Enzymes catalyzing CpG methylation in DNA, including DNMT1 and DNMT3A/B, are indispensable for mammalian tissue development and homeostasis 1-4. They are also implicated in human developmental disorders and cancers 5-8 , supporting a critical role of DNA methylation during cell fate specification and maintenance. Recent studies suggest that histone posttranslational modifications (PTMs) are involved in specifying patterns of DNMT localization and DNA methylation at promoters and actively transcribed gene bodies 9-11. However, mechanisms governing the establishment and maintenance of intergenic DNA methylation remain poorly understood. Germline mutations in DNMT3A define Tatton-Brown-Rahman syndrome (TBRS), a

Studies of human cancer metastasis have been limited by a lack of experimental assays in which cancer cells from patients metastasize in vivo in a way that correlates with clinical outcome. This makes it impossible to study intrinsic differences in the metastatic properties of cancers from different patients. We recently developed an assay in which human melanomas readily engraft in NOD/SCID IL2Rγnull (NSG) mice (1, 2). Here we show that melanomas from 25 patients exhibited reproducible differences in the rate of spontaneous metastasis after transplantation into NSG mice and that these differences correlated with clinical outcome in the patients. Stage IIIB/C melanomas that formed distant metastases within 22 months in patients also formed tumors that metastasized widely in NSG mice, while stage IIIB/C melanomas that did not form distant metastases within 22–50 months in patients metastasized more slowly in NSG mice. These differences in the efficiency of metastasis correlated with the frequency of circulating melanoma cells in the blood of NSG mice, suggesting that the rate of entry into the blood is one factor that limits the rate of metastasis. NSG mice can therefore be used to study the metastasis of human melanomas in vivo, revealing intrinsic differences among stage III melanomas in their ability to circulate/survive in the blood and metastasize.

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