A role for fascin in preventing filopodia breakage in Drosophila tracheal cells

© Pilar Okenve-Ramos and Marta Llimargas. Filopodia are long and thin finger-like protrusions essential for cell migration. They are formed by parallel actin bundles tightly packed by cell type and context dependent actin-bundling proteins. Our recent work analyzing the role of Fascin during tracheal development in Drosophila has shown that Singed (the Drosophila Fascin homolog) acts as a molecular link between the Branchless (FGF)/Breathless (FGFR) pathway and the actin cytoskeleton. We have reported that the lack of Singed (Sn) leads to wavy and flaccid filopodia due to the disorganization of the tracheal actin cytoskeleton. Here we describe for the first time filopodia breakage in Drosophila, and show that Fascin plays a role in this event. We propose that actin filaments in sn mutant filopodia buckle under membrane pressure due to lower bending stiffness, eventually undergoing breakage. Both Filopodia buckling and breakage would impair correct cell navigation and migration.P.O-R. is supported by a FPI fellowship from Ministerio de Ciencia e Innovacion. This work was supported by funds from the Ministerio de Ciencia e Innovacion to M.L (BFU2006-09515/BMC, BFU2009-09041) and from Program Consolider 2007 (CSD2007-00008) projectPeer Reviewe

Fascin, may the Forked be with you

© 2014 Taylor & Francis Group, LLC. The FGFR pathway triggers a wide range of key biological responses. Among others, the Breathless (Btl, Drosophila FGFR1) receptor cascade promotes cell migration during embryonic tracheal system development. However, how the actin cytoskeleton responds to Btl pathway activation to induce cell migration has remained largely unclear. Our recent results shed light into this issue by unveiling a link between the actin-bundling protein Singed (Sn) and the Btl pathway. We showed that the Btl pathway regulates sn, which leads to the stabilization of the actin bundles required for filopodia formation and actin cytoskeleton rearrangement. This regulation contributes to tracheal migration, tracheal branch fusion and tracheal cell elongation. Parallel actin bundles (PABs) are usually cross-linked by more than one actin-bundling protein. Accordingly, we have also shown that sn synergistically interacts with forked (f), another actin crosslinker. In this Extra View we extend f analysis and hypothesize how both actin-bundling proteins may act together to regulate the PABs during tracheal embryonic development. Although both proteins are required for similar tracheal events, we suggest that Sn is essential for actin bundle initiation and stiffening, while F is required for the lengthening and further stabilization of the PABs.P.O-R. is supported by a FPI fellowship from Ministerio de Ciencia e Innovación. This work was supported by funds from the Ministerio de Ciencia e Innovación to M.L (BFU2006–09515/BMC, BFU2009–09041) and from Programme Consolider 2007 (CSD2007–00008) projectPeer Reviewe

Structure of the N-terminal domain of the protein Expansion: an 'Expansion' to the Smad MH2 fold

Gene-expression changes observed in Drosophila embryos after inducing the transcription factor Tramtrack led to the identification of the protein Expansion. Expansion contains an N-terminal domain similar in sequence to the MH2 domain characteristic of Smad proteins, which are the central mediators of the effects of the TGF- signalling pathway. Apart from Smads and Expansion, no other type of protein belonging to the known kingdoms of life contains MH2 domains. To compare the Expansion and Smad MH2 domains, the crystal structure of the Expansion domain was determined at 1.6 A˚ resolution, the first structure of a non-Smad MH2 domain to be characterized to date. The structure displays the main features of the canonical MH2 fold with two main differences: the addition of an -helical region and the remodelling of a protein-interaction site that is conserved in the MH2 domain of Smads. Owing to these differences, to the new domain was referred to as N-MH2. Despite the presence of the N-MH2 domain, Expansion does not participate in TGF- signalling; instead, it is required for other activities specific to the protostome phyla. Based on the structural similarities to the MH2 fold, it is proposed that the N-MH2 domain should be classified as a new member of the Smad/FHA superfamily. 1

Tramtrack Is Genetically Upstream of Genes Controlling Tracheal Tube Size in Drosophila

The Drosophila transcription factor Tramtrack (Ttk) is involved in a wide range of developmental decisions, ranging from early embryonic patterning to differentiation processes in organogenesis. Given the wide spectrum of functions and pleiotropic effects that hinder a comprehensive characterisation, many of the tissue specific functions of this transcription factor are only poorly understood. We recently discovered multiple roles of Ttk in the development of the tracheal system on the morphogenetic level. Here, we sought to identify some of the underlying genetic components that are responsible for the tracheal phenotypes of Ttk mutants. We therefore profiled gene expression changes after Ttk loss- and gain-of-function in whole embryos and cell populations enriched for tracheal cells. The analysis of the transcriptomes revealed widespread changes in gene expression. Interestingly, one of the most prominent gene classes that showed significant opposing responses to loss- and gain-of-function was annotated with functions in chitin metabolism, along with additional genes that are linked to cellular responses, which are impaired in ttk mutants. The expression changes of these genes were validated by quantitative real-time PCR and further functional analysis of these candidate genes and other genes also expected to control tracheal tube size revealed at least a partial explanation of Ttk's role in tube size regulation. The computational analysis of our tissue-specific gene expression data highlighted the sensitivity of the approach and revealed an interesting set of novel putatively tracheal genes

Apical constriction and invagination: a very self-reliant couple

Perspective.-- Open Archive.-- El pdf es la versión post-print.Research from both laboratories is supported by grants from the Generalitat de Catalunya and grants from the Spanish Ministerio de Ciencia e Innovación and its Consolider-Ingenio 2010 Program.Peer Reviewe

A role for fascin in preventing filopodia breakage in Drosophila tracheal cells

© Pilar Okenve-Ramos and Marta Llimargas. Filopodia are long and thin finger-like protrusions essential for cell migration. They are formed by parallel actin bundles tightly packed by cell type and context dependent actin-bundling proteins. Our recent work analyzing the role of Fascin during tracheal development in Drosophila has shown that Singed (the Drosophila Fascin homolog) acts as a molecular link between the Branchless (FGF)/Breathless (FGFR) pathway and the actin cytoskeleton. We have reported that the lack of Singed (Sn) leads to wavy and flaccid filopodia due to the disorganization of the tracheal actin cytoskeleton. Here we describe for the first time filopodia breakage in Drosophila, and show that Fascin plays a role in this event. We propose that actin filaments in sn mutant filopodia buckle under membrane pressure due to lower bending stiffness, eventually undergoing breakage. Both Filopodia buckling and breakage would impair correct cell navigation and migration.P.O-R. is supported by a FPI fellowship from Ministerio de Ciencia e Innovacion. This work was supported by funds from the Ministerio de Ciencia e Innovacion to M.L (BFU2006-09515/BMC, BFU2009-09041) and from Program Consolider 2007 (CSD2007-00008) projectPeer Reviewe

Specific activities of epithelial complexes and junctions during morphogenesis: the contribution of crb and the SAR to tracheal development

Trabajo presentado en el EMBO 17th Biennial Workshop on the Molecular & Developmental biology of drosophila, celebrado en Kolymbari, Grecia, del 20 al 26 de junio de 2010Peer Reviewe

The genetic programme triggering timely and spatially regulated chitin deposition

Trabajo presentado en la 4th JEDI (Junior European Drosophila Investigators) meeting, celebrado en Carry-le-Rouet, Marseille, del 9 al 12 de septiembre de 2014Peer Reviewe

Intrinsic and extrinsic mechanisms regulating the morphogenesis of tubular epithelia

Trabajo presentado en EMBO Molecular and Developmental Biology of Drosophila workshop, celebrado en modalidad virtual del 21 al 27 de junio de 2020

Mechanisms of tubulogenesis

Trabajo presentado en la 1st Spanish Conference on the Molecular, Cellular and Developmental Biology of Drosophila, celebrada en Girona, España, del 25 al 28 de septiembre de 2012Peer Reviewe