Stem cells must tread a fine line between producing sufficient cells for normal development and dividing excessively, leading to cancerous growth. How they achieve this delicate balance is a key question for developmental biologists and oncologists alike. The intestinal stem cells of fruit flies regulate their behaviour with calcium signalling: the concentration of calcium inside the cells increases in response to environmental factors such as diet and tissue damage, which in turn activates genes controlling cellular growth and division. Pictured are two sections through fly guts, showing stem cells in green and regular intestinal cells in red, with blue nuclei. Compared to the healthy gut on the left, the right one has an excess of stem cells, caused by prolonged exposure to high levels of calcium. Studying how diet in particular affects calcium in these cells could lead to new insights into the mechanisms behind intestinal cancers in humans too.
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