Biology subjects

Kepple, D.

Publications and source records attributed to Kepple, D..

8 recordsLinked to original sources

bioRxiv2024

Copy number variations of Plasmodium vivax DBP1, EBP/DBP2, and RBP2b in Duffy-positive and Duffy-negative Ethiopians

Recent evidence challenges the belief that Duffy-negative individuals are resistant to Plasmodium vivax due to lacking Duffy Antigen Receptor for Chemokines (DARC). Erythrocyte Binding Protein (EBP/DBP2) has shown moderate binding to Duffy-negative erythrocytes in vitro. Reticulocyte Binding Protein 2b (RBP2b) interactions with Transferrin Receptor 1 (TfR1) suggest involvement in Duffy-negative infections. Gene copy number variations in PvDBP1, PvEBP/DBP2, and PvRBP2b were investigated in Duffy-positive and Duffy-negative P. vivax-infected individuals from Ethiopia. Among Duffy-positive samples, 34% displayed PvDBP1 duplications (Cambodian-type). In Duffy-negative infections, 30% showed duplications, mostly Cambodian-type. For PvEBP/DBP2 and PvRBP2b, Duffy-positive samples exhibited higher duplication rates (1-8 copies for PvEBP/DBP2, 1-5 copies for PvRBP2b 46% and 43% respectively) compared to Duffy-negatives (20.8% and 26% respectively). The range of copy number variations was lower in Duffy-negative infections. Demographic and clinical factors associated with gene multiplications in both Duffy types were explored, enhancing understanding of P. vivax evolution in Duffy-negative Africans.

microbiology↗

bioRxiv2023

Comparative transcriptomics reveal differential gene expression in Plasmodium vivax geographical isolates and implications on erythrocyte invasion mechanisms

Plasmodium vivax uses Duffy binding protein (PvDBP1) to bind to the Duffy Antigen-Chemokine Receptor (DARC) to invade human erythrocytes. Individuals who lack DARC expression (Duffy-negative) are thought to be resistance to P. vivax. In recent years, P. vivax malaria is becoming more prevalent in Africa with a portion of these cases detected in Duffy-negatives. Apart from DBP1, members of the reticulocyte binding protein (RBP) and tryptophan-rich antigen (TRAg) families may also play a role in erythrocyte invasion. While the transcriptomes of the Southeast Asian and South American P. vivax are well documented, the gene expression profile of P. vivax in Africa and more specifically the expression level of several erythrocyte binding gene candidates as compared to DBP1 are largely unknown. This paper characterized the first P. vivax transcriptome in Africa and compared with those from the Southeast Asian and South American isolates. The expression of 4,404 gene transcripts belong to 12 functional groups including 43 specific erythrocyte binding gene candidates were examined. Overall, there were 10-26% differences in the gene expression profile amongst the geographical isolates, with the Ethiopian and Cambodian P. vivax being most similar. Majority of the gene transcripts involved in protein transportation, housekeeping, and host interaction were highly transcribed in the Ethiopian P. vivax. Erythrocyte binding genes including PvRBP2a and PvRBP3 expressed six-fold higher than PvDBP1and 60-fold higher than PvEBP/DBP2. Other genes including PvRBP1a, PvMSP3.8, PvMSP3.9, PvTRAG2, PvTRAG14, and PvTRAG22 also showed relatively high expression. Differential expression was observed among geographical isolates, e.g., PvDBP1 and PvEBP/DBP2 were highly expressed in the Cambodian but not the Brazilian and Ethiopian isolates, whereas PvRBP2a and PvRBP2b showed higher expression in the Ethiopian and Cambodian than the Brazilian isolates. Compared to Pvs25, the standard biomarker for detecting female gametocytes, PvAP2-G (PVP01_1440800), GAP (PVP01_1403000), and Pvs47 (PVP01_1208000) were highly expressed across geographical samples. These findings provide an important baseline for future comparisons of P. vivax transcriptomes from Duffy-negative infections and highlight potential biomarkers for improved gametocyte detection.

cell biology↗

bioRxiv2020

Extensive genetic diversity in Plasmodium vivax from Sudan and its genetic relationships with other geographical isolates

Plasmodium vivax malaria is a neglected tropical disease in Africa due to low occurrence rates and lack of accurate diagnosis. Recently, there has been a dramatic increase in P. vivax cases in East Africa and reportedly spreading to western countries. This study investigated the geographical origin and genetic diversity of P. vivax in Sudan by 14 microsatellite markers. A total of 113 clinical P. vivax samples were collected from two districts, New Halfa and Khartoum in Sudan. In addition, data from 841 geographical samples retrieved from the database for global genetic analysis were included in the analysis to further the genetic relationships among the P. vivax isolates at regional and worldwide scales. On a regional scale, we observed 91 unique and 8 shared haplotypes amongst the Sudan samples. Such a high genetic diversity compared to other geographical isolates lends support to hypothesis that P. vivax was originated from Africa. On a global scale, as already demonstrated, we observed distinct genetic clustering of P. vivax isolates from Africa, South America, and Asia (including Papua New Guinea and Solomon Island) with limited admixture in all three clusters. The principal component analysis and phylogenetic tree showed similar clustering patterns and highlighted the contribution of the African isolates to the genetic variation observed globally. The East African P. vivax showed similarity with some of the Asian isolates suggesting potential recent introductions. Our results show extensive genetic diversity co-occurring with significant multi-locus linkage disequilibrium, demonstrating the effectiveness of using microsatellite markers to implement effective control measures.

genetics↗

bioRxiv2020

Whole Genome Sequencing of Plasmodium vivax Isolates Reveals Frequent Sequence and Structural Polymorphisms in Erythrocyte Binding Genes

Plasmodium vivax malaria is much less common in Africa than the rest of the world because the parasite relies primarily on the Duffy antigen/chemokine receptor (DARC) to invade human erythrocytes, and the majority of Africans are Duffy negative. Recently, there has been a dramatic increase in the reporting of P. vivax cases in Africa, with a high number of them being in Duffy negative individuals, potentially indicating P. vivax has evolved an alternative invasion mechanism that can overcome Duffy negativity. Here, we analyzed single nucleotide polymorphism (SNP) and copy number variation (CNV) in Whole Genome Sequence (WGS) data from 44 P. vivax samples isolated from symptomatic malaria patients in southwestern Ethiopia, where both Duffy positive and Duffy negative individuals are found. A total of 236,351 SNPs were detected, of which 21.9% was nonsynonymous and 78.1% was synonymous mutations. The largest number of SNPs were detected on chromosomes 9 (33,478 SNPs; 14% of total) and 10 (28,133 SNPs; 11.9%). There were particularly high levels of polymorphism in erythrocyte binding gene candidates including reticulocyte binding protein 2c (RBP2c), merozoite surface protein 1 (MSP1), and merozoite surface protein 3 (MSP3.5, MSP3.85 and MSP3.9). Thirteen genes related to immunogenicity and erythrocyte binding function were detected with significant signals of positive selection. Variation in gene copy number was also concentrated in genes involved in host-parasite interactions, including the expansion of the Duffy binding protein gene (PvDBP) on chromosome 6 and several PIR genes. Based on the phylogeny constructed from the whole genome sequences, the expansion of these genes was an independent process among the P. vivax lineages in Ethiopia. We further inferred transmission patterns of P. vivax infections among study sites and showed various levels of gene flow at a small geographical scale. The genomic features of P. vivax provided baseline data for future comparison with those in Duffy-negative individuals, and allowed us to develop a panel of informative Single Nucleotide Polymorphic markers diagnostic at a micro-geographical scale.

genomics↗

bioRxiv2019

Frequent expansion of Plasmodium vivax Duffy Binding Protein in Ethiopia and its epidemiological significance

Plasmodium vivax invasion of human erythrocytes depends on the Duffy Binding Protein (PvDBP) which interacts with the Duffy antigen. PvDBP copy number varies between P. vivax isolates, but the prevalence of PvDBP multiplications in Sub-Saharan Africa and its impact are unknown. We determined the prevalence and type of PvDBP duplications, as well as PvDBP copy number variation among 178 Ethiopian P. vivax isolates using a PCR-based diagnostic method, a novel quantitative real-time PCR assay and whole genome sequencing. For the 145 symptomatic samples, PvDBP duplications were detected in 95 isolates, of which 81 had the Cambodian and 14 Malagasy-type PvDBP duplications. PvDBP varied from 1 to >4 copies. Isolates with multiple PvDBP copies were found to be higher in symptomatic than asymptomatic infections. For the 33 asymptomatic samples, PvDBP was detected with two copies in two of the isolates, and both were the Cambodian-type PvDBP duplication. PvDBP copy number in Duffy-negative heterozygotes was not significantly different from that in Duffy-positives, providing no support for the hypothesis that increased copy number is a specific association with Duffy-negativity, although the number of Duffy-negatives was small and further sampling is required to test this association thoroughly. Author summaryPlasmodium vivax invasion of human erythrocytes relies on interaction between the Duffy antigen and P. vivax Duffy Binding Protein (PvDBP). Whole genome sequences from P. vivax field isolates in Madagascar identified a duplication of the PvDBP gene and PvDBP duplication has also been detected in non-African P. vivax-endemic countries. Two types of PvDBP duplications have been reported, termed Cambodian and Malagasy-type duplications. Our study used a combination of PCR-based diagnostic method, a novel quantitative real-time PCR assay, and whole genome sequencing to determine the prevalence and type of PvDBP duplications, as well as PvDBP copy number on a broad number of P. vivax samples in Ethiopia. We found that over 65% of P. vivax isolated from the symptomatic infections were detected with PvDBP duplications and PvDBP varied from 1 to >4 copies. The majority of PvDBP duplications belongs to the Cambodian-type while the Malagasy-type duplications was also detected. For the asymptomatic infections, despite a small sample size, the majority of P. vivax were detected with a single-copy based on both PCR and qPCR assays. There was no significant difference in PvDBP copy number between Duffy-null heterozygote and Duffy-positive homozygote/heterozygote. Further investigation is needed with expanded Duffy-null homozygotes to examine the functional significance of PvDBP expansion.

epidemiology↗

bioRxiv2018

DeepNose: Using artificial neural networks to represent the space of odorants

The olfactory system employs an ensemble of odorant receptors (ORs) to sense odorants and to derive olfactory percepts. We trained artificial neural networks to represent the chemical space of odorants and used that representation to predict human olfactory percepts. We hypothesized that ORs may be considered 3D spatial filters that extract molecular features and can be trained using conventional machine learning methods. First, we trained an autoencoder, called DeepNose, to deduce a low-dimensional representation of odorant molecules which were represented by their 3D spatial structure. Next, we tested the ability of DeepNose features in predicting physical properties and odorant percepts based on 3D molecular structure alone. We found that despite the lack of human expertise, DeepNose features led to perceptual predictions of comparable accuracy to molecular descriptors often used in computational chemistry. We propose that DeepNose network can extract de novo chemical features predictive of various bioactivities and can help understand the factors influencing the composition of ORs ensemble.

neuroscience↗

bioRxiv2018

Computational algorithms and neural circuitry for compressed sensing in the mammalian main olfactory bulb

A major challenge for many sensory systems is the representation of stimuli that vary along many dimensions. This problem is particularly acute for chemosensory systems because they require sensitivity to a large number of molecular features. Here we use a combination of computational modeling and in vivo electrophysiological data to propose a solution for this problem in the circuitry of the mammalian main olfactory bulb. We model the input to the olfactory bulb as an array of chemical features that, due to the vast size of chemical feature space, is sparsely occupied. We propose that this sparseness enables compression of the chemical feature array by broadly-tuned odorant receptors. Reconstruction of stimuli is then achieved by a supernumerary network of inhibitory granule cells. The main olfactory bulb may therefore implement a compressed sensing algorithm that presents several advantages. First, we demonstrate that a model of synaptic interactions between the granule cells and the mitral cells that constitute the output of the olfactory bulb, can store a highly efficient representation of odors by competitively selecting a sparse basis set of \"expert\" granule cells. Second, we further show that this model network can simultaneously learn separable representations of each component of an odor mixture without exposure to those components in isolation. Third, our model is capable of independent and odor-specific adaptation, which could be used by the olfactory system to perform background subtraction or sensitively compare a sample odor with an internal expectation. This model makes specific predictions about the dynamics of granule cell activity during learning. Using in vivo electrophysiological recordings, we corroborate these predictions in an experimental paradigm that stimulates memorization of odorants.

neuroscience↗

bioRxiv2018

Mosaic representations of odors in the input and output layers of the mouse olfactory bulb

The elementary stimulus features encoded by the olfactory system remain poorly understood. We examined the relationship between 1,666 physical-chemical descriptors of odors and the activity of olfactory bulb inputs as well as outputs in awake mice. Glomerular and M/T cell responses were sparse and locally heterogeneous, with only a coarse dependence of glomerular positions on physical-chemical properties. Odor features represented by ensembles of M/T cells were overlapping, but distinct from those represented in glomeruli, consistent with extensive interplay between feedforward and feedback inputs to the bulb. This reformatting was well-described as a rotation in odor space. The descriptors accounted for a small fraction in response variance, and the similarity of odors in physical-chemical space was a poor predictor of similarity in neuronal representations. Our results suggest that commonly used physical-chemical properties are not systematically represented in bulbar activity and encourage further search for better descriptors of odor space.

neuroscience↗