Biology subjects

Katsioudi, G.

Publications and source records attributed to Katsioudi, G..

4 recordsLinked to original sources

bioRxiv2023

Diurnal control of iron responsive element (IRE)-containing mRNAs through iron regular proteins IRP1 and IRP2 is mediated by feeding rhythms

BackgroundCellular iron homeostasis is regulated by iron regulatory proteins (IRP1 and IRP2) that sense iron levels (and other metabolic cues) and modulate mRNA translation or stability via interaction with iron regulatory elements (IREs). IRP2 is viewed as the primary regulator in liver, yet our previous datasets showing diurnal rhythms for certain IRE-containing mRNAs suggest a nuanced temporal control mechanism. The purpose of this study is to gain insights into the daily regulatory dynamics across IRE-bearing mRNAs, specific IRP involvement, and underlying systemic and cellular rhythmicity cues in mouse liver. ResultsWe uncover high-amplitude diurnal oscillations in the regulation of key IRE containing transcripts in liver, compatible with maximal IRP activity at the onset of the dark phase. Although IRP2 protein levels also exhibit some diurnal variations and peak at the light-dark transition, ribosome profiling in IRP2-deficient mice reveals that maximal repression of target mRNAs at this time-point still occurs. We further find that diurnal regulation of IRE-containing mRNAs can continue in the absence of a functional circadian clock as long as feeding is rhythmic. ConclusionsOur findings suggest temporally controlled redundancy in IRP activities, with IRP2 mediating regulation of IRE-containing transcripts in the light phase and redundancy, conceivably with IRP1, at dark onset. Moreover, we highlight the significance of feeding-associated signals in driving rhythmicity. Our work highlights the dynamic nature and regulatory complexity in a metabolic pathway that had previously been considered well-understood.

molecular biology↗

bioRxiv2022

A novel Smg6 mouse model reveals regulation of circadian period and daily CRY2 accumulation through the nonsense-mediated mRNA decay pathway

Nonsense-mediated mRNA decay (NMD) has been intensively studied as a surveillance pathway that degrades erroneous transcripts arising from mutations or RNA processing errors. While additional roles in controlling regular mRNA stability have emerged, possible functions in mammalian physiology in vivo have remained unclear. Here, we report a novel conditional mouse allele that allows converting the NMD effector nuclease SMG6 from wild-type to nuclease domain-mutant protein. We analyzed how NMD downregulation affects the function of the circadian clock, a system known to require rapid mRNA turnover. We uncover strong lengthening of free-running circadian periods for liver and fibroblast clocks, and direct NMD regulation of Cry2 mRNA, encoding a key transcriptional repressor within the rhythm-generating feedback loop. In the entrained livers of Smg6 mutant animals we reveal transcriptome-wide alterations in daily mRNA accumulation patterns, altogether expanding the known scope of NMD regulation in mammalian gene expression and physiology.

genetics↗

bioRxiv2021

Infraslow locus coeruleus activity coordinates spindle rhythms and heart rate to gate fluctuating non-REM sleep substates

One promising approach towards understanding what makes sleep vulnerable in disease is to look at how wake-promoting mechanisms affect healthy sleep. Wake-promoting neuronal activity is inhibited during non-REM sleep (NREMS). However, many mammalian species, including humans, show recurrent moments of sleep fragility during which sensory reactivity is elevated. Wake-related neuronal activity could thus remain active in NREMS, but its roles in dynamic variations of sensory reactivity remain unknown. Here, we demonstrate that mouse NREMS is a brain state with recurrent fluctuations of the wake-promoting neurotransmitter noradrenaline on the [~]50-seconds time-scale. These fluctuations occurred around mean noradrenaline levels greater than the ones of quiet wakefulness, while they declined steeply in REMS. They coincided with a clustering of sleep spindle rhythms in the forebrain and with heart rate variations. We addressed the origins of these fluctuations by using closed-loop optogenetic locus coeruleus (LC) activation or inhibition timed to moments of low and high spindle activity during NREMS. We could suppress, lock or entrain sleep spindle clustering or heart rate variations, demonstrating that both fore- and hindbrain-projecting LC neurons show synchronized infraslow activity variations in natural NREMS. Noradrenergic modulation of thalamic but not cortical circuits was required for sleep spindle clustering and involved noradrenaline release into primary sensory and reticular thalamic nuclei that activated both 1- and {beta}-adrenergic receptors to cause slowly decaying membrane depolarizations. Noradrenergic signaling by LC, primarily known for attention promotion in wakefulness, renders mammalian NREMS more wake-like on the close-to-minute-time scale through sustaining thalamocortical and autonomic sensory arousability.

neuroscience↗

bioRxiv2019

A thalamic reticular circuit for head direction cell tuning and spatial navigation

To navigate in space, an animal must refer to sensory cues to orient and move. Circuit and synaptic mechanisms that integrate cues with internal head-direction (HD) signals remain, however, unclear. We identify an excitatory synaptic projection from the presubiculum (PreS) and the multisensory-associative retrosplenial cortex (RSC) to the anterodorsal thalamic reticular nucleus (TRN), so far classically implied in gating sensory information flow. In vitro, projections to TRN involved AMPA/NMDA-type glutamate receptors that initiated TRN cell burst discharge and feedforward inhibition of anterior thalamic nuclei. In vivo, chemogenetic anterodorsal TRN inhibition modulated PreS/RSC-induced anterior thalamic firing dynamics, broadened the tuning of thalamic HD cells, and led to preferential use of allo-over egocentric search strategies in the Morris water maze. TRN-dependent thalamic inhibition is thus an integral part of limbic navigational circuits wherein it coordinates external sensory and internal HD signals to regulate the choice of search strategies during spatial navigation.

neuroscience↗