Pigmentary mosaicism and specific forms of phylloid hypoand hypermelanosis

Pigmentary mosaicism is proposed to encompass all pigment anomalies caused by chromosomal mosaicism. The concept includes, not only pigment anomalies following the lines of Blaschko, but also pigmentary disorders with phylloid, checkerboard and patchy pigmentation without midline separation. The representative disorders are hypomelanosis of Ito(pigmentary mosaicism of hypopigmented or Ito type), linear and whorled nevoid hypermelanosis(pigmentary mosaicism of hyperpigmented type), pigmentary mosaicism of hypopigmented and hyperpigmented type, and phylloid hypo- and hypermelanosis. Pigmentary mosaicism is nowadays recognized as a pigmentary disorder caused by somatic chromosomal abnormalities disrupting or accelerating the function of pigmentary genes. Affected individuals with pigmentary mosaicism commonly have multiple congenital abnormalities, developmental delays and/or mental retardation. However, the complication is not a syndrome because functional loss or acquisition due to various chromosomal abnormalities induces pigment abnormalities and specific complications. Cytogenetic abnormalities, including polyploidy, aneuploidy, deletions, insertions and translocations, are associated with almost any chromosome and tissue-limited mosaicism for chromosome abnormalities. Cytogenetic find-ings in cases with the phylloid pattern demonstrate the obvious causal relationship between phylloid hypomelanosis and mosaic trisomy 13. The pattern of cutaneous mosaicism depends on the trajectory of migration and proliferation during embryogenesis. The chromosomal regions of hot breakpoints in pigmentary mosaicism may contain pigmentation-associated genes. The accumulation of relationships between cases and chromosomal analyses may provide the opportunity to identify and understand the pigmentation-associated genes because more than 800 phenotypic alleles are known in the mice models of pigmentary anomalies and not all color loci have been identified. Here, we summarize the clinical features of pigmentary mosaicism and specific forms of phylloid hypo- and hypermelanosis.

Transcriptome analysis and candidate gene identification reveals insights into the molecular mechanisms of hypermelanosis in Chinese tongue sole(Cynoglossus semilaevis)

Blind-side hypermelanosis has emerged as a major concern in flatfish aquaculture worldwide,including tongue sole(Cynoglossus semilaevis)in China.The causative gene and the molecular basis are still unclear.In this study,comparative transcriptome analyses were performed using different skin tissues of tongue sole:ocular-side normal(pigmented)skin,blind-side normal(non-pigmented)skin and blind-side hypermelanotic(pigmented)skin.Finally,60 key hypermelanosis-related genes were mined,providing potential candidate gene resources involved in blind-side hypermelanosis.These genes were selected based on the log2(FoldChange)and false discovery rate(FDR)values(with corresponding P-Values<0.05),and they were verified in other species to assess if they were directly or indirectly related to melanogenesis.The protein-protein interaction network of these 60 genes and the relationship between tyr and other key hypermelanosis-related genes were illustrated.The qRT-PCR validation of 16 differentially expressed genes(DEGs)showed that the data of qRT-PCR were consistent with those of RNA-seq.Further analyses revealed that the selected DEGs were significantly overrepresented in several pigment metabolic processes and in the melanogenesis pathway.Our results may imply that blind-side hypermelanosis is a pattern of environmental regulation of gene expression and adaptation in flatfish.Membrane transport proteins(such as OCA2 and SLC45A2)may serve as a“switch”for melanogenesis in tongue sole.Overall,this study provided novel insights into the molecular mechanism of hypermelanosis in flatfish species and will facilitate future selective breeding of tongue sole for this market-favoured trait in aquaculture.