Changes in presynaptic gene expression during homeostatic compensation at a central synapse

Abstract

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.

A rise-to-threshold signal for a relative value deliberation

“…Kir2.1* and Kir2.1*Mut had been developed and used to hyperpolarize neurons in mice 36 ; we introduce the transgenes into flies here (Methods). A similar strategy of using Kir2.1 paired with a non-conducting control has been recently used in flies 37 , but in those experiments the human, not a modified mouse, isoform was used. Kir2.1* and Kir2.1*Mut gene expression was restricted to a 23-hour period prior to experiments (Methods).…”

Endogenous tagging of Unc-13 reveals nanocluster reorganization at active zones during presynaptic homeostatic potentiation

“…In addition to its role in docking and priming of synaptic vesicles Unc-13 is involved in diverse presynaptic plasticity processes including Ca 2+ , DAG or RIM-dependent short-term plasticity (Betz et al, 2001; Dulubova et al, 2005; Shin et al, 2010; Xu et al, 2017) and presynaptic homeostatic potentiation (PHP, Böhme et al, 2019; Harrell et al, 2021). In Drosophila , upregulated Unc-13A levels and increased numbers of Unc-13A nanomodules at presynaptic AZs in acute and chronic PHP were observed (Böhme et al, 2019).…”

“…Munc-13 interacts with the SNARE-complex protein Syntaxin (Richmond et al, 2001; Madison et al, 2005; Hammarlund et al, 2007) via its C-terminal MUN-domain (Guan et al, 2008). The MUN-domain is surrounded by two C2-domains (C2B and C2C; Liu et al, 2021) and plays an essential role in synaptic transmission including presynaptic homeostatic potentiation (PHP, Böhme et al, 2019; Harrell et al, 2021). Due to its central role in SNARE-complex formation Munc-13 is a key molecular marker of individual release sites (Böhme et al, 2016; Reddy-Alla et al, 2017; Sakamoto et al, 2018; Dittman 2019).…”

Homeostatic Synaptic Plasticity Rescues Neural Coding Reliability

“…Notably, the ORN-PN synapse is surprisingly resilient to reduced AZ Ca 2+ channel expression and compensates the drop in release probability by increasing the number of AZs to yield normal eEPSC amplitudes. Homeostatic synaptic plasticity features at the Drosophila NMJ 11,12 , mushroom body 67 , and also operates in the antennal lobe to match synaptic strength to PN excitability 30,68 . Interestingly, Cac RNAi decreases synaptic transmission to a greater extent from ORNs to iLNs than from ORNs to PNs (compare Figures 1C and 3C).…”