Researchers at Stanford established a direction by making a detailed cell-by-cell gene blueprint of the fruit fly's olfactory neurons. Scientists have been working to zoom in and identify how brain circuits form so they can learn to rewire troublemaking neurons. The human nervous system is like a complex circuit board. When wires cross or circuits malfunction, conditions such as schizophrenia or bipolar disorder can arise. Their study has been published in Cell.

The basic idea behind the research is to understand the neuronal cell types of the relatively simple fly brain, and to identify the molecules that direct the precise wiring of different types of neurons in the fly brain. Over time, researchers want to use a similar approach to study the far more complex cellular makeup of the human brain, and maybe one day even repair the miswiring in brain disorders.

Single-cell RNA sequencing

Reaching back into high school biology, remember that cells have DNA and RNA. DNA is the genetic code that represents the blueprint of an entire organism. The fruit fly, a model organism for the human because it shares approximately 75 percent of our known disease genes, has about 15,000 genes. Each individual cell expresses a specific subset of genes, which in turn make a specific set of proteins. Messenger RNA molecules carry the genetic codes to create, or express, whatever proteins may be required by any specific cell at any point in time.

The fruit fly is one of the most studied organisms in biology. Prior experimental research has proven the fly's olfactory system to be a clean and simple circuit, making it the ideal test bed for developing a new genetic technology to probe how brain circuits are wired up. The smell center of the fly brain has 50 types of central processing neurons that grow threadlike filaments to connect with 50 types of sensory neurons. Each connected pair of neurons allows the fruit fly to smell one group of odors, and in combination, the fruit fly can detect the myriad odors of the fruits in your kitchen.

New insights

Though researchers are still a long way from that goal, their finding has already yielded some interesting insights into the minds of flies.  Horns said, "Once the brain is wired up, the fly doesn't need to express those genes that help them in choosing the connection partners." The goal is to develop new and powerful tools for understanding the genetic blueprints that wire the human brain. Li said, "By further developing this approach, we hope to one day reverse-engineer and perhaps even repair defective circuitry in the human brain."