A gene controls neuronal traffic in the assembly of this electrical circuit.
To form the complex circuits of the brain, neurons have to know when to grow and when to stop. The above image displays light-sensing neurons in the eye of a fruit fly (red and green). Those in green have just finished extending projections, known as axons, from the retina (top) into the brain (bottom), where they will connect with other neurons in the circuit. By studying flies with abnormal connections in these circuits, scientists identified a gene that directs the green neurons to stop extending their axons at the correct time and place.
Kniss JS, Holbrook S, Herman TG. R7 Photoreceptor Axon Growth Is Temporally Controlled by the Transcription Factor Ttk69, Which Inhibits Growth in Part by Promoting Transforming Growth Factor-β/Activin Signaling. The Journal of Neuroscience. 23 January, 33(4): 1509-1520 (2013).