A new method of growing mini-brains produces some startling results.
- Researchers find a new and inexpensive way to keep organoids growing for a year.
- Axons from the study's organoids attached themselves to embryonic mouse spinal cord cells.
- The mini-brains took control of muscles connected to the spinal cords.
How brainy is an organoid?<p>Before getting too creeped out, it's worth taking a moment to understand the rudimentary nature of organoids as they currently exist. The human brain is believed to contain some <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2776484/" target="_blank" data-vivaldi-spatnav-clickable="1">100 billion neurons</a>. The most advanced organoids so far possess just a couple of million — <a href="https://en.wikipedia.org/wiki/List_of_animals_by_number_of_neurons" target="_blank" data-vivaldi-spatnav-clickable="1">twice</a> what a cockroach has and much less than an adult zebrafish. Still quite capable, but hardly human, it's becoming clearer that animals with fewer neurons than we have are <a href="https://bigthink.com/surprising-science/do-animals-feel-pain?rebelltitem=3#rebelltitem3" target="_self" data-vivaldi-spatnav-clickable="1">likely sentient</a>. The value of having organoids for research, however, is obvious, opening a window into all manner of human processes and diseases.</p><p>All that having been said, it can be expected that mini-brains will grow more and more sophisticated over time. This raises all sorts of <a href="https://theconversation.com/fresh-urgency-in-mapping-out-ethics-of-brain-organoid-research-107186" target="_blank" data-vivaldi-spatnav-clickable="1">ethical questions</a> we should be addressing now, before we have a problem on our hands, if we don't already.</p>
Happy ‘birthday,’ mini-brain<p>Most organoids don't grow for very long, because as the organoid grows, the nutrient solution in which it bathes can no longer reach its innermost neurons, and they die, terminating the growth cycle. In this research, scientists employed an "air-liquid interface culture." The primary purpose of the research was to verify the value of such an approach.</p><p>Each organoid was sliced into 1/2 millimeter-thick slices and attached to a membrane that was then introduced to a nutrient solution. This allowed the central neurons of each ALI-CO (for "air-liquid interface cerebral organoid") to continue receiving oxygen and nutrients. The organoids grew and produced new, healthy cells for more than one full year. </p><p>Because the ALI-COs' slice cultures were relatively easily to manipulate, the scientists were able to perform live imaging of them to assess their progress and the structures they developed. To identify the cells being produced, the team employed single-cell RNA (<a href="https://www.ncbi.nlm.nih.gov/pubmed/29851283" target="_blank" data-vivaldi-spatnav-clickable="1">scRNA</a>) sequencing to analyze six slices from three ALI-COs' cells, with an average of 4,427 cells per sample.</p><p>The live imaging revealed that axons, the nerve fibers that connect neurons, produced healthy outgrowths "reminiscent of nerve tracts" in the ALI-COs throughout the study, and various natural turning behaviors were observed. Neurons also successfully developed complex dendrites — connectors — as the organoids continued to grow. The complement of cells in the organoids was reminiscent of those in an organic embryonic brain.</p><p>Overall, the study found that that air-liquid interface culturation provides a viable, and less expensive, means of successfully growing healthy, fully-functional organoids for research purposes. The final proof of its efficacy was the spinal-cord connection.</p>
Reach out and touch…something<p>As the final test of the ALI-COs' complexity, cells of spinal column attached to back muscle tissue from embryonic mice were co-cultured with the organoids.</p><p>"After 2–3 weeks in co-culture," reports the study, "dense axon tracts from the ALI-COs could be seen innervating the mouse spinal cord, and synapses were visible between human projecting axons and neurons of the mouse spinal cord." One might reasonably ask <em>why: </em>What did the "brain" have in "mind?" Let's hope it's simply instinctive behavior on a cellular level.</p><p>Next, the back muscles started twitching. While random muscle contraction occurs in disconnected tissue, these were much stronger, were arhythmic pulses, and could be switched off by severing the axonal connections. To further verify what seemed to be happening, researchers directly stimulated remaining axonal connections and verified their ability to produce muscle contractions. Also, the "evoked muscle contractions were intensity-dependent such that larger stimulation currents increased the amplitude of the muscle contraction." There's thus little doubt that the mini-brains were controlling the muscles connected to the spinal cords they'd reached out to and connected to. Welcome to the future.</p>
Using a new process, a mini-brain develops retinal cells.
- Mini-brains, or "neural organoids," are at the cutting edge of medical research.
- This is the first one that's started developing eyes.
- Stem cells are key to the growing of organoids of various body parts.
Mini-brains<p>Neural, or cerebral, organoids begin with cells extracted from skin or urine cells of volunteers. These cells are converted into undifferentiated stem cells first, and then into neurons and other nervous system cells. Immersed in nutrient-rich fluid suspensions and carefully agitated, mini-brains emerge through a self-regulated process of agglomeration.</p><p>The resulting organoids "partly reproduce fetal brain development in vitro," says earlier <a href="https://bmcdevbiol.biomedcentral.com/articles/10.1186/s12861-019-0183-y" target="_blank" data-vivaldi-spatnav-clickable="1">research</a> from IDOR's team, led by <a href="https://loop.frontiersin.org/people/5771/overview" target="_blank" data-vivaldi-spatnav-clickable="1">Stevens K. Rehen</a>. Incomplete as organoids are, they nonetheless constitute "a demonstration that it is possible to repeat, in the laboratory, increasingly advanced gradients of human brain development," he <a href="https://neurosciencenews.com/complex-mini-brains-organoids-10870/" target="_blank" data-vivaldi-spatnav-clickable="1">says</a>. They provide a platform for studying normal brain development and brain disorders, and can serve as models for understanding pathologies — as they did for identifying the manner in which the Zika virus affects fetal brain development — no computer model or animal testing can address.</p><iframe width="560" height="315" src="https://www.youtube.com/embed/GuhUb9-Syzo" frameborder="0" allow="accelerometer; autoplay; encrypted-media; gyroscope; picture-in-picture" allowfullscreen></iframe>
Shaken, not spun<p>The IDOR team's announcement is just a detail in a<a href="https://bmcdevbiol.biomedcentral.com/articles/10.1186/s12861-019-0183-y" target="_blank" data-vivaldi-spatnav-clickable="1"> paper</a> whose primary purposes was presenting an alternative methodology for growing these complex 3D structures, using an orbital shaker — a device that gently stirs liquid suspensions to promote cell-cluster aggregation — instead of the more expensive <a href="http://www.3dnamics.com/technology/" target="_blank" data-vivaldi-spatnav-clickable="1">SpinΩ bioreactor</a>. IDOR asserts that their shaker produces a similar reduction in shear as the lowest spinning velocities for the SpinΩ, while still effectively promoting the growth of complex organoids.</p><p>The mini-brains grown with IDOR's process actually exhibited the presence of precursor cells for key architectures such as the forebrain, dorsal telencephalon, retinal cells and midbrain, and hindbrain in about 30 days. By 45 days, the organoids had "pigmented regions, which were previously described to reproduce the formation of retinal pigmented epithelium." These regions tested positive for glycogen synthetase, an enzyme linked to vision. These regions are the mini-brains' primitive eyes.</p><img type="lazy-image" data-runner-src="https://assets.rebelmouse.io/eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJpbWFnZSI6Imh0dHBzOi8vYXNzZXRzLnJibC5tcy8xOTI2NDEzNS9vcmlnaW4uanBnIiwiZXhwaXJlc19hdCI6MTYyNjU0MDgxMX0.5ofRjlr5iaTvZaZe5yqBRxEeWJqfCr-P5JOSc_pTNFQ/img.jpg?width=980" id="dadb4" class="rm-shortcode" data-rm-shortcode-id="700fa7f2a21b32336ef7fb8623b91fd3" data-rm-shortcode-name="rebelmouse-image" />
A: Image of an organoid with pigmented regions (bar = 1 mm). B: Box shows pigmented regions of organoid after 45 days (bar = 1 mm). C: Pigmented regions (bar = 500 μm)
(Rehen, et al)