Changes in presynaptic gene expression during homeostatic compensation at a central synapse
Homeostatic matching of pre- and postsynaptic function has been observed in many species and neural structures, but whether transcriptional changes contribute to this form of trans-synaptic coordination remains unknown. To identify genes whose expression is altered in presynaptic neurons as a result of perturbing postsynaptic excitability, we applied a transcriptomics-friendly, temperature-inducible Kir2.1-based activity clamp at the first synaptic relay of the Drosophila olfactory system, a central synapse known to exhibit trans-synaptic homeostatic matching. Twelve hours after adult-onset suppression of activity in postsynaptic antennal lobe projection neurons, we detected changes in the expression of many genes in the third antennal segment, which houses the somata of presynaptic olfactory receptor neurons. These changes affected genes with roles in synaptic vesicle release and synaptic remodeling, including several genes implicated in homeostatic plasticity at the neuromuscular junction. At 48 hours and beyond, the transcriptional landscape was tilted toward proteostasis, energy metabolism, and cellular stress defenses, indicating that the system had been pushed to its homeostatic limits. Our data provide insights into the nature of homeostatic compensation at a central synapse and identify many genes engaged in synaptic homeostasis. The presynaptic transcriptional response to genetically targeted postsynaptic perturbations could be exploited for the construction of novel connectivity tracing tools. Significance StatementHomeostatic feedback mechanisms adjust intrinsic and synaptic properties of neurons to keep their average activity levels constant. We show that, at a central synapse in the fruit fly brain, these mechanisms include changes in presynaptic gene expression that are instructed by an abrupt loss of postsynaptic excitability. The trans-synaptically regulated genes have roles in synaptic vesicle release and synapse remodeling; protein synthesis, folding, and degradation; and energy metabolism. Our analysis suggests that similar homeostatic machinery operates at peripheral and central synapses, identifies some of its components, and potentially opens new opportunities for the development of connectivity-based gene expression systems.