Buckling without bending: a new paradigm in morphogenesis

A curious feature of organ and organoid morphogenesis is that in certain cases, spatial oscillations in the thickness of the growing "film" are out-of-phase with the deformation of the slower-growing "substrate," while in other cases, the oscillations are in-phase. The former cannot be explained by elastic bilayer instability, and contradict the notion that there is a universal mechanism by which brains, intestines, teeth, and other organs develop surface wrinkles and folds. Inspired by the microstructure of the embryonic cerebellum, we develop a new model of 2d morphogenesis in which system-spanning elastic fibers endow the organ with a preferred radius, while a separate fiber network resides in the otherwise fluid-like film at the outer edge of the organ and resists thickness gradients thereof. The tendency of the film to uniformly thicken or thin is described via a "growth potential". Several features of cerebellum, +blebbistatin organoid, and retinal fovea morphogenesis, including out-of-phase behavior and a film thickness amplitude that is comparable to the radius amplitude, are readily explained by our simple analytical model, as may be an observed scale-invariance in the number of folds in the cerebellum. We also study a nonlinear variant of the model, propose further biological and bio-inspired applications, and address how our model is and is not unique to the developing nervous system.Comment: version accepted by Physical Review

The unique chemistry of Eastern Mediterranean water masses selects for distinct microbial communities by depth

Peer reviewedPublisher PD

The Effectors of the Transient Receptor Vanilloid Potential Type 4 in the Choroid Plexus

poster abstractHydrocephalus is a deadly disease that affects 1-2 births in 1000. When severe, this disease can result in irreversible brain damage. There are no drugs to treat hydrocephalus and the standard therapy is to surgically implant shunts to drain the excess cerebrospinal fluid (CSF) into other parts of the body. However this approach often results in a less than optimal outcomes. Shunt failures due to blockage, infection, and other causes are as high as 50% even in major medical centers which specialize in these procedures. Our laboratory is using a Meckel-Gruber syndrome rat model to study the development of severe hydrocephalus. Immunohistochemistry has been used to show the overexpression of Transient Receptor Vanilloid Potential Type 4, TRPV4 on the choroid plexus epithelial membrane. Because the choroid plexus is responsible for the majority of the cerebrospinal fluid that contributes to the progression of hydrocephalus, the TRPV4 calcium channel is a potential target that could contribute to the disease development. The endogenous activators of this channel in the choroid plexus are yet to be determined. Consequently, the current study is using a cultured choroid plexus cell line to identify endogenous activators of this channel. Potential activators include homovanillic acid (HVA), lysophosphatidic acid, and arachidonic acid. In addition, the introduction of novel compounds that act as sensitizers of the channel led to a set of experiments that were conducted to confirm the existence and identification of the sensitizers such as inflammatory cytokines. The effect of these compounds on the activation of the TRPV4 channel are being investigated using electrophysiological techniques in a porcine choroid plexus cell line with the characteristics of the in vivo choroid plexus. This cell line exhibits a robust increase in ion transport in response to a TRPV4 agonist. . The determination of the endogenous TRPV4 activators and sensitizers will provide important information in the development of a drug that can be used to treat hydrocephalus with minimal side effects by altering the activity of TRPV4

Robust Chauvenet Outlier Rejection

Sigma clipping is commonly used in astronomy for outlier rejection, but the number of standard deviations beyond which one should clip data from a sample ultimately depends on the size of the sample. Chauvenet rejection is one of the oldest, and simplest, ways to account for this, but, like sigma clipping, depends on the sample's mean and standard deviation, neither of which are robust quantities: Both are easily contaminated by the very outliers they are being used to reject. Many, more robust measures of central tendency, and of sample deviation, exist, but each has a tradeoff with precision. Here, we demonstrate that outlier rejection can be both very robust and very precise if decreasingly robust but increasingly precise techniques are applied in sequence. To this end, we present a variation on Chauvenet rejection that we call "robust" Chauvenet rejection (RCR), which uses three decreasingly robust/increasingly precise measures of central tendency, and four decreasingly robust/increasingly precise measures of sample deviation. We show this sequential approach to be very effective for a wide variety of contaminant types, even when a significant -- even dominant -- fraction of the sample is contaminated, and especially when the contaminants are strong. Furthermore, we have developed a bulk-rejection variant, to significantly decrease computing times, and RCR can be applied both to weighted data, and when fitting parameterized models to data. We present aperture photometry in a contaminated, crowded field as an example. RCR may be used by anyone at https://skynet.unc.edu/rcr, and source code is available there as well.Comment: 62 pages, 48 figures, 7 tables, accepted for publication in ApJ

Semiclassical approach to discrete symmetries in quantum chaos

We use semiclassical methods to evaluate the spectral two-point correlation function of quantum chaotic systems with discrete geometrical symmetries. The energy spectra of these systems can be divided into subspectra that are associated to irreducible representations of the corresponding symmetry group. We show that for (spinless) time reversal invariant systems the statistics inside these subspectra depend on the type of irreducible representation. For real representations the spectral statistics agree with those of the Gaussian Orthogonal Ensemble (GOE) of Random Matrix Theory (RMT), whereas complex representations correspond to the Gaussian Unitary Ensemble (GUE). For systems without time reversal invariance all subspectra show GUE statistics. There are no correlations between non-degenerate subspectra. Our techniques generalize recent developments in the semiclassical approach to quantum chaos allowing one to obtain full agreement with the two-point correlation function predicted by RMT, including oscillatory contributions.Comment: 26 pages, 8 Figure

Quantifying sympathetic neuro-haemodynamic transduction at rest in humans:Insights into sex, ageing and blood pressure control

KEY POINTS: We have developed a simple analytical method for quantifying the transduction of sympathetic activity into vascular tone. This method demonstrates that as women age, the transfer of sympathetic nerve activity into vascular tone is increased, so that for a given level of sympathetic activity there is more vasoconstriction. In men, this measure decreases with age. Test–re‐test analysis demonstrated that the new method is a reliable estimate of sympathetic transduction. We conclude that increased sympathetic vascular coupling contributes to the age‐related increase in blood pressure that occurs in women only. This measure is a reliable estimate of sympathetic transduction in populations with high sympathetic nerve activity. Thus, it will provide information regarding whether treatment targeting the sympathetic nervous system, which interrupts the transfer of sympathetic nerve activity into vascular tone, will be effective in reducing blood pressure in hypertensive patients. This may provide insight into which populations will respond to certain types of anti‐hypertensive medication. ABSTRACT: Sex and age differences in the sympathetic control of resting blood pressure (BP) may be due to differences in the transduction of sympathetic nerve activity (SNA) into vascular tone. Current methods for dynamically quantifying transduction focus on the relationship between SNA and vasoconstriction during a pressor stimulus, which increases BP and may be contra‐indicated in patients. We describe a simple analytical method for quantifying transduction under resting conditions. We performed linear regression analysis of binned muscle SNA burst areas against diastolic BP (DBP). We assessed whether the slope of this relationship reflects the transduction of SNA into DBP. To evaluate this, we investigated whether this measure captures differences in transduction in different populations. Specifically, we (1) quantified transduction in young men (YM), young women (YW), older men (OM) and postmenopausal women (PMW); and (2) measured changes in transduction during β‐blockade using propranolol in YW, YM and PMW. YM had a greater transduction vs. OM (0.10 ± 0.01 mmHg (% s)(−1), n = 23 vs. 0.06 ± 0.01 mmHg (% s)(−1), n = 18; P = 0.003). Transduction was lowest in YW (0.02 ± 0.01 mmHg (% s)(−1), n = 23) and increased during β‐blockade (0.11 ± 0.01 mmHg (% s)(−1); P < 0.001). Transduction in PMW (0.07 ± 0.01 mmHg (% s)(−1), n = 23) was greater compared to YW (P = 0.001), and was not altered during β‐blockade (0.06 ± 0.01 mmHg (% s)(−1); P = 0.98). Importantly, transduction increased in women with age, but decreased in men. Transduction in women intersected that in men at 55 ± 1.5 years. This measure of transduction captures age‐ and sex‐differences in the sympathetic regulation of DBP and may be valuable in quantifying transduction in disease. In particular, this measure may help target treatment strategies in specific hypertensive subpopulations

Small and mighty: adaptation of superphylum Patescibacteria to groundwater environment drives their genome simplicity.

BackgroundThe newly defined superphylum Patescibacteria such as Parcubacteria (OD1) and Microgenomates (OP11) has been found to be prevalent in groundwater, sediment, lake, and other aquifer environments. Recently increasing attention has been paid to this diverse&nbsp;superphylum including &gt;&nbsp;20 candidate phyla&nbsp;(a large part of the candidate phylum radiation, CPR) because it refreshed our view of the tree of life. However, adaptive traits contributing to its prevalence are still not well known.ResultsHere, we investigated the genomic features and metabolic pathways of Patescibacteria in groundwater through genome-resolved metagenomics analysis of &gt; 600 Gbp sequence data. We observed that, while the members of Patescibacteria have reduced genomes (~ 1 Mbp) exclusively, functions essential to growth and reproduction such as genetic information processing were retained. Surprisingly, they have sharply reduced redundant and nonessential functions, including specific metabolic activities and stress response systems. The Patescibacteria have ultra-small cells and simplified membrane structures, including flagellar assembly, transporters, and two-component systems. Despite the lack of CRISPR viral defense, the bacteria may evade predation through deletion of common membrane phage receptors and other alternative strategies, which may explain the low representation of prophage proteins in their genomes and lack of CRISPR. By establishing the linkages between bacterial features and the groundwater environmental conditions, our results provide important insights into the functions and evolution of this CPR group.ConclusionsWe found that Patescibacteria has streamlined many functions while acquiring advantages such as avoiding phage invasion, to adapt to the groundwater environment. The unique features of small genome size, ultra-small cell size, and lacking CRISPR of this large lineage are bringing new understandings on life of Bacteria. Our results provide important insights into the mechanisms for adaptation of the superphylum in the groundwater environments, and demonstrate a case where less is more, and small is mighty

Statistical modeling of ground motion relations for seismic hazard analysis

We introduce a new approach for ground motion relations (GMR) in the probabilistic seismic hazard analysis (PSHA), being influenced by the extreme value theory of mathematical statistics. Therein, we understand a GMR as a random function. We derive mathematically the principle of area-equivalence; wherein two alternative GMRs have an equivalent influence on the hazard if these GMRs have equivalent area functions. This includes local biases. An interpretation of the difference between these GMRs (an actual and a modeled one) as a random component leads to a general overestimation of residual variance and hazard. Beside this, we discuss important aspects of classical approaches and discover discrepancies with the state of the art of stochastics and statistics (model selection and significance, test of distribution assumptions, extreme value statistics). We criticize especially the assumption of logarithmic normally distributed residuals of maxima like the peak ground acceleration (PGA). The natural distribution of its individual random component (equivalent to exp(epsilon_0) of Joyner and Boore 1993) is the generalized extreme value. We show by numerical researches that the actual distribution can be hidden and a wrong distribution assumption can influence the PSHA negatively as the negligence of area equivalence does. Finally, we suggest an estimation concept for GMRs of PSHA with a regression-free variance estimation of the individual random component. We demonstrate the advantages of event-specific GMRs by analyzing data sets from the PEER strong motion database and estimate event-specific GMRs. Therein, the majority of the best models base on an anisotropic point source approach. The residual variance of logarithmized PGA is significantly smaller than in previous models. We validate the estimations for the event with the largest sample by empirical area functions. etc

M. T. Joyner & Son- Mrs. R. H. Walker, September 19, 1928

Correspondence: From L.A. Joyner, M.T. Joyner & Son, 515 Main Street, Jacksonville, Florida, to Rosa G. Holmes Walker, Jacksonville, Florida, letter asking for a couple of days grace

Cultural Mythology and Anxieties of Belonging: Reconstructing the "bi-cultural" subject in the fiction of Toni Morrison, Amy Tan and Annie Proulx

PhDThe thesis considers the construction of cultural identity in the writings of Tom Morrison, Annie Proulx, and Amy Tan. It consists of three chapters, one dedicated to each of the writers. In the examination of these writers the focus is upon the construction of the "bicultural" subject in the contemporary United States. The paradigm of analysis is constructed through discourses of space, landscape and physical geography. The first chapter is devoted to Toni Morrison and is divided into two sections dealing with the novels Beloved and Jazz. The first section examines how spatial discourses disrupt binaries that marginalise the black community. It concentrates upon the location of the "porch" in the novel and parallels it with the "porch" as a black spatial icon. The Jazz section examines the idealised space of the City. It focuses on the material layout of American Cities and discusses its relationship to constructions of American cultural identity. The debate is used to highlight how the geographical marginalisation of communities parallels their cultural alienation. The second chapter is split into two sections, the first focuses upon The Joy Luck Club, the second concerns The Kitchen God's Wife. Tan's work is discussed in relation to cultural geographic debates about mythic geography. It deals with the different ways in which Tan's texts try to palliate cultural anxieties about "belonging" by constructing a culturally soothing mythic location. An idealised version of the Chinese-American community is sustained through her constructions of both San Francisco and China, which she employs and negotiates in different ways in the two texts. The third chapter examines three Proulx texts, Postcards, Accordion Crimes, and Close Range Wyoming Stories. The chapter explores the different ways these texts negotiate cultural belonging in relation to geographic migration. Postcards is considered in relation to the literary discourse of migration. In Accordion Crimes the employment of similarly positivist conceptions of the construction of a "home" in North America is examined. The final section examines the problematic nature of "location" as both geographically and textually soothing. The Epilogue suggests the possible extension of the thesis and foregrounds the importance of the materiality of spatial construction to the cultural anxieties the thesis examines