Biology subjects

Freeman, E.

Publications and source records attributed to Freeman, E..

7 recordsLinked to original sources

bioRxiv2026

The dynamics of nucleolus-centromeres interaction in living cells

Nucleoli and centromeres play essential roles in cellular proliferation and homeostasis, and are structurally and functionally interconnected. Centromeres frequently cluster around nucleoli, and some centromere assembly factors are known to reside in the nucleoli. To investigate the spatial and temporal relationships between these nuclear domains, we examined their dynamics in living cells. We imaged HeLa cells stably expressing mCherry-NPM1 and GFP-CENP-A using time-lapse microscopy. The results show that a subset of centromeres exhibits dynamic behavior during interphase, migrating over micrometer-scale distances within two hours. On average, 40-50% of centromeres maintain an association with nucleoli throughout interphase, with some cells displaying nucleolar-centromere association and dissociation within hours. Upon entry into mitosis, nucleoli are disassembled, and NPM1 localizes to the periphery of mitotic chromosomes. Nucleolar-centromere interactions are re-established in early G1, coinciding with the assembly of new centromeres. Treatment with actinomycin D, an inhibitor of RNA polymerase I, significantly reduces nucleolar size, nucleolar-centromere interactions, and centromere dynamics. Furthermore, post-mitotic nucleolar reformation is impaired. These findings highlight the dynamic nature of centromeres in interphase nuclei and their interactions with nucleoli. This behavior is partially dependent on rDNA transcription and nucleolar integrity, underscoring the critical roles of nucleoli, centromeres, and their interaction in 4D genome organization.

cell biology↗

bioRxiv2024

The GABAA receptor RDL modulates the auditory sensitivity of malaria mosquitoes.

Malaria mosquitoes mate in crowded, and noisy, swarms. A vital stage of their precopulatory behaviour involves detecting the faint flight tone of a mating partner amidst the noise from hundreds of other mosquitoes. This exquisite sensory performance is enabled by a complex auditory system with remarkable features. One such feature is their vast efferent control system, which provides the mosquito ear with the required plasticity to adapt to various external and internal changes. In this paper, we study the auditory role of GABA, one of the main efferent signalling molecules in the mosquito ear, and its interactions with octopamine, another neurotransmitter of the efferent network. We show that GABA is released in the malaria mosquito auditory nerve and that GABA receptors are expressed in the ear, including the GABAA receptor Resistance to Dieldrin (RDL), a target for the evolution of insecticide resistance. Using picrotoxin to antagonize RDL receptors, we discovered multiple auditory effects of GABA at the mechanical and electrical level. At the mechanical level, blocking RDL promotes the erection of antennal fibrillae and the cessation of flagellar self-sustained oscillations. These effects are not observed in knockouts of the octopamine receptor AgOct{beta}2, suggesting that RDL auditory mechanical effects are mediated through octopamine release in the mosquito ear. Electrically, picrotoxin injection increases the spontaneous firing of auditory neurons and direct current (DC) responses of the nerve to mechanical stimulation both in wildtype and AgOct{beta}2 mutants, indicating that RDL may also modulate auditory sensitivity via octopamine-independent pathways. In summary, our experiments uncover distinct auditory roles of GABA, as well as synergistic roles with octopamine. The data show a fundamental role of RDL in controlling the auditory function of malaria mosquitoes and implicate RDL signalling in mating of natural malaria mosquito populations.

neuroscience↗

bioRxiv2022

GENLIB: new function to simulate haplotype transmission in large complex genealogies

SummaryFounder populations with deep genealogical data are well suited for investigating genetic variants contributing to diseases. Here, we present a new function added to the genealogical analysis R package GENLIB, which can simulate the transmission of haplotypes from founders to probands along very large and complex user-specified genealogies. Availability and implementationThe new function is available in the latest version of the GENLIB package (v1.1.6), available on the CRAN repository and from https://github.com/R-GENLIB/GENLIB. Stand-alone scripts for analyzing the output of the function can be accessed at https://github.com/R-GENLIB/simuhaplo_scripts.

bioinformatics↗

bioRxiv2022

Nucleoli and the nucleoli-centromere association are dynamic during normal development and in cancer

Centromeres are known to cluster around nucleoli in drosophila and mammalian cells. However, the functional significance of nucleoli-centromere interaction remains underexplored. We hypothesize that if this conserved interaction is functionally important, it should be dynamic under different physiological and pathological conditions. We examined the nucleolar structure and centromeres at various differentiation stages using cell culture models. The results show dynamic changes of nucleolar number, area, and nucleoli-centromere interactions at differentiation stages and in cancer cells. Embryonic stem cells usually have a single large nucleolus, which associates with a high percentage of centromeres. As cells differentiate into intermediate states, the nucleolar number increases and the association with centromeres decreases. In terminally differentiated cells, including myotubes, neurons and keratinocytes, the number of nucleoli and their association with centromeres are at the lowest. Cancer cells demonstrate the pattern of nucleoli number and nucleoli-centromere association that is akin to proliferative less differentiated cell types, suggesting that nucleolar reorganization and changes in nucleoli-centromere interactions may help facilitate malignant transformation. This idea is supported in a case of pediatric rhabdomyosarcoma, in which induced differentiation inhibits cell proliferation and reduces nucleolar number and centromere association. These findings suggest active roles of nucleolar structure in centromere function and genome organization critical for cellular function in both normal development and cancer.

cell biology↗

bioRxiv2022

Thermal Effects on Neurons During Stimulation of the Brain

All artificial stimulation of the brain deposits thermal energy in the brain. This occurs through either Joule heating of the conductors carrying current through electrodes and magnetic coils, or through dissipation of energy in the conductive brain. Similarly, temperature affects all biological processes and chemical reactions. Although electrical interaction with brain tissue is inseparable from thermal effects when electrodes are used, magnetic induction enables us to separate Joule heating from induction effects by contrasting AC and DC driving of magnetic coils using the same energy deposition within the conductors. Since mammalian cortical neurons have no known sensitivity to static magnetic fields, and if there is no evidence of effect on spike timing to oscillating magnetic fields, we can presume that the induced electrical currents within the brain are below the molecular shot noise where any interaction with tissue is purely thermal. In this study, we examined a range of frequencies produced from micromagnetic coils operating below the molecular shot noise threshold for electrical interaction with single neurons. We found that small temperature increases and decreases of 1{degrees}C caused consistent transient suppression and excitation of neurons during temperature change. Numerical modeling of the biophysics demonstrated that the Na-K pump, and to a lesser extent the Nernst potential, could account for these transient effects. Such effects are dependent upon compartmental ion fluxes, and the rate of temperature change. A new bifurcation is described in the model dynamics that accounts for the transient suppression and excitation; in addition, we note the remarkable similarity of this bifurcations rate dependency with other thermal rate-dependent tipping points in planetary warming dynamics. Furthermore, bifurcations in the steady state dynamics leading to stable firing suppression are described for slightly higher temperatures. These experimental and theoretical findings demonstrate that stimulation of the brain must take into account small thermal effects that are ubiquitously present in electrical and magnetic stimulation. More sophisticated models of electrical current interaction with neurons combined with thermal effects will be required in order to more accurately enable model-based control of neuronal circuitry.

biophysics↗

bioRxiv2020

NAT8L mRNA oxidation is linked to neurodegeneration in multiple sclerosis

RNA oxidation has been implicated in neurodegeneration, but the underlying mechanism for such effects is unclear. Recently, we demonstrated extensive RNA oxidation within the neurons in multiple sclerosis (MS) brain. In this report we identified selectively oxidized mRNAs in neuronal cells that pertained to neuropathological pathways. N-acetyl aspartate transferase 8 like (NAT8L) mRNA is one such transcript, whose translated product enzymatically synthesizes N-acetyl aspartic acid (NAA), a neuronal metabolite important for myelin synthesis. We reasoned that impediment of translation of an oxidized NAT8L mRNA will result in reduction in its cognate protein, thus lowering NAA level. This assertion is directly supported by our studies on a model cellular system, an MS animal model and postmortem human MS brain. Reduced NAA level in the brain hampers myelin integrity making neuronal axons more susceptible to damage, which contributes in MS neurodegeneration. Overall, this work provides a framework for mechanistic understanding of the link between RNA oxidation and neurodegenerative diseases.

molecular biology↗

bioRxiv2019

A positively selected, common, missense variant in FBN1 confers a 2.2 centimeter reduction of height in the Peruvian population

Peruvians are among the shortest people in the world. To understand the genetic basis of short stature in Peru, we examined an ethnically diverse group of Peruvians and identified a novel, population-specific, missense variant in FBN1 (E1297G) that is significantly associated with lower height in the Peruvian population. Each copy of the minor allele (frequency = 4.7%) reduces height by 2.2 cm (4.4 cm in homozygous individuals). This is the largest effect size known for a common height-associated variant. This variant shows strong evidence of positive selection within the Peruvian population and is significantly more frequent in Native American populations from coastal regions of Peru compared to populations from the Andes or the Amazon, suggesting that short stature in Peruvians is the result of adaptation to the coastal environment. One Sentence SummaryA mutation found in Peruvians has the largest known effect on height for a common variant. This variant is specific to Native American ancestry.

genomics↗