Your brain may actually be two brains in one

The discovery that the front and back of the brain developed separately could open new ways to study ALS and other diseases affecting the brain stem.(CN) — For decades, scientists thought the entire brain started from the same type of progenitor cell. But in findings published Friday in Nature Neuroscience, researchers say the brain’s front and back begin from entirely different cells, following separate developmental paths.“We’ve shown for the first time that the front of the brain arises from a totally different progenitor cell than the back of the brain,” said Kyle Loh, an associate professor of developmental biology at Stanford Medicine and senior author of the study, in a news release. “Our discovery means that we can now grow neurons from the back of the brain, the hindbrain, in a petri dish and study their functions.”The different parts of the brain have very different jobs. The forebrain is involved in language, consciousness and abstract reasoning. The hindbrain, which includes the brain stem, controls many of the automatic functions needed to stay alive, including breathing, sleeping and regulating heartbeat and hunger. Its neurons also control muscles involved in speaking and swallowing.Despite those important roles, scientists have struggled to grow human hindbrain neurons in the lab, making it harder to study diseases that damage them, including spinal muscular atrophy, or SMA, and amyotrophic lateral sclerosis, or ALS.Researchers traced the divide back to gastrulation, an early stage of embryonic development when the body begins taking shape.By examining mouse embryos, the team identified two populations of brain progenitor cells. Cells expressing a gene called Otx2 went on to form the forebrain and midbrain, while cells expressing Gbx2 formed the hindbrain. The two populations did not overlap.The researchers also examined chromatin, the way DNA is packaged inside cells and which helps determine which genes are accessible. The two types of progenitor cells had different chromatin configurations, effectively committing them to separate developmental paths.“Previous attempts to make hindbrain neurons likely tried to coax forebrain and midbrain progenitors into hindbrain cells, which our study shows is not possible,” graduate student and co-first author Rayyan Jokhai said in the release.Once researchers understood the separate path taken by the hindbrain, they were able to coax human pluripotent stem cells into functional hindbrain motor neurons in the laboratory for the first time.The resulting cells behaved like hindbrain neurons, producing electrical activity and proteins associated with regions that control facial and swallowing muscles.The researchers then looked further back in evolutionary history and found evidence of the same two-part pattern in chickens, zebrafish and acorn worms, which share a distant common ancestor with humans.Jellyfish, which diverged from humans about 600 million to 700 million years ago, have two nervous systems at opposite ends of their bodies.“Our research suggests that evolution took two existing neural systems and pushed them together spatially,” Loh said. “Having the brain as one organ would probably be more efficient, but we rely on this primordial way to make the brain as two separate pieces.”Being able to grow hindbrain neurons could give researchers a new way to investigate SMA, ALS and other diseases affecting the brain stem.Scientists cannot obtain brain stem tissue from living patients, making laboratory models particularly important for understanding how these diseases damage neurons.Researchers next want to investigate the developmental origins of the spinal cord and how SMA and ALS interfere with hindbrain neurons.“Now we have a model to better understand these devastating diseases, and work toward regenerative therapies for them,” Jokhai said. “This is a very exciting new frontier in brain research.”Categories / Health, ScienceSubscribe to our free newslettersOur weekly newsletter Closing Arguments offers the latest about ongoing trials, major litigation and rulings in courthouses around the U.S. and the world, while the monthly Under the Lights dishes the legal dirt from Hollywood, sports, Big Tech and the arts.Additional Reads