Biology subjects

Wong, H. H.-W.

Publications and source records attributed to Wong, H. H.-W..

4 recordsLinked to original sources

bioRxiv2025

Neocortical Layer-5 tLTD Relies on Non-Ionotropic Presynaptic NMDA Receptor Signaling

In the textbook view, NMDA receptors (NMDARs) act as coincidence detectors in Hebbian plasticity by fluxing Ca2+ when simultaneously depolarized and glutamate bound. Hebbian coincidence detection requires that NMDARs be located postsynaptically, but enigmatic presynaptic NMDARs (preNMDARs) also exist. It is known that preNMDARs regulate neurotransmitter release, but precisely how remains poorly understood. Emerging evidence suggest that NMDARs can also signal non-ionotropically, without the need for Ca2+ flux. At synapses between developing visual cortex layer-5 (L5) pyramidal cells (PCs), preNMDARs rely on Mg2+ and Rab3-interacting molecule 1{beta} (RIM1{beta}) to regulate evoked release during periods of high-frequency firing, but they signal non-ionotropically via c-Jun N-terminal kinase 2 (JNK2) to regulate spontaneous release regardless of frequency. At the same synapses, timing-dependent long-term depression (tLTD) depends on preNMDARs but not on frequency. We therefore tested if tLTD relies on non-ionotropic preNMDAR signaling. We found that tLTD at L5 PC[->]PC synapses was abolished by pre- but not postsynaptic NMDAR deletion, cementing the view that tLTD requires preNMDARs. In agreement with non-ionotropic NMDAR signaling, tLTD prevailed after channel pore blockade with MK-801, unlike tLTP. Homozygous RIM1{beta} deletion did not affect tLTD, but wash-in of the JNK2 blocker SP600125 abolished tLTD. Consistent with a presynaptic need for JNK2, a peptide blocking the interaction between JNK2 and Syntaxin-1a (STX1a) abolished tLTD if loaded pre- but not postsynaptically, regardless of frequency. Finally, low-frequency tLTD was not blocked by the channel pore blocker MK-801, nor by 7-CK, a non-competitive NMDAR antagonist at the co-agonist site. We conclude that neocortical L5 PC[->]PC tLTD relies on non-ionotropic preNMDAR signaling via JNK2/STX1a. Our study brings closure to long-standing controversy surrounding preNMDARs and highlights how the textbook view of NMDARs as ionotropic coincidence detectors in plasticity needs to be reassessed.

neuroscience↗

bioRxiv2023

Principles of visual cortex excitatory microcircuit organization

Microcircuit function is determined by patterns of connectivity and short-term plasticity that vary with synapse type. Elucidating microcircuit function therefore requires synapse-specific investigation. The state of the art for synapse-specific measurements has long been paired recordings. Although powerful, this method is slow, leading to a throughput problem. To improve yield, we therefore created optomapping -- an approximately 100-fold faster 2-photon optogenetic method -- which we validated with paired-recording data. Using optomapping, we tested 15,433 candidate excitatory inputs to find 1,184 connections onto pyramidal, basket, and Martinotti cells in mouse primary visual cortex, V1. We measured connectivity, synaptic weight, and short-term dynamics across the V1 layers. We found log-normal synaptic strength distributions, even in individual inhibitory cells, which was previously not known. We reproduced the canonical circuit for pyramidal cells but found surprising and differential microcircuit structures, with excitation of basket cells concentrated to layer 5, and excitation of Martinotti cells dominating in layer 2/3. Excitation of inhibitory cells was denser, stronger, and farther-reaching than excitation of excitatory cells, which promotes stability and difference-of-Gaussian connectivity. We gathered an excitatory short-term plasticitome, which revealed that short-term plasticity is simultaneously target-cell specific and dependent on presynaptic cortical layer. Peak depolarization latency in pyramidal cells also emerged as more heterogeneous, suggesting heightened sensitivity to redistribution of synaptic efficacy. Optomapping additionally revealed high-order connectivity patterns including shared-input surplus for interconnected pyramidal cells in layer 6. Optomapping thus offered both resolution to the throughput problem and novel insights into the principles of neocortical excitatory fine structure. HIGHLIGHTSO_LI2-photon optomapping of microcircuits is verified as fast, accurate, and reliable C_LIO_LISynaptic weights distribute log-normally even for individual inhibitory neurons C_LIO_LIMaximal excitation of basket and Martinotti cells in layer 5 and 2/3, respectively C_LIO_LIShort-term plasticity depends on layer in addition to target cell C_LI

neuroscience↗

bioRxiv2022

Local axonal translation sustains synapse-type-specific neurotransmission

Dendritic protein synthesis is a well-known regulator of neurotransmission in the central nervous system. For example, local on-demand protein synthesis in dendrites is required for hippocampal long-term1,2 and homeostatic plasticity3. Although axonal protein synthesis is a key regulator in neural circuit assembly during early development4-6, it is unclear if local translation in mature axons plays a functional role in neurotransmission of the mammalian central nervous system. Here we show that local translation in axons regulates pyramidal cell neurotransmission in primary visual cortex microcircuits in a synapse-type-specific manner7,8. Using paired recordings to manipulate pre- and postsynaptic neurons independently, we found that presynaptic translation sustains neurotransmission and regulates short-term plasticity. This was mediated via mTOR and cap-dependent translation, with presynaptic NMDA receptors acting as an up-stream trigger. By isolating the axon from the soma with laser microsurgery, we unveiled that axonal translation was required to sustain neurotransmission. With live endogenous RNA imaging, we found that RNA granules stably docked in individual presynaptic compartments, suggesting bouton-specific regulation. In agreement, presynaptic translation influenced pyramidal cell synapses to neighbouring pyramidal cells, but not to inhibitory Martinotti cells. Our study establishes local protein synthesis in mature axons as a fundamental regulatory principle that governs information transfer at central synapses.

neuroscience↗

bioRxiv2018

On-site ribosome remodeling by locally synthesized ribosomal proteins in axons

Ribosomes are known to be assembled in the nucleolus, yet recent studies have revealed robust enrichment and translation of mRNAs encoding ribosomal proteins (RPs) in axons, far away from neuronal cell bodies. Using subcellular proteomics and live-imaging, we show that locally synthesized RPs incorporate into axonal ribosomes in a nucleolus-independent fashion. We revealed that axonal RP translation is regulated through a novel sequence motif, CUIC, that forms a RNA-loop structure in the region immediately upstream of the initiation codon. Inhibition of axonal CUIC-regulated RP translation leads to defects in local translation activity and axon branching, demonstrating the physiological relevance of the axonal ribosome remodeling. These results indicate that axonal translation supplies cytoplasmic RPs to maintain/modify local ribosomal function far from the nucleolus.

neuroscience↗