Glypicans define unique roles for the Hedgehog co-receptors boi and ihog in cytoneme-mediated gradient formation.

The conserved family of Hedgehog (Hh) signaling proteins plays a key role in cell-cell communication in development, tissue repair, and cancer progression, inducing distinct concentration-dependent responses in target cells located at short and long distances. One simple mechanism for long distance dispersal of the lipid modified Hh is the direct contact between cell membranes through filopodia-like structures known as cytonemes. Here we have analyzed in Drosophila the interaction between the glypicans Dally and Dally-like protein, necessary for Hh signaling, and the adhesion molecules and Hh coreceptors Ihog and Boi. We describe that glypicans are required to maintain the levels of Ihog, but not of Boi. We also show that the overexpression of Ihog, but not of Boi, regulates cytoneme dynamics through their interaction with glypicans, the Ihog fibronectin III domains being essential for this interaction. Our data suggest that the regulation of glypicans over Hh signaling is specifically given by their interaction with Ihog in cytonemes. Contrary to previous data, we also show that there is no redundancy of Ihog and Boi functions in Hh gradient formation, being Ihog, but not of Boi, essential for the long-range gradient.

Drosophila Zic family member odd-paired is needed for adult post-ecdysis maturation.

Specific neuropeptides regulate in arthropods the shedding of the old cuticle (ecdysis) followed by maturation of the new cuticle. In Drosophila melanogaster, the last ecdysis occurs at eclosion from the pupal case, with a post-eclosion behavioural sequence that leads to wing extension, cuticle stretching and tanning. These events are highly stereotyped and are controlled by a subset of crustacean cardioactive peptide (CCAP) neurons through the expression of the neuropeptide Bursicon (Burs). We have studied the role of the transcription factor Odd-paired (Opa) during the post-eclosion period. We report that opa is expressed in the CCAP neurons of the central nervous system during various steps of the ecdysis process and in peripheral CCAP neurons innerving the larval muscles involved in adult ecdysis. We show that its downregulation alters Burs expression in the CCAP neurons. Ectopic expression of Opa, or the vertebrate homologue Zic2, in the CCAP neurons also affects Burs expression, indicating an evolutionary functional conservation. Finally, our results show that, independently of its role in Burs regulation, Opa prevents death of CCAP neurons during larval development.

From intra- to extracellular vesicles: extracellular vesicles in developmental signalling.

Signalling from cell-to-cell is fundamental for determining differentiation and patterning. This communication can occur between adjacent and distant cells. Extracellular vesicles (EVs) are membrane-based structures thought to facilitate the long-distance movement of signalling molecules. EVs have recently been found to allow the transport of two major developmental signalling pathways: Hedgehog and Wnt. These signalling molecules undergo crucial post-translational lipid modifications, which anchor them to membranes and impede their free release into the extracellular space. Preparation of these ligands in EVs involves intracellular vesicle sorting in an endocytosis-dependent recycling process before secretion. In the present review, we discuss the most recent advances with regard to EV involvement in developmental signalling at a distance. We focus on the role of the protein complexes involved in EV genesis, and provide a comprehensive perspective of the contribution of these complexes to intracellular vesicle sorting of developmental signals for their extracellular secretion, reception and transduction.

Perspectives on Intra- and Intercellular Trafficking of Hedgehog for Tissue Patterning.

Intercellular communication is a fundamental process for correct tissue development. The mechanism of this process involves, among other things, the production and secretion of signaling molecules by specialized cell types and the capability of these signals to reach the target cells in order to trigger specific responses. Hedgehog (Hh) is one of the best-studied signaling pathways because of its importance during morphogenesis in many organisms. The Hh protein acts as a morphogen, activating its targets at a distance in a concentration-dependent manner. Post-translational modifications of Hh lead to a molecule covalently bond to two lipid moieties. These lipid modifications confer Hh high affinity to lipidic membranes, and intense studies have been carried out to explain its release into the extracellular matrix. This work reviews Hh molecule maturation, the intracellular recycling needed for its secretion and the proposed carriers to explain Hh transportation to the receiving cells. Special focus is placed on the role of specialized filopodia, also named cytonemes, in morphogen transport and gradient formation.

The transcription factor optomotor-blind antagonizes Drosophila haltere growth by repressing decapentaplegic and hedgehog targets.

In Drosophila, decapentaplegic, which codes for a secreted signaling molecule, is activated by the Hedgehog signaling pathway at the anteroposterior compartment border of the two dorsal primordia; the wing and the haltere imaginal discs. In the wing disc, Decapentaplegic and Hedgehog signaling targets are implicated in cell proliferation and cell survival. However, most of their known targets in the wing disc are not expressed in the haltere disc due to their repression by the Hox gene Ultrabithorax. The T-box gene optomotor-blind escapes this repression in the haltere disc, and therefore is expressed in both the haltere and wing discs. Optomotor-blind is a major player during wing development and its function has been intensely investigated in this tissue, however, its role in haltere development has not been reported so far. Here we show that Optomotor-blind function in the haltere disc differs from that in the wing disc. Unlike its role in the wing, Optomotor-blind does not prevent apoptosis in the haltere but rather limits growth by repressing several Decapentaplegic and Hedgehog targets involved both in wing proliferation and in modulating the spread of morphogens similar to Ultrabithorax function but without disturbing Ultrabithorax expression.

Balancing Hedgehog, a retention and release equilibrium given by Dally, Ihog, Boi and shifted/DmWif.

Hedgehog can signal both at a short and long-range, and acts as a morphogen during development in various systems. We studied the mechanisms of Hh release and spread using the Drosophila wing imaginal disc as a model system for polarized epithelium. We analyzed the cooperative role of the glypican Dally, the extracellular factor Shifted (Shf, also known as DmWif), and the Immunoglobulin-like (Ig-like) and Fibronectin III (FNNIII) domain-containing transmembrane proteins, Interference hedgehog (Ihog) and its related protein Brother of Ihog (Boi), in the stability, release and spread of Hh. We show that Dally and Boi are required to prevent apical dispersion of Hh; they also aid Hh recycling for its release along the basolateral part of the epithelium to form a long-range gradient. Shf/DmWif on the other hand facilitates Hh movement restrained by Ihog, Boi and Dally, establishing equilibrium between membrane attachment and release of Hh. Furthermore, this protein complex is part of thin filopodia-like structures or cytonemes, suggesting that the interaction between Dally, Ihog, Boi and Shf/DmWif is required for cytoneme-mediated Hh distribution during gradient formation.