Biology subjects

Ijaz, S.

Publications and source records attributed to Ijaz, S..

8 recordsLinked to original sources

bioRxiv2026

Electrical and chemical synapses share similar organizational principle

Electrical transmission is mediated by intercellular channels that cluster into structures known as gap junctions (GJ). In vertebrates, GJ channels are encoded by the gene family of connexin (Cx) proteins that assemble as hexamers, termed hemichannels, in the pre- and postsynaptic membranes, and that subsequently dock to form GJ channels. Auditory contacts on the fish Mauthner cells serve as model to study the properties and organization of vertebrate electrical synapses. Electrical transmission at these synapses is mediated by multiple co-existing GJs at which the presence of intercellular channels is regulated by a molecular scaffold. Zebrafish contain four homologs of the neuronal Cx36: Cx35.5 and Cx35.1 (gjd2a and b, respectively), and Cx34.1 and Cx34.7 (gjd1a and b). Cx mutations suggested that GJs are formed by heterotypic channels made of presynaptic Cx35.5 and postsynaptic Cx34.1. Using transgenic fish in which Cxs were tagged, we found that a second Cx, Cx34.7, is present together with Cx34.1 on the postsynaptic side at some but not all GJs at these terminals. When exogenously expressed, both Cx34.1 and Cx34.7 formed heterotypic functional channels with Cx35.5, each with substantially different voltage-dependent properties, indicating they can serve differential functions. However, we previously demonstrated that electrical transmission is lost in Cx34.1 but not Cx34.7 null mutants, suggesting that Cx34.7 cannot compensate for the loss of Cx34, despite the intrinsic ability of Cx34.1 and Cx34.7 to create functional channels. The findings reveal an unanticipated functional organization in the electrical synapse, where Cx34.1 is obligatory and Cx34.7 accessory, roles that appear to be defined by the postsynaptic molecular scaffold, with two postsynaptic Cxs possibly assembling under specific functional contexts. Thus, our results indicate that electrical synapses share an organizational motif with chemical synapses, akin to how they combine postsynaptic receptor types to modify synaptic function.

neuroscience↗

bioRxiv2026

ATP13A2 Loss of Function-Driven Polyamine Dysregulation Induces SAM Depletion and Epigenetic Astrocyte Toxicity

Aging is the strongest risk factor for neurodegeneration, yet how the human brain ages remains poorly understood. Loss-of-function (LOF) variants in ATP13A2 cause severe juvenile-onset Parkinsons disease, providing a window into the mechanisms that accelerate age-related neurodegeneration. ATP13A2-LOF causes lysosomal polyamine sequestration, but how this promotes pathogenesis remains unclear. We discovered that ATP13A2-LOF depletes cytosolic polyamines in astrocytes, triggering compensatory upregulation of de novo polyamine biosynthesis, which diverts S-adenosyl methionine (SAM) from DNA and histone methylation, leading to increased chromatin accessibility and epigenetic reprogramming of astrocytes into a neuroinflammatory state that releases neurotoxic cytokines that promote dopaminergic neuron death. In ATP13A2 knockout mice and human models, we find that genetic and pharmacological inhibition of SAM utilization in polyamine biosynthesis prevents astrocytic epigenetic reprogramming and promotes dopaminergic neuron survival. These findings reveal a direct link between polyamine metabolism, epigenetic dysfunction, and neurotoxic inflammation, uncovering new therapeutic opportunities in Parkinsons disease.

neuroscience↗

bioRxiv2024

RFX3 is essential for the development and maturation of human pancreatic islets derived from pluripotent stem cells

RFX3 in human pancreatic islet development has not been explored. This study aims to investigate the function of RFX3 in human pancreatic islet development using human islet organoids derived from iPSCs, hypothesizing that RFX3 regulates human islet cell differentiation. We generated RFX3 knockout (RFX3 KO) iPSC lines using CRISPR/Cas9 and differentiated them into pancreatic islet organoids. Various techniques were employed to assess gene expression, cell markers, apoptosis, proliferation, and glucose-stimulated insulin secretion. Single-cell RNA sequencing (scRNA-seq) datasets from hESC-derived pancreatic islets were re-analyzed to investigate RFX3 expression in specific cell populations at various developmental stages. Furthermore, bulk RNA sequencing was conducted to further assess transcriptomic changes. RFX3 was found to be highly expressed in pancreatic endocrine cell populations within pancreatic progenitors (PPs), endocrine progenitors (EPs), and mature islet stages derived from iPSCs. scRNA-seq further confirmed RFX3 expression across different endocrine cell clusters during differentiation. RFX3 loss disrupted pancreatic endocrine gene regulation, reduced hormone-secreting islet cells, and impaired beta-cell function and insulin secretion. Despite a significant reduction in pancreatic islet hormones, the pan-endocrine marker CHGA remained unchanged at both EP and islet stages, likely due to an increase in enterochromaffin cells (ECs). This was supported by our findings of high EC marker expression in RFX3 KO EPs and islets. In addition, RFX3 loss led to smaller islet organoids, elevated TXNIP levels, and increased apoptosis in EPs and islets. These findings underscore the crucial role of RFX3 in regulating human islet cell differentiation and its role in suppressing enterochromaffin cell specification. These insights into RFX3 function have implications for understanding islet biology and potential diabetes susceptibility.

developmental biology↗

bioRxiv2024

Deletion of RFX6, a Diabetes-Associated Gene, Impairs iPSC-Derived Islet Organoid Development and Survival, With No Impact on the Generation of PDX1+/NKX6.1+ Progenitors

RFX6 is essential for pancreatic development and insulin secretion, while its role in diabetes pathogenesis is unclear. Here, RFX6 expression was detected in PDX1+ cells in the hESC-derived posterior foregut (PF). However, in the pancreatic progenitors (PPs), RFX6 did not co-localize with PDX1 and NKX6.1, but instead with NEUROG3, NKX2.2, and islet hormones in the endocrine progenitor (EPs) and islets. Single-cell analysis revealed high RFX6 expression in endocrine clusters across various hESC-derived pancreatic differentiation stages. Upon differentiating iPSCs lacking RFX6 into pancreatic islets, a significant decrease in PDX1 expression at the PF stage was observed, although it did not affect PPs co-expressing PDX1 and NKX6.1. RNA sequencing showed the downregulation of essential genes involved in pancreatic endocrine differentiation, insulin secretion, and ion transport due to RFX6 deficiency. Furthermore, RFX6 deficiency resulted in the formation of smaller islet organoids due to increased cellular apoptosis, linked to reduced Catalase (CAT) expression, implying a protective role for RFX6. Overexpression of RFX6 reversed defective phenotypes in PPs and EPs. These findings suggest that pancreatic hypoplasia and reduced islet cell formation associated with RFX6 mutations are not due to alterations in PDX1+/NKX6.1+ PPs but instead result from cellular apoptosis and downregulation of pancreatic endocrine genes.

developmental biology↗

bioRxiv2023

The components of an electrical synapse as revealed by expansion microscopy of a single synaptic contact

Most nervous systems combine both transmitter-mediated and direct cell-cell communication, known as chemical and electrical synapses, respectively. Chemical synapses can be identified by their multiple structural components. Electrical synapses are, on the other hand, generally defined by the presence of a gap junction (a cluster of intercellular channels) between two neuronal processes. However, while gap junctions provide the communicating mechanism, it is unknown whether electrical transmission requires the contribution of additional cellular structures. We investigated this question at identifiable single synaptic contacts on the zebrafish Mauthner cells, at which gap junctions coexist with specializations for neurotransmitter release and where the contact defines the anatomical limits of a synapse. Expansion microscopy of these contacts revealed a detailed map of the incidence and spatial distribution of proteins pertaining to various synaptic structures. Multiple gap junctions of variable size were identified by the presence of their molecular components. Remarkably, most of the synaptic contacts surface was occupied by interleaving gap junctions and components of adherens junctions, suggesting a close functional association between these two structures. In contrast, glutamate receptors were confined to small peripheral portions of the contact, indicating that most of the synaptic area works as an electrical synapse. Thus, our results revealed the overarching organization of an electrical synapse that operates with not one, but multiple gap junctions, in close association with structural and signaling molecules known to be components of AJs. The relationship between these intercellular structures will aid in establishing the boundaries of electrical synapses found throughout animal connectomes and provide insight into the structural organization and functional diversity of electrical synapses.

neuroscience↗

bioRxiv2020

Electrical synaptic transmission requires a postsynaptic scaffolding protein

Electrical synaptic transmission relies on neuronal gap junctions containing channels constructed by Connexins. While at chemical synapses neurotransmitter-gated ion channels are critically supported by scaffolding proteins, it is unknown if channels at electrical synapses require similar scaffold support. Here we investigated the functional relationship between neuronal Connexins and Zonula Occludens 1 (ZO1), an intracellular scaffolding protein localized to electrical synapses. Using model electrical synapses in zebrafish Mauthner cells, we demonstrated that ZO1 is required for robust synaptic Connexin localization, but Connexins are dispensable for ZO1 localization. Disrupting this hierarchical ZO1/Connexin relationship abolishes electrical transmission and disrupts Mauthner-cell-initiated escape responses. We found that ZO1 is asymmetrically localized exclusively postsynaptically at neuronal contacts where it functions to assemble intercellular channels. Thus, forming functional neuronal gap junctions requires a postsynaptic scaffolding protein. The critical function of a scaffolding molecule reveals an unanticipated complexity of molecular and functional organization at electrical synapses.

neuroscience↗

bioRxiv2020

Evaluation of Antimicrobial, Antioxidant, Total Phenolic, Total Flavonoids, Metal Content and Proximate Potential of Solanum xanthocarpum L. (Solanaceae)

The current research work is focused on screening of antimicrobial, antioxidant, total phenolic, total flavonoid, metal estimation and proximate potential of four parts (fruits, leaves, stem bark and root bark) of S. xanthocarpum. Antimicrobial potential of dried crude extracts of S. xanthocarpum were evaluated against two gram positive bacteria (S. aureus, P. vulgaris), three gram negative bacteria (P. aeruginosa, K. pneumonia, E. coli), three fungi (A. flavus, F. solani, stolonifer) and two yeasts (S. cerevisiae, C. albicans) by using disc diffusion assay. Five organic solvents ranging from non-polar to highly polar were used for extraction of active metabolites. Amongst all the parts of S. xanthocarpum tested, antimicrobial activity of methanol extract of fruits (14.67{+/-}0.33) against P. aeruginosa, ethanolic extract of leaves against P. vulgaris (14{+/-}0.58), stem bark methanolic extract against S. aureus (13{+/-}0.58) and stem bark methanolic extract against P. vulgaris (17.67{+/-}0.33) were found to be more significant. All other extracts also showed promising antimicrobial activity against bacterial pathogens. Among fungal pathogens, R. stolonifer and S. cerevisiae were found to be more sensitive to extracts of S. xanthocarpum. Gram negative bacteria exhibited more resistance than gram positive bacteria. However, fungi were found to be more resistant than bacteria. All the extracts showed antioxidant activity. However, methanol extract of stem bark of S. xanthocarpum with IC50 value of 0.323102 mg mL-1 showed maximum antioxidant potential. Total phenolic contents ranged from 12.3541{+/-}1.73 to 23.2942{+/-}1.33 Pmol GA/ug. However, highest flavonoid content was found in the stem bark extract (17.8480{+/-}1.75 ugRutin/ug) and lowest in leaves extract of S. xanthocarpum (2.4806{+/-}0.59 ugRutin/ug). Total metal contamination in four parts of Solanum xanthocarpum (fruits, leaves, stem bark and root bark) was estimated by atomic absorption spectroscopy and results showed Cadmium contamination in its stem bark and root bark, Chromium contamination in leaves, stem bark and root bark, Copper and Magnesium contamination in all parts of S. xanthocarpum and Maganese contamination in leaves critically above the standard permissible limits. The proximate analysis of the Solanum xanthocarpum revealed that stem bark is a poor source of lipid (3.42%) and high carbohydrate (50.07%) and ash (16.50%) contents. Whereas, root bark has highest wet moisture content (65%), dry moisture content (20%) and lowest fiber (13%). Highest energy (285.455%), protein (8.32%), fat (9.79%) and lowest amount of ash (13%) was found in fruits. This composition shows that the Solanum xanthocarpum could be considered as a good source of carbohydrate, moisture and energy. These results revealed that over all, methanolic extract of the S. xanthocarpum is richest in phenolic, flavonoid and nutritional contents as well as most potent against bacterial and fungal pathogens. Therefore, further investigation is recommended to isolate, screen and characterize their active metabolites.

plant biology↗

bioRxiv2019

Modulated Zika virus NS1 conjugate offers advantages for accurate detection of Zika virus specific antibody in double antigen binding and Ig capture enzyme immunoassays

The accurate diagnosis and seroprevalence investigations of Zika virus (ZKV) infections remain complex due to cross reactivity with other flaviviruses. Two assay formats, both using labelled Zika virus NS1 antigen as a revealing agent (a double antigen binding assay, DABA, and an immunoglobulin Ig capture assay, IgG capture) were initially developed and compared with the indirect EuroimmunZ assay for the detection of anti-Zika antibody. Of 147 pre-Zika period serum samples, 39 (27%) were reactive in the EuroimmunZ or the DABA assays, 28 sera concordantly so. Such false reactivity was influenced by the serotype of Dengue virus (DV) to which individuals had been exposed to. Thus, of sera from patients undergoing secondary Dengue virus infection of known serotype, 91%, 45% and 28% of Dengue virus serotype 2, 3 and 4 respectively were reactive in one or more of the three assays. A novel method of quenching false sero-reactivity was therefore developed for the DABA and IgG capture assays. Initial addition of a single homologous Dengue virus serotype 3 NS1Ag quench significantly ablated false reactivities in the pre-Zika period sera. An equipotent quadrivalent quench comprising homologous Dengue virus serotypes 1 to 4 NS1Ag was shown to be optimum yet retained sensitivity for the detection of specific anti-Zika antibody. Comparing DABA and IgG capture assays using quenched and unquenched conjugates in comparison with EuroimmunZ early in the course of PCR-confirmed infection indicated that a significant component of the apparent early anti-ZIKA antibody response is likely to be due to a Zika virus-driven anamnestic anti-Dengue virus response. The increased specificity provided by homologous antigen quenching is likely to provide a significant improvement in sero-diagnostics and to be of clinical value.

microbiology↗