"After about 14 days, the embryo elongates and forms layers, revealing a rough plan for the body. But this dramatic transformation, called gastrulation, has never been directly observed in human embryos: Growing them to this stage in a lab is technically difficult and ethically fraught. Now, researchers have made structures from human stem cells that mimic some features of embryos after gastrulation, an advance that could reveal how genetic mutations and chemical exposures can lead to miscarriages and birth defects."
"The structures, created from stem cells and called gastruloids, are the first to form a 3D assembly that lays out how the body will take shape. The gastruloids developed rudimentary components of a heart and nervous system, but lacked the components to form a brain and other cell types that would make them capable of becoming a viable fetus. ... Human embryos take a momentous leap in their third week, when the largely homogeneous ball of cells starts to differentiate and develop specific characteristics of the body parts they will become, a process known as gastrulation. During this process, the embryo elongates and lays down a body plan with a head and tail, often called the head-to-tail axis.
But scientists have never seen this process in action. That is partly because many countries have regulations that stop embryos from being grown in the laboratory for research beyond 14 days after conception. ... Moris says the most thrilling result was the formation of pockets of cells that symmetrically straddle the head-to-tail axis. Genetic analysis showed that the cells were those that would eventually go on to form muscles in the trunk, vertebrae, heart and other organs. ..."
Balls of cells mimic an unseen stage of human embryo development | Science | AAAS
Lab-grown cells mimic crucial moment in embryo development Artificial structures developed the rudimentary components of a heart and nervous system.
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