Predictive model for cytoneme guidance in Hedgehog signaling based on Ihog- Glypicans interaction

The Drosophila epidermal growth factor receptor pathway regulates Hedgehog signalling and cytoneme behaviour

During Drosophila epithelial development, dynamic signalling filopodia (cytonemes) establish direct contacts between distant cells to facilitate the formation of the Hedgehog signalling gradient. However, not much is known about how cytonemes are regulated. In this study, we show that cytoneme dynamics and Hedgehog signalling in the Drosophila epithelia depend on the Epidermal Growth Factor pathway and on its downstream effector Ras1. We describe that EGFR/Ras1 pathway is required to maintain in the wing disc epithelium the basal plasma membrane levels of Interference Hedgehog (Ihog), a critical Hh co-receptor and adhesion protein. In addition, our data demonstrate that filamin A or Cheerio in Drosophila, responds to both Ihog and EGFR pathway and recruited to the basal site of the plasma membrane. This recruitment contributes to Ihog's role in stabilizing cytonemes.

Hedgehog on the Move: Glypican-Regulated Transport and Gradient Formation in Drosophila

Glypicans (Glps) are a family of heparan sulphate proteoglycans that are attached to the outer plasma membrane leaflet of the producing cell by a glycosylphosphatidylinositol anchor. Glps are involved in the regulation of many signalling pathways, including those that regulate the activities of Wnts, Hedgehog (Hh), Fibroblast Growth Factors (FGFs), and Bone Morphogenetic Proteins (BMPs), among others. In the Hh-signalling pathway, Glps have been shown to be essential for ligand transport and the formation of Hh gradients over long distances, for the maintenance of Hh levels in the extracellular matrix, and for unimpaired ligand reception in distant recipient cells. Recently, two mechanistic models have been proposed to explain how Hh can form the signalling gradient and how Glps may contribute to it. In this review, we describe the structure, biochemistry, and metabolism of Glps and their interactions with different components of the Hh-signalling pathway that are important for the release, transport, and reception of Hh.

Actin-based protrusions at a glance

Actin-based protrusions are at the base of many fundamental cellular processes, such as cell adhesion, migration and intercellular communication. In recent decades, the discovery of new types of actin-based protrusions with unique functions has enriched our comprehension of cellular processes. However, as the repertoire of protrusions continues to expand, the rationale behind the classification of newly identified and previously known structures becomes unclear. Although current nomenclature allows good categorization of protrusions based on their functions, it struggles to distinguish them when it comes to structure, composition or formation mechanisms. In this Cell Science at a Glance article, we discuss the different types of actin-based protrusions, focusing on filopodia, cytonemes and tunneling nanotubes, to help better distinguish and categorize them based on their structural and functional differences and similarities.

Mechanotransduction in tumor dynamics modeling

Mechanotherapy is a groundbreaking approach to impact carcinogenesis. Cells sense and respond to mechanical stimuli, translating them into biochemical signals in a process known as mechanotransduction. The impact of stress on tumor growth has been studied in the last three decades, and many papers highlight the role of mechanics as a critical self-inducer of tumor fate at the in vitro and in vivo biological levels. Meanwhile, mathematical models attempt to determine laws to reproduce tumor dynamics. This review discusses biological mechanotransduction mechanisms and mathematical-biomechanical models together. The aim is to provide a common framework for the different approaches that have emerged in the literature from the perspective of tumor avascularity and to provide insight into emerging mechanotherapies that have attracted interest in recent years.

Establishing Hedgehog Gradients during Neural Development

A morphogen is a signaling molecule that induces specific cellular responses depending on its local concentration. The concept of morphogenic gradients has been a central paradigm of developmental biology for decades. Sonic Hedgehog (Shh) is one of the most important morphogens that displays pleiotropic functions during embryonic development, ranging from neuronal patterning to axon guidance. It is commonly accepted that Shh is distributed in a gradient in several tissues from different origins during development; however, how these gradients are formed and maintained at the cellular and molecular levels is still the center of a great deal of research. In this review, we first explored all of the different sources of Shh during the development of the nervous system. Then, we detailed how these sources can distribute Shh in the surrounding tissues via a variety of mechanisms. Finally, we addressed how disrupting Shh distribution and gradients can induce severe neurodevelopmental disorders and cancers. Although the concept of gradient has been central in the field of neurodevelopment since the fifties, we also describe how contemporary leading-edge techniques, such as organoids, can revisit this classical model.

Drosophila hedgehog signaling range and robustness depend on direct and sustained heparan sulfate interactions

Morphogens determine cellular differentiation in many developing tissues in a concentration dependent manner. As a central model for gradient formation during animal development, Hedgehog (Hh) morphogens spread away from their source to direct growth and pattern formation in the Drosophila wing disc. Although heparan sulfate (HS) expression in the disc is essential for this process, it is not known whether HS regulates Hh signaling and spread in a direct or in an indirect manner. To answer this question, we systematically screened two composite Hh binding areas for HS in vitro and expressed mutated proteins in the Drosophila wing disc. We found that selectively impaired HS binding of the second site reduced Hh signaling close to the source and caused striking wing mispatterning phenotypes more distant from the source. These observations suggest that HS constrains Hh to the wing disc epithelium in a direct manner, and that interfering with this constriction converts Hh into freely diffusing forms with altered signaling ranges and impaired gradient robustness.