Why rely on mouse brains to help us understand our most complex organ when you can grow a model of a human one? Tiny “brains” that include parts of the cortex, hippocampus and even retinas, have been made for the first time using stem cells. The 3D tissue structures will let researchers study the early stages of human brain development in unprecedented detail.
Because human brains are so different from those of most animals, looking at how animal brains develop only gives us a crude understanding of the process in humans. “Mouse models don’t cut it,” saysJuergen Knoblich at the Institute of Molecular Biology (IMB) in Vienna, Austria.
To grow their miniature brains, Knoblich and colleagues took induced pluripotent stem (iPS) cells – adult cells reprogrammed to behave like embryonic stem cells – and gave them a mix of nutrients thought to be essential for brain development. The stem cells first differentiated into neuroectoderm tissue, the layer of cells that would eventually become an embryo’s nervous system. The tissue was suspended in a gel scaffold to help it develop a 3D structure.
In less than a month, the stem cells grew into brain-like “organoids” 3 to 4 millimetres across and containing structures that corresponded to most of the regions of the brain. For example, all the organoids they made appeared to contain parts of the cortex, about 70 per cent contained a choroid plexus – which produces spinal fluid – and about 10 per cent contained retinal tissue.
"If you provide the right nutrients, they have amazing capacity to self-organise," says team member Madeline Lancaster, also at the IMB.
However, one brain region that wasn’t present was the cerebellum, the part of the brain that handles motor skills and language, among other functions. This isn’t surprising, says Lancaster, since this region develops later than the others.
Using imaging techniques, the researchers were even able to detect neural activity (see video, above), although this doesn’t mean the brain is conscious in anyway.