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McDonald, K.

Publications and source records attributed to McDonald, K..

17 recordsLinked to original sources

High-resolution transcriptomic profiling of Arabidopsis thaliana across a 37°C-40°C thermal gradient

Thermal adaptation is critical for organismal viability, with acquired thermotolerance (AT) in Arabidopsis thaliana typically conferred by acclimation temperatures between 34{degrees}C and 37{degrees}C, while acclimation at 40{degrees}C fails to protect against lethal heat stress. To elucidate the transcriptional mechanisms underlying the loss of AT at higher temperatures we performed RNA-seq profiling of Arabidopsis seedlings across a single-degree thermal gradient from 37{degrees}C to 40{degrees}C. Our analysis reveals that all of these temperatures result in a robust heat shock response, characterized by the upregulation of genes involved in protein folding and stress responses. However, each temperature elicits a distinct transcriptional signature. These findings demonstrate that temperature-specific fine-tuning of the heat shock response occurs within this narrow range and that these differences may dictate the successful acquisition of thermotolerance. This dataset provides a valuable resource for understanding the molecular architecture of heat-stress adaptation and the distinct transcriptional states associated with different thermal regimes.

plant biology↗

Aggregation of misfolded proteins in the sperm head impairs preimplantation embryo development

Paternal contributions to embryogenesis extend beyond DNA, yet the molecular cargo carried by sperm and its impact on development remain poorly defined. Aggresomes (AGG), cytoplasmic inclusions formed by misfolded proteins, are present in mammalian gametes, but their functional consequences are unclear. Here, we show that excessive AGG content in bovine sperm head compromises preimplantation embryo development. Using image-based flow cytometry, sperm from 32 sires were classified into low-, moderate-, and high-AGG groups. AGG levels were unrelated to sire age and did not affect in vitro capacitation or acrosome remodeling. However, embryos derived from high-AGG sires exhibited reduced blastocyst formation, delayed cleavage timing, and a higher incidence of developmental arrest at the 4-6 cell stage. Embryos from high-AGG sires also accumulated more AGG during development, showed elevated reactive oxygen species (ROS) levels, and displayed altered mitophagy dynamics. Supplementation with an ER stress inhibitor temporarily improved cleavage but did not enhance overall blastocyst formation, indicating a limited and stage-specific effect. In vivo, embryos from high-AGG sires showed lower transferable quality compared with those from low-AGG sires. These findings establish sperm head AGG content as a novel paternal determinant of embryo quality. By linking sperm-borne misfolded protein aggregates to disrupted developmental pathways in the resulting embryo, our study reveals a previously unrecognized mechanism of paternal influence on fertility and suggests new opportunities for molecular screening for male fertility. Significance StatementSperm contribute more to the embryo than DNA alone, yet the consequences of sperm-borne molecular cargo for early development remain largely unknown. We show that aggregates of misfolded proteins in the sperm head, a marker of disrupted protein quality control, impair preimplantation embryo development in cattle. Sires with elevated sperm aggregate content produce embryos that cleave later, arrest more frequently, and reach the blastocyst stage at lower rates, both in vitro and in vivo. These embryos carry greater aggregate loads, show heightened oxidative stress, and display dysregulated mitochondrial clearance. Our findings establish paternal proteostasis as a determinant of embryo quality and identify a class of sperm defects invisible to conventional semen analysis, opening new avenues for molecular fertility screening.

cell biology↗

Submaximal running energetics are maintained despite local muscle fatigue

When running, metabolic cost increases as muscles are simultaneously fatigued. However, the contribution of an individual muscle group to fatigue-related increase in metabolic costs remains unclear. We investigated the metabolic consequence of running with local plantar flexor or knee extensor fatigue and associated neuromuscular control strategies. Recreational and experienced male runners (N=20) completed two sessions (one per muscle group), with each including two 10 min running bouts: without and with local fatigue ([~]20% reduction in peak joint torque). Net metabolic power and muscle activity (initial and final minutes) were determined. Metabolic power was unaffected by plantar flexor (p=0.367) or knee extensor (p=0.607) fatigue in both cohorts. Plantar flexor fatigue recovered during the fatigued run (p=0.033), while knee extensor fatigue only recovered for the recreational cohort (p=0.009; experienced: p=0.826). With plantar flexor fatigue, plantar flexor muscle activity was unchanged between runs (p[≥]0.312), however initial soleus activity was greater in the unfatigued than fatigued run for experienced runners (p=0.022), and initial medial gastrocnemius activity was greater in the unfatigued than fatigued run for the combined cohort (p=0.009). With knee extensor fatigue, knee extensor muscle activity was mostly lower in the unfatigued than fatigued run (p[≤]0.009), except for final vastus lateralis activity, which was unchanged between runs (p=0.061). Therefore, muscle groups respond with different activation strategies when fatigued. Running with plantar flexor or knee extensor fatigue, at levels like those induced by prolonged running (10-42 km), does not increase metabolic power and thus, submaximal running energetics may be maintained despite local muscle fatigue. NEW & NOTEWORTHYWhile muscle fatigue is suggested to increase the metabolic cost of running, the individual contributions of key lower limb muscle groups have not been explored. We examined responses after fatigue of only the plantar flexors or the knee extensors. Results indicate that local fatigue did not affect the metabolic power of male runners for either fatigued muscle group. These findings enhance our understanding of running performance and the interaction between fundamental criteria dictating human locomotion.

physiology↗

Predicting bacterial-mediated entomopathogenicity through comparative genomics and statistical modeling

Bacterial genomes encode for vast functional diversity and have both beneficial and detrimental effects on insect hosts. However, connecting bacterial genotype to a host-associated phenotype can be experimentally time-consuming, particularly if insecticidal mechanisms are highly host-specific. To streamline the identification of virulence genes on a new host, we tested if merging existing mechanistic knowledge with in vivo tests on a small number of bacterial isolates could predict bacterial genes associated with entomopathogenesis. We used a model consisting of Drosophila melanogaster interactions with pathogenic and commensal genome-sequenced strains of Pseudomonas bacteria. We compiled a database of previously described insecticidal and biocontrol genes within the Pseudomonas genus and used comparative genomics to probe the distribution of these genes across Pseudomonas strains. We found natural variation in the presence of known insecticidal genes across the genus. We tested the insect-killing capacity of 13 Pseudomonas spp. strains against D. melanogaster and found natural variation in insecticidal activity. To identify bacterial genes associated with fly mortality, we employed two statistical models to correlate bacterial virulence with the presence of previously described insecticidal activity. To validate our predictions, we used a P. aeruginosa PAO1 transposon mutant library and identified 8 operons that are necessary for killing D. melanogaster. We show that by combining existing literature with phenotyping a small number of strains, we can identify genes necessary for insecticidal activity in a previously untested insect model. More broadly these findings illustrate a discovery pipeline for bacterial virulence mechanisms, accelerating the discovery of insect pest biocontrol mechanisms.

microbiology↗

Short- and long-term effects of uterine disease on oocyte developmental capacity in postpartum dairy cows

The hypothesis was that early postpartum uterine disease would reduce the developmental capacity of oocytes thus contributing to the reduced fertility of dairy cows with uterine disease. Dairy cows were diagnosed healthy or with metritis at 7 to 10 d postpartum. The reproductive tract was collected at approximately 1 mo (Exp. 1) or approximately 80 or 165 d (Exp. 2) postpartum for the collection of cumulus-oocyte complexes (COC). The COC were matured, co- incubated with sperm for fertilization, and cultured to the blastocyst stage (8 d) in vitro. For Exp.1, the disease diagnosis (healthy or metritis) did not affect the number of collected COC or the subsequent embryo development to the blastocyst stage. The presence of purulent material in the uterine lumen (endometritis) at time of oocyte collection, however, was associated with a reduced cleavage rate evaluated 3 d following fertilization. For Exp. 2, there was no effect of disease diagnosis (healthy or metritis) on the number of COC or their subsequent development. Reduced cleavage rates were observed in COC retrieved from cows slaughtered at 80 d postpartum, but not at 165 d postpartum, and this reduction was associated with a vaginal microbiome indicative of uterine disease at 4 to 5 wk postpartum. Regression analyses that included plasma haptoglobin or energy metabolite concentrations or uterine bacterial genera abundance did not explain a large percentage of the variation in oocyte development in vitro. We conclude that there is an effect of uterine disease at one month postpartum on the oocyte and its capacity for development (Exp. 1) and this effect may be present at 80 d postpartum (Exp. 2). In later postpartum cows (165 d postpartum; Exp. 2) there was no effect of uterine disease on in vitro oocyte development. GRAPHICAL ABSTRACT O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=141 SRC="FIGDIR/small/636469v1_ufig1.gif" ALT="Figure 1"> View larger version (44K): org.highwire.dtl.DTLVardef@7ab5d7org.highwire.dtl.DTLVardef@3845e3org.highwire.dtl.DTLVardef@743f52org.highwire.dtl.DTLVardef@1e95c38_HPS_FORMAT_FIGEXP M_FIG C_FIG HIGHLIGHTSO_LIOocytes collected at 1 month postpartum from dairy cows with endometritis (purulent uterine lumen) had a lower cleavage rate following in vitro fertilization when compared with oocytes collected from healthy cows (Exp. 1). C_LIO_LIOocytes collected at approximately 80 d postpartum from dairy cows with evidence of uterine disease at 4 to 5 wk postpartum had a lower cleavage rate following in vitro fertilization but this disease-associated difference was not observed when oocytes were collected from cows later postpartum (approximately 165 d postpartum; Exp. 2). C_LIO_LIRegardless of the study (Exp. 1 or 2), uterine disease primarily affected the percentage of oocytes that cleaved after fertilization. C_LIO_LIStatistical associations between circulating metabolites or relative abundance of uterine bacteria were either not significant or explained only a small percentage of the variation in the in vitro embryo development in either experiment. C_LI

physiology↗

Postglacial recolonization of the Southern Ocean by elephant seals occurred from multiple glacial refugia

The Southern Ocean is warming more rapidly than other parts of our planet. How this regions endemic biodiversity will respond to such changes can be illuminated by studying past events, through genetic analyses of time-series data sets including historic and fossil remains. Archaeological and subfossil remains show that the southern elephant seal (Mirounga leonina) was common along the coasts of Australia and New Zealand in the recent past. This species is now mostly confined to sub-Antarctic islands and the southern tip of South America. We analysed ancient seal samples from Australia (Tasmania), New Zealand, and the Antarctic mainland to examine how southern elephant seals have responded to a changing climate and anthropogenic pressures during the Holocene. Our analyses show that these seals formed part of a broader Australasian lineage, comprising seals from all sampled locations from the south Pacific sector of the Southern Ocean. Our study demonstrates that southern elephant seal populations have dynamically altered both range and population sizes under climatic and human pressures, over surprisingly short evolutionary timeframes for such a large, long-lived mammal. Significance StatementGenetic data, alongside historic, archaeological, and subfossil remains show that Australasian populations of the southern elephant seal have been shaped by range expansions and contractions following the Last Glacial Maximum, with subsequent contractions during the late Holocene. These expansion and contraction events are likely to have been a direct result of climate change-induced habitat expansion and contraction, along with Indigenous and European sealing. Prehistoric climate change and more recent human pressures have substantially altered the geographic distribution and population size of southern elephant seals over short evolutionary timescales.

ecology↗

EGF and IgA in maternal milk, donor milk and milk fortifiers in the Neonatal Intensive Care Unit setting

Human milk contains a variety of factors that positively contribute to neonatal health, including epidermal growth factor (EGF) and immunoglobulin A (IgA). When maternal milk cannot be the primary diet, maternal milk alternatives like donor human milk or formula can be provided. Donor human milk is increasingly provided to infants born preterm or low birth weight with the aim to supply immunological factors at similar concentrations to maternal milk. We sought to assess the concentrations of human EGF and IgA in the diet and stool of neonates between exclusive maternal milk, donor human milk, or formula-based diets. Using a prospective cohort study, we collected samples of diet and stool weekly from premature and low birth weight neonates starting at 10 days postnatal through five weeks of life while admitted to a neonatal intensive care unit (NICU). Compared to formula, there was significantly more EGF in both the milk and the stool of the infants fed human milk. Donor milk pooled from multiple donors contained similar concentrations of EGF and IgA to maternal milk, which was also significantly more compared to formula diets. Maternal milk fortified with fortifier derived from human milk contained significantly more EGF and IgA compared to unfortified maternal milk or maternal milk fortified with fortifier derived from bovine milk. Further analysis of human milk-derived fortifiers confirmed these fortifiers contained significant concentrations of EGF and IgA, contributing to an increased concentration of those factors when added to maternal milk compared to bovine milk-derived fortifiers. These findings illustrate how the choice of diet for a newborn, and even how that diet is modified through fortifiers or pasteurization before ingestion, impacts the beneficial biomolecules the infant receives from feeding.

immunology↗

Gene-by-environment interactions and adaptive body size variation in mice from the Americas

The relationship between genotype and phenotype is often mediated by the environment. Moreover, gene-by-environment (GxE) interactions can contribute to variation in phenotypes and, in turn, fitness. Nevertheless, understanding the impact of GxE interactions in wild systems remains challenging. In the last 500 years, house mice have invaded the Americas. Despite their short residence time, there is evidence of rapid climate adaptation, including shifts in body size and aspects of metabolism with latitude. Previous studies in this system have identified candidate genes for metabolic adaptation using selection scans, however, environmental variation in diet as well as GxE interactions affecting metabolism are likely important factors in shaping body mass variation in wild populations. Here, we investigate the role of the environment and GxE interactions in shaping adaptive phenotypic variation with an experimental manipulation of diet. Using new locally adapted inbred strains from North and South America, we evaluated response to a high-fat diet, finding that sex, strain, diet, and the interaction between strain and diet contribute significantly to variation in aspects of body size. We also found that transcriptional response to diet is largely strain-specific, indicating that GxE interactions affecting gene expression are pervasive. Next, we used crosses between strains from contrasting climates (New York x Brazil and New York x Florida) to characterize gene expression regulatory divergence on a standard breeder diet and on a high-fat diet. We found that gene regulatory divergence is often condition-specific, particularly for trans-acting changes. Finally, we find evidence for lineage-specific selection on cis-regulatory variation involved in diverse processes, including lipid metabolism. Overlap with scans for selection identified candidate genes for environmental adaptation with diet-specific effects. Together, our results underscore the importance of environmental variation and GxE interactions to adaptive variation in complex traits.

evolutionary biology↗

Combined Right Ventricular Preload and Afterload Challenge Induces Contractile Dysfunction and Ventricular Arrhythmia in an Age-dependent Manner in Isolated Hearts of Dystrophin-deficient Mice

Duchenne muscular dystrophy (DMD) is an X-linked recessive myopathy due to mutations in the dystrophin gene. Diaphragmatic weakness in DMD causes restrictive lung disease and excessive afterload on the right ventricle (RV). Thus, RV dysfunction in DMD develops early in disease progression. Herein, we deliver a 30-minute sustained RV preload and afterload challenge to isolated hearts of wildtype (Wt) and dystrophic (mdx4CV) mice at both young (2-6 month) and middle-age (8-12 month). Young dystrophic hearts exhibited greater pressure development than wildtype under unloaded conditions but following RV preload/afterload challenge exhibited similar contractile function as wildtype. Following RV preload/afterload challenge, young dystrophic hearts had an increased incidence of ventricular arrhythmias compared to wildtype. Hearts of middle-aged wildtype and dystrophic mice had similar contractile function during unloaded conditions, yet, after RV preload/afterload challenge, hearts of middle-aged dystrophic mice had severe RV contractile dysfunction and ventricular arrhythmogenesis, including ventricular tachycardia. Following load challenge, young and middle-aged dystrophic hearts had greater damage, measured via tissue LDH release, than wildtype mice of similar age. Our data indicate complex age-dependent changes in RV function and arrhythmogenesis with load in dystrophin deficiency, highlighting the need to avoid sustained RV load to forestall RV dysfunction and arrhythmia.

physiology↗

Four-dimensional quantitative analysis of cell plate development using lattice light sheet microscopy identifies robust transition points between growth phases

Cell plate formation during cytokinesis entails multiple stages occurring concurrently and requiring orchestrated vesicle delivery, membrane remodeling, and timely polysaccharide deposition, such as callose. Such a dynamic process requires dissection in time and space; hence this has been a major hurdle in studying cytokinesis. Using lattice light sheet microscopy (LLSM) we studied cell plate development in four dimensions, monitored by the behavior of the cytokinesis specific GTPase RABA2a. We monitored the entire length of cell plate development, from its first emergence, with the aid of RABA2a, both in the presence and absence of cytokinetic callose. By developing a robust cytokinetic vesicle volume analysis, we identified distinct behavioral patterns allowing for the identification of three easily trackable, cell plate developmental phases. Notably, the phase transition between phase I and phase II is striking, indicating a switch from membrane accumulation to the recycling of excess membrane material. We interrogated the role of callose using pharmacological inhibition with LLSM and electron microscopy. Loss of callose inhibited phase transition, establishing quantitatively the critical role and timing of the polysaccharide in cell plate expansion and maturation. This study exemplifies the power of LLSM, combined with quantitative analysis to decode and untangle such a complex process. HighlightWe employed lattice light sheet 4D microscopy in plants to dissect cytokinesis, a multistage process involving orchestrating delivery of membranes and timely polysaccharide deposition. Robust quantitative analysis revealed distinct phase shifts, while inhibition of callose deposition abolished the phase transition.

plant biology↗

Evolution of the ribbon-like organization of the Golgi apparatus in animal cells

The Golgi ribbon is a structural organization formed by linked Golgi stacks that is believed to be exclusive to vertebrate cells. Its functional contribution to cellular processes is unclear, yet its disruption is associated with several human pathologies. In this study we address the evolutionary origin of the Golgi ribbon, describe a potential molecular mechanism for its emergence and identify a cellular process in which it may be involved. We observed the ribbon-like architecture in the cells of several metazoan taxa, suggesting its early appearance during animal evolution before the emergence of vertebrates. Supported by AlphaFold2 modelling, we propose that the evolution of the complex between two Golgi resident proteins, Golgin-45 and GRASP, led to the tethering of Golgi stacks into the ribbon-like configuration. Finally, we find that the ribbon is assembled during the early embryogenesis of deuterostome animals, a strong indication of its role in development. Overall, our study indicates that the Golgi ribbon is functionally relevant beyond vertebrates and calls for further investigations to decipher its elusive functions. O_FIG O_LINKSMALLFIG WIDTH=89 HEIGHT=200 SRC="FIGDIR/small/528797v2_ufig1.gif" ALT="Figure 1"> View larger version (33K): org.highwire.dtl.DTLVardef@17a404forg.highwire.dtl.DTLVardef@11413b4org.highwire.dtl.DTLVardef@119c036org.highwire.dtl.DTLVardef@19a512f_HPS_FORMAT_FIGEXP M_FIG Graphical abstract C_FIG

cell biology↗

Mesenchymal Stromal Cell secretome is affected by tissue source, donor age and sex.

Variation in Mesenchymal Stromal Cell (MSC) function depending on their origin is problematic, as it may confound clinical outcomes of MSC therapy. Current evidence suggests that the therapeutic benefits of MSCs is primarily attributed to secretion of various biologically active factors (secretome). However, the effect of donor characteristics on the MSC secretome composition remains largely unknown. Here, we examined the influence of donor age, sex and tissue source, on the protein profile of the equine MSC secretome. Initially, we used dynamic metabolic labelling with stable isotopes combined with liquid chromatography-tandem mass spectrometry (LC-MS/MS) to identify secreted proteins in MSC conditioned media (CM). Seventy proteins were classified as classically-secreted based on the rate of isotope label incorporation into newly synthesised proteins released into the extracellular space. Next, we analysed CM of bone marrow- (n = 14) and adipose-derived MSCs (n = 16) with label-free LC-MS/MS proteomics. Clustering analysis of 314 proteins detected across all samples identified tissue source as the main factor driving variability in MSC CM proteomes. Linear modelling applied to the subset of 70 secreted proteins identified tissue-related difference in the abundance of 23 proteins. There was an age-related decrease in the abundance of two proteins (CTHRC1, LOX), which has been validated with western blot and enzymatic activity assay. There was limited evidence of sex-related differences in protein abundance. In conclusion, this study provides evidence that tissue source and donor age contribute to heterogeneity in the protein composition of MSC secretomes which may influence the effects of MSC-based cell therapy. Significance statementThis research shows for the first time that donor age can influence the proteins secreted by mesenchymal stromal cells (MSC), which is considered the main mechanism through which they mediate their biological actions. This information may improve our understanding of the variable outcomes observed in MSC clinical studies, as well as identify optimal sources and donor selection for specific clinical applications.

cell biology↗

Plant-based Production and Characterization of a Promising Fc-fusion Protein against Bone Mass Density Loss

Microgravity-induced bone loss is a main obstacle for long term space missions as it is difficult to maintain bone mass when loading stimuli is reduced. With a typical bone mineral density loss of 1.5% per month of microgravity exposure, the chances for osteoporosis and fractures may endanger astronauts health. Parathyroid Hormone or PTH (1-34) is an FDA approved treatment for osteoporosis, and may reverse microgravity-induced bone loss. However, PTH proteins requires refrigeration, daily subcutaneous injection, and have a short shelf-life, limiting its use in a resource-limited environment, like space. In this study, PTH was produced in an Fc-fusion form via transient expression in plants, to improve the circulatory half-life which reduces dosing frequency and to simplify purification if needed. Plant-based expression is well-suited for space medicine application given its low resource consumption and short expression timeline. The PTH-Fc accumulation profile in plant was established with a peak expression on day 5 post infiltration of 373 {+/-} 59 mg/kg leaf fresh weight. Once the PTH-Fc was purified, the amino acid sequence and the binding affinity to its target, PTH 1 receptor (PTH1R), was determined utilizing biolayer interferometry (BLI). The binding affinity between PTH-Fc and PTH1R was 2.30 x 10-6 M, similar to the affinity between PTH (1-34) and PTH1R (2.31 x 10-6 M). Its function was also confirmed in a cell-based receptor stimulation assay, where PTH-Fc was able to stimulate the PTH1R producing cyclic adenosine monophosphate (cAMP) with an EC50 of (8.54 {+/-} 0.12) x 10-9 M, comparable to the EC50 from the PTH (1-34) of 1.49 x 10-8 M. These results suggest that plant recombinant PTH-Fc exhibits a similar potency compared to PTH. Furthermore, it can be produced rapidly at high levels with minimal resources and reagents, making it ideal for production in low resource environments such as space.

synthetic biology↗

SARS-Cov-2 Spike binding to ACE2 is stronger and longer ranged with glycans

Highly detailed steered Molecular Dynamics simulations are performed on differently glycosylated receptor binding domains of the SARS-CoV-2 spike protein. The binding strength and the binding range increases with glycosylation. The interaction energy rises very quickly with pulling the proteins apart and only slowly drops at larger distances. We see a catch slip type behavior where interactions during pulling break and are taken over by new interactions forming. The dominant interaction mode are hydrogen bonds but Lennard-Jones and electrostatic interactions are relevant as well. Statement of SignificanceGlycosylation of the receptor binding domain of the Spike protein of SARS-CoV-2 as well as the ACE2 receptor leads to stronger and longer ranged binding interactions between the proteins. Particularly, at shorter distances the interactions are between residues of the proteins themselves whereas at larger distances these interactions are mediated by the glycans. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=164 SRC="FIGDIR/small/452507v2_ufig1.gif" ALT="Figure 1"> View larger version (32K): org.highwire.dtl.DTLVardef@7b9021org.highwire.dtl.DTLVardef@338aadorg.highwire.dtl.DTLVardef@1d5921eorg.highwire.dtl.DTLVardef@6c27e7_HPS_FORMAT_FIGEXP M_FIG C_FIG

biophysics↗

Bioprinting transgenic plant cells for production of a recombinant biodefense agent

Transgenic rice cells (Oryza sativa) producing recombinant butyrylcholinesterase (BChE) as a prophylactic/therapeutic against organophosphate nerve agent poisoning, cocaine toxicity, and neurodegenerative diseases like Alzheimers were immobilized in a polyethylene glycol-based hydrogel. The cells were sustained for 14 days in the semi-solid matrix, undergoing a growth phase from days 0-6, a BChE production phase in sugar-free medium from days 6-12, and a growth/recovery phase from days 12-14. Throughout this period, the cells maintained similar viability to those in suspension cultures and displayed analogous sugar consumption trends. The rice cells in the bioprintable hydrogel also produced a significant amount of active BChE, comparable to the levels produced in liquid cultures. A considerable fraction of this BChE was secreted into the media, allowing for easier product separation. Overall, we demonstrate a simple, efficient, robust, modular, and potentially field-deployable bioreactor system for the manufacture of biologics.

plant biology↗

The architecture of cell differentiation in choanoflagellates and sponge choanocytes

Collar cells are ancient animal cell types which are conserved across the animal kingdom [1] and their closest relatives, the choanoflagellates [2]. However, little is known about their ancestry, their subcellular architecture, or how they differentiate. The choanoflagellate Salpingoeca rosetta [3] expresses genes necessary for animal multicellularity and development [4] and can alternate between unicellular and multicellular states [3,5], making it a powerful model to investigate the origin of animal multicellularity and mechanisms underlying cell differentiation [6,7]. To compare the subcellular architecture of solitary collar cells in S. rosetta with that of multicellular \"rosettes\" and collar cells in sponges, we reconstructed entire cells in 3D through transmission electron microscopy on serial ultrathin sections. Structural analysis of our 3D reconstructions revealed important differences between single and colonial choanoflagellate cells, with colonial cells exhibiting a more amoeboid morphology consistent with relatively high levels of macropinocytotic activity. Comparison of multiple reconstructed rosette colonies highlighted the variable nature of cell sizes, cell-cell contact networks and colony arrangement. Importantly, we uncovered the presence of elongated cells in some rosette colonies that likely represent a distinct and differentiated cell type. Intercellular bridges within choanoflagellate colonies displayed a variety of morphologies and connected some, but not all, neighbouring cells. Reconstruction of sponge choanocytes revealed both ultrastructural commonalities and differences in comparison to choanoflagellates. Choanocytes and colonial choanoflagellates are typified by high amoeboid cell activity. In both, the number of microvilli and volumetric proportion of the Golgi apparatus are comparable, whereas choanocytes devote less of their cell volume to the nucleus and mitochondria than choanoflagellates and more of their volume to food vacuoles. Together, our comparative reconstructions uncover the architecture of cell differentiation in choanoflagellates and sponge choanocytes and constitute an important step in reconstructing the cell biology of the last common ancestor of the animal kingdom.

evolutionary biology↗

Bayesian Nonparametric Models Characterize Instantaneous Strategies in a Competitive Dynamic Game

Previous approaches to investigating strategic social interaction in game theory have predominantly used games with clearly-defined turns and limited choices. However, most real-world social behaviors involve dynamic, coevolving decisions by interacting agents, which pose challenges for creating tractable models of behavior. Here, using a competitive game in which human participants control the dynamics of an on-screen avatar against either another human or a computer opponent, we show that it is possible to quantify the dynamic coupling between agents using nonparametric models. We use Gaussian Processes to model the joint distributions of players' actions and identities (human or computer) as a function of game state. Borrowing from a reinforcement learning framework, we successfully approximated both the policy and the value functions used by each human player in this competitive context. This approach offers a natural set of metrics for facilitating analysis at multiple timescales and suggests new classes of tractable paradigms for assessing human behavior.

neuroscience↗