Biology subjects

Isaacson, J. R.

Publications and source records attributed to Isaacson, J. R..

7 recordsLinked to original sources

bioRxiv2025

Mistranslation protects against lifespan reduction due to mating in Drosophila melanogaster females.

Accurate translation of genes into proteins is critical to organism fitness, and errors in this process are usually detrimental and cause proteotoxic stress. Mistranslation occurs when the amino acid that is incorporated into the nascent polypeptide chain does not match what is dictated by the genetic code. Valine-to-serine (V[->]S) and threonine-to-serine (T[->]S) mistranslating models of the fruit fly Drosophila melanogaster have demonstrated a surprising, sex-specific increase in virgin female longevity. We predict that the added stressor of reproduction would eliminate this mistranslation-induced lifespan increase since females prioritize reproductive tissues over somatic tissues, and proteotoxic stress would therefore lead to higher protein damage in the soma of mated females. We measured the impact of reproduction on V[->]S and T[->]S mistranslating D. melanogaster by measuring longevity, egg laying, and fecundity. Counter to our prediction, both V[->]S and T[->]S mistranslation led to a sex-specific increase in mated female longevity compared to non-mistranslating controls. Additionally, the risk of death decreased for mated females with mistranslation, beyond the pure additive benefits of mistranslation alone. These effects could not be explained by reduced egg laying or fertilization rates in mistranslating females. Thus, we find that the added proteotoxic stress caused by mistranslation does not exacerbate the detrimental effects of reproduction and instead can ameliorate lifespan decreases due to female reproduction.

genetics↗

bioRxiv2024

Neuroligin 3 highlights sexually dimorphic circuitry in Drosophila social spacing

In Drosophila melanogaster, the autism-related Neuroligin 3 (Nlg3) protein is a postsynaptic membrane protein important for synapse development and regulation, which plays a role in social spacing behaviour. Here, we report the localization of Nlg3 to the calyx of the mushroom bodies (MB), optic lobes (OL), and protocerebral bridge (PB). Using RNA interference, nlg3 knockdown in each of these structures recapitulated the effect of knocking down it in all nlg-3 neurons. Hyperactivation and silencing of these neurons in the MB, but not the PB, controls social space in males and females, while hyperactivating and silencing of all nlg3-expressing neurons, including within the MB, PB, and OL, regulates male and female social space. Knocking down neurotransmitter biosynthesis enzymes, which decreases the amount of neurotransmitter release, showed that reducing acetylcholine release from the MB decreased female social space, whereas knocking down any dopamine receptor in the MB increased male social space. Lastly, to investigate the sexually dimorphic effects on social spacing previously seen in nlg3 mutants, we examined a subset of sexually dimorphic fruitless-expressing (fru)P1 neurons known to regulate sexually dimorphic behaviours. Hyperactivation of those fruP1 neurons decreased social space in both sexes, while silencing those fruP1 neurons specifically increased male social space without affecting females. Our findings highlight a sex-specific social space neural circuitry that includes the OL, MB, and fruP1 neurons, while uncovering the underlying basis of some of the sex differences in this behaviour. Article SummaryIn vinegar flies (Drosophila melanogaster), the autism-related Neuroligin 3 protein (Nlg3) controls neuronal development and regulation but also affects fly social behaviour. Nlg3 is localized to the mushroom bodies (MB), protocerebral bridge, and the optic lobes. We show that those structures are important in determining social space in a sex dependant manner. In addition, reducing acetylcholine release from the MB affects female social space, while reducing dopamine receptors of the MB only affect male behaviour. Finally, the fruitless sexually dimorphic neurons control social behavior differently in males and females.

animal behavior and cognition↗

bioRxiv2024

Mistranslating tRNA variants have anticodon- and sex-specific impacts on Drosophila melanogaster

Transfer RNAs (tRNAs) are vital in determining the specificity of translation. Mutations in tRNA genes can result in the misincorporation of amino acids into nascent polypeptides in a process known as mistranslation. Since mistranslation has different impacts, depending on the type of amino acid substitution, our goal here was to compare the impact of different mistranslating tRNASer variants on fly development, lifespan, and behaviour. We established two mistranslating fly lines, one with a tRNASer variant that misincorporates serine at valine codons (VS) and the other that misincorporates serine at threonine codons (TaS). While both mistranslating tRNAs increased development time and developmental lethality, the severity of the impacts differed depending on amino acid substitution and sex. The VS variant extended embryonic, larval, and pupal development whereas the TS only extended larval and pupal development. Females, but not males, containing either mistranslating tRNA presented with significantly more anatomical deformities than controls. Mistranslating females also experienced extended lifespan whereas mistranslating male lifespan was unaffected. In addition, mistranslating flies from both sexes showed improved locomotion as they aged, suggesting delayed neurodegeneration. Therefore, although mistranslation causes detrimental effects, we demonstrate that mistranslation also has positive effects on complex traits such as lifespan and locomotion. This has important implications for human health given the prevalence of tRNA variants in humans. PLAIN LANGUAGE SUMMARYMutant tRNA genes can cause mistranslation, the misincorporation of amino acids into proteins, and are associated with several human diseases. This study investigated the role of two tRNA variants that cause threonine-to-serine (TS) or valine-to-serine (VS) substitution. Both variants caused developmental delays and lethality in both sexes and increase prevalence of deformities in females. Surprisingly, female TS and VS flies experienced increased lifespan and mistranslating males and females showed improved locomotion. These results suggest that mistranslation has both positive and negative effects that depend on the tRNA variant and sex of the fly.

genetics↗

bioRxiv2024

Impact of tRNA-induced proline-to-serine mistranslation on the transcriptome of Drosophila melanogaster

Mistranslation is the misincorporation of an amino acid into a polypeptide. Mistranslation has diverse effects on multicellular eukaryotes and is implicated in several human diseases. In Drosophila melanogaster, a serine transfer RNA (tRNA) that misincorporates serine at proline codons (P[->]S) affects male and female flies differently. The mechanisms behind this discrepancy are currently unknown. Here, we compare the transcriptional response of male and female flies to P[->]S mistranslation to identify genes and cellular processes that underlie sex-specific differences. Both males and females downregulate genes associated with various metabolic processes in response to P[->]S mistranslation. Males downregulate genes associated with extracellular matrix organization and response to negative stimuli such as wounding, whereas females downregulate aerobic respiration and ATP synthesis genes. Both sexes upregulate genes associated with gametogenesis, but females also upregulate cell cycle and DNA repair genes. These observed differences in the transcriptional response of male and female flies to P[->]S mistranslation have important implications for the sex-specific impact of mistranslation on disease and tRNA therapeutics. ARTICLE SUMMARYProline-to-serine mistranslation affects male and female flies differently, but the mechanisms underlying this discrepancy are unknown. We present a transcriptomic analysis of male and female flies showing that mistranslation disrupts metabolic pathways and gametogenesis in both sexes, whereas processes such as DNA repair and cell cycle regulation are affected only in one sex. This is the first analysis that characterizes sex-specific effects of mistranslation and provides intriguing avenues for future research to understand how mistranslation affects males and females.

genetics↗

bioRxiv2022

Dual orexin antagonist DORA-22 suppressed posttraumatic seizures and enhances GABAergic inhibition in dentate granule cells

BackgroundTraumatic brain injury (TBI) can result in posttraumatic epilepsy (PTE) and sleep disturbances. We hypothesized that treatment with sleep aids after TBI can ameliorate PTE. MethodsCD-1 mice underwent controlled cortical impact (CCI), sham craniotomy or no craniotomy. Sham and CCI groups underwent a month-long treatment with sleep aids including a dual orexin antagonist (DORA-22) or THIP (gaboxadol). We performed week-long EEG recordings during week-1 of treatment and again at months 1, 2 and 3. Seizure analysis occurred at all-time points and sleep analysis occurred in week-1 and month-1 recordings in all groups. Subsets of animals in sleep aid-treated and untreated CCI, and sham groups were subjected to voltage clamp experiments. ResultsDORA-22 treated group had seizures at week-1 but none at months 1-3. TBI reduced amplitude and frequency of miniature inhibitory synaptic currents (mIPSCs) in dentate granule cells and these changes were rescued by DORA-22 treatment. Sleep analysis showed that DORA-22 increased non-rapid eye movement sleep (NREM) in the first 4hours of lights-off whereas THIP increased REM sleep in the first 4-hours of lights-on in week-1, At month-1 both treatments reduced time in NREM during lights-off. TBI increased NREM delta power (N{Delta}) along with loss of the homeostatic overnight decline of N{Delta} in week-1 regardless of treatment. DORA-22 and THIP treatment restored N{Delta} to levels similar to no craniotomy animals at month-1. ConclusionsDORA-22 treatment suppressed posttraumatic seizures possibly due to enhanced GABAergic inhibition in dentate granule cells. DORA-22 may have therapeutic potential in suppressing PTE. Summary for Social MediaTraumatic brain injury (TBI) can result is posttraumatic epilepsy and sleep disturbances. There are no treatments to prevent these complications. We tested whether treatment with sleep aids after TBI can mitigate seizures and sleep disturbances. We found that a sleep aid DORA-22 but not THIP suppressed post traumatic seizures possibly be enhancing GABAergic inhibition in the hippocampus. Sleep analysis showed that TBI disrupts the sleep homeostatic drive and DORA treatment restored it. Findings may lead to potential disease modifying therapy for posttraumatic epilepsy.

neuroscience↗

bioRxiv2021

A Novel Mistranslating tRNA Model in Drosophila melanogaster has Diverse, Sexually Dimorphic Effects

Transfer RNAs (tRNAs) are the adaptor molecules required for reading of the genetic code and the accurate production of proteins. tRNA variants can lead to genome-wide mistranslation, the misincorporation of amino acids not specified by the standard genetic code into nascent proteins. While genome sequencing has identified putative mistranslating tRNA variants in human populations, little is known regarding how mistranslation affects multicellular organisms. Here, we create a Drosophila melanogaster model for mistranslation by integrating a serine tRNA variant that mistranslates serine for proline (tRNASerUGG, G26A) into the fly genome. Using mass spectrometry, we find that tRNASerUGG, G26A misincorporates serine for proline at a frequency of [~] 0.6% per codon. We find that mistranslation extends development time and decreases the number of flies that reach adulthood. Adult flies containing tRNASerUGG, G26A present with more morphological deformities and worse climbing performance than flies expressing only wild type tRNA. Female flies with the serine tRNA variant have more deformities and experience a faster decline in climbing performance than males, suggesting sex-specific effects. This model will enable studies into the synergistic effects of mistranslating tRNA variants and disease-causing alleles.

molecular biology↗

bioRxiv2021

Regulating expression of mistranslating tRNAs by readthrough RNA polymerase II transcription

Transfer RNA (tRNA) variants that alter the genetic code increase protein diversity and have many applications in synthetic biology. Since the tRNA variants can cause a loss of proteostasis, regulating their expression is necessary to achieve high levels of novel protein. Mechanisms to positively regulate transcription with exogenous activator proteins like those often used to regulate RNA polymerase II (RNAP II) transcribed genes are not applicable to tRNAs as their expression by RNA polymerase III requires elements internal to the tRNA. Here, we show that tRNA expression is repressed by overlapping transcription from an adjacent RNAP II promoter. Regulating the expression of the RNAP II promoter allows inverse regulation of the tRNA. Placing either Gal4 or TetR-VP16 activated promoters downstream of a mistranslating tRNASer variant that mis-incorporates serine at proline codons in Saccharomyces cerevisiae allows mistranslation at a level not otherwise possible because of the toxicity of the unregulated tRNA. Using this inducible tRNA system, we explore the proteotoxic effects of mistranslation on yeast cells. High levels of mistranslation cause cells to arrest in G1 phase. These cells are impermeable to propidium iodide, yet growth is not restored upon repressing tRNA expression. High levels of mistranslation increase cell size and alter cell morphology. This regulatable tRNA expression system can be applied to study how native tRNAs and tRNA variants affect the proteome and other biological processes. Variations of this inducible tRNA system should be applicable to other eukaryotic cell types.

molecular biology↗