Use-dependent, untapped dual kinase signaling localized in brain learning circuitry

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Abstract
Imaging brain learning and memory circuit kinase signaling is a monumental challenge. Theseparation ofphases-basedactivityreporter ofkinase (SPARK) biosensors allow circuit-localized studies of multiple interactive kinasesin vivo, including protein kinase A (PKA) and extracellular signal-regulated kinase (ERK) signaling. In the precisely-mappedDrosophilabrain learning/memory circuit, we find PKA and ERK signaling differentially enriched in distinct Kenyon cell connectivity nodes. We discover that potentiating normal circuit activity induces circuit-localized PKA and ERK signaling, expanding kinase function within new presynaptic and postsynaptic domains. Activity-induced PKA signaling shows extensive overlap with previously selective ERK signaling nodes, while activity-induced ERK signaling arises in new connectivity nodes. We find targeted synaptic transmission blockade in Kenyon cells elevates circuit-localized ERK induction in Kenyon cells with normally high baseline ERK signaling, suggesting lateral and feedback inhibition. We discover overexpression of the pathway-linking Meng-Po (human SBK1) serine/threonine kinase to improve learning acquisition and memory consolidation results in dramatically heightened PKA and ERK signaling in separable Kenyon cell circuit connectivity nodes, revealing both synchronized and untapped signaling potential. Finally, we find that a mechanically-induced epileptic seizure model (easily shocked“bang-sensitive” mutants) has strongly elevated, circuit-localized PKA and ERK signaling. Both sexes were used in all experiments, except for the hemizygous male-only seizure model. Hyperexcitable, learning-enhanced, and epileptic seizure models have comparably elevated interactive kinase signaling, suggesting a common basis of use-dependent induction. We conclude that PKA and ERK signaling modulation is locally coordinated in use-dependent spatial circuit dynamics underlying seizure susceptibility linked to learning/memory potential.Significance StatementCritical protein kinases act in learning/memory circuits to enable experience-dependent plasticity. This work images kinase signalingin vivoto elucidate circuit-level organization relative to mapped connectivity nodes. We discover different kinases exhibit heightened signaling in different circuit domains, which is dramatically reorganized by use-dependent synaptic transmission and circuit activity levels. We discover the newest learning/memory kinase, Meng-Po/SBK1, co-regulates different kinases within distinct circuit connectivity nodes. Targeted over-expression of Meng-Po/SBK1 improves learning and memory, and elevates kinase signaling, indicating untapped kinase signaling potential may enhance capabilities to learn and remember. Linked heightened seizure susceptibility similarly increases kinase signaling in learning/memory circuitry, indicating a trade-off of benefit for instability. This work mechanistically connects hyperexcitation seizure susceptibility and learning/memory via circuit-level kinase signaling.
Funding Information
  • HHS | NIH | National Institute of Mental Health (MH084989)
  • HHS | NIH | National Institute of Neurological Disorders and Stroke (NS131557)

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