Biology subjects

Bender, N.

Publications and source records attributed to Bender, N..

7 recordsLinked to original sources

bioRxiv2026

A Practical Assay for Assessing Mean Red Blood Cell Age Using the Protein 4.1a/4.1b Ratio

BACKGROUND: The protein 4.1a/4.1b ratio is an intrinsic molecular marker of mean red blood cell (RBC) age resulting from progressive deamidation of protein 4.1b during RBC circulation. Despite its potential for estimating mean RBC age from a single blood sample, its application has been limited by labor-intensive RBC membrane preparation, and its interindividual variability has not been characterized in a large human population. METHODS: We developed a low-volume method for direct RBC membrane isolation from whole blood using saponin permeabilization and differential centrifugation without prior RBC washing. Membrane proteins were separated by SDS-PAGE, and protein 4.1a/4.1b ratios were determined by densitometric analysis with Gaussian peak fitting. Assay conditions, sample-volume requirements, membrane protein recovery, and analytical reproducibility were evaluated. The method was subsequently applied to 114 anonymized residual samples from routine diagnostic testing selected for complete blood count parameters within the corresponding laboratory reference intervals. RESULTS: The optimized procedure used 50 uL of whole blood, 0.06% saponin, and centrifugation at 9000 g, although protein 4.1a/4.1b remained measurable from starting volumes as low as 5 uL. Mean within-subject CVs were 3.90% for electrophoretic/densitometric determination and 5.39% for membrane protein recovery; whole-procedure CVs in 3 subjects were 1.40% to 3.50%. In the population analysis, the mean protein 4.1a/4.1b ratio was 1.428 (SD 0.146), with an observed range of 1.052 to1.799 and a central 95% interval of 1.151 to 1.695. Ratios did not differ significantly between females and males (P=0.246) or among females aged 18 to 50 years, females aged >50 years, and males (P=0.151). The ratio showed modest positive correlations with chronological age in females (Spearman p=0.26, P=0.047) and males (p=0.33, P=0.015), while substantial interindividual variability remained across the age range. CONCLUSIONS: Direct isolation of RBC membranes from small volumes of whole blood enables reproducible determination of the protein 4.1a/4.1b ratio using a simplified workflow. Application of the assay to a comparatively large human population revealed substantial interindividual variation in this molecular marker of mean RBC age that was not explained by sex or chronological age alone. The method provides a practical approach for investigating biological variation in mean RBC age and its potential contribution to laboratory measurements influenced by RBC survival.

biochemistry↗

bioRxiv2025

A maternal-fetal PIEZO1 incompatibility as a barrier to Neanderthal-modern human admixture

When Neanderthals and anatomically modern humans interbred, they may have faced conditional reproductive barriers. We identify a likely maternal-fetal incompatibility involving a Neanderthal PIEZO1 gene variant predicted to increase red blood cell oxygen affinity. While potentially advantageous in Neanderthals, this trait became detrimental in hybrids: heterozygous mothers carrying one Neanderthal allele could deliver insufficient oxygen to fetuses inheriting two modern alleles, reducing their survival. We tested this hypothesis using in vitro physiology, population genetic simulations, and genomic surveys. Pharmacological activation of Piezo1 in human red blood cells reproduced the high-affinity phenotype, providing a biochemical basis for impaired placental oxygen transfer. Simulations showed that maternal-fetal mismatch drives frequency-dependent selection against the Neanderthal allele, promoting demographic decline. Genomic data confirm that the variant is virtually absent in modern humans, consistent with strong purifying selection. Our findings reveal how subtle physiological mismatches plausibly restricted gene flow, contributing to Neanderthal extinction, and highlight a mechanism potentially underlying unexplained pregnancy complications today. TeaserMaternal-fetal oxygen affinity mismatches resulting from a Neanderthal PIEZO1 gene variant may have hastened their extinction. O_FIG O_LINKSMALLFIG WIDTH=142 HEIGHT=200 SRC="FIGDIR/small/679417v1_ufig1.gif" ALT="Figure 1"> View larger version (29K): org.highwire.dtl.DTLVardef@1132476org.highwire.dtl.DTLVardef@1bec6b5org.highwire.dtl.DTLVardef@1e7ae96org.highwire.dtl.DTLVardef@1772d17_HPS_FORMAT_FIGEXP M_FIG O_FLOATNOGraphical AbstractC_FLOATNO Conceptual model of maternal-fetal oxygen affinity mismatch caused by PIEZO1 gain-of-function (GOF) variants. Upper panel: In uncomplicated pregnancies, maternal RBCs exhibit lower hemoglobin-oxygen affinity (higher P50) than fetal RBCs, creating a gradient that facilitates placental oxygen transfer. PIEZO1 GOF variants increase maternal oxygen affinity (lower P50), narrowing this gradient and reducing fetal oxygen supply. Lower panel: Genetic inheritance scenarios illustrate how this physiological effect translates into a hybrid incompatibility. While heterozygous mothers (WT/GOF) can be healthy, pregnancies with wild-type fetuses (WT/WT) are at risk of impaired oxygen transfer, leading to growth restriction, hydrops, or fetal loss. Other maternal-fetal genotype combinations are not affected. Together, these data support a model in which PIEZO1-driven maternal-fetal mismatch acts as a non-immune reproductive barrier with relevance for both evolutionary admixture and modern pregnancy complications. C_FIG

evolutionary biology↗

bioRxiv2022

Collective polarization dynamics in gonococcal colonies

Membrane potential in bacterial systems has been shown to be dynamic and tightly related to survivability at the single cell level. However, little is known about spatio-temporal patterns of membrane potential in bacterial colonies and biofilms. Here, we discovered a switch from uncorrelated to collective dynamics within colonies formed by the human pathogen Neisseria gonorrhoeae. In freshly assembled colonies, polarization is heterogeneous with instances of transient and uncorrelated hyper- or depolarization of individual cells. As colonies reach a critical size, the polarization behaviour switches to collective dynamics: A hyperpolarized shell forms at the centre, travels radially outward, and halts several micrometres from the colony periphery. Once the shell has passed, we detect an influx of potassium correlated with depolarisation. Transient hyperpolarization also demarks the transition from volume to surface growth. By combining simulations and the use of an alternative electron acceptor for the respiratory chain, we provide strong evidence that local oxygen gradients shape the collective polarization dynamics. Finally, we show that within the hyperpolarized shell, tolerance against aminoglycoside antibiotics but not against {beta}-lactam antibiotics is increased, suggesting that depolarization instantaneously protects cells, while the protective effect of growth arrest does not set in immediately. These findings highlight that the polarization pattern can demark the differentiation into distinct subpopulations with different growth rates and antibiotic tolerance. Significance statementAt the level of single bacteria, membrane potential is surprisingly dynamic and transient hyperpolarization has been associated with increased death rate. Yet, little is known about the spatiotemporal dynamics of membrane polarization during biofilm development. Here, we reveal a discrete transition from uncorrelated to collective polarization dynamics within spherical colonies. Suddenly, a shell of hyperpolarized cells forms at the colony centre and hyperpolarization travels radially outward. In the wake of this shell, bacteria depolarize, reduce their growth rate, and become tolerant against antibiotics, indicating the onset of habitat diversity. Single cell live imaging and modelling link hyperpolarization to an oxygen gradient formed within the colonies. We anticipate that dynamical polarization patterns are tightly connected to biofilm differentiation in various bacterial species.

biophysics↗

bioRxiv2021

Spatio-temporal dynamics of growth and death within spherical bacterial colonies

Bacterial growth within colonies and biofilms is heterogeneous. Local reduction of growth rates has been associated with tolerance against various antibiotics. However, spatial gradients of growth rates are poorly characterized in three-dimensional bacterial colonies. Here, we report two spatially resolved methods for measuring growth rates in bacterial colonies. As bacteria grow and divide, they generate a velocity field that is directly related to the growth rates. We derive profiles of growth rates from the velocity field and show that they are consistent with the profiles obtained by single cell counting. Using these methods, we reveal that even small colonies comprising a few thousand cells of the human pathogen Neisseria gonorrhoeae develop a steep gradient of growth rates within two generations. Furthermore, we show that stringent response decelerates growth inhibition at the colony centre. Based on our results, we suggest that aggregation-related growth inhibition can protect gonococci from external stresses even at early biofilm stages.

biophysics↗

bioRxiv2021

Sexually Transmitted Infections Select for Different Levels of Immunocompetence And Reproductive Efforts in The Two Sexes

1.Sex differences in immunity have been described in humans and other mammal species. Females have a lower incidence of infections and non-reproductive malignancies and exhibit higher antibody levels after vaccination. Existing evolutionary explanations are based on differences in reproductive strategies and reaction to extrinsic differences in susceptibility and virulence between the sexes. Here, we test the hypothesis that known differences in the probability of transmission and outcome of sexually transmitted infections contribute to sex differences in immunocompetence. We modelled reproductive and immune investments against a fertility limiting Sexually Transmitted Infection (STI). We show that, in line with previous findings, increased susceptibility selects for tolerance to the parasite while increased virulence selects for resistance against it. Differences in reproductive strategies between the sexes lead to sex differences in immunocompetence, mostly with higher competence in females. Extrinsic differences in susceptibility and virulence between the sexes can augment or alleviate the evolutionary consequences of intrinsic differences depending on their direction and magnitude. This indicates that the selection of sex-specific immune strategies is less predictable than thought before and explains why sex differences in immunity have been found to be not universal and pervasive across animal species.

evolutionary biology↗

bioRxiv2020

The Evolution of Immune Sensitivity under Immunopathological and Autoimmune Costs

Hosts with high immune sensitivity benefit from rapid recovery but suffer multiple costs thereof. We distinguish between immunopathological costs due to collateral damage and autoimmune costs due to false positives against self. Selection on sensitivity follows different trajectories depending on the cost nature and the overlap degree between host- and parasitic molecular signatures. Increased parasite virulence selects for higher immune sensitivity under immunopathological costs but low sensitivity when the costs are autoimmune, contradicting previous theoretical results. Longer lifespan of the host selects for low sensitivity under immunopathology to avoid accumulated tissue damage. Under autoimmune costs, hosts with a shorter lifespan cannot afford to shorten it further due to autoimmunity and evolve lower immune sensitivity. Longer lifespan selects for high or low sensitivity depending on the presence of immune memory. These results extend our understanding of selection on immune sensitivity and help explain phenomena like the cytokine shock and chronic infections.

evolutionary biology↗

bioRxiv2020

Circumventing the optical diffraction limit with customized speckles

Speckle patterns have been widely used in imaging techniques such as ghost imaging, dynamic speckle illumination microscopy, structured illumination microscopy, and photoacoustic fluctuation imaging. Recent advances in the ability to control the statistical properties of speckles has enabled the customization of speckle patterns for specific imaging applications. In this work, we design and create special speckle patterns for parallelized nonlinear pattern-illumination microscopy based on fluorescence photoswitching. We present a proof-of-principle experimental demonstration where we obtain a spatial resolution three times higher than the diffraction limit of the illumination optics in our setup. Furthermore, we show that tailored speckles vastly outperform standard speckles. Our work establishes that customized speckles are a potent tool in parallelized super-resolution microscopy.

biophysics↗