Islet Cells in the Pancreas Are the Only Cells in the Human

Islet cells in the pancreas are the only cells in the human body that produce the hormone insulin. The table below compares the extent of methylation within the promoter region upstream of the gene encoding the insulin protein in three types of human cells. The results provide an example illustrating that methylation of DNA is correlated with transcriptional _______.
$$\begin{array} { | c | c | } \hline \text { Cell type } & \begin{array} { c } \text { Extent of methylation of the } \\\text { insulin promoter }\end{array} \\\hline \text { Pancreatic islet cells } & 0 \\\hline \text { Fibroblasts (skin cells) } & + + + \\\hline \text { Leukocytes (white blood cells) } & + + + \\\hline\end{array}$$