Although almost everyone has the same amount of melanocytes, the amount and size of the melanosomes and melanin particles produced can differ immensely in humans, resulting in the different races of the world. Dendritic prolongations take contact with nearby keratinocytes, and serve as melanosomes carriers.

1. Biology of melanocyte Torello Lotti Department of Dermatologic Science University of Florence, Italy The International School of Vitiligo & Pigmentary Disorders Barcelona, 2-5 November 2011

6. Confocal photograph showing melanosome (yellow), actin (red) and microtubules (violet)

7. Melanosome in motion: filamentous actin (red), microtubules (blue) and melansomes (green)

11. In human epidermic, melanocyte rside on the basement membrane, at the epidermal–dermal junction, and they form a close association with keratinocytes via their dendrites - Melanocyte of the epidermis -

12. Each melanocyte makes contact with around 30-40 keratinocytes. This constitutes the epidermal-melanin unit. Epidermal Melanin Unit 36 K KLM Unit 53 K - Melanocyte of the epidermis -

13. - Melanocyte of the epidermis - Immunohistochemical analysis : melanocytes are identified by using the marker D5, which stains the nuclear transcription factor. Haematoxylin and eosin stain of human skin: normal melanocytes have smaller nuclei and inconspicuous cytoplasm compared with the surrounding keratinocytes.

15. Longevity and resistance to apoptosis make melanocytes vulnerable to mutations that arise over the years, particularly due to sun exposure, and might culminate in melanoma formation in high-risk individuals. . Immune suppression INITIATION PROMOTION Eicosanoid production DNA DAMAGE PRE CANCER Displastic nevi Reactive O2 species CANCER Gene mutation Common nevi MELANOMA - Melanocyte of the epidermis -

16. Multipotent epidermal stem cells exist in the bulge region, at the bottom of the permanent portion of the follicle - Melanocytes in the hair follicle - Differentiated melanocyte reside in the hair bulb

23. Summing up…. Locations and functions of melanocytes HAIR FOLLICLE Melanocyte stem cell reservoir for skin. Hair pigmentation, Removal of toxic byproducts EAR Inner ear : balance Cochlea : hearing EYE Choroid : Constitutive eye pigmentation, protection against UV Retinal pigment epithelium : vision, metabolism of rod outer segments and retinoids BRAIN Neuroendocrine function and detoxification HEART unknown ADIPOSE TISSUE Anti-inflammation, reduction/binding of ROS EPIDERMIS Constitutive skin pigmentation. Responses to and protection against the environment (primarily UV)

24. And also….

30. Eumelanin is a nitrogenous and insoluble pigment. Pheomelanin is a sulfur-containing and alkali-soluble pigment. EUMELANIN VS PHEOMELANIN Pheomelanin and eumelanin differ not only in colour but also in the size, shape and packaging of their granules.

32. Both melanins derive from a common tyrosinase-dependent pathway with the same precursor, tyrosine. The obligatory step is hydroxylation of tyrosine to dopaquinone, (DQ) from which L-DOPA can also be derived. From DQ, the two pathways diverge. EUMELANIN VS PHEOMELANIN Pheomelanin is derived from conjugation by thiol-containing cysteine or glutathione. It is more photolabile and can produce, among its by-products, hydrogen peroxide, superoxide and hydroxyl radicals. . Land, E. J. & Riley, P. A. Spontaneous redox reactions of dopaquinone and the balance between the eumelanic and phaeomelanic pathways. Pigment Cell Res 2000; 13, 273–277..

36. Miller AJ, Tsao H. New Insights into Pigmentary Pathways and Skin Cancer. The British Journal of Dermatology 2010;162(1):22-28. 1 2 3

40. Sinthesis passages of eu- and pheomelanin from tyrosine

41. Melanosomes are formed from two sources: - In the Smooth Endoplasmic Reticulum (SER), pre-melanosomes are produced by coalescence of vesicles, and appear to contain parallel filamentous contents. - In the Rough Endoplasmic Reticulum (RER) and Golgi complex, tyrosinase and other enzymes are synthesised and packaged into vesicles. Melanosomes synthesis These fuse with the pre-melanosomes.

43. Post-Golgi transport of melanosomes in melanocyte citosol

45. Once in keratinocytes, melanosomes are distributed and -in response to UVR- positioned strategically over the ‘sun-exposed’ side of nuclei, to form cap-like structures resembling umbrellas.

47. Summary of the major participants in the paracrine/autocrine network that regulates melanocyte functions and survival.

48. Factors of the paracrine/autocrine network that regulates melanocyte functions, proliferation and survival, with their cellular origin, role in pigmentation and effects on melanocytes Abdel-Malek ZA, Swope VB. Epidermal melanocytes: regulation of their survivial, proliferation and function in human skin. In: Melanoma Development: Molecular Biology, Genetics and Clinical Application. A Bosserhoff ed. Springer-Verlag, Wien 2011. p.11.

49. Key molecules and signaling pathways implicated in melanocyte-keratinocyte interactions

50. Role of ET-1 and melanocortins in the DNA Damage Response Abdel-Malek ZA, Swope VB. Epidermal melanocytes: regulation of their survivial, proliferation and function in human skin. In: Melanoma Development: Molecular Biology, Genetics and Clinical Application. A Bosserhoff ed. Springer-Verlag, Wien 2011. p.22. ET-1 : endothelin-1; ETBR :endothelin-1 B receptor , MC1R : melanocortin-1 receptor

51. Tsatmali M, Ancas J, Thody JA. Melanocyte functions and its control by melanocortin peptides. J Histoc & Cytochemistry 2002; 50(2):125-133. Effects of melanocortins (MSH and ACTH) stimulation on melanocyte in response to environmental stress

52. Corticotropin Releasing Hormon central role in the skin response to stress Slominski A, Wortsman J, Pisarchik A, et al. Cutaneous expression of corticotropin-releasing hormone (CRH), urocortin, and CRH receptors . The FASEB Journal. 2001;15:1678-1693

60. Co-culture of human epidermal keratinocytes (red) and melanocytes (green), showing melanosome transfer into keratinocytes with DNA counterstaining (blue).

61. … for your attention. yo for your for attention…. Thank you… www.torellolotti.it professor @ torellolotti.it