Biology subjects

Czirok, A.

Publications and source records attributed to Czirok, A..

9 recordsLinked to original sources

bioRxiv2025

Petasol Exhibits Rapid and Efficient Epithelial Transport in Epithelial Barrier Models

The epithelial permeability of petasol, a sesquiterpene derivative with reported antiviral properties, remains largely unexplored despite its potential as a therapeutic candidate. Here, we systematically characterize the transport of petasol across epithelial barriers using a combination of in vitro transwell models, automated millifluidic sampling, mathematical modeling, optical- and HPLC-mass spectroscopy. Vero E6 and Caco-2 cell layers were employed as epithelial barrier models, with transepithelial electrical resistance (TEER) measurements confirming the formation of functionally intact epithelial layers. Mathematical modeling of passive diffusion and cellular uptake allowed estimation of key transport parameters, including permeability coefficients and intracellular sequestration rates. Trans-barrier transport of petasol was compared to that of nitazoxanide, chloroquine, and FITC-dextran. Our results reveal that petasol exhibits efficient and rapid transport across both epithelial cell types without substantial intracellular accumulation or metabolic degradation, suggesting favorable properties for systemic delivery.

pharmacology and toxicology↗

bioRxiv2025

Barrier Function of the Vero E6 Cell Monolayer

Vero E6 cells are a standard model in virology research because of their broad susceptibility to viral infection. However, their ability to form functional barrier layers has received less attention. Here, we show that Vero E6 cells cultured on transwell inserts develop continuous monolayers with moderate transepithelial electrical resistance (TEER), reaching approximately 30 {Omega}{middle dot}cm2 in serum-containing medium and 45 {Omega}{middle dot}cm2 in virus production medium. The permeability coefficient (Papp) for 4 kDa FITC-dextran, a common measure for paracellular transport, is 3.7 x 10-6 cm/s, comparable to established endothelial models such as HUVEC or corneal endothelium. Immunofluorescence confirms the presence of tight junction (ZO-1) and adherens junction ({beta}-catenin) proteins. Chelation of calcium with EGTA causes a dose-dependent, reversible decrease in TEER and a marked increase in permeability, confirming the calcium sensitivity of the barrier. These findings suggest that Vero E6 cells serve as a valuable epithelial barrier model, facilitating studies on viral entry, immune evasion, and drug delivery.

cell biology↗

bioRxiv2025

Characterizing Solute Transport Across Cell Layers: Artifact Correction and Parameter Extraction from a Simplified Three-Compartment Model

Quantifying solute transport across epithelial cell layers grown on transwell inserts is a common approach in early-stage drug development to estimate pharmacokinetic properties such as absorption and bioavailability. To increase throughput and reduce variability, these assays are increasingly automated, including the use of robotic or microfluidic systems for time-resolved sampling. However, both automated and manual sampling can introduce systematic artifacts, such as residual volume retention and surface adsorption, that distort concentration time series and affect downstream analysis. To fully realize the potential precision of automated measurements, we propose a mathematical correction to account for sampling artifacts; then to fit the corrected data to a three-compartment model that captures membrane diffusion, cellular sequestration, and metabolic loss. The method is demonstrated on datasets from transwell epithelial barrier transport assays. We suggest that the considered three-compartment model yields mechanistically more meaningful parameters than the conventional apparent permeability (Papp) measure. The proposed approach thus enables more accurate characterization of analyte interactions with the barrier cell layer, supporting better-informed assessments of compound behavior in in vitro transport systems.

pharmacology and toxicology↗

bioRxiv2022

Novel insights into the fundamentals of palatal shelf elevation dynamics in normal mouse embryos

Embryonic palate development involves bilateral vertical growth of palatal shelves - extensions from the maxillary processes - next to the tongue until embryonic day (E) 13.5. Following vertical growth, palatal shelves elevate and adhere above the tongue by E14.5. Current models indicate that this process of elevation involves a complex vertical to horizontal reorienting of the palatal shelves. While earlier studies have implied that this is a rapid process, the precise timing has not been resolved. To understand the dynamics of palatal shelf elevation, we employed time-restricted pregnancies with a one-hour resolution and magnetic resonance imaging of intermediate stages. Our data showed that in almost all C57BL/6J embryos, palatal shelves have not yet elevated by E14.0. However, six hours later at E14.25, palatal shelves have completed elevation in 80% of embryos. Interestingly, all E14.25 embryos with unelevated palatal shelves (20%) were female, suggesting a delay in female embryos. In FVB/NJ embryos, the elevation window started earlier (E13.875-E14.25) without any noticeable sex differences. We frequently captured an intermediate stage with unilateral elevation of either right or left palatal shelf. Magnetic resonance imaging of various stages showed that palatal shelf elevation began with the formation of bilateral bulges in the posterior. These bulges progressed laterally and anteriorly over time. During elevation, we observed increased cell proliferation in the lingual region of the palatal shelf. Within the bulge, cell orientation was acutely tilted towards the tongue and actomyosin activity was increased, which together may participate in the projection of the bulge in the horizontal direction. Thus, our data reveal novel insights into the rapid dynamic changes in palatal shelf elevation that lay the foundation for future studies of normal and abnormal palatogenesis.

developmental biology↗

bioRxiv2021

In-frame deletion of SPECC1L microtubule binding domain results in embryonic tissue movement and fusion defects

Embryonic morphogenesis of the neural tube, palate, ventral body wall and optic fissure require precise sequence of tissue movement and fusion, which if incomplete, leads to anencephaly/exencephaly, cleft palate, omphalocele and coloboma, respectively. These are genetically heterogeneous birth defects, so there is a continued need to identify etiologic genes. Patients with autosomal dominant SPECC1L mutations show syndromic malformations, including hypertelorism, cleft palate and omphalocele. These SPECC1L mutations cluster in the second coiled-coil domain (CCD2), which facilitates association with microtubules. To study SPECC1L function in mice, we first generated a null allele (Specc1l{Delta}Ex4) lacking the entire SPECC1L protein. Homozygous mutants for these truncations died perinatally without cleft palate or exencephaly. Given the clustering of human mutations in CCD2, we hypothesized that targeted perturbation of CCD2 may be required. Indeed, homozygotes for in-frame deletions involving CCD2 (Specc1l{Delta}CCD2) resulted in ~50% exencephaly and ~50% cleft palate. Interestingly, these two phenotypes are never observed in the same embryo. Examination of embryos with and without exencephaly revealed that the oral cavity was narrower in exencephalic embryos, which allowed palatal shelves to elevate despite their defect. In contrast to an evenly distributed subcellular expression pattern, mutant SPECC1L-{Delta}CCD2 protein showed abnormal subcellular localization, decreased overlap with microtubules, increased actin bundles, and dislocated non-muscle myosin II to the cell cortex. Thus, we show that perturbations of CCD2 in the context of full SPECC1L protein affects tissue fusion dynamics, indicating that human SPECC1L CCD2 mutations are gain-of-function. Improper SPECC1L subcellular localization appears to disrupt connections between actomyosin and microtubule networks, which in turn may affect cell alignment and coordinate movement during tissue morphogenesis.

developmental biology↗

bioRxiv2020

Theoretical analysis of neural crest cell migration

The neural crest cells are embryonic stem cells that migrate throughout embryos and, at different target locations, give rise to the formation of a variety of tissues and organs. The directional migration of the neural crest cells is experimentally described using a process referred to as contact inhibition of locomotion (CIL), by which cells redirect their movement upon the cell-cell contacts. However, it is unclear how the migration alignment is affected by the motility properties of the cells. Here, we computationally model the migration alignment and the average time to reach a target location as functions of the motility dynamics and interaction of the cells in an open domain with a channel geometry. The results indicate that by varying the properties of the CIL interaction a transition takes place from random movement of the cells to an organized collective migration, where the migration alignment is maximised and the migration time is minimised. This phase transition is accelerated and strengthened with the influx rate of the cells into the domain through increasing the density of the migrating cells. The model further suggests that the migration is more coordinated when the cells with a large CIL radius move fast in a narrow domain.

biophysics↗

bioRxiv2020

Multiscale modelling of motility wave propagation in cell migration

The collective motion of cell monolayers within a tissue is a fundamental biological process that occurs during tissue formation, wound healing, cancerous invasion, and viral infection. Experiments have shown that at the onset of migration, the motility is self-generated as a polarization wave starting from the leading edge of the monolayer and progressively propagates into the bulk. However, it is unclear how the propagation of this motility wave is influenced by cellular properties. Here, we investigate this using a computational model based on the Potts model coupled to the dynamics of intracellular polarization. The model captures the propagation of the polarization wave initiated at the leading edge and suggests that the cells cortex can regulate the migration modes: strongly contractile cells may depolarize the monolayer, whereas less contractile cells can form swirling movement. Cortical contractility is further found to limit the cells motility, which (i) decelerates the wave speed and the leading edge progression, and (ii) destabilises the leading edge into migration fingers. Together, our model describes how different cellular properties can contribute to the regulation of collective cell migration.

biophysics↗

bioRxiv2019

SPECC1L-deficient palate mesenchyme cells show speed and directionality defect

Clefts of the lip and/or palate (CL/P) are common anomalies that occur in 1/800 live births. Pathogenic SPECC1L variants identified in patients with rare atypical clefts and syndromic CL/P suggest the gene plays a primary role in face and palate development. We have generated Specc1l gene-trap (Specc1lcGT) and truncation (Specc1l{Delta}C510) alleles that cause embryonic or perinatal lethality, respectively. Specc1lcGT/{Delta}C510 compound mutants show delayed and abnormal palatal shelf elevation at E14.5. By E15.5, the mutant shelves do elevate and fuse, however, the palatal rugae form abnormally. Palatogenesis requires extensive mesenchymal remodeling, especially during palatal shelf elevation. We posit that this remodeling involves collective movement of neural crest-derived palatal mesenchyme cells. Live time-lapse microscopy was performed to visualize in vitro wound-repair assays with wildtype and SPECC1L-deficient primary mouse embryonic palatal mesenchyme (MEPM) cells. SPECC1L-deficient MEPM cells consistently showed delayed closure in wound-repair assays. To evaluate which features of cellular movement were responsible, we performed automated particle image velocimetry (PIV) and manual cell tracking. The analyses revealed that both cell speed and directionality are disrupted in SPECC1L-deficient cells compared to controls. To determine if primary MEPM cells can move collectively, we assayed stream formation, which is a hallmark of collective movement. Indeed, MEPM cultures displayed correlated movement of neighboring cells. Importantly, correlation length was reduced in SPECC1L-deficient cultures, consistent with a role for SPECC1L in collective migration. Furthermore, we demonstrated that activation of the PI3K-AKT pathway with the 740Y-P small molecule can rescue the wound-closure delay in SPECC1L-deficient MEPM cells. Cell tracking analyses showed that this rescue was due to both increased speed and improved directionality. Altogether, our data showed a novel role for SPECC1L in guided movement through modulation of PI3K-AKT signaling.

cell biology↗

bioRxiv2019

Viscoelastic properties of ECM-rich embryonic microenvironments

The material properties of tissues and their mechanical state is an important factor during development, disease, regenerative medicine and tissue engineering. Here we describe a microrheological measurement technique utilizing aggregates of microinjected ferromagnetic nickel particles to probe the viscoelastic properties of embryonic tissues. Quail embryos were cultured in a plastic incubator chamber located at the center of two pairs of crossed electromagnets. We estimate the Youngs modulus of the ECM-rich region separating the mesoderm and endoderm in Hamburger Hamilton stage 6-10 quail embryos as 300{+/-}100 Pa. We found a pronounced viscoelastic behavior consistent with a Zener (standard generalized solid) model. The viscoelastic response is about 45% of the total response, with a characteristic relaxation time of 1.3 sec.

developmental biology↗