Two independent research teams successfully regenerated brain circuits in mice using neurons grown from rat stem cells. These two studies, published on the 25th in the journal Cell, provide valuable insights into how brain tissue forms and offer new avenues for restoring brain function lost due to disease and aging. Columbia University professor Christian Baldwin stated that these studies demonstrate the potential flexibility in using synthetic neural circuits to restore brain function. The Baldwin team used stem cells from rats to restore the olfactory neural circuit in mice. Associate Professor Wu Jun at the University of Texas Southwest Medical Center believes that using cells from one species to produce brain tissue in another species can help people understand the brain development and evolution of different species. The Wu Jun team has developed a CRISPR based platform that can effectively identify and drive specific genes for tissue development. They tested the platform by silencing the genes required for forebrain development in mice and then using rat stem cells to restore tissue. Wu Jun's team used CRISPR technology to test seven different genes and found that knocking out Hesx1 reliably produced mice without forebrain. Then, the research team injected rat stem cells into the blastocysts of Hesx1 knockout mice, and rat cells filled niches to form the forebrain of the mice. The brain of rats is larger than that of mice, but the development speed and size of their forebrain are the same as those of mice. In addition, rat neurons are able to transmit signals to neighboring mouse neurons, and vice versa. In another study, the Baldwin team used specific genes to kill or silence olfactory neurons in mice. The killing model completely removes neurons and simulates degenerative diseases; The silent model mimics neurodevelopmental disorders, in which some neurons are unable to communicate with the brain. Then they injected rat stem cells into mouse embryos to observe the differences between these two disease models. This study helps to determine the mechanism of brain function recovery. The brain is like a precision instrument, its function can be damaged or degraded due to disease and aging. Many patients with brain tumors, brain trauma, and dementia are experiencing this process and enduring a decline in their quality of life. How to restore damaged or degraded brain function? This has been a long-standing medical challenge. The latest research utilizes brain cell fusion technology to provide new ideas for brain function recovery. (Lai Xin She)