Single Astrocyte Labeling Approaches to Uncover Circadian Structural Plasticity

The earth’s rotation around the sun creates cycles of light and darkness, prompting organisms to develop adaptations known as circadian rhythms. Drosophila melanogaster has about 240 clock neurons responsible for regulating these rhythms through the expression of clock proteins that constitute the molecular clockwork. The axonal terminals of a key group of clock neurons, the small lateral ventral neurons (sLNvs), undergo rhythmic circadian remodeling. They are more complex and highly branched at the start of the day, before daily activity begins, and less complex at night during the rest. This process is known as circadian structural plasticity. Astrocytes, a specific type of glial cell that also harbor a molecular clock, make contacts with clock neurons. Our preliminary results show that cell-to-cell contact between astrocytes and sLNvs changes throughout the day, with a maximum early in the day, when neuronal terminals are more highly branched. These findings raise the possibility that astrocytes themselves may undergo circadian structural remodeling. Recently, using Astro-TRACT, we identify the conditions to express mCD8-GFP in single astrocytes engaged in synaptic interactions with clock neurons. The sparse labeling of isolated astrocytes provides an ideal platform for examining changes in morphology throughout the day. These findings will pave the way for future research.