Phosphatases have many important functions within the cell, but little has been known about the roles these proteins play in tumor suppression. In September Development, Gang Li and colleagues from Howard Hughes Medical Institute and UCLA School of Medicine, California, US, show that the absence of PTEN (phosphatase and tensin homolog deleted from chromosome 10, or MMAC1/TEP1) leads to precocious development and neoplasia in the mammary gland (Development 2002, 129:4159-4170).

Li et al. generated mice with a mammary-specific deletion of the Pten gene and observed that mutant females developed mammary tumors early in life. The mammary tissue of these animals displayed precocious lobulo-alveolar development, excessive ductal branching, delayed involution and severely reduced apoptosis. In addition Pten null mammary epithelial cells were disregulated and hyperproliferative.

These results confirm that "PTEN plays an essential and cell-autonomous role in controlling the proliferation, differentiation and apoptosis of mammary...

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