Biology subjects

VijayRaghavan, K.

Publications and source records attributed to VijayRaghavan, K..

7 recordsLinked to original sources

bioRxiv2022

Structured and disordered regions of Ataxin-2 contribute differently to the specificity and efficiency of mRNP granule formation.

Ataxin-2 (ATXN2) is a gene implicated in spinocerebellar ataxia type II (SCA2), amyotrophic lateral sclerosis (ALS) and Parkinsonism. The encoded protein is a therapeutic target for ALS and related conditions. ATXN2 (or Atx2 in insects) can function in translational activation, translational repression, mRNA stability and in the assembly of mRNP-granules, a process mediated by intrinsically disordered regions (IDRs). Previous work has shown that the LSm (Like-Sm) domain of Atx2, which can help stimulate mRNA translation, antagonizes mRNP-granule assembly. Here we advance these findings through a series of experiments on Drosophila and human Ataxin-2 proteins. Results of Targets of RNA-Binding Proteins Identified by Editing (TRIBE), co-localization and immunoprecipitation experiments indicate that a polyA-binding protein (PABP) interacting, PAM2 motif of Ataxin-2 may be a major determinant of the mRNA and protein content of Ataxin-2 mRNP granules. Transgenic experiments in Drosophila indicate that while the Atx2-LSm domain may protect against neurodegeneration, structured PAM2- and unstructured IDR- interactions both support Atx2-induced cytotoxicity. Taken together, the data lead to a proposal for how Ataxin-2 interactions are remodelled during translational control and how structured and non-structured interactions contribute differently to the specificity and efficiency of RNP granule condensation as well as to neurodegeneration.

neuroscience↗

bioRxiv2020

Heterogeneous distribution of mRNAs within flight muscle fibers, and implications for function

Muscle heterogeneity has been explored in terms of fiber-type distribution, structural organisation, and differences at their junctions with neurons and tendons. We amplify on such observation to additionally suggest that muscle syncytia have nonuniform protein requirements along their length, deployed for developmental and functional uses. An exploration of regionalized proteins or their mRNA across muscle syncytia has not been done. We investigated mRNA localization in regions of Drosophila melanogaster dorsal longitudinal muscle (DLM) syncytia over their entire transcriptome. Dissection of muscle regions, their RNA-seq and stringent Differential Gene Expression analysis indeed reveals statistically significant regionalization of nearly a hundred mRNA over the length of DLMs. Functions of over half of these genes require experimental verification. A preponderance of mRNA coding for catabolic and proteolytic enzymes is conspicuous among transcripts enriched in the posterior of DLMs. Our findings provide a foundation for exploring molecular processes that contribute to syncytial maturation and muscle homeostasis in a spatially non-homogenous manner.

developmental biology↗

bioRxiv2020

Differential activation of JAK-STAT signaling in blood cell progenitors reveals functional compartmentalization of the Drosophila lymph gland.

Blood cells arise from diverse pools of stem and progenitor cells. Understanding progenitor heterogeneity is a major challenge. The Drosophila larval lymph gland is a well-studied model to understand blood progenitor maintenance and recapitulates several aspects of vertebrate hematopoiesis. However in-depth analysis has focused on progenitors located in lymph gland anterior lobes (AP), ignoring the progenitors from the posterior lobes (PP). Using in situ expression mapping and transcriptome analysis we reveal PP heterogeneity and identify molecular-genetic tools to study this abundant progenitor population. Functional analysis shows that PP resist differentiation upon immune challenge, in a JAK-STAT-dependent manner. Upon wasp parasitism, AP downregulate JAK-STAT signaling and form lamellocytes. In contrast, we show that PP activate STAT92E and remain undifferentiated. Stat92E knockdown in PP or genetically reducing JAK-STAT signaling permits PP lamellocyte differentiation. We discuss how heterogeneity and compartmentalization allow functional segregation in response to systemic cues and could be widely applicable. HighlightsWe provide an in situ and transcriptome map of larval blood progenitors Posterior lymph gland progenitors are refractory to immune challenge STAT activation after wasp parasitism maintains posterior progenitors

developmental biology↗

bioRxiv2019

Adult Drosophila Muscle Morphometry through MicroCT reveals dynamics during aging

Indirect Flight Muscles (IFMs) in adult Drosophila have served as a valuable model for studying muscle development. In terms of function, they provide the key power stroke in adult insect flight. Variability in their architecture including of fiber numbers, shape and arrangement may provide insightful clues into adult muscle function. Conventional histological preparations in imaging techniques severely limit exact morphometric analysis of flight muscles, thereby impeding causal or correlative studies between muscle morphology and function. In this study we employ MicroCT scanning on a tissue preparation that retains muscle morphology under homeostatic conditions. We use this method to deliver precise measurements of a subset of IFMs, the Direct Longitudinal Muscles (DLMs) size and shape, in male and female Drosophila and changes therein, with age. Our findings reveal several unexpected characteristics of muscle fibers. We also demonstrate application to other insect species making it a valuable tool for histological analysis of insect biodiversity.\n\nSignificance StatementAdult Drosophila muscles serve as models of homeostatic muscles. Accurate analysis of their form and function is key to understanding affects of genetic and physiological states on them. Recording adult muscle shape and volume has so far depended on protocols that inevitably distort tissue. Here, we use a MicroCT scanning based method that delivers changes in shape, size and organization between males and females, with time. This method is a significant step forward in recording muscle structure in situ with applications across species.

developmental biology↗

bioRxiv2018

A cost effective high-resolution climbing assay applied to Drosophila Parkinson’s and proprioception mutants reveal novel behavioural phenotypes

Severe locomotor impairment is a common phenotype of neurodegenerative disorders such as Parkinsons disease (PD). Drosophila models of PD, studied from more than a decade, have helped in understanding the interaction between various genetic factors, such as parkin and PINK1, in this disease. To characterize locomotor behavioural phenotypes for these genes, fly climbing assays have been widely used. While these simple current assays for locomotor defects in Drosophila mutants measure some locomotor phenotypes well, it is possible that detection of subtle changes in behaviour is important to understand the early manifestation of locomotor disorders. We introduce a novel climbing behaviour assay which provides such fine-scale behavioural data and tests this proposition for the Drosophila model. We use this inexpensive, fully automated, high resolution assay to quantitatively characterize the parameters of climbing behaviour in three contexts. First, we characterize wild type flies and uncover a hitherto unknown sexual dimorphism in climbing behaviour. Second, we study climbing behaviour of heterozygous mutants of genes implicated in the fly PD model and reveal previously unreported prominent locomotor defects in some of these heterozygous fly lines. Finally, we study locomotor defects in a homozygous proprioceptory mutation (Trp-{gamma}1) known to affect fine motor control in Drosophila. Moreover, we identify aberrant geotactic behaviour in Trp-{gamma}1 mutants, thereby opening up a finer assay for geotaxis and its genetic basis. Our assay is therefore a cost-effective, general tool for measuring locomotor behaviours of wild type and mutant flies in fine detail and can reveal mild motor defects.\n\nSignificance statementFine control of neuronal activity is required for proper motor output. Severe locomotor impairment is a common result of neurodegenerative disorders such as Parkinsons disease (PD). The fruitfly, Drosophila, has been widely used as a model system to study the genetics of these disorders and simple climbing assays have been used to study the behavioural phenotypes of mutations in these genes. Here we introduce a novel, fully automated, high resolution climbing behaviour assay and use this assay to characterize climbing behaviour in wild type flies and in various fly mutant lines related to PD and defects in proprioception. Our assay is a general tool for measuring locomotor behaviours of flies in fine detail and can reveal very mild motor defects.

neuroscience↗

bioRxiv2017

GABAergic inhibition of leg motoneurons is required for normal walking behavior in freely moving Drosophila

Walking is a complex rhythmic locomotor behaviour generated by sequential and periodical contraction of muscles essential for coordinated control of movements of legs and leg joints. Studies of walking in vertebrates and invertebrates have revealed that premotor neural circuitry generates a basic rhythmic pattern that is sculpted by sensory feedback and ultimately controls the amplitude and phase of the motor output to leg muscles. However, the identity and functional roles of the premotor interneurons that directly control leg motoneuron activity are poorly understood. Here we take advantage of the powerful genetic methodology available in Drosophila to investigate the role of premotor inhibition in walking by genetically suppressing inhibitory input to leg motoneurons. For this, we have developed a novel algorithm for automated analysis of leg motion to characterize the walking parameters of wildtype flies from high speed video recordings. Further, we use genetic reagents for targeted RNAi knockdown of inhibitory neurotransmitter receptors in leg motoneurons together with quantitative analysis of resulting changes in leg movement parameters in freely walking Drosophila. Our findings indicate that targeted downregulation of GABAA receptor Rdl in leg motoneurons results in a dramatic reduction of walking speed and step-length without the loss of general leg coordination during locomotion. Genetically restricting the knockdown to the adult stage and subsets of motoneurons yields qualitatively identical results. Taken together,these findings identify GABAergic premotor inhibition of motoneurons as an important determinant of correctly coordinated leg movements and speed of walking in freely behaving Drosophila.

neuroscience↗

bioRxiv2017

Identification of single pair of interneurons for bitter taste processing in the Drosophila brain

Drosophila has become an excellent model system for investigating the organization and function of the gustatory system due to the relatively simple neuroanatomical organization of its brain and the availability of powerful genetic and transgenic technology. Thus, at the molecular and cellular level, a great deal of insight into the peripheral detection and coding of gustatory information has already been attained. In contrast, much less is known about the central neural circuits that process this information and induce behaviorally appropriate motor output. Here we combine functional behavioral tests with targeted transgene expression through specific driver lines to identify a single bilaterally homologous pair of bitter sensitive interneurons that are located in the subesophageal zone of the brain. Anatomical and functional data indicate that these interneurons receive specific synaptic input from bitter sensitive gustatory receptor neurons. Targeted transgenic activation and inactivation experiments show that these bitter sensitive interneurons can largely suppress the proboscis extension reflex to appetitive stimuli such as sugar and water. These functional experiments together with calcium-imaging studies indicate that these first order local interneurons play an important role in the inhibition of the proboscis extension reflex that occurs in response to bitter tastants. Taken together, our studies present a cellular identification and functional characterization of a key gustatory interneuron in the bitter sensitive gustatory circuitry of the adult fly.

neuroscience↗