Piebald Trait: Implication of kit Mutation on In Vitro Melanocyte Survival and on the Clinical Application of Cultured Epidermal Autografts

Striking contiguous depigmentation across the lower limbs in piebaldism and its implications for understanding melanocytic migration and development

Piebaldism is a rare autosomal dominant disorder of pigmentation that is characterized by variable patches of depigmentation on the face, chest, abdomen, and extremities. We describe two cases of piebaldism, in whom the remarkable asymmetric distribution of the depigmented patches in a connected, contiguous pattern across the legs provides embryologic insights. This finding is not explained by the traditional theory that melanocytic migration only originates in the neural crest and progresses unilaterally down each leg. We propose that our cases, and other similar cases, can be explained by a recent theory of mesodermal melanocyte migration.

Cellular and ultrastructural characterization of the grey-morph phenotype in southern right whales (Eubalaena australis)

Southern right whales (SRWs, Eubalena australis) are polymorphic for an X-linked pigmentation pattern known as grey morphism. Most SRWs have completely black skin with white patches on their bellies and occasionally on their backs; these patches remain white as the whale ages. Grey morphs (previously referred to as partial albinos) appear mostly white at birth, with a splattering of rounded black marks; but as the whales age, the white skin gradually changes to a brownish grey color. The cellular and developmental bases of grey morphism are not understood. Here we describe cellular and ultrastructural features of grey-morph skin in relation to that of normal, wild-type skin. Melanocytes were identified histologically and counted, and melanosomes were measured using transmission electron microscopy. Grey-morph skin had fewer melanocytes when compared to wild-type skin, suggesting reduced melanocyte survival, migration, or proliferation in these whales. Grey-morph melanocytes had smaller melanosomes relative to wild-type skin, normal transport of melanosomes to surrounding keratinocytes, and normal localization of melanin granules above the keratinocyte nuclei. These findings indicate that SRW grey-morph pigmentation patterns are caused by reduced numbers of melanocytes in the skin, as well as by reduced amounts of melanin production and/or reduced sizes of mature melanosomes. Grey morphism is distinct from piebaldism and albinism found in other species, which are genetic pigmentation conditions resulting from the local absence of melanocytes, or the inability to synthesize melanin, respectively.

A novel splicing mutation of KIT results in piebaldism and auburn hair color in a Chinese family

Piebaldism is a rare autosomal dominant disorder of melanocyte development, which is mostly caused by KIT gene. The key characteristics of piebaldism include localized poliosis, congenital leukoderma, and other variable manifestations. The previous study has illustrated that the homogeneous MC1R (a gene which is associated with the hair color) variant (p.I120T) coordinating with KIT mutation may lead to auburn hair color and piebaldism. In this study, we have investigated a Chinese family with piebaldism and auburn hair color; the mutation screening of KIT and MC1R genes identified that only a splicing mutation (c. 2484+1G>A) of KIT gene cosegregated with the auburn hair color and piebaldism. The data of this study and others suggests that the KIT mutation may causes of the auburn hair color in the piebaldism patients.

Piebaldism

Piebaldism is an uncommon autosomal dominantly inherited pigment anomaly characterized by a congenital white forelock and leukoderma on the frontal scalp, forehead, ventral trunk and extremities. It is caused by a loss-of-function mutation in the KIT gene. Genetic analyses reveal a consistent genotype-phenotype relationship in piebaldism. However, recently reported cases of piebaldism that are milder or severer than genetically expected indicate that other factors, such as a modifier gene of MC1R, influence skin and hair color. The KIT ligand/KIT that triggers the Ras/mitogen-activated protein kinase signaling pathway play essential functions in the migration, proliferation, survival, melanogenesis and melanosome transfer of the melanocytes. We summarize current research progress in piebaldism and related disorders.

Involvement of melanocortin-1 receptor in the hyperpigmentation of human skin autografts

Hyperpigmentation frequently occurs in human skin autografts resulting in an unsatisfactory appearance. This study aimed to elucidate the role of melanocortin-1 receptor in the hyperpigmentation process of skin autografts by analyzing the expression of melanocortin-1 receptor. The data were correlated with the amount of melanin in autografted human skin and normal skin determined in a previous study. Immunohistochemistry, western blotting and quantitative real-time polymerase chain reaction were carried out to detect the expression and distribution of melanocortin-1 receptor in skin autografts including full-thickness skin autografts, split-thickness skin autografts and normal full-thickness skin. Fontana-Masson stain was used to detect melanin in all types of skin specimens. The expression level of melanocortin-1 receptor in autografted skin was much higher than that in control normal skin, and thinner split-thickness skin autografts had higher levels of expression of melanocortin-1 receptor than thicker grafts. The amount of melanin in skin autografts was significantly increased compared with normal skin. The expression of melanocortin-1 receptor correlated well with the amount of melanin in the epidermis of skin autografts. These results indicate that melanogenesis is dramatically enhanced in skin autografts by the melanocortin-1 receptor, and suggest that overexpression of melanocortin-1 receptor may play an important role in the hyperpigmented process of skin autografts. This study provides a novel mechanism for hyperpigmentation in skin autografts.

Using regulatory and epistatic networks to extend the findings of a genome scan: identifying the gene drivers of pigmentation in merino sheep

Extending genome wide association analysis by the inclusion of gene expression data may assist in the dissection of complex traits. We examined piebald, a pigmentation phenotype in both human and Merino sheep, by analysing multiple data types using a systems approach. First, a case control analysis of 49,034 ovine SNP was performed which confirmed a multigenic basis for the condition. We combined these results with gene expression data from five tissue types analysed with a skin-specific microarray. Promoter sequence analysis of differentially expressed genes allowed us to reverse-engineer a regulatory network. Likewise, by testing two-loci models derived from all pair-wise comparisons across piebald-associated SNP, we generated an epistatic network. At the intersection of both networks, we identified thirteen genes with insulin-like growth factor binding protein 7 (IGFBP7), platelet-derived growth factor alpha (PDGFRA) and the tetraspanin platelet activator CD9 at the kernel of the intersection. Further, we report a number of differentially expressed genes in regions containing highly associated SNP including ATRN, DOCK7, FGFR1OP, GLI3, SILV and TBX15. The application of network theory facilitated co-analysis of genetic variation with gene expression, recapitulated aspects of the known molecular biology of skin pigmentation and provided insights into the transcription regulation and epistatic interactions involved in piebald Merino sheep.

The involvement of alpha-melanocyte-stimulating hormone in the hyperpigmentation of human skin autografts

Hyperpigmentation occurs frequently in human skin autografts, resulting in an unsatisfactory appearance.

OBJECTIVE

This study aims to elucidate the role of alpha-melanocyte-stimulating hormone (alpha-MSH) in the hyperpigmentation process of skin autografts by analysing the expression of alpha-MSH and the amount of melanin in human autografted skin and normal skin.

METHODS

Immunohistochemistry and reverse transcription-polymerase chain reaction methods were carried out to detect the expression and distribution of alpha-MSH and pro-opiomelanocortin (POMC) in skin autografts, including full-thickness skin autografts, split-thickness skin autografts and normal skin. The Fontana-Masson stain was used to detect the amount of melanin in all the skin specimens.

RESULTS

The level of alpha-MSH and POMC expression in autografted skin was much higher than that of control normal skin, and thinner split-thickness skin autografts expressed higher levels of POMC mRNA and alpha-MSH protein. The amount of melanin in skin autografts was significantly higher compared with normal skin. The expression of alpha-MSH correlated well with the amount of melanin in skin autograft epidermis.

CONCLUSIONS

These results indicate that the function of melanogenesis, transfer of melanin in melanocytes, was dramatically enhanced in skin autografts by alpha-MSH. The over-expression of alpha-MSH may play an important role in the hyperpigmentation process of skin autografts and provide a novel mechanism of this process.

A novel KIT missense mutation in one Chinese family with piebaldism

Piebaldism is an autosomal dominant disorder characterized by congenital leukoderma, mostly affecting forehead, abdomen and knee. Previous studies have revealed that piebaldism is caused by mutations of the KIT gene, which encodes the cell surface transmembrane tyrosine kinase receptor for KIT ligand. We reported here a Chinese Han family with piebaldism, and performed mutation detection of KIT gene by direct sequencing. A novel missense mutation C58G was identified in the patients, but not in the healthy individuals from the family and 100 unrelated controls. This study contributes to the database on KIT in piebaldism and enriches the knowledge about the genotype/phenotype correlation.

Keratinocyte cultures from involved skin in vitiligo patients show an impaired in vitro behaviour

Vitiligo depigmentation is considered a consequence of either melanocyte disappearance or loss of functioning melanocytes in the involved areas. However, it has been reported that keratinocytes in involved vitiligo skin are damaged too. Based on this evidence, we evaluated the in vitro behaviour, in life span cultures, of involved and uninvolved vitiligo keratinocytes and their expression of proliferation, differentiation and senescence markers. An additional purpose was to investigate whether vitiligo keratinocytes from depigmented skin are able to sustain survival and growth of normal melanocytes (when added in co-culture experiments), as normal human keratinocytes manage to do. Our results demonstrate that almost all involved vitiligo keratinocytes have a shorter life span in vitro than the uninvolved cells and all of them do not maintain melanocytes in culture in a physiological ratio. Modification of proliferation and senescence marker expression also occurs. Indeed, we detected low initial expression levels of the senescence marker p16 in involved vitiligo keratinocytes, despite their shorter in vitro life span, and increased expression of proliferating cell nuclear antigen and p53. This preliminary analysis of a small number of in vitro cultured vitiligo keratinocytes suggests an impaired senescence process in lesional vitiligo keratinocytes and attempts to regulate it.