusive approach to better understand hair biology by integrating hair microscopy with genetics for genotype-phenotype correlation research.

Biological Activities of Paper Mulberry (Broussonetia papyrifera): More than a Skin-Lightening Agent

Background: Paper mulberry is one of the most common skin-lightening agents in the beauty industry due to its strong anti-tyrosinase activity. This narrative review aims to summarize the chemical composition, biological activities, and applications of paper mulberry in cosmetics. Method: The literature for this article was acquired from the PubMed, Web of Science, and Google Scholar databases before September 2022. The keywords for searching included “paper mulberry”, “Broussonetia papyrifera”, “skin-lightening”, “skin-whitening”, “depigmentation”, “pharmacological activity”, and “biological activity”. Results: Paper mulberry consists of various components, including flavonoids, tannins, alkaloids, phenols, saponins, coumarins, glycosides, and polysaccharides, which possess a wide range of pharmacological properties. Apart from its anti-tyrosinase activity, paper mulberry and its compounds exhibited anti-inflammatory, antioxidant, antimicrobial, antiviral, anticancer, antidiabetic, anticholinesterase, antigout, antinociceptive, and hepatoprotective effects. Phenols and flavonoids were demonstrated to be the main contributors to the biological activities of paper mulberry. Paper mulberry is widely applied in cosmetics for skin lightening and skin moisturizing purposes and shows potential for application in hair care products due to the hair nourishing effects. The safety of paper mulberry for topical application was proven in clinical studies. Conclusion: The current review provides a better understanding of paper mulberry’s properties and allows us to extend the application of this plant and its bioactive components in cosmetics.

Improved Antioxidative, Anti-Inflammatory, and Antimelanogenic Effects of Fermented Hydroponic Ginseng with Bacillus Strains

Compared with traditionally cultured ginseng, hydroponic ginseng (HG) contains more remarkable bioactive compounds, which are known to exert diverse functional effects. This study aimed to enhance the multifunctional effects, including the antioxidative, anti-inflammatory, and antimelanogenic effects, exhibited by fermented HG with Bacillus strains, such as Bacillus subtilis KU43, Bacillus subtilis KU201, Bacillus polyfermenticus SCD, and Bacillus polyfermenticus KU3, at 37 °C for 48 h. After fermentation by B. subtilis KU201, the antioxidant activity, determined using ABTS and FRAP assays, increased from 25.30% to 51.34% and from 132.10% to 236.27%, respectively, accompanied by the enhancement of the phenolic compounds and flavonoids. The inflammation induced in RAW 264.7 cells by lipopolysaccharide (LPS) was ameliorated with fermented HG, which regulated the nitric oxide (NO), prostaglandin E₂ (PGE₂), and proinflammatory markers (tumor necrosis factor (TNF)-α, and interleukin (IL)-1β and IL-6). The treatment with fermented HG inhibited the melanin accumulation in B16F10 cells induced by α-melanocyte-stimulating hormone (α-MSH) by controlling the concentrations of melanin synthesis and tyrosinase activity. These results indicate that the HG exhibited stronger antioxidative, anti-inflammatory, and antimelanogenic effects after fermentation. Consequently, HG fermented by Bacillus strains can potentially be used as an ingredient in cosmetological and pharmaceutical applications.

Plant-Derived Compounds as Promising Therapeutics for Vitiligo

Vitiligo is the most common depigmenting disorder characterized by white patches in the skin. The pathogenetic origin of vitiligo revolves around autoimmune destruction of melanocytes in which, for instance, oxidative stress is responsible for melanocyte molecular, organelle dysfunction and melanocyte specific antigen exposure as well as melanocyte cell death and thus serves as an important contributor for vitiligo progression. In recent years, natural products have shown a wide range of pharmacological bioactivities against many skin diseases, and this review focuses on the effects and mechanisms of natural compounds against vitiligo models. It is showed that some natural compounds such as flavonoids, phenols, glycosides and coumarins have a protective role in melanocytes and thereby arrest the depigmentation, and, additionally, Nrf2/HO-1, MAPK, JAK/STAT, cAMP/PKA, and Wnt/β-catenin signaling pathways were reported to be implicated in these protective effects. This review discusses the great potential of plant derived natural products as anti-vitiligo agents, as well as the future directions to explore.

Novel Chemically Modified Curcumin (CMC) Analogs Exhibit Anti-Melanogenic Activity in Primary Human Melanocytes

Hyperpigmentation is a dermatological condition characterized by the overaccumulation and/or oversecretion of melanin pigment. The efficacy of curcumin as an anti-melanogenic therapeutic has been recognized, but the poor stability and solubility that have limited its use have inspired the synthesis of novel curcumin analogs. We have previously reported on comparisons of the anti-melanogenic activity of four novel chemically modified curcumin (CMC) analogs, CMC2.14, CMC2.5, CMC2.23 and CMC2.24, with that of parent curcumin (PC), using a B16F10 mouse melanoma cell model, and we have investigated mechanisms of inhibition. In the current study, we have extended our findings using normal human melanocytes from a darkly pigmented donor (HEMn-DP) and we have begun to study aspects of melanosome export to human keratinocytes. Our results showed that all the CMCs downregulated the protein levels of melanogenic paracrine mediators, endothelin-1 (ET-1) and adrenomedullin (ADM) in HaCaT cells and suppressed the phagocytosis of FluoSphere beads that are considered to be melanosome mimics. All the three CMCs were similarly potent (except CMC2.14, which was highly cytotoxic) in inhibiting melanin production; furthermore, they suppressed dendricity in HEMn-DP cells. CMC2.24 and CMC2.23 robustly suppressed cellular tyrosinase activity but did not alter tyrosinase protein levels, while CMC2.5 did not suppress tyrosinase activity but significantly downregulated tyrosinase protein levels, indicative of a distinctive mode of action for the two structurally related CMCs. Moreover, HEMn-DP cells treated with CMC2.24 or CMC2.23 partially recovered their suppressed tyrosinase activity after cessation of the treatment. All the three CMCs were nontoxic to human dermal fibroblasts while PC was highly cytotoxic. Our results provide a proof-of-principle for the novel use of the CMCs for skin depigmentation, since at low concentrations, ranging from 5 to 25 µM, the CMCs (CMC2.24, CMC2.23 and CMC2.5) were more potent anti-melanogenic agents than PC and tetrahydrocurcumin (THC), both of which were ineffective at melanogenesis at similar doses, as tested in HEMn-DP cells (with PC being highly toxic in dermal fibroblasts and keratinocytes). Further studies to evaluate the efficacy of CMCs in human skin tissue and in vivo studies are warranted.

Forensic determination of hair deposition time in crime scenes using electron paramagnetic resonance

Several types of biological samples, including hair strands, are found at crime scenes. Apart from the identification of the value and the contributor of the probative evidence, it is important to prove that the time of shedding of hair belonging to a suspect or victim matches the crime window. To this end, to estimate the ex vivo aging of hair, we evaluated time-dependent changes in melanin-derived free radicals in blond, brown, and black hairs by using electron paramagnetic resonance spectroscopy (EPR). Hair strands aged under controlled conditions (humidity 40%, temperature 20-22°C, indirect light, with 12/12 hour of light/darkness cycles) showed a time-dependent decay of melanin-derived radicals. The half-life of eumelanin-derived radicals in hair under our experimental settings was estimated at 22 ± 2 days whereas that of pheomelanin was about 2 days suggesting better stabilization of unpaired electrons by eumelanin. Taken together, this study provides a reference for future forensic studies on determination of degradation of shed hair in a crime scene by following eumelanin radicals by utilizing the non-invasive, non-destructive, and highly specific EPR technique.

From Bioinspired Glue to Medicine: Polydopamine as a Biomedical Material

Biological structures have emerged through millennia of evolution, and nature has fine-tuned the material properties in order to optimise the structure-function relationship. Following this paradigm, polydopamine (PDA), which was found to be crucial for the adhesion of mussels to wet surfaces, was hence initially introduced as a coating substance to increase the chemical reactivity and surface adhesion properties. Structurally, polydopamine is very similar to melanin, which is a pigment of human skin responsible for the protection of underlying skin layers by efficiently absorbing light with potentially harmful wavelengths. Recent findings have shown the subsequent release of the energy (in the form of heat) upon light excitation, presenting it as an ideal candidate for photothermal applications. Thus, polydopamine can both be used to (i) coat nanoparticle surfaces and to (ii) form capsules and ultra-small (nano)particles/nanocomposites while retaining bulk characteristics (i.e., biocompatibility, stability under UV irradiation, heat conversion, and activity during photoacoustic imaging). Due to the aforementioned properties, polydopamine-based materials have since been tested in adhesive and in energy-related as well as in a range of medical applications such as for tumour ablation, imaging, and drug delivery. In this review, we focus upon how different forms of the material can be synthesised and the use of polydopamine in biological and biomedical applications.

Impact of ultraviolet radiation on dermal and epidermal DNA damage in a human pigmented bilayered skin substitute

Our laboratory has developed a scaffold-free cell-based method of tissue engineering to produce bilayered tissue-engineered skin substitutes (TESs) from epidermal and dermal cells. However, TES pigmentation is absent or heterogeneous after grafting, due to a suboptimal number of melanocytes in culture. Our objectives were to produce TESs with a sufficient quantity of melanocytes from different pigmentation phototypes (light and dark) to achieve a homogeneous color and to evaluate whether the resulting pigmentation was photoprotective against ultraviolet radiation (UVR)-induced DNA damage in the dermis and the epidermis. TESs were cultured using different concentrations of melanocytes (100, 200, and 1,500 melanocytes/mm² ), and pigmentation was evaluated in vitro and after grafting onto an athymic mouse excisional model. Dermal and epidermal DNA damage was next studied, exposing pigmented TESs to 13 and 32.5 J/cm² UVR in vitro. We observed that melanocyte cell density increased with culture time until reaching a plateau corresponding to the cell distribution of native skin. Pigmentation of melanocyte-containing TESs was similar to donor skin, with visible melanin transfer from melanocytes to keratinocytes. The amount of melanin in TESs was inversely correlated to the UVR-induced formation of cyclobutane pyrimidine dimer in dermal fibroblasts and keratinocytes. Our results indicate that the pigmentation conferred by the addition of melanocytes in TESs protects against UVR-induced DNA damage. Therefore, autologous pigmented TESs could ensure photoprotection after grafting.

Exosomal miRNA derived from keratinocytes regulates pigmentation in melanocytes

BACKGROUND

Pigmentation is controlled by complex mechanisms. Evidence suggests that miRNAs can regulate pigmentation. However, the mechanism has not been fully elucidated. Objective In this study, we revealed a novel mechanism that regulates pigmentation involving exosomes, miRNAs and the crosstalk between keratinocytes and melanocytes.

METHODS

The expression and localization of exosome specific marker TSG101 in keratinocytes and melanocytes; Changes of melanin content in melanocytes after co-culture of exosome and melanocytes; Expression changes of target gene TYR and its related genes and inhibitory effect of miR-330-5p on pigmentation were studied by using various molecular biological techniques.

RESULTS

In this experiment, we used miR-330-5p in keratinocytes to verify the effect of keratinocyte derived exosome on melanocyte pigmentation. First, we found that keratinocytes secrete exosomes carrying miR-330-5p; moreover, greater miR-330-5p expression was found in exosomes derived from keratinocytes that overexpressed miR-330-5p. Second, we found that exosomes derived from keratinocytes with overexpression of miR-330-5p caused a significant increase in miR-330-5p in melanocytes. Finally, exosomes derived from keratinocytes that overexpressed miR-330-5p induced a significant decrease in the production of melanin and expression of TYR in melanocytes. Meanwhile, we overexpressed miR-330-5p in melanocytes, which also proved the inhibitory effect of miR-330-5p on pigmentation.

CONCLUSION

These findings suggest that keratinocytes crosstalk with melanocytes in the epidermal melanin unit via exosomal miRNAs. These studies reveal an important role of exosomes in melanocyte pigmentation, which opens a new pathway of melanogenesis.

Amine derivatives of furocoumarin induce melanogenesis by activating Akt/GSK-3β/β-catenin signal pathway

Background

Melanogenesis, or the biosynthesis of melanin, plays a critical role in the pigmentation of skin, hair, and eyes. Reduced melanogenesis may lead to depigmentation conditions such as vitiligo. Psoralen, a furocoumarin derivative, is closely associated with melanogenesis, and its derivative 8-methoxypsoralen is used in psoralen and ultraviolet A therapy for pigmentation disorders. In a previous study, we synthesized a new series of amine derivatives of furocoumarin, of which 5-(morpholinomethyl)-3-phenyl-7H-furo[3,2-g]chromen-7-one (encoded as D206008) showed a remarkable melanogenic effect in B16 murine cells.

Methods

In this study, we examined the effects of D206008 on the melanogenesis-related pathways in B16 cells. D206008 increased melanin production and tyrosinase (TYR) activity, as well as the mRNA and protein expression levels of the melanogenic enzymes TYR, TRP-1 and TRP-2, and the melanogenesis-related transcription factor microphthalmia-associated transcription factor (MITF) in a dose-dependent (0–100 µM) and time-dependent (0–48 hours) manner.

Results

Mechanistically, D206008 inhibited β-catenin degradation by enhancing the phosphorylation of Akt and glycogen synthase kinase-3β (GSK-3β), which increased the accumulation of β-catenin in the cytoplasm. Nuclear translocation of β-catenin also increased in response to D206008 treatment.

Conclusion

Taken together, these data indicate that D206008 promotes melanin synthesis by stimulating the nuclear translocation of β-catenin, which activates MITF transcription and eventually melanogenesis.

Anti-melanogenic effects of oyster hydrolysate in UVB-irradiated C57BL/6J mice and B16F10 melanoma cells via downregulation of cAMP signaling pathway

ETHNOPHARMACOLOGICAL RELEVANCE

Pacific oyster (Crassostrea gigas) has been used to treat pigmentary disorders such as freckles, melasma, and moles in Korea.

AIM OF THE STUDY

We aimed to investigate the inhibitory effects of oyster hydrolysate (OH) on melanogenesis in B16F10 melanoma cells and UVB-irradiated C57BL/6J mice.

MATERIAL AND METHODS

The molecular weight distribution and peptide sequences of OH were detected using MALDI-TOF and UHPLC. To evaluate the anti-melanogenic effects of OH, cell viability, melanin content, tyrosinase activity, intracellular cyclic adenosine monophosphate (cAMP) and protein expressions levels were measured in B16F10 cells. In addition, OH was orally administered to UVB-irradiated mice for 9 weeks. After sacrificing the mice, the whitening effects of OH were evaluated based on histological observations and protein expression levels.

RESULTS

In B16F10 cells, OH decreased melanin content and tyrosinase activity in a dose-dependent manner. OH exhibited anti-melanogenic activities via downregulation of cAMP signaling pathway, which consequently decreased melanin synthesis. In UVB-irradiated mice groups, OH decreased the number of active melanocytes and melanin granules. The expression of tyrosinase-related proteins and microphthalmia-associated transcription factor (MITF) decreased in the OH-administered groups.

CONCLUSIONS

These results show that OH inhibits melanin synthesis in B16F10 cells via downregulation of cAMP signaling pathway and in UVB-irradiated mice, by decreasing the number of active melanocytes and melanin granules.

Kojic acid applications in cosmetic and pharmaceutical preparations

Skin color disorders can be caused by various factors, such as excessive exposure to sunlight, aging and hormonal imbalance during pregnancy, or taking some medications. Kojic acid (KA) is a natural metabolite produced by fungi that has the ability to inhibit tyrosinase activity in synthesis of melanin. The major applications of KA and its derivatives in medicine are based on their biocompatibility, antimicrobial and antiviral, antitumor, antidiabetic, anticancer, anti-speck, anti-parasitic, and pesticidal and insecticidal properties. In addition, KA and its derivatives are used as anti-oxidant, anti-proliferative, anti-inflammatory, radio protective and skin-lightening agent in skin creams, lotions, soaps, and dental care products. KA has the ability to act as a UV protector, suppressor of hyperpigmentation in human and restrainer of melanin formation, due to its tyrosinase inhibitory activity. Also, KA could be developed as a chemo sensitizer to enhance efficacy of commercial antifungal drugs or fungicides. In general, KA and its derivatives have wide applications in cosmetics and pharmaceutical industries.

Effect of puerarin on melanogenesis in human melanocytes and vitiligo mouse models and the underlying mechanism

Puerarin is the major bioactive ingredient derived from the root of the Pueraria lobata (Willd.), and its antioxidative stress effects have been demonstrated in several previous studies. Moreover, Puerarin can upregulate melanin synthesis and microphthalmia-associated transcription factor (MITF) transcription by increasing cAMP level of intracellular cyclic adenosine monophosphate. Vitiligo is an acquired cutaneous disorder of pigmentation, and the pathogenesis has remained elusive. Current treatment modalities are directed towards achieving repigmentation. In this study, we found that after treating with puerarin at various concentrations of 40 μmol/L, the melanin content of human melanocytes increased significantly and the apparent level of protein and the RNA levels of MITF, tyrosinase (TYR), and tyrosinase-related protein 1 (TRP-1) were also increased. Further, puerarin was shown to inhibit phosphorylation and activation of extracellular signal-regulated kinase 1 and 2 (ERK1/2) without significantly affecting p38 and c-Jun N-terminal kinase phosphorylation. These results demonstrated that puerarin stimulated melanogenesis in human melanocytes via inhibition of ERK1/2 signaling pathways, which leads to upregulation of MITF and TYR as well as TRP-1 subsequently. Additionally, mice vitiligo models with puerarin treatment showed lighter pathological changes. Therefore, we suggested that puerarin might be a potential medicine for vitiligo.

Optimization of Flavonoids Extraction Process in Panax notoginseng Stem Leaf and a Study of Antioxidant Activity and Its Effects on Mouse Melanoma B16 Cells

The Panax notoginseng (P. notoginseng) stem leaf is rich in flavonoids. However, because of a lack of research on the flavonoid extraction process and functional development of P. notoginseng stem leaf, these parts are discarded as agricultural wastes. Therefore, in this study, we intend to optimize the extraction process and develop the skin-whitening functions of P. notoginseng stem leaf extracts. The extraction process of the stem and leaf of P. notoginseng flavonoid (SLPF) is optimized based on the Box⁻Behnken design (BBD) and the response surface methodology (RSM). The optimum extraction conditions of the SLPF are as follows: the extraction time, the ethanol concentration, the sodium dodecyl sulfate (SDS) content and the liquid material ratio (v/w, which are 52 min, 48.7%, 1.9%, and 20:1, respectively. Under the optimal extraction conditions, the average total SLPF content is 2.10%. The antioxidant activity and anti-deposition of melanin of mouse B16 cells of P. notoginseng stem leaf extracts are studied. The results indicate that the EC₅₀ values of reducing activity, 2,2-diphenyl-1-picrylhydrazyl (DPPH) free radical scavenging activities, the superoxide anion removal ability, and the 2,2-azino-bis-3-ethylbenzthiazoline-6-sulphonic acid (ABTS) free radical removal ability are 7.212, 2.893, 2.949, and 0.855 mg/mL, respectively. The extracts IC₅₀ values of the tyrosinase and melanin synthesis are 0.045 and 0.046 mg/mL, respectively. Therefore, the optimal processing technology for the SLPF obtained in this study not only increases its utilization rate, but also decreases material costs. The extracts from the P. notoginseng stem leaf may be developed as food or beauty products.

Depigmenting effect of argan press-cake extract through the down-regulation of Mitf and melanogenic enzymes expression in B16 murine melanoma cells

Oil extraction from the kernels of Argania spinosa (L.) Skeels (Sapotaceae), an endemic tree of Morocco, produces argan press-cake (APC) used as a shampoo and to treat sprains, scabies, and for healing wounds. We have previously reported that argan oil has antimelanogenesis effect. Here, we determined if the by-product, APC, has melanogenesis regulatory effect using B16 murine melanoma cells. The effect of APC ethanol extract on cell proliferation and melanin content of B16 cells were measured, and to elucidate the mechanism involved, the expression level of melanogenic enzymes tyrosinase (TYR), dopachrome tautomerase (DCT), and tyrosinase-related protein 1 (TRP1) were determined and mRNA expression level of microphthalmia- associated transcription factor (Mitf) and Tyr genes were quantified. APC ethanol extract showed a significant melanin biosynthesis inhibitory effect on B16 cells in a time-dependent manner without cytotoxicity, which could be due to the decreased expression of TYR, TRP1, and DCT in a time-dependent manner. APC extract down regulated Mitf and Tyr. Decreased TRP1 and DCT levels could be due to post-translational modifications. These results suggest that APC extract may be used as a new source of natural whitening products and may be introduced as an important pharmacological agent for the treatment of hyperpigmentation disorders.

A novel psoralen derivative-MPFC enhances melanogenesis via activation of p38 MAPK and PKA signaling pathways in B16 cells

As an active compound, psoralen is present in various Chinese herbal medicines and has exhibited significant activity in skin disease treatment. Its derivative 8-methoxypsoralan (8-MOP) is the most commonly used drug to induce repigmentation of vitiligo. In our previous screening assays, 4-methyl-6-phenyl-2H-furo[3,2-g]chromen-2-one (MPFC), a psoralen derivative, was identified as more effective tyrosinase and melanin activator than the positive control 8-MOP in consideration of low doses, as well as low toxicity. The overall purpose of this study was to characterize the melanogenic effect and mechanisms of MPFC in B16 cells. The melanin biosynthesis effects of MPFC were determined by examination of cellular melanin contents, tyrosinase activity assay, cyclic adenosinemonophosphate (cAMP) assay, and western blotting of MPFC-stimulated B16 mouse melanoma cells. Our results showed that MPFC enhanced both melanin synthesis and tyrosinase activity in a concentration-dependent manner as well as significantly activated the expression of melanogenic proteins such as tyrosinase, tyrosinase-related protein-1 and tyrosinase-related protein-2. Western blot analysis showed that MPFC increased the phosphorylation of p38 mitogen-activated protein kinase and cAMP response element-binding protein (CREB) as well as the expression of microphthalmia-associated transcription factor (MITF). Moreover, MPFC stimulated intracellular cAMP levels and induced tyrosinase activity and melanin synthesis were attenuated by H89, a protein kinase A inhibitor. These results indicated that MPFC-mediated activation of the p38 MAPK and the protein kinase A (PKA) pathway may shed light on a novel approach for an effective therapy for vitiligo.

Human Adipose Mesenchymal Cells Inhibit Melanocyte Differentiation and the Pigmentation of Human Skin via Increased Expression of TGF-β1

There is accumulating evidence that interactions between epidermal melanocytes and stromal cells play an important role in the regulation of skin pigmentation. In this study we established a pigmented dermo-epidermal skin model, melDESS, of human origin to investigate the effects of distinct stromal cells on melanogenesis. melDESS is a complex, clinically relevant skin equivalent composed of an epidermis containing both melanocytes and keratinocytes. Its dermal compartment consists either of adipose tissue-derived stromal cells, dermal fibroblasts (Fbs), or a mixture of both cell types. These skin substitutes were transplanted for 5 weeks on the backs of immuno-incompetent rats and analyzed. Gene expression and Western blot analyses showed a significantly higher expression of transforming growth factor-β1 by adipose tissue-derived stromal cells compared with dermal Fbs. In addition, we showed that melanocytes responded to the increased levels of transforming growth factor-β1 by down-regulating the expression of key melanogenic enzymes such as tyrosinase. This caused decreased melanin synthesis and, consequently, greatly reduced pigmentation of melDESS. The conclusions are of utmost clinical relevance, namely that adipose tissue-derived stromal cells derived from the hypodermis fail to appropriately interact with epidermal melanocytes, thus preventing the sustainable restoration of the patient's native skin color in bioengineered skin grafts.

FGF21 regulates melanogenesis in alpaca melanocytes via ERK1/2-mediated MITF downregulation

Fibroblast growth factor 21 (FGF21) is known as a metabolic regulator to regulate the metabolism of glucose and lipids. However, the underlying mechanism of FGF21 on melanin synthesis remains unknown. Therefore, the current study investigates the effect of FGF21 on melanogenesis in alpaca melanocytes. We transfected the FGF21 into alpaca melanocytes, then detected the melanin contents, protein and mRNA levels of pigmentation-related genes in order to determine the melanogenesis-regulating pathway of FGF21. The results showed that FGF21 overexpression suppressed melanogenesis and decreased the expression of the major target genes termed microphthalmia-associated transcription factor (MITF) and its downstream genes, including tyrosinase (TYR) and tyrosinase-related protein 2 (TRP2). However FGF21 increased the expression of phospho-extracellular signal-regulated kinase (p-Erk1/2). In contrast, FGF21-siRNA, a small interference RNA mediating FGF21 silencing, abolished the inhibition of melanogenesis. Altogether, FGF21 may decrease melanogenesis in alpaca melanocytes via ERK activation and subsequent MITF downregulation, which is then followed by the suppression of melanogenic enzymes and melanin production.

EFFECT OF FUCOIDAN ON B16 MURINE MELANOMA CELL MELANIN FORMATION AND APOPTOSIS

Background: :

Fucoidan is a complex sulfated polysaccharide extracted from brown seaweed and has a wide variety of biological activities. It not only inhibits cancer cell growth but also inhibits tyrosinase in vitro. Therefore, it is of interest to investigate the effect of fucoidan on B16 murine melanoma cells as the findings may provide new insights into the underlying mechanism regarding the inhibition of melanin formation by fucoidan. In the present study, we aimed to investigate the anti-melanogenic effect of fucoidan and its inhibitory effect on B16 cells.

Materials and Methods:

The influence of fucoidan on B16 melanoma cells and cellular tyrosinase was examined. Cell viability was examined by the cell counting kit-8 assay. Cellular tyrosinase activity and melanin content were determined using spectrophotometric methods and protein expression was analyzed by immunoblotting. Morphological changes in B16 melanoma cells were examined by phase contrast microscopy and apoptosis was analyzed by flow cytometry.

Results:

In vitro studies were performed using cell viability analysis and showed that fucoidan significantly decreased viable cell number in a dose-response manner with an IC₅₀ of 550 ±4.3 µg/mL. Cell morphology was altered and significant apoptosis was induced when cells were exposed to 550 µg/mL fucoidan for 48 h.

Conclusion:

This study provides substantial evidence to show that fucoidan inhibits B16 melanoma cell proliferation and cellular tyrosinase activity. Fucoidan may be useful in the treatment of hyperpigmentation and as a skin-whitening agent in the cosmetics industry.

Aryl Hydrocarbon Receptor Activation Contributes to Benzanthrone-Induced Hyperpigmentation via Modulation of Melanogenic Signaling Pathways

Benzanthrone (BA), an oxidized polycyclic aromatic hydrocarbon (PAH), has been found to be a potential health threat to occupational workers involved in dye manufacturing factories. It has been observed that occupational workers become exposed to BA either during manufacturing, pulverization, or storage and developed various kinds of skin diseases like contact dermatitis, itching, erythema, roughness, and foremost, hyperpigmentation. It has been shown that some environmental organic pollutants (POPs) like dioxins, furans, and polychlorinated biphenyls (PCBs) may act as ligands for the aryl hydrocarbon receptor (AhR) and regulate hyperpigmentation. Here, we hypothesized that BA may also act as a ligand for AhR and possibly regulate the melanogenic pathway to induced hyperpigmentation. Our computation results indicate that BA has a high binding affinity toward AhR for the initiation of melanogenic signaling. Following the in silico predictions, we used primary mouse melanocytes (PMMs) and confirmed that exposure to BA (5, 10, and 25 μM) resulted in an increase in AhR expression, tyrosinase activity, and melanin synthesis. Moreover, to study the physiological relevance of these findings, C57BL/6 mice were topically exposed to BA, and enhanced pigmentation and melanin synthesis were observed. Furthermore, the study was extended to assess the mechanistic aspects involved in BA-induced hyperpigmentation in PMMs as well as in mouse skin. Our results suggest that BA exposure initiates AhR signaling and increases tyrosinase enzyme activity and melanin synthesis. Moreover, the genes that regulate the melanin synthesis, such as TRP-1, TRP-2 and the transcription factor MITF, were also found to be increased. Thus, altogether, we suggest that BA-AhR interactions are critical for BA-induced hyperpigmentation.

Effect of apigenin-7-glucoside, genkwanin and naringenin on tyrosinase activity and melanin synthesis in B16F10 melanoma cells

AIMS

In this study, we have investigated the effects of apigenin-7-glucoside, genkwanin and naringenin, on mouse melanoma B16F10 cell proliferation. Influence of these natural products on percentage cell distribution in cycle phases and melanogenesis was also studied.

MAIN METHODS

Cell viability was determined at various periods using the MTT assay, whereas effects of tested compounds on progression through the cell cycle were analyzed by flow cytometry. In addition, amounts of melanin and tyrosinase were measured spectrophotometrically at 475 nm. Besides, the mechanism involved on the death route induced by the tested molecules was evaluated using the bis-benzimide trihydrochloride coloration method (Hoechst 33258).

KEY FINDINGS

Apigenin-7-glucoside, genkwanin and naringenin exhibited significant anti-proliferative activity against B16F10 melanoma cells after 24 and 48 h of incubation. Furthermore, apigenin-7-glucoside, genkwanin and naringenin provoked an increase of subG0/G1, S and G2/M phase cell proportion with a significant decrease of cell proportion in G0/G1 phases. The results evaluated using Hoechst 33,258, confirm that the percentage of B16F10 cells observed in the sub G0/G1 phase were undergoing apoptosis. Moreover, apigenin-7-glucoside and naringenin revealed an ability to enhance melanogenesis synthesis and tyrosinase activity of B16F10 melanoma cells. Whereas genkwanin induces a decrease of melanin synthesis by inhibiting tyrosinase activity.

SIGNIFICANCE

Our results promote the introduction of genkwanin in cosmetic preparations, as skin whitening agent, whereas apigenin-7-glucoside and naringenin should be introduced into cosmetic products as natural tanning agents.

Characterization of pigmented dermo-epidermal skin substitutes in a long-term in vivo assay

In our laboratory, we have been using human pigmented dermo-epidermal skin substitutes for short-term experiments since several years. Little is known, however, about the long-term biology of such constructs after transplantation. We constructed human, melanocyte-containing dermo-epidermal skin substitutes of different (light and dark) pigmentation types and studied them in a long-term animal experiment. Developmental and maturational stages of the epidermal and dermal compartment as well as signs of homoeostasis were analysed 15 weeks after transplantation. Keratinocytes, melanocytes and fibroblasts from human skin biopsies were isolated and assembled into dermo-epidermal skin substitutes. These were transplanted onto immuno-incompetent rats and investigated 15 weeks after transplantation. Chromameter evaluation showed a consistent skin colour between 3 and 4 months after transplantation. Melanocytes resided in the epidermal basal layer in physiological numbers and melanin accumulated in keratinocytes in a supranuclear position. Skin substitutes showed a mature epidermis in a homoeostatic state and the presence of dermal components such as Fibrillin and Tropoelastin suggested advanced maturation. Overall, pigmented dermo-epidermal skin substitutes show a promising development towards achieving near-normal skin characteristics and epidermal and dermal tissue homoeostasis. In particular, melanocytes function correctly over several months whilst remaining in a physiological, epidermal position and yield a pigmentation resembling original donor skin colour.

Whitening Effect of Watersoluble Royal Jelly from South Korea

Royal jelly has been widely used as a health supplement worldwide. However, royal jelly has been implicated in allergic reactions, and we developed a water-soluble royal jelly (WSRJ) without the allergy inducing protein. In this study, we aimed to identify the anti-melanogenic efficacy of WSRJ. B16F1 melanoma cells were first treated with 10 nM α-melanocyte stimulating hormone (α-MSH) and then with various doses of WSRJ. In addition, we investigated the mRNA and protein expression of melanogenesis-related genes such as tyrosinase, tyrosinase related protein-1 (TRP-1) and TRP-2 by reverse transcription-polymerase chain reaction and western blotting. WSRJ directly inhibited tyrosinase and cellular tyrosinase activity, which decreased melanin synthesis in α-MSH stimulated B16F1 melanoma cells a level comparable to that observed with arbutin. WSRJ decreased the mRNA and protein expressions of tyrosinase, TRP-1, and TRP-2, which was comparable to that observed with arbutin. WSRJ has strong anti-melanogenic activity, which invoice direct inhibition of tyrosinase enzyme activity and suppression of expression of melanogenesis related genes. Results from this study suggests that WSRJ is a potential candidate for the treatment of skin pigmentation.

Hyperpigmentation mechanism of methyl 3,5-di-caffeoylquinate through activation of p38 and MITF induction of tyrosinase

Methyl 3,5-di-caffeoylquinate (3,5-diCQM) has been used for the treatment of various diseases in oriental medicine, but its effect on melanogenesis has not been reported yet. In this study, the molecular mechanism of 3,5-diCQM-induced melanogenesis was investigated. It was found that 3,5-diCQM induced synthesis of melanin pigments in murine B16F10 melanoma cells in a concentration-dependent manner. Treatment of cells with 3,5-diCQM for 48 h increased extracellular and intracellular melanin production and tyrosinase activity. The expressions of tyrosinase, tyrosinase-related protein 1 (TRP1), and TRP2 were up-regulated in a dose-dependent manner 48 h after 3,5-diCQM treatment. Western blot analysis showed that 3,5-diCQM increased the phosphorylation of p38 mitogen-activated protein kinase and cAMP responsive element binding as well as the expression of microphthalmia-associated transcription factor. In addition, 3,5-diCQM-stimulated cAMP production, and 3,5-diCQM-induced tyrosinase activity and melanin synthesis were attenuated by H89, a protein kinase A inhibitor. These results suggested that 3,5-diCQM-mediated activation of the p38 pathway may represent a novel approach for an effective therapy for vitiligo and hair graying.

STAP-2 Protein Expression in B16F10 Melanoma Cells Positively Regulates Protein Levels of Tyrosinase, Which Determines Organs to Infiltrate in the Body

Melanoma is the most serious type of skin cancer, with a highly metastatic phenotype. In this report, we show that signal transducing adaptor protein 2 (STAP-2) is involved in cell migration, proliferation, and melanogenesis as well as chemokine receptor expression and tumorigenesis in B16F10 melanoma cells. This was evident in mice injected with STAP-2 shRNA (shSTAP-2)-expressing B16F10 cells, which infiltrated organs in a completely different pattern from the original cells, showing massive colonization in the liver, kidney, and neck but not in the lung. The most important finding was that STAP-2 expression determined tyrosinase protein content. STAP-2 colocalized with tyrosinase in lysosomes and protected tyrosinase from protein degradation. It is noteworthy that B16F10 cells with knocked down tyrosinase showed similar cell characteristics as shSTAP-2 cells. These results indicated that tyrosinase contributed to some cellular events beyond melanogenesis. Taken together, one possibility is that STAP-2 positively regulates the protein levels of tyrosinase, which determines tumor invasion via controlling chemokine receptor expression.

Melanogenesis-inducing effect of cirsimaritin through increases in microphthalmia-associated transcription factor and tyrosinase expression

The melanin-inducing properties of cirsimaritin were investigated in murine B16F10 cells. Cirsimaritin is an active flavone with methoxy groups, which is isolated from the branches of Lithocarpus dealbatus. Tyrosinase activity and melanin content in murine B16F10 melanoma cells were increased by cirsimaritin in a dose-dependent manner. Western blot analysis revealed that tyrosinase, tyrosinase-related protein (TRP) 1, TRP2 protein levels were enhanced after treatment with cirsimaritin for 48 h. Cirsimaritin also upregulated the expression of microphthalmia-associated transcription factor (MITF) after 24 h of treatment. Furthermore, cirsimaritin induced phosphorylation of cyclic adenosine monophosphate (cAMP) response element-binding protein (CREB) in a dose-dependent manner after treatment for 15 min. The cirsimaritin-mediated increase of tyrosinase activity was significantly attenuated by H89, a cAMP-dependent protein kinase A inhibitor. These findings indicate that cirsimaritin stimulates melanogenesis in B16F10 cells by activation of CREB as well as upregulation of MITF and tyrosinase expression, which was activated by cAMP signaling. Finally, the melanogenic effect of cirsimaritin was confirmed in human epidermal melanocytes. These results support the putative application of cirsimaritin in ultraviolet photoprotection and hair coloration treatments.

The peripheral clock regulates human pigmentation

Although the regulation of pigmentation is well characterized, it remains unclear whether cell-autonomous controls regulate the cyclic on-off switching of pigmentation in the hair follicle (HF). As human HFs and epidermal melanocytes express clock genes and proteins, and given that core clock genes (PER1, BMAL1) modulate human HF cycling, we investigated whether peripheral clock activity influences human HF pigmentation. We found that silencing BMAL1 or PER1 in human HFs increased HF melanin content. Furthermore, tyrosinase expression and activity, as well as TYRP1 and TYRP2 mRNA levels, gp100 protein expression, melanocyte dendricity, and the number gp100+ HF melanocytes, were all significantly increased in BMAL1 and/or PER1-silenced HFs. BMAL1 or PER1 silencing also increased epidermal melanin content, gp100 protein expression, and tyrosinase activity in human skin. These effects reflect direct modulation of melanocytes, as BMAL1 and/or PER1 silencing in isolated melanocytes increased tyrosinase activity and TYRP1/2 expression. Mechanistically, BMAL1 knockdown reduces PER1 transcription, and PER1 silencing induces phosphorylation of the master regulator of melanogenesis, microphthalmia-associated transcription factor, thus stimulating human melanogenesis and melanocyte activity in situ and in vitro. Therefore, the molecular clock operates as a cell-autonomous modulator of human pigmentation and may be targeted for future therapeutic strategies.

Compounds isolated from the aerial part of Crataegus azarolus inhibit growth of B16F10 melanoma cells and exert a potent inhibition of the melanin synthesis

Poor therapeutic results have been reported for treatment of malignant melanoma; therefore in this study, we have investigated inhibitory capacity of vitexin-2''-O-rhamnoside as well as the extract from which it was isolated, i.e. the ethyl acetate extract obtained from the leaves of Crataegus azarolus, on mouse melanoma (B16F10) proliferation. Cell viability was determined using the 3-(4, 5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. In addition, amounts of melanin and tyrosinase were measured spectrophotometrically at 475nm. Ethyl acetate extract and vitexin-2''-O-rhamnoside exhibited significant anti-proliferative activity against B16F10 melanoma cells after incubation for 48hours with IC50s of 50μg/mL and 20μM, respectively. Furthermore, these two compounds have the ability to reduce the melanin content by inhibiting the tyrosinase activity of B16F10 cells. Thus, further investigations are merited to ascertain their potential application in treating hyperpigmentation disorders.

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.

PAX6 regulates melanogenesis in the retinal pigmented epithelium through feed-forward regulatory interactions with MITF

During organogenesis, PAX6 is required for establishment of various progenitor subtypes within the central nervous system, eye and pancreas. PAX6 expression is maintained in a variety of cell types within each organ, although its role in each lineage and how it acquires cell-specific activity remain elusive. Herein, we aimed to determine the roles and the hierarchical organization of the PAX6-dependent gene regulatory network during the differentiation of the retinal pigmented epithelium (RPE). Somatic mutagenesis of Pax6 in the differentiating RPE revealed that PAX6 functions in a feed-forward regulatory loop with MITF during onset of melanogenesis. PAX6 both controls the expression of an RPE isoform of Mitf and synergizes with MITF to activate expression of genes involved in pigment biogenesis. This study exemplifies how one kernel gene pivotal in organ formation accomplishes a lineage-specific role during terminal differentiation of a single lineage.

It is currently poorly understood how a single developmental transcription regulator controls early specification as well as a broad range of highly specialized differentiation schemes. PAX6 is one of the most extensively investigated factors in central nervous system development, yet its role in execution of lineage-specific programs remains mostly elusive. Here, we directly investigated the involvement of PAX6 in the differentiation of one lineage, the retinal pigmented epithelium (RPE), a neuroectodermal-derived tissue that is essential for retinal development and function. We revealed that PAX6 accomplishes its role through a unique regulatory interaction with the transcription factor MITF, a master regulator of the pigmentation program. During the differentiation of the RPE, PAX6 regulates the expression of an RPE-specific isoform of Mitf and importantly, at the same time, PAX6 functions together with MITF to directly activate the expression of downstream genes required for pigment biogenesis. These findings provide comprehensive insight into the gene hierarchy that controls RPE development: from a kernel gene (a term referring to the upper-most gene in the gene regulatory network) that is broadly expressed during CNS development through a lineage-specific transcription factor that together with the kernel gene creates cis-regulatory input that contributes to transcriptionally activate a battery of terminal differentiation genes.