Differential methylation of TSP50 and mTSP50 genes in different types of human tissues and mouse spermatic cells

Earlier studies identified human TSP50 as a testis-specific gene that encoded a threonine protease. Most importantly, TSP50 could be a cancer/testis antigen since there was a high frequency of reactivation in breast cancer biopsies. It was also found to be negatively regulated by the p53 gene. To further characterize this gene, we recently examined the DNA methylation patterns of the TSP50 gene promoter in normal human testis, as well as breast tissue and a testicular embryonic carcinoma cell line (HTECCL). Bisulfite genomic sequencing results demonstrated that the promoter exhibited mixed DNA methylation patterns in normal human testis, mainly non-methylation versus slight methylation, which could be attributed to the different stages spermatic cells go through during spermatogenesis. In contrast, it was methylated to a much greater extent in both breast tissue and HTECCL. To find out whether DNA methylation status was related to spermatogenesis stages, we analyzed DNA methylation patterns of the mTSP50 (the mouse ortholog of TSP50) promoter in spermatocytes and spermatozoa isolated from sexually mature mice. The results clearly demonstrated that each group of cells exhibited its preferential DNA methylation pattern that apparently was consistent with the gene expression status observed before. Taken together, our findings suggested that DNA methylation might regulate the TSP50 and mTSP50 gene expressions in different types of tissues and spermatic cells.     

A balance between activating and repressive histone modifications regulates cystic fibrosis transmembrane conductance regulator (CFTR) expression in vivo

The genetic mechanisms that regulate CFTR, the gene responsible for cystic fibrosis, have been widely investigated in cultured cells. However, mechanisms responsible for tissue-specific and time-specific expression are not completely elucidated in vivo. Through the survey of public databases, we found that the promoter of CFTR was associated with bivalent chromatin in human embryonic stem (ES) cells. In this work, we analyzed fetal (at different stages of pregnancy) and adult tissues and showed that, in digestive and lung tissues, which expressed CFTR, H3K4me3 was maintained in the promoter. Histone acetylation was high in the promoter and in two intronic enhancers, especially in fetal tissues. In contrast, in blood cells, which did not express CFTR, the bivalent chromatin was resolved (the promoter was labeled by the silencing mark H3K27me3). Cis-regulatory sequences were associated with lowly acetylated histones. We also provide evidence that the tissue-specific expression of CFTR is not regulated by dynamic changes of DNA methylation in the promoter. Overall, this work shows that a balance between activating and repressive histone modifications in the promoter and intronic enhancers results in the fine regulation of CFTR expression during development, thereby ensuring tissue specificity.     

A balance between activating and repressive histone modifications regulates cystic fibrosis transmembrane conductance regulator (CFTR) expression in vivo

The genetic mechanisms that regulate CFTR, the gene responsible for cystic fibrosis, have been widely investigated in cultured cells. However, mechanisms responsible for tissue-specific and time-specific expression are not completely elucidated in vivo. Through the survey of public databases, we found that the promoter of CFTR was associated with bivalent chromatin in human embryonic stem (ES) cells. In this work, we analyzed fetal (at different stages of pregnancy) and adult tissues and showed that, in digestive and lung tissues, which expressed CFTR, H3K4me3 was maintained in the promoter. Histone acetylation was high in the promoter and in two intronic enhancers, especially in fetal tissues. In contrast, in blood cells, which did not express CFTR, the bivalent chromatin was resolved (the promoter was labeled by the silencing mark H3K27me3). Cis-regulatory sequences were associated with lowly acetylated histones. We also provide evidence that the tissue-specific expression of CFTR is not regulated by dynamic changes of DNA methylation in the promoter. Overall, this work shows that a balance between activating and repressive histone modifications in the promoter and intronic enhancers results in the fine regulation of CFTR expression during development, thereby ensuring tissue specificity.