We determined that the astrocyte glia in the central brain in the vicinity of the pacemaker neurons do not express PER. These results are consistent with a previous report that the astrocytes of the central brain are PER/TIM negative (Suh and Jackson, 2007). The absence of PER in fly astrocytes is somewhat unexpected given that mammalian astrocyte cultures from Per1::luciferase transgenic rats and knock-in mice are capable of maintaining modest rhythms in circadian clock genes expression (Prolo et al., 2005; Marpegan et al., 2011). In fact, several recent studies have demonstrated that mammalian astrocytes are important for controlling circadian timekeeping. Astrocyte-specific loss of core clock gene BMAL1 (the mammalian ortholog of cycle) via two independent methods was shown to alter circadian locomotor activity whereas expression of clock-associated kinase CK1ε in astrocytes was sufficient to lengthen the period of PER oscillations (Tso et al., 2017). Other recent studies also demonstrated astrocytes roles in circadian timekeeping through glia-neuron communication involving different signaling molecules (Barca-Mayo et al., 2017; Brancaccio et al., 2017). Consistent with the lack of PER in the fly central brain astrocytes, a study of the astrocyte transcriptome did not identify any of the core circadian clock genes (Ng et al., 2016). While astrocytes in both flies and mammals associate with neuronal synapses and have similar star-shaped morphologies and molecular markers, it is conceivable that circadian clock function could have been acquired later in evolution aided by the substantial proliferation of glia in mammals (Kremer et al., 2017).