PgmNr D1446: Cytoneme-mediated cellular synapsis for Hh signaling.

Authors:
L. GONZÁLEZ-MÉNDEZ; I. GUERRERO


Institutes
CBMSO, MADRID, MADRID, ES.


Keyword: wing disc

Abstract:

Hedgehog (Hh) is a morphogen with a central role in development, and also implicated in other processes in the adult organism, including stem cells maintenance, cell migration, axon guidance and cancer. In many systems, Hh morphogen is secreted from a defined group of cells and specifically distributed to create a concentration gradient that drives differential genes expression and subsequent specification in target cells. The mechanism/s responsible for Hh gradient establishment through a tightly controlled dispersion of the morphogen remains controversial. Increasing evidences support the role of specialized and highly dynamic filopodia (cytonemes) in the transport of morphogens during development, facilitating the concentration and spatial restriction of the signal. In this context, we have recently demonstrated that Hh transport via exosomes along cytonemes emanating from Hh producing cells is an essential mechanism for the restricted distribution of Hh in Drosophila epithelia development. It has recently suggested that signaling between epithelial cells occurs through direct cell-cell contacts even if they are separated by several cell diameters, in a similar manner to a synaptic connection. Currently, we are focusing on the study of the cytoneme-mediated communication between Hh producing and receiving cells during Drosophila wing disc patterning. In order to identify the physical interaction sites along these cytonemes, we use CD4-based GRASP technique combined with LexA/lexO and Gal4/UAS binary expression systems. We observe a strong connection between A and P compartments cytonemes at the basal surface of the epithelium. In addition, we study this interaction between Hh sending and receiving cytonemes during Hh reception by expressing some of the components of the Hh reception complex, such as Ihog/Boi, Patched (Ptc) and the proteoglycans Dally and Dlp. Interestingly, high levels of Dally, Dlp and Ihog accumulate at the contact sites along A and P cytonemes. Also, we have evidences for the presence of both Ptc (Hh receptor) and Hh at cytonemes emanating from Hh receiving cells. We find besides a recycling process of Ptc and Ihog to reach the plasma membrane as exosomes; Ptc and iHog colocalize with exosome markers, and different conditions (UAS-RNAi) that disturb the exosome formation in the Hh receiving cells lead to a block in Ptc recycling, modifying the Hh gradient. Our results agree with a cytoneme-mediated Hh release and reception, and suggest a mechanism of cell-cell signaling mediated by exosomes containing Hh and Ptc, resembling synaptic contacts.