Beyond guidance: A novel role for Sema–PlxnD1 signaling in vascular development

Abstract

Sprouting angiogenesis expands the primitive vasculature of the embryo and its essential for survival and homeostasis. However, the mechanisms that allocate the capacity to form sprouts among endothelial cells to ensure the reproducible anatomy of stereotypical vascular beds remain unknown. Using the zebrafish model system, confocal imaging, RNA in situ hybridization, cell transplantation/ competition experiments and both loss and gain-of-function approaches here we show that Sema-PlxnD1 signaling, previously implicated in sprout guidance, plays precisely this role. Molecularly, Sema-PlxnD1 signaling exerts this effect by modulating the effects of other vascular development pathways.Program/Abstract # 2 Specialized ribosomes control Hox mRNA translation and vertebrate tissue patterning Control of gene expression in space and time plays an important role in enabling cells to "know" where they are in the developing vertebrate embryo and what to become. Decades of research have demonstrated numerous layers of regulation in gene expression that coordinate this process, although translational control has received less experimental attention. Here we unexpectedly show that a single component of the ribosome establishes the mammalian body plan. Our data reveal that mutations of the Ribosomal Protein L38 (Rpl38) gene in mice lead to tissue specific patterning defects, including pronounced homeotic transformations of the axial skeleton. By optimizing genetic and molecular approaches to study translational regulation within the vertebrate embryo, we uncover an important role for RPL38 in transcript-specific translational control. In Rpl38 mutant embryos, global protein synthesis is unchanged however the translation of a select subset of Homeobox mRNAs is perturbed. Our data reveal that RPL38 facilitates 80S complex formation on these mRNAs as a regulatory component of the ribosome and uncover novel complexity in regulation of Hox gene expression at the level of translational control. We further show that Rpl38 expression is markedly enriched in regions of the embryo, such as somites, where lossof-function phenotypes occur. We extended these findings by performing an expression-profiling screen for the majority of the 79 ribosomal proteins associated with both small and large ribosome subunits. This analysis unexpectedly identified dynamic regulation in the expression of ribosomal proteins, which historically have been considered to be ubiquitously expressed housekeeping genes, within the vertebrate embryo. Collectively, these findings suggest that a "ribosomal protein code" established by distinct expression levels and translational specificity of ribosomal proteins may provide a new level of regulation in gene expression and mammalian development.To understand how secretory organs acquire their final form and function, we focus on a simple well-developed genetic system, the Drosophila salivary gland (SG). The SG is a simple tube that undergoes the same morphogenetic events that occur in organs of more complicated systems,...

Filopodia are dispensable for endothelial tip cell guidance

“…Curiously, many of the conserved 'guidance' pathways that operate in growth cones serve to modulate the activity of the Vegf signalling pathway in ECs. Recent studies suggest that this might function to fine-tune the tip cell response to Vegf, which is the primary angiogenic cue for tip cell migration (Adams and Eichmann, 2010;Zygmunt et al, 2011). Our current study proposes another difference between neuronal growth cones and tip cells: although filopodia are required for the guided migration of growth cones (Bentley and Toroian-Raymond, 1986;Chien et al, 1993;Zheng et al, 1996), filopodia of endothelial tip cells are dispensable for their migration trajectory.…”

“…In the zebrafish trunk, spatial organisation of the vasculature is regulated by Vegf (Covassin et al, 2006;Hogan et al, 2009b;Krueger et al, 2011), Netrin 1/Unc5B (Lu et al, 2004) and Semaphorin/Plexin D1 signalling Torres-Vázquez et al, 2004), with the latter acting to repress proangiogenic activities of Vegf signalling by ensuring expression of sFlt1 by ECs (Zygmunt et al, 2011). Perturbation of different components of these pathways affects angiogenesis and leads to mispatterning of the vasculature (Covassin et al, 2006;Hogan et al, 2009b;Krueger et al, 2011;Zygmunt et al, 2011). Thus, ECs receive and integrate a multitude of signals that aid their directed migration so as to enable the development of a stereotypic network of blood vessels with a reproducible pattern from animal to animal (Isogai et al, 2001;Isogai et al, 2003).…”

miR-1 and miR-206 regulate angiogenesis by modulating VegfA expression in zebrafish

“…VEGF promotes the differentiation of endothelial progenitors and stimulates endothelial cell growth, survival and migration (Carmeliet and Jain, 2011;Ferrara et al, 2003). By contrast, Semaphorin-Plexin D1 signaling represses angiogenic potential by antagonizing Vegf function and ensures proper guidance of intersomitic sprouts (Torres-Vázquez et al, 2004;Zygmunt et al, 2011). To determine whether these systems are regulated by miR-1/206, we analyzed the 3ЈUTRs of candidate genes in each pathway for putative miR-1/206 target sites.…”

The novel transmembrane protein Tmem2 is essential for coordination of myocardial and endocardial morphogenesis

“…We employed Tol2 transposase-mediated transgenesis for both transient transgene expression and generation of transgenic founders (Fisher et al, 2006). Additional transgenic lines used were Tg(kdrl:GRCFP) (Cross et al, 2003) and Tg(fliep:gal4ff) ubs4 , which drives endothelium-specific expression of the GAL4-VP16 derivative Gal4FF and is described elsewhere (Zygmunt et al, 2011).…”

“…3G-I; n5). In an effort to generate a more thorough rescue of the frv endocardium, we next employed the stably integrated driver Tg(fliep:gal4ff) (Zygmunt et al, 2011). Unfortunately, stable integration of both Tg(fliep:gal4ff) and Tg(uas:tmem2-gfp) did not result in uniform expression of tmem2 throughout the endocardium (Fig.…”