Biology subjects

Stewart, T. A.

Publications and source records attributed to Stewart, T. A..

9 recordsLinked to original sources

bioRxiv2026

Macrophage calcium signaling dynamics revealed using genetically-encoded sensors

Macrophages (M{Phi}s) inhabit all mammalian organs, adapting to and influencing the tissues in which they reside. These versatile cells rapidly respond to tissue-specific signals, clean up debris and serve as the first line of defense against pathogens. Their ability to act quickly relates to their abundance and specific arrangement in tissues, as well as the systems they possess for detecting, processing and integrating emergent signals. Ca2+ is a fast second messenger that has been linked to many of the core functions of M{Phi}s. However, spatiotemporal features of physiologically-relevant Ca2+ signals in M{Phi}s remain largely uncharacterized. Using mouse models expressing genetic biosensors and fluorescently tagged channels, we visualize M{Phi} Ca2+ signal dynamics and heterogeneity, uncover a remarkable degree of mechanosensitivity in these cells, and characterize the physiological consequences of genetic ablation of Piezo1 channels via analysis of knockout models across their lifetime. Our in-depth investigation of M{Phi} Ca2+ signaling dynamics has broad relevance for the field of M{Phi} biology and the tissues that these cells support.

immunology↗

bioRxiv2024

Plasticity in the pectoral fin skeleton is induced by altered foraging regime in a South American cichlid

The fins of fishes are remarkably diverse, and this variation is tied to the ecology and locomotor mode of a species. While numerous genetic factors are known to pattern fins in development, it is unclear how developmental plasticity shapes the fin skeleton. Here, we analyze the cichlid Satanoperca daemon, raised under three distinct feeding regimes, and show that plasticity is pervasive across the pectoral fin skeleton with foraging mode impacting patterning of both the endoskeleton and dermal skeleton. Radials and fin rays were {micro}CT scanned and analyzed using a combination of linear measures and geometric morphometrics. Anteroposterior patterning of both radials and fin rays are affected by feeding regime. Notably, S. daemon pectoral fin rays show distinct patterns of fin ray branching between treatments, suggesting altered fin stiffness. We argue that the observed changes in the fin likely reflect developmental plasticity resultant from altered swimming behaviors when fishes are challenged to forage in different ways. These data show how non-genetic mechanisms can shape both the endoskeleton and dermal skeleton of fins, and that foraging mode can induce plastic changes in skeletal elements that do not directly interface with food items.

evolutionary biology↗

bioRxiv2023

Distinct ossification trade-offs illuminate the shoulder girdle reconfiguration at the water-to-land transition.

The mechanisms of the pectoral girdle transformation at the origin of terrestrial locomotion in vertebrates remains an outstanding problem in evolutionary biology1. The loss of dermal bones and the enlargement of endochondral bones resulted in the disarticulation of the pectoral girdle from the skull and the formation of the neck during the fish-to-tetrapod transition2-5. Despite the functional implications of this skeletal shift in the emergence of terrestrial vertebrates, the underlying genetic-developmental alterations have remained enigmatic. Here, we discovered that in zebrafish pectoral girdle mesodermal cells expressing gli3, a transcription factor in the Hedgehog signaling pathway, contribute to both dermal and endochondral bones. We show that Gli3 regulates expression of activin A receptor type 1-like, a BMP type 1 receptor lost in tetrapod lineages, and thereby determines endochondral and dermal ossification. Intriguingly, Gli and Hedgehog compound knockout fish exhibited an unexpected combination of actinopterygian fish and stem-tetrapod pectoral girdle characteristics. These ontogenetic and anatomical data suggest that a trade-off between the two distinct ossification pathways is a deeply embedded developmental program in bony fishes, with potential for tuning of this trade-off to generate novel pectoral girdle forms akin to stem-tetrapods at the dawn of vertebrate terrestrialization.

evolutionary biology↗

bioRxiv2023

Axial regionalization in Tiktaalik roseae and the origin of quadrupedal locomotion

The origin of quadrupedal locomotion in tetrapods entailed the evolution of a regionalized axial skeleton with sacral ribs. These ribs provide linkage between the pelvis and vertebral column and contribute to body support and propulsion by the hind limb. The closest relatives of limbed vertebrates are not known to possess such a connection and, therefore, have typically been described as primarily supporting their bodies against the substrate with pectoral fins. However, data on the axial skeletons of stem tetrapods are sparce, with key features of specimens potentially concealed by matrix. Here we provide micro-computed tomography data of the axial skeleton of Tiktaalik roseae and show that its vertebrae and ribs are regionalized along the craniocaudal axis, including expanded and ventrally curved ribs in the sacral region. The sacral ribs would have contacted the expanded iliac blade of the pelvis in a soft tissue connection. No atlas-axis complex is observed, however the basioccipital-exoccipital complex is deconsolidated from the rest of the neurocranium, suggesting increased mobility at occipital-vertebral junction. Thus, axial regionalization that allowed for innovations in head mobility, body support and buttressing the pelvic fin evolved prior to the origin of limbs.

paleontology↗

bioRxiv2020

The coevolution of mammae number and litter size

Mammals are unique in provisioning their offspring with milk, lactiferous nourishment produced in glandular organs called mammae. Mammae number is hypothesized to coevolve with litter size, acting as a constraint on offspring survival. However, predicted canonical relations between mammae number and litter size (i.e., the one-half and identity rules) are untested across Mammalia. Here we analyze data for 2,301 species and show how these characters coevolve. In Mammalia, mammae number approximates the maximum reported litter size of a species, and mammae number explains more variation in litter size than other species-level traits (mass, gestation length, diet, and seasonality of contemporary geographic distribution). Clades show differences in these patterns, indicating that certain life history strategies might break the rules of mammary evolution. Mammae number is an underappreciated constraint on fecundity that has influenced the radiation of mammals.

evolutionary biology↗

bioRxiv2019

Developmental stage-specific distribution of macrophages in mouse mammary gland

Mammary gland development begins in the embryo and continues throughout the reproductive life of female mammals. Tissue macrophages (M{phi}s), dependent on signals from the M{phi} colony stimulating factor 1 receptor (CSF1R), have been shown to regulate the generation, regression and regeneration of this organ, which is central for mammalian offspring survival. However, the distribution of M{phi}s in the pre- and post-natal mammary gland, as it undergoes distinct phases of development and regression, is unknown or has been inferred from immunostaining of thin tissue sections. Here, we used optical tissue clearing and 3-dimensional imaging of mammary tissue obtained from Csf1r-EGFP mice. Whilst tissue M{phi}s were observed at all developmental phases, their abundance, morphology, localization and association with luminal and basal epithelial cells exhibited stage-specific differences. Furthermore, sexual dimorphism was observed at E14.5, when the male mammary bud is severed from the overlying epidermis. These findings provide new insights into the localization and possible functions of heterogeneous tissue M{phi} populations in mammogenesis.

developmental biology↗

bioRxiv2019

Multiscale activity imaging in the mammary gland reveals how oxytocin enables lactation

The mammary epithelium is indispensable for the continued survival of more than 5000 mammalian species. For some, the volume of milk ejected in a single day exceeds their entire blood volume. Here, we unveil the spatiotemporal properties of physiological signals that orchestrate milk ejection. Using quantitative, multidimensional imaging of mammary cell ensembles, we reveal how stimulus evoked Ca2+ oscillations couple to contractions in basal epithelial cells. Moreover, we show that Ca2+-dependent contractions generate the requisite force to physically deform the innermost layer of luminal cells, compelling them to discharge the fluid that they produced and housed. Through the collective action of thousands of these biological positive displacement pumps, each linked to a contractile ductal network, milk is delivered into the mouth of the dependent neonate, seconds after the command. Significance StatementThe mammary gland is functional for only a brief period of a females lifetime--if at all. During this time, it operates not for the survival of the individual, but for the survival of her species. Here, we visualize the nature of alveolar contractions in the functionally-mature mammary gland, revealing how specialized epithelial cells, which possess the ability to behave like smooth muscle cells, undergo Ca2+-dependent contractions. We demonstrate that individual oscillators can be electrically coupled to achieve global synchrony, a phenomenon that has not yet been observed in the mammary gland. By imaging activity across scales, we provide a window into the organization, dynamics and role of epithelial Ca2+ oscillations in the organ principally responsible for sustaining neonatal life in mammals.

cell biology↗

bioRxiv2019

Mammary mechanobiology: PIEZO1 mechanically-activated ion channels in lactation and involution

A mothers ability to produce a nutritionally-complete neonatal food source has provided a powerful evolutionary advantage to mammals. Milk production by secretory mammary epithelial cells is adaptive, its release is exquisitely timed and its own glandular stagnation with the permanent cessation of suckling triggers the programmed cell death and tissue remodeling that enables female mammals to nurse successive progeny. Both chemical and mechanical signals control epithelial expansion, function and remodeling. Despite this duality of input, however, the nature and function of mechanical forces in the mammary gland remain unknown. Here, we characterize the mammary force landscape and the capacity of luminal and basal epithelial cells to experience and exert force. We explore the molecular instruments for force-sensing in the mammary gland and the physiological requirement for PIEZO1 in lactation and involution. Our study supports the existence of a multifaceted system of chemical and mechanical sensing in the mammary gland, and a protective redundancy that ensures continued lactational competence and offspring survival.

cell biology↗

bioRxiv2017

Evidence against tetrapod-wide digit identities and for a limited frame shift in bird wings

In crown group tetrapods, individual digits are homologized in relation to a pentadactyl ground plan. However, testing hypotheses of digit homology is challenging because it is unclear whether digits develop with distinct and conserved gene regulatory states. Here we show dramatic evolutionary dynamism in the gene expression profiles of digits, challenging the notion that five digit identities are conserved across amniotes. Transcriptomics of developing limbs shows diversity in the patterns of genetic differentiation of digits, although the anterior-most digit of the pentadactyl limb has a unique, conserved expression profile. Further, we identify a core set of transcription factors that are differentially expressed among the digits of amniote limbs; their spatial expression domains, however, vary between species. In light of these results, we reevaluate the frame shift hypothesis of avian wing evolution and conclude that only the identity of the anterior-most digit has shifted position, suggesting a 1,3,4 digit identity in the bird wing.

evolutionary biology↗