Three organs in one? Researchers unscramble mysterious roles of human yolk sac

Like chickens, duck-billed platypuses, and other animals that hatch from eggs, you had a yolk sac when you were an embryo. For many vertebrates, this pouch serves multiple developmental roles, including holding, well, yolk, the nutrient-rich liquid that helps nourish the embryo. However, the function of the human yolk sac is unclear. It contains no yolk and dwindles during the second trimester of pregnancy—the placenta instead provides the key route for feeding the offspring. Now, a study out in Science today reveals the human yolk sac stands in for organs such as the liver and kidneys that arise later in development. The findings could help researchers create better embryo mimics in the lab and devise new ways to cultivate immune cells for treating diseases. There’s been “a dearth of studies on the human yolk sac,” says developmental biologist Anthony Carter of the University of Southern Denmark, who wasn’t connected to the research. The new work, he says, “is a huge breakthrough in terms of getting data” about what happens in the first few weeks after conception. Although the yolk sac never produces its namesake substance in most mammals, it’s not vestigial. In mice, the yolk sac manufactures the embryo’s first blood cells and relays nutritious molecules produced by the uterus. And in some tissues of adult rodents, the immune cells known as macrophages are descended from yolk sac cells , not the bone marrow c...
Source: Science of Aging Knowledge Environment - Category: Geriatrics Source Type: research