Biology subjects

Sambrani, N.

Publications and source records attributed to Sambrani, N..

4 recordsLinked to original sources

bioRxiv2025

Editing-independent effects of Adar in Drosophila melanogaster

Vertebrate ADAR RNA editing enzymes prevent cellular dsRNA from aberrantly activating antiviral dsRNA sensors. ADARs inhibit antiviral sensor activation by deaminating selected adenosines to inosines in dsRNA and by engaging in inhibitory protein interactions with sensors on dsRNA. ADARs interact with Dicers and, in the Drosophila Adar5G1 null mutant Dicer 2 acts as the antiviral dsRNA sensor mediating aberrant innate immune induction. We overexpressed active Adar isoforms or a catalytically-inactive Adar E374A protein from UAS-Adar constructs under the control of a temperature-regulated Act5Cts-GAL4 driver. Overexpression of the edited AdarG isoform or AdarEA cause larval lethality with aberrant innate immune induction. Some escaper pupae are formed with head eversion defects. AdarS overexpression is also lethal with no progeny pupae. Ecdysone signaling gene and innate immune gene expression are aberrantly elevated in the AdarG overexpressing pupae. RNAi knockdown of Ecdysone Receptor A (EcR A) or increasing expression of HP1 partially rescue AdarG overexpression defects and normalize gene expression in progeny flies, indicating that aberrant epigenetic silencing is also involved. The structure of an ADAR2 dimer on dsRNA shows the the glycine in AdarG is suitably positioned for Adar contacts with other proteins on dsRNA.

developmental biology↗

bioRxiv2024

The Drosophila tyramine-beta-hydroxylase gene encodes multiple isoforms with different functions

The Tyramine-beta-hydroxylase (Tbh) is required for octopamine synthesis. To better understand the function of Tbh in neurotransmitter synthesis, we analyzed the molecular genetic organization of the Drosophila melanogaster Tbh gene and found that the Tbh gene encodes multiple transcripts. The transcripts differ in their 5UTR, which results in proteins that differ in their size and putative phosphorylation sites, suggesting that the Tbh function is regulated at translational and posttranslational levels. We generated a new Tbh mutant - TbhDel3 - using FLP/FRT recombination mutagenesis to remove the translational start site still that is present in TbhnM18mutants. The TbhDel3 mutants share ethanol tolerance and larval locomotion defects with the TbhnM18 mutants. But, they differ in terms of their cellular stress response. To develop normal levels of ethanol tolerance, Tbh is required in a subset of Tbh expressing neurons in the adult brain, which was identified using a newly generated Tbh-Gal4 driver. Taking advantage of a newly generated Tbh antibody serum, we show that one Tbh isoform is expressed in a group of peptidergic Hugin-positive and noradrenergic neurons uncoupling Tbh function from octopamine synthesis. The existence of different functional Tbh isoforms impacts our understanding of the regulatory mechanisms of neurotransmitter synthesis and the function of the octopaminergic neurotransmitter system in cellular processes and the regulation of behavior. Author SummaryVertebrates and insects have structurally identical signaling molecules in their nervous system, such as the neurotransmitter dopamine. But, there are also neurotransmitters that are thought to only occur in the vertebrate or insect brain. Noradrenaline is one such neurotransmitter that regulates flight and fight responses in vertebrates. In insects such as the fruit fly Drosophila melanogaster, the structurally very similar neurotransmitter octopamine is considered to be an invertebrate-specific neurotransmitter that performs similar functions to noradrenaline. The functional similarities also extend to enzymes required for synthesis. Our analysis shows that the enzyme for octopamine synthesis exists in several variations and that the connection between the enzymes and the synthesized neurotransmitter may not be as simple as presumed. Exploiting molecular, behavioral and neuroanatomical studies, we show that different variants might be used in response to different environmental conditions and/or the synthesis of alternative, structurally similar neurotransmitters, such as noradrenaline. These results challenge our view on the functions of octopamine and noradrenaline in the regulation of behavior.

neuroscience↗

bioRxiv2017

Enhancer identification and activity evaluation in the red flour beetle, Tribolium castaneum

Evolution of cis-properties (such as enhancers) often plays an important role in the production of diverse morphology. However, a mechanistic understanding is often limited by the absence of methods to study enhancers in species outside of established model systems. Here, we sought to establish methods to identify and test enhancer activity in the red flour beetle, Tribolium castaneum. To identify possible enhancer regions, we first obtained genome-wide chromatin profiles from various tissues and stages of Tribolium via FAIRE (Formaldehyde Assisted Isolation of Regulatory Elements)-sequencing. Comparison of these profiles revealed a distinct set of open chromatin regions in each tissue and stage. Second, we established the first reporter assay system that works in both Drosophila and Tribolium, using nubbin in the wing and hunchback in the embryo as case studies. Together, these advances will be useful to study the evolution of cis-language and morphological diversity in Tribolium and other insects.

developmental biology↗

bioRxiv2017

Translational Repression Of The Drosophila nanos mRNA Involves The RNA Helicase Belle And RNA Coating By Me31B And Trailer hitch

Translational repression of maternal mRNAs is an essential regulatory mechanism during early embryonic development. Repression of the Drosophila nanos mRNA, required for the formation of the anterior-posterior body axis, depends on the protein Smaug binding to two Smaug recognition elements (SREs) in the nanos 3 UTR. In a comprehensive mass-spectrometric analysis of the SRE-dependent repressor complex, we identified Smaug, Cup, Me31B, Trailer hitch, eIF4E and PABPC, in agreement with earlier data. As a novel component, the RNA-dependent ATPase Belle (DDX3) was found, and its involvement in deadenylation and repression of nanos was confirmed in vivo. Smaug, Cup and Belle bound stoichiometrically to the SREs, independently of RNA length. Binding of Me31B and Tral was also SRE-dependent, but their amounts were proportional to the length of the RNA and equimolar to each other. We suggest that coating of the RNA by a Me31B*Tral complex may be at the core of repression.

biochemistry↗