Biology subjects

Lloyd-Lewis, B.

Publications and source records attributed to Lloyd-Lewis, B..

4 recordsLinked to original sources

bioRxiv2022

Positional cues underlie cell fate specification during branching morphogenesis of the embryonic mammary epithelium

How cells coordinate morphogenetic cues and fate specification during development is a fundamental question at the basis of tissue formation. Lineage tracing studies have demonstrated that many stratified epithelia, including the mammary gland, first arise from multipotent stem cells, which are progressively replaced by distinct pools of unipotent progenitors that maintain tissue homeostasis postnatally. The lack of specific markers for early fate specification in the mammary gland has prevented the delineation of the features and spatial localization of lineage-committed progenitors that co-exist with multipotent stem cells (MaSCs) during tissue development. Here, using single-cell RNA-sequencing across 4 stages of embryonic development, we reconstructed the differentiation trajectories of multipotent mammary stem cells towards basal and luminal fate. Our data revealed that MaSCs can already be resolved into distinct populations exhibiting lineage commitment at the time coinciding with the first sprouting events of mammary branching morphogenesis (E15.5). By visualizing gene expression across our developmental atlas, we provide novel molecular markers for committed and multipotent MaSCs, and define their spatial distribution within the developing tissue. Furthermore, we show that the mammary embryonic mesenchyme is composed of two spatially-restricted cell populations, representing the sub-epithelial and dermal mesenchyme. Mechanistically, we explored the communication between different subsets of mesenchymal and epithelial cells, using time-lapse analysis of mammary embryonic explant cultures, and reveal that mesenchymal-produced FGF10 accelerates embryonic mammary branching morphogenesis without affecting cell proliferation. Altogether, our data elucidate the spatiotemporal signals underlying lineage specification of multipotent mammary stem cells and uncover the paracrine interactions between epithelial and mesenchymal cells that guide mammary branching morphogenesis.

developmental biology↗

bioRxiv2021

In vivo imaging of mammary epithelial cell dynamics in response to lineage-biased Wnt/Beta-catenin activation

Real-time, in vivo imaging provides an essential window into the spatiotemporal cellular and molecular events contributing to tissue development and pathology. By coupling longitudinal intravital imaging with genetic lineage tracing, here we captured the earliest cellular events underlying the impact of active Wnt/{beta}-catenin signaling on the organization and differentiation of the mammary epithelium. This enabled us to interrogate how Wnt/{beta}-catenin regulates the dynamics of distinct subpopulations of mammary epithelial cells in vivo and in real time. We show that {beta}-catenin stabilization, when targeted to either of the mammary luminal or basal epithelial lineages, invariably leads to cellular rearrangements that precipitate the formation of hyperplastic lesions that undergo squamous transdifferentiation. These results enhance our understanding of the earliest stages of hyperplastic lesion formation in vivo, and reveal that in mammary neoplastic development, {beta}-catenin activation dictates a hair-follicle/epidermal differentiation program independently of the targeted cell of origin.

cell biology↗

bioRxiv2021

Longitudinal high-resolution imaging through a flexible intravital imaging window

Intravital microscopy (IVM) is a powerful technique that enables imaging of internal tissues at (sub)cellular resolutions in living animals. Here, we present a silicone-based imaging window consisting of a fully flexible, suture-less design that is ideally suited for long-term, longitudinal IVM of growing tissues and tumors. Crucially, we show that this window, without any customization, is suitable for numerous anatomical locations in mice using a rapid and standardized implantation procedure. This low-cost device represents a substantial technological and performance advance that facilitates intravital imaging in diverse contexts in higher organisms, opening new avenues for in vivo imaging of soft and fragile tissues. One-sentence summaryThis study presents a versatile, fully flexible imaging window that acts as an implantable transparent second skin for small laboratory animal in vivo imaging.

cell 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↗