Limits...
Repulsion by Slit and Roundabout prevents Shotgun/E-cadherin-mediated cell adhesion during Drosophila heart tube lumen formation.

Santiago-Martínez E, Soplop NH, Patel R, Kramer SG - J. Cell Biol. (2008)

Bottom Line: Genetic evidence suggests that Robo and Shotgun (Shg)/E-Cad function together in modulating CB adhesion. robo and shg/E-Cad transheterozygotes have lumen defects.In robo loss-of-function or shg/E-Cad gain-of-function embryos, lumen formation is blocked because of inappropriate CB adhesion and an accumulation of E-Cad at the apical membrane.In contrast, shg/E-Cad loss-of-function or robo gain-of-function blocks lumen formation due to a loss of CB adhesion.

View Article: PubMed Central - PubMed

Affiliation: Department of Pathology and Laboratory Medicine, Robert Wood Johnson Medical School, University of Medicine and Dentistry of New Jersey, Piscataway, NJ 08854, USA.

ABSTRACT
During Drosophila melanogaster heart development, a lumen forms between apical surfaces of contralateral cardioblasts (CBs). We show that Slit and its receptor Roundabout (Robo) are required at CB apical domains for lumen formation. Mislocalization of Slit outside the apical domain causes ectopic lumen formation and the mislocalization of cell junction proteins, E-cadherin (E-Cad) and Enabled, without disrupting overall CB cell polarity. Ectopic lumen formation is suppressed in robo mutants, which indicates robo's requirement for this process. Genetic evidence suggests that Robo and Shotgun (Shg)/E-Cad function together in modulating CB adhesion. robo and shg/E-Cad transheterozygotes have lumen defects. In robo loss-of-function or shg/E-Cad gain-of-function embryos, lumen formation is blocked because of inappropriate CB adhesion and an accumulation of E-Cad at the apical membrane. In contrast, shg/E-Cad loss-of-function or robo gain-of-function blocks lumen formation due to a loss of CB adhesion. Our data show that Slit and Robo pathways function in lumen formation as a repulsive signal to antagonize E-Cad-mediated cell adhesion.

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Summary of heart tube lumen formation in wild-type and mutant embryos. Lumen formation in the D. melanogaster heart depends on specific sites of adhesion and de-adhesion between contralateral CBs. We propose that Slit/Robo signaling is required to maintain de-adhesion along the central apical domain of contralateral CBs. In wild-type embryos, CBs are specifically adhered at dorsal and ventral attachment points where E-Cad accumulates. Between these points, the apical membranes of the CBs are repelled from each other, allowing for the formation of a lumen. In robo LOF or shg/E-Cad GOF embryos, contralateral CBs remain adhered to each other, resulting in a block in lumen formation and an apical accumulation of E-Cad.
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fig5: Summary of heart tube lumen formation in wild-type and mutant embryos. Lumen formation in the D. melanogaster heart depends on specific sites of adhesion and de-adhesion between contralateral CBs. We propose that Slit/Robo signaling is required to maintain de-adhesion along the central apical domain of contralateral CBs. In wild-type embryos, CBs are specifically adhered at dorsal and ventral attachment points where E-Cad accumulates. Between these points, the apical membranes of the CBs are repelled from each other, allowing for the formation of a lumen. In robo LOF or shg/E-Cad GOF embryos, contralateral CBs remain adhered to each other, resulting in a block in lumen formation and an apical accumulation of E-Cad.

Mentions: For D. melanogaster heart lumen formation, CBs must be attached at specific sites but also have apical surfaces that are not adhered (Fig. 5). Our studies show that Slit/Robo signaling is required for lumen formation between CBs by inhibiting E-Cad–mediated cell adhesion. Slit and Robo localize to the apical surface of the CBs facing the lumen. In robo LOF or shg/E-Cad GOF embryos, contralateral CBs are tightly bound, resulting in a failure of lumen formation (Fig. 5). However, when Slit is ectopically expressed on basal and lateral surfaces, we observe an inappropriate loss of cell adhesion in these regions, resulting in the formation of ectopic lumens (Fig. 2, F and H). These phenotypes are accompanied by mislocalization of the cell junction markers E-Cad, Ena (Fig. 4), and Baz (Fig. S1) to these sites. How might Slit and Robo regulate cell adhesion and lumen formation? Much of our understanding of Slit and Robo signaling has emerged from studies of how Robo's activation by Slit regulates downstream cytoskeletal changes during axon guidance (Dickson and Gilestro, 2006). Two recent in vitro studies support our findings that, in addition to their known role in cell migration, Robo proteins also function to either positively or negatively regulate cell adhesion (Rhee et al., 2002; Kaur et al., 2006). Here, we provide in vivo genetic evidence that Slit and Robo negatively regulate cell adhesion during lumen formation. The next step will be to identify the downstream mechanisms by which Slit and Robo signaling negatively regulate E-Cad–mediated cell adhesion.


Repulsion by Slit and Roundabout prevents Shotgun/E-cadherin-mediated cell adhesion during Drosophila heart tube lumen formation.

Santiago-Martínez E, Soplop NH, Patel R, Kramer SG - J. Cell Biol. (2008)

Summary of heart tube lumen formation in wild-type and mutant embryos. Lumen formation in the D. melanogaster heart depends on specific sites of adhesion and de-adhesion between contralateral CBs. We propose that Slit/Robo signaling is required to maintain de-adhesion along the central apical domain of contralateral CBs. In wild-type embryos, CBs are specifically adhered at dorsal and ventral attachment points where E-Cad accumulates. Between these points, the apical membranes of the CBs are repelled from each other, allowing for the formation of a lumen. In robo LOF or shg/E-Cad GOF embryos, contralateral CBs remain adhered to each other, resulting in a block in lumen formation and an apical accumulation of E-Cad.
© Copyright Policy
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC2483515&req=5

fig5: Summary of heart tube lumen formation in wild-type and mutant embryos. Lumen formation in the D. melanogaster heart depends on specific sites of adhesion and de-adhesion between contralateral CBs. We propose that Slit/Robo signaling is required to maintain de-adhesion along the central apical domain of contralateral CBs. In wild-type embryos, CBs are specifically adhered at dorsal and ventral attachment points where E-Cad accumulates. Between these points, the apical membranes of the CBs are repelled from each other, allowing for the formation of a lumen. In robo LOF or shg/E-Cad GOF embryos, contralateral CBs remain adhered to each other, resulting in a block in lumen formation and an apical accumulation of E-Cad.
Mentions: For D. melanogaster heart lumen formation, CBs must be attached at specific sites but also have apical surfaces that are not adhered (Fig. 5). Our studies show that Slit/Robo signaling is required for lumen formation between CBs by inhibiting E-Cad–mediated cell adhesion. Slit and Robo localize to the apical surface of the CBs facing the lumen. In robo LOF or shg/E-Cad GOF embryos, contralateral CBs are tightly bound, resulting in a failure of lumen formation (Fig. 5). However, when Slit is ectopically expressed on basal and lateral surfaces, we observe an inappropriate loss of cell adhesion in these regions, resulting in the formation of ectopic lumens (Fig. 2, F and H). These phenotypes are accompanied by mislocalization of the cell junction markers E-Cad, Ena (Fig. 4), and Baz (Fig. S1) to these sites. How might Slit and Robo regulate cell adhesion and lumen formation? Much of our understanding of Slit and Robo signaling has emerged from studies of how Robo's activation by Slit regulates downstream cytoskeletal changes during axon guidance (Dickson and Gilestro, 2006). Two recent in vitro studies support our findings that, in addition to their known role in cell migration, Robo proteins also function to either positively or negatively regulate cell adhesion (Rhee et al., 2002; Kaur et al., 2006). Here, we provide in vivo genetic evidence that Slit and Robo negatively regulate cell adhesion during lumen formation. The next step will be to identify the downstream mechanisms by which Slit and Robo signaling negatively regulate E-Cad–mediated cell adhesion.

Bottom Line: Genetic evidence suggests that Robo and Shotgun (Shg)/E-Cad function together in modulating CB adhesion. robo and shg/E-Cad transheterozygotes have lumen defects.In robo loss-of-function or shg/E-Cad gain-of-function embryos, lumen formation is blocked because of inappropriate CB adhesion and an accumulation of E-Cad at the apical membrane.In contrast, shg/E-Cad loss-of-function or robo gain-of-function blocks lumen formation due to a loss of CB adhesion.

View Article: PubMed Central - PubMed

Affiliation: Department of Pathology and Laboratory Medicine, Robert Wood Johnson Medical School, University of Medicine and Dentistry of New Jersey, Piscataway, NJ 08854, USA.

ABSTRACT
During Drosophila melanogaster heart development, a lumen forms between apical surfaces of contralateral cardioblasts (CBs). We show that Slit and its receptor Roundabout (Robo) are required at CB apical domains for lumen formation. Mislocalization of Slit outside the apical domain causes ectopic lumen formation and the mislocalization of cell junction proteins, E-cadherin (E-Cad) and Enabled, without disrupting overall CB cell polarity. Ectopic lumen formation is suppressed in robo mutants, which indicates robo's requirement for this process. Genetic evidence suggests that Robo and Shotgun (Shg)/E-Cad function together in modulating CB adhesion. robo and shg/E-Cad transheterozygotes have lumen defects. In robo loss-of-function or shg/E-Cad gain-of-function embryos, lumen formation is blocked because of inappropriate CB adhesion and an accumulation of E-Cad at the apical membrane. In contrast, shg/E-Cad loss-of-function or robo gain-of-function blocks lumen formation due to a loss of CB adhesion. Our data show that Slit and Robo pathways function in lumen formation as a repulsive signal to antagonize E-Cad-mediated cell adhesion.

Show MeSH
Related in: MedlinePlus