Short-Range and Long-Range Guidance by Slit and Its Robo Receptors

Heart morphogenesis requires the coordinated regulation of cell movements and cell-cell interactions between distinct populations of cardiac precursor cells. Little is known about the mechanisms that organize cardiac cells into this complex structure. In this study, we analyzed the role of Slit, an extracellular matrix protein and its transmembrane receptors Roundabout (Robo) and Roundabout2 (Robo2) during morphogenesis of the Drosophila heart tube, a process analogous to early heart formation in vertebrates. During heart assembly, two types of progenitor cells align into rows and coordinately migrate to the dorsal midline of the embryo, where they merge to assemble a linear heart tube. Here we show that cardiac-specific expression of Slit is required to maintain adhesion between cells within each row during dorsal migration. Moreover, differential Robo expression determines the relative distance each row is positioned from the dorsal midline. The innermost CBs express only Robo, whereas the flanking pericardial cells express both receptors. Removal of robo2 causes pericardial cells to shift toward the midline, whereas ectopic robo2 in CBs drives them laterally, resulting in an unfused heart tube. We propose a model in which Slit has a dual role during assembly of the linear heart tube, functioning to regulate both cell positioning and adhesive interactions between migrating cardiac precursor cells.cell adhesion ͉ dorsal vessel ͉ heart morphogenesis

Section: Discussionsupporting

confidence: 83%

“…There are three known receptors for Slit in Drosophila: Robo, Robo2, and Robo3 (11,16,17). We detected the expression of two of the three receptors, Robo and Robo2, in specific heart cell types during heart tube assembly.…”

Section: Expression Of Slit and Robo Proteins In The Embryonicmentioning

confidence: 89%

Lateral positioning at the dorsal midline: Slit and Roundabout receptors guide Drosophila heart cell migration

Santiago-Martínez

Soplop

Kramer

2006

“…Together, these studies provide evidence that the robo family of guidance receptors have a critical role in vascular development in vertebrates. The role of robo as a repulsive guidance receptor in the neural system has been well documented in Drosophila (19). Previous studies of robo in mesenchymal tissues (20) and in leukocyte migration (7) have hinted at nonneural functions.…”

Section: Discussionmentioning

confidence: 99%

“…The conventional thinking for robo is that they are negative regulators of cell migration. The role of slit in repulsive-guidance mechanisms have been documented in growth cones through robo (19) and in endothelial cells through robo4 (12). Recently, attraction mechanisms have also been reported for slit in relation to tumor vasculature through robo1 (27) and in Drosophila tracheal branches by robo2 (28).…”

Section: Discussionmentioning

confidence: 99%

roundabout4 is essential for angiogenesis in vivo

Bedell

Yeo

Park

et al. 2005

199

189

Stereotypical patterns of vascular and neuronal networks suggest that specific genetic programs tightly control path determination and, consequently, angiogenesis and axon-guidance mechanisms. Our study focuses on one member of the roundabout family of receptors, which traditionally mediate repulsion from the midline. Here, we characterize a fourth member of this family, roundabout4 (robo4), which is the predominant roundabout (robo) that is expressed in embryonic zebrafish vasculature. Gene knockdown and overexpression approaches show that robo4 is essential for coordinated symmetric and directed sprouting of intersomitic vessels and provide mechanistic insights into this process. Also, human robo4 gene functionally compensates for loss of robo4 gene function, suggesting evolutionary conservation. This article reports an endothelial-specific function for a robo gene in vertebrates in vivo.axon guidance ͉ endothelial cell ͉ zebrafish V ascular and neural networks established by angiogenesis and neurogenesis are essential for the regulation of physiological processes. Whether the processes of blood-vessel and peripheralnerve formation are intimately associated at a mechanistic level is a subject of active investigation (1). Recently, description of cellsurface molecules that are shared by neuronal and endothelial cells has suggested that this association may be more prevalent than previously thought. Neuropilin (2), ephrin (3), and plexin (4) are a few examples of molecules that are implicated in both processes. Recently, roundabout (robo), a class of neural guidance receptors that bind slit ligands have joined this group (5). slit-robo signaling mediates axonal repulsion (6) and inhibition of leukocyte migration (7). In vertebrate systems, three robo receptor family members were identified, all with prominent neural expression (8, 9). More recently, a fourth member of the robo gene family, roundabout4 (robo4) was identified (10). Compared with the canonical robo structure, robo4 is smaller in that it possesses only two of the five Ig and two of the three fibronectin domains present in the extracellular component of robo1, robo2, and robo3 (11). robo4 has been described as endothelial-specific, and it binds to slit and inhibits the migration of heterologous cells that express robo4 and primary endothelial cells (12). Although studies of robo4 in endothelial cells suggest that robo signaling is important for regulating endothelial cell migration, there are no reports that document the role of robo signaling in vascular development in vivo. Here, we cloned a zebrafish (Danio rerio) ortholog of human robo4 (hrobo4) and studied its expression and role in vascular development by gene knockdown and overexpression approaches. In contrast to the endothelial-specific expression of murine robo4, zebrafish robo4 is expressed in both endothelial and neural tissues with vascular expression seen in angioblasts, the dorsal aorta (DA), the posterior cardinal vein, and intersomitic vessels (ISV). Morpholino (MO) knockdown of robo...

“…To create a model for studying the role of DSCR1 in mental retardation in DS, we generated transgenic flies overexpressing nebula by using the UAS͞GAL4 system (29). Flies containing the nebula transgene on the third chromosome (nla t1 ) were crossed with both the Act5C-GAL4 (Act5C) and Elav-GAL4 (Elav) driver lines to yield nebula overexpression throughout the fly or specifically in the neurons, respectively (15,16). Fig.…”

Section: Transgenic Flies Overexpressing Nebula Exhibit Severe Defectmentioning

confidence: 99%

The Drosophila homolog of Down's syndrome critical region 1 gene regulates learning: Implications for mental retardation

Chang

Shi

Min

2003

126

118

Mental retardation is the most common phenotypic abnormality seen in Down's syndrome (DS) patients, yet the underlying mechanism remains mysterious. DS critical region 1 (DSCR1), located on chromosome 21, is overexpressed in the brain of DS fetus and encodes an inhibitor of calcineurin, but its physiological significance is unknown. To study its functional importance and role in mental retardation in DS, we generated Drosophila mutants of nebula, an ortholog of human DSCR1. Here, we report that both nebula loss-of-function and overexpression mutants exhibit severe learning defects that are attributed by biochemical perturbations rather than maldevelopment of the brain. These results, combined with our data showing that the same biochemical signaling pathway is altered in human DS fetal brain tissue overexpressing DSCR1, suggest that alteration of DSCR1 expression could contribute to mental retardation in DS.