Emergence of coordinated activity in the motor circuits of Drosophila embryos
Tappei Kawasaki, Sawako Niki, Akinao Nose
Dept of Complexity Sci and Eng, Grad Sch of Frontier Sci, Univ of Tokyo, Chiba, Japan
We are interested in the mechanism of how neuronal populations in the central nervous system wire together to generate coordinated activity during development. Drosophila embryonic and larval motor circuits provide an ideal model system to address this question, since activity of specific component neurons can be visualized and manipulated using sophisticated genetic and optical techniques. Previous studies used muscle imaging to indirectly follow the development of motor circuits. In this study, we used calcium imaging to directly observe the emergence of motor-related neuronal activities during embryogenesis.
We used GAL4-UAS system to express the genetically-encoded calcium indicator GCaMP in all (with elav-Gal4), motor (OK6-Gal4), or GABAergic (Gad1-Gal4) neurons and imaged their activities for 5 min in dissected embryos at different developmental stages. In all of these neuronal populations, we observed the following sequence of activity development. First, sporadic activity in a small number of neurons appears. Then, partial activity propagation along a few segments occurred. Finally, integrated activity propagation along the entire CNS emerged. Such sequence in activity development is consistent with the previous report on muscle imaging in this system and also similar to what has been observed in vertebrate motor circuits (e.g., Warp et al., 2011; O'Donovan et al., 1994). While the activity of the three neuronal populations followed the same sequence of development, the timing was different: elav-Gal4 neurons show the coordinated activity first, followed by motor neurons and then GABAergic neurons. Thus, neurons other than motor neurons and GABAergic neurons are activated and recruited to the circuits first and may have leading roles in the organization of the circuits. We are currently trying to identify these neurons by using Gal4 lines expressed in different subsets of neurons. We are also searching for genes involved in the development of the coordinated activity and the results will be presented at the meeting.