If you are asking about the process of how a stem cell can turn into a nerve cell or a caridac cell this is unknown.

Scientists are just beginning to understand how cues interact to guide a cell toward its final destiny. Decades of work in developmental biology have provided a start: Biologists have used mutant frogs, flies, mice, chicks, and fish to identify some of the main genes that control a developing cell's decision to become a bone cell or a muscle cell. But observing what goes wrong when a gene is missing is easier than learning to orchestrate differentiation in a culture dish. Understanding how the roughly 25,000 human genes work together to form tissues—and tweaking the right ones to guide an immature cell's development—will keep researchers occupied for decades. If they succeed, however, the result will be worth far more than its weight in gold.