Biology subjects

Pelletier, J.

Publications and source records attributed to Pelletier, J..

At least 19 recordsLinked to original sources

bioRxiv2026

P2Y6 signaling selectively regulates TLR3-induced chemokine release in murine bone marrow-derived macrophages, with opposing effects on CCL2 and CXCL1

Extracellular nucleotides regulate diverse inflammatory responses through the activation of P2 receptors. Here, we show that nucleotides regulate TLR3-induced chemokine responses in murine bone marrow-derived macrophages (BMDMs). Stimulation with the TLR3 agonist, poly(I:C), induced CCL2 and CXCL1 secretion, whereas degradation of extracellular nucleotides with apyrase reduced CCL2 but enhanced CXCL1 release. In agreement, the non-selective P2 receptor antagonists suramin and RB2 reduced poly(I:C)-induced CCL2 production. Among the highly expressed P2 receptors examined, selective inhibition of P2Y6 with MRS2578 reproduced the effects of apyrase, decreasing CCL2 while increasing CXCL1 secretion. The absence of effects of MRS2578 in P2ry6-deficient BMDMs confirmed the specificity of this antagonist. Transcriptional analysis further revealed that P2Y6 inhibition reduced early poly(I:C)-induced Ccl2 and Cxcl10 expression while enhancing later Cxcl1 and Cxcl2 expression. In line with our previous works on other pattern-recognition receptors pathways and innate immune cells, this study further supports a role for extracellular nucleotides in shaping TLR-induced chemokine responses in macrophages.

immunology↗

bioRxiv2026

The essential molecular components for cellular CO2 sensing via connexins

CO2 opens a subset of connexin hemichannels by binding to a site in the cytoplasmic domain of the channel. From outside the cell, CO2 must cross at least one membrane to reach this site. We have used Neuro-2A cells, which exhibit very low expression of CO2 permeable aquaporins (AQPs) and do not express any of the connexins (Cxs) known to be CO2 sensitive, to evaluate the minimal complement of molecular components required to recapitulate whole cell CO2 sensitivity mediated by connexins (assayed by either whole cell patch clamp recordings or real time recordings of ATP release via a co-expressed genetically encoded ATP sensor). Neuro-2A cells that expressed either Cx26, Cx32 or Cx43 on their own did not exhibit CO2-dependent connexin hemichannel gating. Expression of AQP1 or AQP5 either with or without carbonic anhydrase 2 (CA2) did not reveal any endogenous CO2 sensitivity of Neuro-2A cells. Only by expressing one of Cx26, Cx32 or Cx43 with either AQP1 or AQP5, plus CA2 were we able to reconstitute whole cell CO2 sensitivity. We found that expression of Cx26 with either AQP1 or AQP5 resulted in high levels of cell death. This was prevented by co-expression of CA2. Simulations of the influx and diffusion of CO2 show that CA2 prevents accumulation of intracellular CO2 and excessive activation of Cx26, thus protecting the cells from death. Surveying the transcriptome of cells that express CO2 sensitive connexins shows that many also express CO2 permeable aquaporins and CA2. We suggest that connexins, aquaporins and carbonic anhydrases represent the minimal trifecta of components required for cellular CO2 sensing.

cell biology↗

bioRxiv2025

CO2 sensitive connexin channel synapses in the VTA release 5HT to regulate dopaminergic neurons

Hypercapnic arousal is a life-preserving reflex that promotes awakening in response to elevated PCO2, yet the cellular mechanisms by which CO2 is detected remain incompletely understood. Serotonergic neurons of the dorsal raphe (DR) have been implicated in hypercapnic responses, but the molecular sensor that directly detects CO2 within this circuit is unknown. Here, we show that the CO2-gated connexin 26 (Cx26) hemichannel is expressed on serotonergic terminals projecting from the DR to the ventral tegmental area (VTA). Brief elevations in PCO2 modulated the excitability of VTA dopamine neurons through serotonergic signaling without altering glutamatergic transmission, and these effects were abolished by pharmacological inhibition of hemichannels. By expressing Cx26 and genetically encoded GRAB5HT sensors in cultured cells, we further demonstrate that Cx26 hemichannels opened by elevated PCO2 are directly permeable to serotonin. Selective removal of CO2 sensitivity from Cx26 in DR serotonergic neurons delayed arousal from sleep during transient hypercapnia and reduced activation of VTA dopamine neurons in vivo. Together, these findings identify Cx26 hemichannels as a direct CO2 sensor that enables serotonin release through a channel co-synapse and contributes to hypercapnic arousal.

neuroscience↗

bioRxiv2025

Untangling dopamine and glutamate in the ventral tegmental area

Ventral tegmental area (VTA) dopamine neurons are of great interest for their central roles in motivation, learning, and psychiatric disorders. While hypotheses of VTA dopamine neuron function posit a homogenous role in behavior (e.g., prediction error), they do not account for molecular heterogeneity. We find that glutamate-dopamine, nonglutamate-dopamine, and glutamate-only neurons are dissociable in their signaling of reward and aversion-related stimuli, prediction error, and electrical properties. In addition, glutamate-dopamine and nonglutamate-dopamine neurons differ in dopamine release dynamics. Aversion-related recordings of all dopamine neurons (not considering glutamate co-transmission) showed a mixed response that obscured dopamine subpopulation function. Within glutamate-dopamine neurons, glutamate and dopamine release had dissociable contributions toward reward and aversion-based learning and performance. Based on our results, we propose a new hypothesis on VTA dopamine neuron function: that dopamine neuron signaling patterns and their roles in motivated behavior depend on whether or not they co-transmit dopamine with glutamate.

neuroscience↗

bioRxiv2025

Signals from the bone marrow B cell niches shape pre-leukemic fate in murine B cell acute lymphoblastic leukemia

The bone marrow (BM) microenvironment plays a key role in supporting B cell development. In acute lymphoblastic leukemia (B-ALL), the acquisition of oncogenic driver mutations blocks B cell differentiation at specific stages. When these pre-leukemic cells acquire secondary mutations, B-ALL develops. However, the role of the BM microenvironment in pre-leukemic cell fate remains unknown. Here, using a murine model of spontaneous B-ALL development, we show that disrupted pre-BCR signaling in pre-leukemic cells modifies their fate. Blocking expression of the pre-BCR ligand Galectin-1 by the microenvironment impaired pre-leukemic cell proliferation and leukemia-initiating capacity. Consequently, B-ALL development was delayed, and B-ALL had a more mature phenotype, with cells expressing a BCR. Secondary mutations were also altered by changes to Galectin-1 expression, in its absence mutations almost exclusively affected IL-7R signaling rather than both pre-BCR and IL-7R signaling. These results show that signals from BM niches can directly influence pre-leukemic B cell fate.

cancer biology↗

bioRxiv2025

VGluT3 BNST neurons transmit GABA and restrict feeding without affecting rewarding or aversive processing

The bed nucleus of the stria terminalis (BNST) is involved in feeding, reward, aversion, and anxiety-like behavior. We identify BNST neurons defined by the expression of vesicular glutamate transporter 3, VGluT3. VGluT3 neurons were localized to anteromedial BNST, were molecularly distinct from accumbal VGluT3 neurons, and co-express vesicular GABA transporter (VGaT). Cell-type specific presynaptic processes were identified in arcuate nucleus (ARC) and the paraventricular nucleus of the hypothalamus (PVN), regions critical for feeding and homeostatic regulation. Whole-cell patch-clamp electrophysiology revealed that, while these neurons co-express VGluT3 and VGaT, they functionally transmit GABA to both ARC and PVN, with rare glutamate co-transmission to ARC. Neuronal recordings of VGluT3 BNST neurons showed greater calcium-dependent signaling in response to sucrose consumption while sated compared with fasted. When fasted, optogenetic stimulation of BNST VGluT3 neurons decreased sucrose consumption using several stimulation conditions but not when stimulation occurred prior to sucrose access, suggesting that BNST VGluT3 activation concurrent with consumption in the fasted state reduces feeding. BNST VGluT3 activation during anxiety-like paradigms (novelty-suppressed feeding, open field, and elevated zero maze) and real-time place conditioning resulted in no changes in anxiety-like or reward/aversion behavior. We interpret these data such that VGluT3 BNST neurons represent a unique cellular population within the BNST that provides inhibitory input to hypothalamic regions to decrease feeding without affecting anxiety-like or reward/aversion behavior.

neuroscience↗

bioRxiv2025

Assessing the role of BNST GABA neurons in backward conditioned suppression

Conditioned suppression is a useful paradigm for measuring learned avoidance. In most conditioned suppression studies, forward conditioning is used where a cue predicts an aversive stimulus. However, backward conditioning, in which an aversive stimulus predicts a cue, provides unique insights into learned avoidance due to its influence on both conditioned excitation and inhibition. We trained mice to consume sucrose in context A, associated an aversive stimulus in context B to few or many forward or backwards paired cues (CS+), and then tested for conditioned suppression in context A in response to the CS+. We found that few or many forward CS+ and few backward CS+ produced conditioned suppression, but many backwards cues did not. Administration of diazepam, a positive allosteric modulator of the GABA-A receptor, prevented conditioned suppression to the backward CS+ but not to the forward CS+. Furthermore, freezing behavior was observed in response to the forward CS+ but not the backward CS+, and diazepam had no effect on freezing or locomotion. We next examined BNST GABA neurons for potential sensitivity to backwards cues and conditioned suppression. VGaT BNST signaling increased in response to sucrose licks during the backward CS+ but not to licks outside the CS+ and not to the backward CS+ onset or offset. Using designer receptors, we found that BNST VGaT neuron activation, but not its inhibition, prevented backward conditioned suppression expression. We conclude that backward conditioned suppression is dependent on both positive allosteric modulation of GABA on GABA-A receptors by diazepam and BNST GABA neurons.

neuroscience↗

bioRxiv2024

Structural Basis for the Improved RNA-Clamping of Amidino-Rocaglates to eIF4A1

Eukaryotic Initiation Factor 4A-1 (eIF4A1) is an ATP-dependent RNA helicase that unwinds 5-UTR mRNA secondary structures to facilitate cap-dependent translation initiation. Rocaglates, a class of natural products typified by rocaglamide A (RocA), possess anti-neoplastic and anti-infectious activity mediated by their interaction with eIF4A1. Rocaglates inhibit cap-dependent translation initiation by "clamping" eIF4A1 onto polypurine RNA, impeding ribosome scanning. A novel class of rocaglate derivatives, amidino-rocaglates (ADRs) which feature an amidine ring fused to the rocaglate core, are particularly effective at promoting eIF4A1-RNA-clamping compared to other rocaglate congeners. Herein, we present the X-ray crystal structure of an ADR in complex with eIF4A1, the nonhydrolyzable ATP ground-state mimic adenylyl-imidodiphosphate (AMPPNP), and poly r(AG)5 RNA refined to 1.69 [A] resolution. The binding pose and interactions of the ADR with eIF4A1 do not differ substantially from those of RocA, prompting investigation of the basis for enhanced target engagement. Computational modeling suggests that the rigidified ADR scaffold is inherently preorganized in an eIF4A1-RNA-binding-competent conformation, thereby avoiding entropic penalties associated with RocA binding. This study illustrates how conformational rigidification of the rocaglate scaffold can be leveraged to improve potency for the development of rocaglates as potential anticancer and anti-infectious agents. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=113 SRC="FIGDIR/small/616674v1_ufig1.gif" ALT="Figure 1"> View larger version (44K): org.highwire.dtl.DTLVardef@3c6dcorg.highwire.dtl.DTLVardef@1f4ae24org.highwire.dtl.DTLVardef@d4e264org.highwire.dtl.DTLVardef@5b1bde_HPS_FORMAT_FIGEXP M_FIG C_FIG

biochemistry↗

bioRxiv2024

Richness and composition of phyllosphere Methylobacterium communities cause variation in Arabidopsis thaliana growth

The phyllosphere - the aerial parts of plants - forms a vast microbial habitat that harbors diverse bacterial communities playing key roles in ecosystem function. The foliar surface is thus a promising study system to investigate biodiversity-ecosystem function relationships. Researchers have found a positive correlation between leaf bacterial diversity and ecosystem productivity, but the causality of this relationship has yet to be demonstrated. To understand how the diversity and composition of phyllosphere bacterial communities could cause variation in the growth of their host plants, we assembled synthetic communities composed of different diversity and compositions of Methylobacterium strains - a plant growth-promoting bacterial genus ubiquitous in the phyllosphere - that we inoculated on Arabidopsis thaliana grown in gnotobiotic conditions. We hypothesized that (1) increasing Methylobacterium diversity should cause an increase in host growth; (2) strains should differ in their impact on host growth; and (3) the relationship between bacterial diversity and plant productivity should be strain-dependent. Our results supported our three hypotheses but revealed unpredicted patterns in how A. thaliana leaf biomass varied according to inoculated Methylobacterium strain richness and identity. Increasing bacterial richness induced a higher host leaf biomass, but only after an initial reduction in biomass, suggesting competition alleviation by multispecies interactions. Two Methylobacterium strains showed beneficial effects on A. thaliana growth, and one strain was detrimental for the plant. Community composition shaped the relationship between diversity and productivity, highlighting the importance of community mutualistic and antagonistic interactions. Furthermore, niche complementarity was likely the main ecological mechanism driving the diversity-productivity relationship in our study system. By demonstrating the causal effects of Methylobacterium community diversity and composition on host plant growth, our experiment shed light on the importance of phyllosphere bacteria in terrestrial ecosystem functioning.

ecology↗

bioRxiv2024

Genome-Wide Profiling of Soybean WRINKLED1 Transcription Factor Binding Sites Provides Insight into the Regulation of Fatty Acid and Triacylglycerol Biosynthesis Program in Seeds

Understanding the regulatory mechanisms controlling storage lipid accumulation will inform strategies to enhance seed oil quality and quantity in crop plants. The WRINKLED1 transcription factor (WRI1 TF) is a central regulator of lipid biosynthesis. We characterized the genome-wide binding profile of soybean (Gm)WRI1 and show that the TF directly regulates genes encoding numerous enzymes and proteins in the fatty acid and triacylglycerol biosynthetic pathways. GmWRI1 binds primarily to regions downstream of target gene transcription start sites. We showed that GmWRI1 bound regions are enriched for the canonical WRI1 DNA binding element, the AW Box (CNTNGNNNNNNNCG), and another DNA motif, the CNC Box (CNCCNCC). Functional assays showed that both DNA elements mediate transcriptional activation by GmWRI1. We also show that GmWRI1 works in concert with other TFs to establish a regulatory state that promotes fatty acid and triacylglycerol biosynthesis. In particular, comparison of genes targeted directly by GmWRI1 and by GmLEC1, a central regulator of the maturation phase of seed development, reveals that the two TFs act in a positive feedback subcircuit to control fatty acid and triacylglycerol biosynthesis. Together, our results provide new insights into the genetic circuitry in which GmWRI1 participates to regulate storage lipid accumulation during seed development. Significance StatementWe report the genome-wide profiling of DNA sequences bound by and the genes directly- regulated by soybean WRINKLED1, a central regulator of storage lipid accumulation in oilseed plants. The information offers new insights into the mechanisms by which WRINKLED1 regulates genes encoding lipid biosynthetic enzymes and establishes a regulatory environment that promotes oil accumulation, and it may aid in the design of strategy to alter storage lipid accumulation in oilseeds.

plant biology↗

bioRxiv2023

Circadian oscillation of perireceptor events influence olfactory sensitivity in diurnal and nocturnal mosquitoes

Olfaction and circadian rhythm gate different behaviors in mosquitoes that are important for their capacity to transmit disease. However, the mechanisms of odor detection, and the circadian-guided changes in olfactory sensitivity across different mosquito species, remain largely unexplored. To this end, we performed a circadian-dependent RNA-sequencing study of the peripheral olfactory- and brain tissues of female Anopheles culicifacies and Aedes aegypti mosquitoes. Data analysis revealed a significant upregulation of genes encoding: (a) odorant binding proteins (OBPs), required for transportation of odorant molecules towards the olfactory receptors, and (b) xenobiotic-metabolizing enzymes (XMEs) during the day time in Aedes aegypti and during the dusk-transition phase in Anopheles culicifacies. While XMEs primarily function in the elimination of toxic xenobiotics, concurrent elevation of XMEs and OBPs are hypothesized to act cumulatively to regulate perireceptor events and odorant sensitivity. Electroantennographic analysis with both Anopheles gambiae and Aedes aegypti against diverse behaviorally relevant odorants, combined with XMEs inhibitors and RNA interference, establish the proof-of-concept that XMEs function in perireceptor events during odorant detection and influence the odorant sensitivity in mosquitoes. Additionally, the RNA-sequencing and RNAi-mediated knockdown data revealed that daily temporal modulation of neuronal serine proteases may facilitate the consolidation of the brain function, and influence the odor detection process in both diurnal and nocturnal mosquitoes. These findings provide the impetus to further explore the species-specific rhythmic expression pattern of the neuro-olfactory encoded molecular factors, which could pave the way to develop and implement successful mosquito control methods. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=108 SRC="FIGDIR/small/563057v1_ufig1.gif" ALT="Figure 1"> View larger version (49K): org.highwire.dtl.DTLVardef@181b845org.highwire.dtl.DTLVardef@168f22dorg.highwire.dtl.DTLVardef@f3994aorg.highwire.dtl.DTLVardef@d4fc06_HPS_FORMAT_FIGEXP M_FIG C_FIG HighlightsO_LICircadian oscillation of perireceptor proteins possibly influences time-of-day dependent change olfactory sensitivity in diurnal and nocturnal mosquitoes C_LIO_LIDiurnal and nocturnal mosquitoes depict distinct dynamic change in perireceptor proteins C_LIO_LIInhibition of cytochrome P450 gene minimizes antennal response to different odorants C_LIO_LINeuronal serine protease may consolidate brain function and odor detection C_LI

molecular biology↗

bioRxiv2023

Thermosensitivity of translation underlies the mammalian nocturnal-diurnal switch

Early mammals were nocturnal until the Cretaceous-Paleogene extinction enabled diurnal niche expansion. Diurnality evolved multiple times independently, but the mechanisms driving this shift remain unclear. We identify a conserved cell-intrinsic signal inversion that facilitates the transition from nocturnality to diurnality. Diurnal and nocturnal mammalian cells respond oppositely to temperature and osmotic cycles, mirroring species activity patterns. Cells exhibit differential global responses to temperature changes, including the phosphoproteome and protein synthesis. mTOR signaling is identified as a central mediator of this inversion, with diurnal mammals converging on modifications to mTOR and WNK pathways during evolution. Reducing mTOR activity induces nocturnal-to-diurnal shifting at cellular, tissue, and organismal levels. Therefore, the mTOR pathway is a cellular nexus that integrates energetic state and environmental signals to determine activity niche.

cell biology↗

bioRxiv2023

Signatures of co-evolution and co-regulation in the CYP3A and CYP4F genes in humans

1Cytochromes P450 (CYP450) are hemoproteins generally involved in the detoxification of the body of xenobiotic molecules. They participate in the metabolism of many drugs and genetic polymorphisms in humans have been found to impact drugs responses and metabolic functions. In this study, we investigate the genetic diversity for CYP450 genes. We found that two clusters, CYP3A and CYP4F, are notably differentiated across human populations with evidence for selective pressures acting on both clusters: we found signals of recent positive selection in CYP3A and CYP4F genes and signals of balancing selection in CYP4F genes. Furthermore, unusual linkage disequilibrium pattern is detected in both clusters, suggesting co-evolution of genes within clusters. Several of these selective signals co-localize with expression quantitative trait loci, which suggest co-regulation and epistasis within these highly important gene families. We also found that SNPs under selection in Africans within the CYP3A cluster are associated to CYP3A5 expression levels which are causally associated with reticulocytes count, as established by mendelian randomization. Furthermore, as the CYP3A and CYP4F subfamilies are involved in the metabolism of nutrients and drugs, our findings linking natural selection and gene expression in these gene clusters are of importance in understanding population differences in human health.

genetics↗

bioRxiv2022

SARS-CoV-2 impairs interferon production via NSP2-induced repression of mRNA translation

Viruses evade the innate immune response by suppressing the production or activity of cytokines such as type I interferons (IFNs). Here we report the discovery of a novel mechanism by which the SARS-CoV-2 virus co-opts an intrinsic cellular machinery to suppress the production of the key immunostimulatory cytokine IFN-{beta}. We reveal that the SARS-CoV-2 encoded Non-Structural Protein 2 (NSP2) directly interacts with the cellular GIGYF2 protein. This interaction enhances the binding of GIGYF2 to the mRNA cap-binding protein 4EHP, thereby repressing the translation of the Ifnb1 mRNA. Depletion of GIGYF2 or 4EHP significantly enhances IFN-{beta} production, leading to reduced viral infection. Our findings reveal a new target for rescuing the antiviral innate immune response to SARS-CoV-2 and other RNA viruses.

microbiology↗

bioRxiv2021

Data-driven approaches for genetic characterization of SARS-CoV-2 lineages

The genome of the Severe Acute Respiratory Syndrome coronavirus 2 (SARS-CoV-2), the pathogen that causes coronavirus disease 2019 (COVID-19), has been sequenced at an unprecedented scale, leading to a tremendous amount of viral genome sequencing data. To understand the evolution of this virus in humans, and to assist in tracing infection pathways and designing preventive strategies, we present a set of computational tools that span phylogenomics, population genetics and machine learning approaches. To illustrate the utility of this toolbox, we detail an in depth analysis of the genetic diversity of SARS-CoV-2 in first year of the COVID-19 pandemic, using 329,854 high-quality consensus sequences published in the GISAID database during the pre-vaccination phase. We demonstrate that, compared to standard phylogenetic approaches, haplotype networks can be computed efficiently on much larger datasets, enabling real-time analyses. Furthermore, time series change of Tajimas D provides a powerful metric of population expansion. Unsupervised learning techniques further highlight key steps in variant detection and facilitate the study of the role of this genomic variation in the context of SARS-CoV-2 infection, with Multiscale PHATE methodology identifying fine-scale structure in the SARS-CoV-2 genetic data that underlies the emergence of key lineages. The computational framework presented here is useful for real-time genomic surveillance of SARS-CoV-2 and could be applied to any pathogen that threatens the health of worldwide populations of humans and other organisms.

bioinformatics↗

bioRxiv2021

ImputeCoVNet: 2D ResNet Autoencoder for Imputation of SARS-CoV-2 Sequences

We describe a new deep learning approach for the imputation of SARS-CoV-2 variants. Our model, ImputeCoVNet, consists of a 2D ResNet Autoencoder that aims at imputing missing genetic variants in SARS-CoV-2 sequences in an efficient manner. We show that ImputeCoVNet leads to accurate results at minor allele frequencies as low as 0.0001. When compared with an approach based on Hamming distance, ImputeCoVNet achieved comparable results with significantly less computation time. We also present the provision of geographical metadata (e.g., exposed country) to decoder increases the imputation accuracy. Additionally, by visualizing the embedding results of SARS-CoV-2 variants, we show that the trained encoder of ImputeCoVNet, or the embedded results from it, recapitulates viral clades information, which means it could be used for predictive tasks using virus sequence analysis.

bioinformatics↗

bioRxiv2020

A Motion Correction Strategy for Multi-Contrast based 3D parametric imaging: Application to Inhomogeneous Magnetization Transfer (ihMT)

PurposeTo propose an efficient retrospective image-based method for motion correction of multi-contrast acquisitions with a low number of available images (MC-MoCo) and evaluate its use in 3D inhomogeneous Magnetization Transfer (ihMT) experiments in the human brain. MethodsA framework for motion correction, including image pre-processing enhancement and rigid registration to an iteratively improved target image, was developed. The proposed method was compared to Motion Correction with FMRIBs Linear Image Registration Tool (MCFLIRT) function in FSL over 13 subjects. Native (pre-correction) and residual (post-correction) motions were evaluated by means of markers positioned at well-defined anatomical regions over each image. ResultsBoth motion correction strategies significantly reduced inter-image misalignment, and the MC-MoCo method yielded significantly better results than MCFLIRT. ConclusionMC-MoCo is a high-performance method for motion correction of multi-contrast volumes as in 3D ihMT imaging.

neuroscience↗

bioRxiv2020

Spatial Variation of Microtubule Depolymerization in Large Asters Suggests Regulation by MAP Depletion

Microtubule plus end depolymerization rate is a potentially important target of physiological regulation, but it has been challenging to measure, so its role in spatial organization is poorly understood. Here we apply a method for tracking plus ends based on time difference imaging to measure depolymerization rates in large interphase asters growing in Xenopus egg extract. We observed strong spatial regulation of depolymerization rates, which were almost two-fold higher in the aster interior compared to the periphery, and much less regulation of polymerization or catastrophe rates. We interpret these data in terms of a limiting component model, where aster growth results in lower levels of soluble tubulin and MAPs in the interior cytosol compared to that at the periphery. The steady-state polymer fraction of tubulin was ∼30%, so tubulin is not strongly depleted in the aster interior. We propose that the limiting component for microtubule assembly is a MAP that inhibits depolymerization, and that egg asters are tuned to low microtubule density.Competing Interest StatementThe authors have declared no competing interest.View Full Text

cell biology↗