The group showed that these “cerebral organoids” can be used as a model system to analyse the origins of the human genetic disorder microcephaly, in which brain size is significantly reduced.
The research, led by Juergen Knoblich at the Institute of Molecular Biotechnology, Austria, in collaboration with scientists at the Medical Research Council (MRC) Human Genetics Unit at the University of Edinburgh, provides a unique new laboratory tool for studying human-specific features of brain development and neurological disorders in a way that has not been possible using animal models.
To create the brain tissue, the researchers developed a finely-tuned culture system that capitalises on stem cells’ innate ability to organise themselves into complex organ structures.
They began with human embryonic and induced pluripotent stem cells, which they used to produce neuroectoderm – the layer of cells in the embryo from which all components of the brain and nervous system develop. Fragments of this tissue were then embedded in gel droplets that provided a scaffold for complex tissue growth and placed into a spinning bioreactor. The circulation of culture media in the bioreactor improves oxygen and nutrient supply allowing the organoids to grow to a larger size.
After a month, the tissue fragments had organised themselves into primitive structures that could be recognised as developing brain regions such as retina, choroid plexus and cerebral cortex. At the microscopic level in the cortex, radial glial stem cells, pivotal in developing the central nervous system, were seen to generate neurons in an identical manner to that known to occur in normal development. At two months, the organoids had reached their maximum size of 4mm, but they lacked the more detailed organisational structure of a fully developed brain.
Using patient induced pluripotent stem cells, the researchers were able to model the development of microcephaly, a disorder that has proved difficult to reproduce in mice. As expected, the organoids created using these cells grew to a smaller size.
On further investigation, they found that genetic mutations in these patients results in an earlier than normal switch in neural stem cells from self-renewal (making copies of themselves) to differentiation into nerve cells, leading to an overall reduction in cell number and size of the organoid.
Dr Andrew Jackson from the MRC Human Genetics Unit at the University of Edinburgh, a medical geneticist who studies neurological disorders and a co-author of the paper, said:
“The human brain is one of the most complex biological structures known to man. This level of complexity isn’t present in model animals such as mice, and so the organoid cell culture system gives us an exciting new way of studying the early events of brain development in tissue culture to learn more about neurodevelopmental disorders such as microcephaly.
“Our colleagues in Austria have made an amazing achievement in developing a 3D culture system that gives us a means of realistically modelling the complex interaction of multiple cell types in early human brain development. Being able to generate tissue with such complexity in cell culture is a significant advance for the study of human disease in the lab.”
Dr Paul Colville Nash, MRC Programme Manager in stem cell and developmental biology, said:
“This is a fascinating piece of research that demonstrates the remarkable potential of using stem cells to develop model systems in order to give us new insights into human development and disease. Model systems like these are likely to become increasingly important for early testing of new therapies before they progress to human trials.”
The research was led by Dr Jeurgen Knoblich at the Institute of Molecular Biotechnology of the Austrian Academy of Sciences and Dr Madeline A Lancaster was first author of the study. Dr Jackson’s team provided microcephaly patient cells and expertise on microcephaly disorders to the study.