Can we recreate a brain in-vitro? Maybe the answer to this very vague question was far fetched for us a few years back. Due to the advancement in biology, this particular question has become a reality today. Yes, a mini brain made in the lab, Brain Organoids- the article is about one of the pioneers who came out to propose a protocol for culturing cerebral organoids in the lab (that mimics the human brain) is Dr. Madeline Lancaster.
One of the biggest barriers that scientists faced was to understand the cellular interactions in the human brain. In 2013 it was Madeline Lancaster who proposed the protocol for making Pluripotent Stem Cell derived Brain organoids that depicts the cellular organisation of the human brain and segregates it into different regions.
Use of the stem cell for disease modelling and regenerative studies is already known to us but to control the pattern of differentiation in-vitro considering there are different combinatorial factors controlling the cell fate in the in-vivo condition has proved to be a tough nut to crack. Although we can direct the fate of PSC by adding certain growth factors externally but still we can’t control the cell cell intrinsic signaling in the culture itself. The researchers studying CNS development already had found that there are early signals which are being produced by differentiating neural cells to decide the fate of a PSC. Taking this as a clue, Knoblich Laboratory made cerebral organoids cultures from PSCs. (Lancaster et al., 2013, p. 374)
The journey of making cerebral organoids glinted more than some 30 years ago, research group led by Honeggar (Honegger et al., 1979, p. 306), showed that culturing of dissociated rat tissues aggregate to form brain like structures (Sasai, 2013, p. 527). There are also several studies which used the self organizing properties of human and rat PSCs to make layer specific neurons, 3D optical cups,etc. Lancaster and group devised a method that took in consideration the earlier studies to aggregate the cells in a spinning bioreactor. These conditions are apt to create big 3D models that have cells specific to a particular region in the brain. They found by using various canonical markers that the cells are being stratified into different layers. The method also shows the formation of ventricular zone areas and the marker of the choroid plexus and also some cells producing the CSF. They also identified the zone of outer radial cells which they hypothesised to vary with brain complexity and also found hippocampus like areas in the brain organoids (Chambers et al., 2013, p. 377).
The main application they did with these cerebral organoids was to study microcephaly, a disorder that normally leads to the formation of a small brain. They actually reprogrammed the fibroblast cells to iPSCs both from the normal person (control) and from a patient who have a mutation in the gene CDK5RAP2, that help in the activation of CDK5 (mutation lead to disorganisation of cortical layers). The organoids formed from the mutant iPSCs showed less SOX2+ neural progenitor because of the small size and also a large number of neurons as compared to the control suggesting premature differentiation of cells. They also reported that overexpression of CDK5RAP2 rescues from this particular phenotype (Lancaster et al., 2013, p. 374).
Although her group was successful in showing the use of the organoid model for the study of neurodevelopmental biology, questions were still raised on the efficiency of this particular method. The only difficulty was to evaluate the yield and reproducibility of a particular brain region considering we don’t have methods to quantify the cell fates (Chambers et al., 2013, p. 377). But, soon after this the Lancaster group faced another question on the nutrient accessibility of the cells at the center- that can restrict the overall organoid size and to introduce blood vessels or meninges type of things is another major challenging situation (Lancaster & Knoblich, 2014, p. 1247125). One of the articles published recently also brings into the context the slow rate of differentiation in the organoids, as Lancaster et. a study in 2013 also lacked to show any evidence of late formed cells like astrocytes and oligodendrocytes. Another add on problem was the lack of control over the composition of the cell and purity due to which it restricts the use of organoids for cell replacement theory as well.
Although there are so many lacunas yet to be answered, there are several positives as well from the study of Lancaster and her group. This particular protocol development helped us to model the brain for better neurodevelopmental studies, directed fate determinations and self organizing property of brains can be combined together to get more efficient architecture of a particular brain region (Chambers et al., 2009, p. 485), it can also be used to study clonal lineage tracing, fate mapping and as well as gain and loss of function of a particular gene. The use of this particular technique can also be explored to study the cell fate potential and migration. This gives us plethora of applications of cerebral organoids as in the study Lancaster et.al rightly mention that creation of Brain in a dish- a valuable tool to understand the functioning of the human brain (Kelava & Lancaster, 2016, p. 737).
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- Kelava, I., & Lancaster, M. A. (2016). Stem Cell Models of Human Brain Development. Cell Stem Cell, 18(6), 736–748. https://doi.org/10.1016/j.stem.2016.05.022
- Lancaster, M. A., Corsini, N. S., Wolfinger, S., Gustafson, E. H., Phillips, A. W., Burkard, T. R., Otani, T., Livesey, F. J., & Knoblich, J. A. (2018). Erratum: Publisher Correction: Guided self-organization and cortical plate formation in human brain organoids. Nature Biotechnology, 36(10), 1016. https://doi.org/10.1038/nbt1018-1016a
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- Lancaster, M. A., Renner, M., Martin, C.-A., Wenzel, D., Bicknell, L. S., Hurles, M. E., Homfray, T., Penninger, J. M., Jackson, A. P., & Knoblich, J. A. (2013). Cerebral organoids model human brain development and microcephaly. Nature, 501(7467), 373–379. https://doi.org/10.1038/nature12517
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