Requirement for Nuclear Calcium Signaling in Drosophila Long-Term Memory

Abstract

Calcium is used throughout evolution as an intracellular signal transducer. In the mammalian central nervous system, calcium mediates the dialogue between the synapse and the nucleus that is required for transcription-dependent persistent neuronal adaptations. A role for nuclear calcium signaling in similar processes in the invertebrate brain has yet to be investigated. Here, we show by in vivo calcium imaging of adult brain neurons of the fruit fly Drosophila melanogaster, that electrical foot shocks used in olfactory avoidance conditioning evoked transient increases in cytosolic and nuclear calcium concentrations in neurons. These calcium signals were detected in Kenyon cells of the flies' mushroom bodies, which are sites of learning and memory related to smell. Acute blockade of nuclear calcium signaling during conditioning selectively and reversibly abolished the formation of long-term olfactory avoidance memory, whereas short-term, middle-term, or anesthesia-resistant olfactory memory remained unaffected. Thus, nuclear calcium signaling is required in flies for the progression of memories from labile to transcription-dependent long-lasting forms. These results identify nuclear calcium as an evolutionarily conserved signal needed in both invertebrate and vertebrate brains for transcription-dependent memory consolidation.

Pathogenic Tau Causes a Toxic Depletion of Nuclear Calcium

“…To determine if depletion of nuclear Ca 2+ signaling is causally associated with neurodegeneration, we overexpressed a recombinant blocker of nuclear Ca 2+ , CaMBP4 ( Weislogel et al, 2013 ), in neurons of the adult Drosophila brain. CaMBP4 is a nuclear protein that contains four copies of a calmodulin-binding peptide (M13).…”

“…UAS-slo RNAi and slo 1 were obtained from the Bloomington Drosophila Stock Center. UAS-GCaMP3.NLS and CaMBP4 transgenic flies were generously provided by Dr. Hilmar Bading ( Weislogel et al, 2013 ).…”

“…To quantify resting nuclear Ca 2+ levels in brains of living flies ( Figures 2A – 2C , 4A , and 4B ), a single fly was placed on a CO 2 gas pad until the fly lost postural control, then transferred into a 100% ethanol bath for 10 s. Using a small Sylgard dissection surface, the fly was then placed in cold HL3 solution (70 mM NaCl, 5 mM KCl, 10 mM NaHCO 3 , 5 mM trehalose, 115 mM sucrose, 5 mM HEPES, 0.5 mM CaCl 2 , 3 mM MgCl 2 ) and pinned using modified minutien pins on its ventral surface ( Mahoney et al, 2014 ). Once positioned, a small piece of cuticle was removed from the posterior side of the head (cuticular window) to reveal the underlying mushroom body ( Weislogel et al, 2013 ). GFP fluorescence resulting from GCaMP3.NLS activation was imaged with a Zeiss LSM 780 NLO with Examiner.…”

“…After a three second recovery, baseline intensity was set to one for both control and tau R406W transgenic Drosophila . The KCl-induced nuclear Ca 2+ response is presented as change from baseline ( Weislogel et al, 2013 ). Six biological replicates were analyzed per group.…”

Lineage divergence of activity-driven transcription and evolution of cognitive ability

“…For simplicity, gains of activity-responsive genes are only shown for mouse and human. The fruit fly is included as an example of an invertebrate that uses excitation-transcription coupling via evolutionary conserved nuclear Ca 2+ regulated mechanisms for core cognitive functions99 .This schematic illustration is not intended to be comprehensive and categorical and does not include all possible scenarios by which activity-responsiveness may be conferred to a gene , through the loss of a repressive DNA element) and does not imply that advancement of cognitive abilities is necessarily linear.…”