Most areas of the brain do not generate new brain cells, or neurons, after we are born. One exception is the olfactory bulb, the brain’s scent processor, which continually produces new neurons. Doctor Troy Ghashghaei, assistant professor of neurobiology, had previously found a gene – known as Foxj1–connected to the production of an area inside the olfactory bulb where stem cells could form. Ghashghaei and his team discovered that Foxj1 was an “off switch” that told neuronal stem cells to stop reproducing and triggered the development of a stem cell “niche” in the olfactory bulbs.
However, further experiments with newly developed genetically modified mice unexpectedly revealed that a fraction of Foxj1-expressing cells actually functioned as stem cells. But they only did so until the mouse reached the age equivalent of a human toddler, not throughout adulthood. In addition, the number of neurons generated by these cells was much lower than expected, which led to more questions about its function.
Ghashghaei: “If the gene was one that stem cells had to express in order to produce neurons, then we should have seen a greater number of neurons produced from the Foxj1-expressing stem cells. Instead, only about three percent of the olfactory neurons came from the Foxj1 stem cells. More importantly, we could not identify these unique neurons as belonging to known types of neurons in the olfactory system.”
These findings and subsequent experimentation helped the team discover that in addition to being an off switch, the Foxj1 cellular lineage (i.e., Foxj1 expressing cells and their descendents) performs an important function as a “conductor,” instructing the other stem cells in the olfactory bulb by secreting various molecules that affect the other stem cells’ behavior and ensure their correct development into neurons. So a small number of Foxj1-expressing cells and their neuronal offspring direct other stem cells to continue reproducing, and may be telling them when to become functionally integrated neurons.
MEDICA.de; Source: North Carolina State University