Biology subjects

Muralidharan, V.

Publications and source records attributed to Muralidharan, V..

6 recordsLinked to original sources

bioRxiv2018

A Cortico- Basal Ganglia Model for choosing an optimal rehabilitation strategy in Hemiparetic Stroke

To facilitate the selection of an optimal therapy for a stroke patient with upper extremity hemiparesis, we propose a cortico-basal ganglia model capable of performing reaching tasks under normal and stroke conditions. The model contains two hemispherical systems, each organized into an outer sensory-motor cortical loop and an inner basal ganglia (BG) loop, controlling their respective hands. In addition to constraint induced movement therapy (CIMT), the model performs both unimanual and bimanual reaching tasks and the simulation results are in congruence with the experiment conducted by Rose et al (2004). Based on our study on the effect of lesion size on arm performance, we hypothesize that the effectiveness of a therapy could greatly depend on this factor. By virtue of the models ability to capture the experimental results effectively, we believe that it can serve as a benchmark for the development and testing of various rehabilitation strategies for stroke.

neuroscience↗

bioRxiv2018

Field evaluation of malachite green loop-mediated isothermal amplification as a malaria parasite detection tool in a health post in Roraima state, Brazil

Malaria is a debilitating parasitic disease that causes significant morbidity and mortality. Microscopic detection of parasites is currently the \"gold standard\" diagnostic. This technique is limited in its ability to detect low-density infections, is time consuming, and requires a highly trained microscopist. Malaria epidemiological surveillance studies especially aimed at the detection of low-density infection and asymptomatic cases will require more sensitive and user-friendly tools. We have shown previously that the molecular-based, colorimetric malachite green loop-mediated isothermal amplification (MG-LAMP) assay is a valuable tool for diagnosing malaria infection in a laboratory setting. In this study, we field evaluated this assay in a malaria diagnostic post in Roraima, Brazil. We prospectively collected 91 patient samples and performed microscopy, MG-LAMP, and real-time PCR (PET-PCR) to detect Plasmodium infection. Two independent readers were used to score the MG-LAMP tests to assess whether the sample was positive (blue/green) or negative (clear). There was 100% agreement between the two readers (Kappa=1). All tests detected 33 positive samples, but both the MG-LAMP and PET-PCR detected 6 and 7 more positive samples, respectively. The PET-PCR assay detected 6 mixed infections (defined as infection with both P. falciparum and P. vivax) while microscopy detected one and MG-LAMP detected two of these mixed infections. Microscopy did not detect any Plasmodium infection in 26 of the enrolled asymptomatic cases while MG-LAMP detected five and PET-PCR assay three positive cases. Overall, MG-LAMP provided a simpler and user-friendly molecular method for malaria diagnosis that is more sensitive than microscopy. Additionally, MG- LAMP has the capacity to test 38 samples per run (one hour), allowing for the screening of large number of samples which is appealing when large-scale studies are necessary e.g. in community surveillance studies. The current MG-LAMP assay was limited in its ability to detect mixed infection when compared to the PET-PCR, but otherwise proved to be a powerful tool for malaria parasite detection in the field and opens new perspectives in the implementation of surveillance studies in malaria elimination campaigns.

epidemiology↗

bioRxiv2018

The ER chaperone PfGRP170 is essential for asexual development and is linked to stress response in malaria parasites.

The vast majority of malaria mortality is attributed to one parasite species: Plasmodium falciparum. Asexual replication of the parasite within the red blood cell is responsible for the pathology of the disease. In Plasmodium, the endoplasmic reticulum (ER) is a central hub for protein folding and trafficking as well as stress response pathways. In this study, we tested the role of an uncharacterized ER protein, PfGRP170, in regulating these key functions by generating conditional mutants. Our data show that PfGRP170 localizes to the ER and is essential for asexual growth, specifically required for proper development of schizonts. PfGRP170 is essential for surviving heat shock, suggesting a critical role in cellular stress response. The data demonstrate that PfGRP170 interacts with the Plasmodium orthologue of the ER chaperone, BiP. Finally, we found that loss of PfGRP170 function leads to the activation of the Plasmodium eIF2 kinase, PK4, suggesting a specific role for this protein in this parasite stress response pathway.

cell biology↗

bioRxiv2018

CRISPR/Cas9 gene editing to make conditional mutants of the human malaria parasite Plasmodium falciparum

Malaria is a significant cause of morbidity and mortality worldwide. This disease, which primarily affects those living in tropical and subtropical regions, is caused by infection with Plasmodium parasites. The development of better drugs to combat malaria can be accelerated by improving our understanding of the biology of this complex parasite. Genetic manipulation of these parasites is key to understanding their biology, but historically, the genome of P. falciparum has been difficult to manipulate. Recently, CRISPR/Cas9 genome editing has been utilized in malaria parasites, allowing for easier protein tagging, generation of conditional protein knockdowns, and deletion of genes. CRISPR/Cas9 genome editing has proven to be a powerful tool for advancing the field of malaria research. Here, we describe a CRISPR/Cas9 method for generating glmS-based conditional knockdown mutants in P. falciparum. The method is highly adaptable to other types of genetic manipulations, including protein tagging and gene knockouts.

cell biology↗

bioRxiv2017

A computational model that explores the effect of environmental geometries on grid cell representations

Grid cells are a special class of spatial cells found in the medial entorhinal cortex (MEC) characterized by their strikingly regular hexagonal firing fields. This spatially periodic firing pattern was originally considered to be invariant to the geometric properties of the environment. However, this notion was contested by examining the grid cell periodicity in environments with different polarity (Krupic et al 2015) and in connected environments (Carpenter et al 2015). Aforementioned experimental results demonstrated the dependence of grid cell activity on environmental geometry. Analysis of grid cell periodicity on practically infinite variations of environmental geometry imposes a limitation on the experimental study. Hence we analyze the grid cell periodicity from a computational point of view using a model that was successful in generating a wide range of spatial cells, including grid cells, place cells, head direction cells and border cells. We simulated the model in four types of environmental geometries such as: 1) connected environments, 2) convex shapes, 3) concave shapes and 4) regular polygons with varying number of sides. Simulation results point to a greater function for grid cells than what was believed hitherto. Grid cells in the model code not just for local position but also for more global information like the shape of the environment. The proposed model is interesting not only because it was able to capture the aforementioned experimental results but, more importantly, it was able to make many important predictions on the effect of the environmental geometry on the grid cell periodicity.

neuroscience↗

bioRxiv2017

The exported chaperone PfHsp70x is dispensable for the Plasmodium falciparum intraerythrocytic lifecycle

Export of parasite proteins into the host erythrocyte is essential for survival of Plasmodium falciparum during its asexual lifecycle. While several studies described key factors within the parasite that are involved in protein export, the mechanisms employed to traffic exported proteins within the host cell are currently unknown. Members of the Hsp70 family of chaperones, together with their Hsp40 co-chaperones, facilitate protein trafficking in other organisms, and are thus likely used by P. falciparum in the trafficking of its exported proteins. A large group of Hsp40 proteins is encoded by the parasite and exported to the host cell, but only one Hsp70, PfHsp70x, is exported with them.\n\nPfHsp70x is absent from most Plasmodium species and is found only in P. falciparum and closely-related species that infect Apes. Herein, we have utilized CRISPR/Cas9 genome editing in P. falciparum to investigate the essentiality of PfHsp70x. We show that parasitic growth was unaffected by knockdown of PfHsp70x using both the DHFR-based Destabilization Domain and the glmS ribozyme system. Similarly, a complete gene knockout of PfHsp70x did not affect the ability of P. falciparum to proceed through its intraerythrocytic lifecycle. The effect of PfHsp70x knockdown/knockout on the export of proteins to the host RBC, including the critical virulence factor PfEMP1, was tested and we found that this process was unaffected. These data show that although PfHsp70x is the sole exported Hsp70, it is not essential for the asexual development of P. falciparum.\n\nImportanceHalf of the worlds population lives at risk for malaria. The intraerythrocytic lifecycle of Plasmodium spp. is responsible for clinical manifestations of malaria; therefore, knowledge of the parasites ability to survive within the erythrocyte is needed to combat the deadliest agent of malaria, P. falciparum. An outstanding question in the field is how P. falciparum undertakes the essential process of trafficking its proteins within the host cell. In most organisms, chaperones such as Hsp70 are employed in protein trafficking. Of the human-disease causing Plasmodium species, the chaperone PfHsp70x is unique to P. falciparum, and it is the only parasite protein of its kind exported to the host (1). This has placed PfHsp70x as an ideal target to inhibit protein trafficking and kill the parasite. However, we show that PfHsp70x is not required for export of parasite effectors nor is it essential for parasite survival inside of the RBC.

microbiology↗