Keio University · Biochemistry, Genetics and Molecular Biology
Professor Kotaro Oka's research lab specializes in developing advanced fluorescent probes and imaging techniques to visualize fundamental cellular processes in real time. The lab focuses on tracking essential cellular ions—particularly magnesium and calcium—within subcellular compartments such as mitochondria, enabling dynamic insights into cellular signaling, metabolism, and neuronal development. A key direction involves applying innovative FRET-based and dual-color imaging strategies to study fast and complex signal transduction in living cells. The lab also explores molecular mechanisms underlying convergent evolution in vocal learning, linking neuroanatomy with gene expression in brain circuits.
Figures are computed from collected data and may differ slightly.
Magnesium (Mg) is the second most abundant cation in mammalian cells, and it is essential for numerous cellular processes including enzymatic reactions, ion channel functions, metabolic cycles, cellular signaling, and DNA/RNA stabilities. Because of the versatile and universal nature of Mg<sup>2+</sup>, the homeostasis of intracellular Mg<sup>2+</sup> is physiologically linked to growth, proliferation, differentiation, energy metabolism, and death of cells. On the cellular and tissue levels, mai
Fluorescence resonance energy transfer (FRET) between fluorescent proteins is a powerful tool for visualization of signal transduction in living cells, and recently, some strategies for imaging of dual FRET pairs in a single cell have been reported. However, these necessitate alteration of excitation light between two different wavelengths to avoid the spectral overlap, resulting in sequential detection with a lag time. Thus, to follow fast signal dynamics or signal changes in highly motile cell
We report a novel near-infrared fluorescent calcium probe (KFCA), which has good optical properties such as intense NIR fluorescence emission (670 nm, QY: 0.24), excellent ON/OFF ratio (120-fold), and good wavelength-compatibility with visible-light-emissive fluorophores (Fluo-4, DsRed2), and which is applicable for real-time dual-colour intracellular Ca(2+) imaging.
Mg(2+) plays important roles in numerous cellular functions. Mitochondria take part in intracellular Mg(2+) regulation and the Mg(2+) concentration in mitochondria affects the synthesis of ATP. However, there are few methods to observe Mg(2+) in mitochondria in intact cells. Here, we have developed a novel Mg(2+)-selective fluorescent probe, KMG-301, that is functional in mitochondria. This probe changes its fluorescence properties solely depending on the Mg(2+) concentration in mitochondria und
Mechanisms for the evolution of convergent behavioral traits are largely unknown. Vocal learning is one such trait that evolved multiple times and is necessary in humans for the acquisition of spoken language. Among birds, vocal learning is evolved in songbirds, parrots, and hummingbirds. Each time similar forebrain song nuclei specialized for vocal learning and production have evolved. This finding led to the hypothesis that the behavioral and neuroanatomical convergences for vocal learning cou
As a neurotransmitter and neuromodulator, serotonin (5-HT) influences neuronal outgrowth in the nervous systems of several species. In PC12 cells, 5-HT is known to have neuritogenic effects, although the signal transduction pathway responsible for these effects is not understood. In this study, we hypothesized that a 5-HT-induced increase in intracellular Ca(2+) concentration ([Ca(2+)](i)) could be involved in mediating the effects of 5-HT. Application of 5-HT to PC12 cells enhanced nerve growth
Cyclic GMP (cGMP) regulates many physiological processes by cooperating with the other signaling molecules such as cyclic AMP (cAMP) and Ca(2+). Genetically encoded sensors for cGMP have been developed based on fluorescence resonance energy transfer (FRET) between fluorescent proteins. However, to analyze the dynamic relationship among these second messengers, combined use of existing sensors in a single cell is inadequate because of the significant spectral overlaps. A single wavelength indicat
An event-related potential called mismatch negativity is known to exhibit physiological evidence of sensory memory. Mismatch negativity is believed to represent complicated neuronal mechanisms in a variety of animals and in humans. We employed the auditory oddball paradigm varying sound durations and observed two types of duration mismatch negativity in anesthetized guinea pigs. One was a duration mismatch negativity whose increase in peak amplitude occurred immediately after onset of the stimul
Excess administration of glutamate is known to induce Ca(2+) overload in neurons, which is the first step in excitotoxicity. Although some reports have suggested a role for Mg(2+) in the excitotoxicity, little is known about its actual contribution. To investigate the role of Mg(2+) in the excitotoxicity, we simultaneously measured intracellular Ca(2+) and Mg(2+), using fluorescent dyes, Fura red, a fluorescent Ca(2+) probe, and KMG-104, a highly selective fluorescent Mg(2+) probe developed by o
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