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Endothelial cell self-fusion during vascular pruning.

Lenard A, Daetwyler S, Betz C, Ellertsdottir E, Belting HG, Huisken J, Affolter M - PLoS Biol. (2015)

Bottom Line: Because of the lack of an in vivo system suitable for high-resolution live imaging, the dynamics of the pruning process have not been described in detail.In pruning segments, endothelial cells first migrate toward opposing sides where they join the parental vascular branches, thus remodeling the multicellular segment into a unicellular connection.Often, the lumen is maintained throughout this process, and transient unicellular tubes form through cell self-fusion.

View Article: PubMed Central - PubMed

Affiliation: Biozentrum der Universität Basel, Basel, Switzerland.

ABSTRACT
During embryonic development, vascular networks remodel to meet the increasing demand of growing tissues for oxygen and nutrients. This is achieved by the pruning of redundant blood vessel segments, which then allows more efficient blood flow patterns. Because of the lack of an in vivo system suitable for high-resolution live imaging, the dynamics of the pruning process have not been described in detail. Here, we present the subintestinal vein (SIV) plexus of the zebrafish embryo as a novel model to study pruning at the cellular level. We show that blood vessel regression is a coordinated process of cell rearrangements involving lumen collapse and cell-cell contact resolution. Interestingly, the cellular rearrangements during pruning resemble endothelial cell behavior during vessel fusion in a reversed order. In pruning segments, endothelial cells first migrate toward opposing sides where they join the parental vascular branches, thus remodeling the multicellular segment into a unicellular connection. Often, the lumen is maintained throughout this process, and transient unicellular tubes form through cell self-fusion. In a second step, the unicellular connection is resolved unilaterally, and the pruning cell rejoins the opposing branch. Thus, we show for the first time that various cellular activities are coordinated to achieve blood vessel pruning and define two different morphogenetic pathways, which are selected by the flow environment.

No MeSH data available.


Related in: MedlinePlus

Dynamic of lumen collapse in a unicellular tube.(A) Stills from a time-lapse movie illustrating lumen collapse in a unicellular tube in a transgenic embryo Tg(fliep:GFF)ubs3,(UAS:mRFP), (5xUAS:cdh5-EGFP)ubs12. A single lumenized “last link” cell connects two major branches (1). The white/black arrow marks lumen length. The asterisk marks the nucleus; the red arrow points to the narrowest lumen part (next to the nucleus). The lumen splits first next to the nucleus (2, red arrow), forming two distinct luminal compartments within the cell (2, white arrows) that are separated by a nonlumenized part (grey dotted line). The nonlumenized part increases in length as the lower luminal compartment collapses (3). The cell body (nucleus, asterisk) moves towards the upper major branch. The last cell extension (gray line) contacts the lower major branch with a spot-like junction (4, arrow). (B) Stills from a time-lapse movie showing lumen collapse in a unicellular tube in a transgenic embryo TgBAC(kdrl:mKate-CAAX)ubs16. Black arrows show continuous lumen, gray dotted lines show nonlumenized unicellular regions, the red arrow shows the point of lumen breakage, and asterisks mark the nucleus, where clearly distinguishable. Lumen breaks at the contact site to the lower major branch, next to the nucleus (1–3). The luminal compartment deflates and inflates again (4–5, arrows). After complete lumen collapse, the last connection is resolved (6–8). See also S14 Movie. (C) Stills from a time-lapse movie showing lumen collapse in higher time resolution. Inflated luminal compartments (1, arrows) are framed by apical membrane (marked by mKate2-CAAX) and separated by a thin bridge of cell body, most likely the nucleus (1, asterisk). The lumen expands and two apical membranes touch (2, arrow) and fuse (3), but the lumen does not completely inflate (4). The lumen breaks again (5–7) and reconnects in a similar fashion (8–11) within a short time. See also S15 Movie. (D) A schematic representing luminal instability, based on still pictures in C. The apical membrane is black, the cell body is dark gray, and the lumen is light gray.
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pbio.1002126.g005: Dynamic of lumen collapse in a unicellular tube.(A) Stills from a time-lapse movie illustrating lumen collapse in a unicellular tube in a transgenic embryo Tg(fliep:GFF)ubs3,(UAS:mRFP), (5xUAS:cdh5-EGFP)ubs12. A single lumenized “last link” cell connects two major branches (1). The white/black arrow marks lumen length. The asterisk marks the nucleus; the red arrow points to the narrowest lumen part (next to the nucleus). The lumen splits first next to the nucleus (2, red arrow), forming two distinct luminal compartments within the cell (2, white arrows) that are separated by a nonlumenized part (grey dotted line). The nonlumenized part increases in length as the lower luminal compartment collapses (3). The cell body (nucleus, asterisk) moves towards the upper major branch. The last cell extension (gray line) contacts the lower major branch with a spot-like junction (4, arrow). (B) Stills from a time-lapse movie showing lumen collapse in a unicellular tube in a transgenic embryo TgBAC(kdrl:mKate-CAAX)ubs16. Black arrows show continuous lumen, gray dotted lines show nonlumenized unicellular regions, the red arrow shows the point of lumen breakage, and asterisks mark the nucleus, where clearly distinguishable. Lumen breaks at the contact site to the lower major branch, next to the nucleus (1–3). The luminal compartment deflates and inflates again (4–5, arrows). After complete lumen collapse, the last connection is resolved (6–8). See also S14 Movie. (C) Stills from a time-lapse movie showing lumen collapse in higher time resolution. Inflated luminal compartments (1, arrows) are framed by apical membrane (marked by mKate2-CAAX) and separated by a thin bridge of cell body, most likely the nucleus (1, asterisk). The lumen expands and two apical membranes touch (2, arrow) and fuse (3), but the lumen does not completely inflate (4). The lumen breaks again (5–7) and reconnects in a similar fashion (8–11) within a short time. See also S15 Movie. (D) A schematic representing luminal instability, based on still pictures in C. The apical membrane is black, the cell body is dark gray, and the lumen is light gray.

Mentions: In type II regression, the vascular lumen collapses in a unicellular context. Here, the continuous apical compartment lining the luminal site of the cell was separated into two compartments when the opposing apical membranes collapsed on each other because of lumen deflation (Fig 5). Interestingly, in many cases the lumen split right next to the nucleus, where the cell body takes up the most space (Fig 5A and Fig 5C1, asterisks), thereby facilitating the separation of luminal compartments (Fig 5B and S14 Movie). Even though in several cases it took up to 12 hours to complete this step of the pruning process, the lumen collapse itself was very fast. When we analyzed luminal membrane using high-resolution time-lapse imaging, we found that the lumen broke and reconnected multiple times before completely separating the two remaining luminal compartments (Fig 5C and Fig 5D and S15 Movie).


Endothelial cell self-fusion during vascular pruning.

Lenard A, Daetwyler S, Betz C, Ellertsdottir E, Belting HG, Huisken J, Affolter M - PLoS Biol. (2015)

Dynamic of lumen collapse in a unicellular tube.(A) Stills from a time-lapse movie illustrating lumen collapse in a unicellular tube in a transgenic embryo Tg(fliep:GFF)ubs3,(UAS:mRFP), (5xUAS:cdh5-EGFP)ubs12. A single lumenized “last link” cell connects two major branches (1). The white/black arrow marks lumen length. The asterisk marks the nucleus; the red arrow points to the narrowest lumen part (next to the nucleus). The lumen splits first next to the nucleus (2, red arrow), forming two distinct luminal compartments within the cell (2, white arrows) that are separated by a nonlumenized part (grey dotted line). The nonlumenized part increases in length as the lower luminal compartment collapses (3). The cell body (nucleus, asterisk) moves towards the upper major branch. The last cell extension (gray line) contacts the lower major branch with a spot-like junction (4, arrow). (B) Stills from a time-lapse movie showing lumen collapse in a unicellular tube in a transgenic embryo TgBAC(kdrl:mKate-CAAX)ubs16. Black arrows show continuous lumen, gray dotted lines show nonlumenized unicellular regions, the red arrow shows the point of lumen breakage, and asterisks mark the nucleus, where clearly distinguishable. Lumen breaks at the contact site to the lower major branch, next to the nucleus (1–3). The luminal compartment deflates and inflates again (4–5, arrows). After complete lumen collapse, the last connection is resolved (6–8). See also S14 Movie. (C) Stills from a time-lapse movie showing lumen collapse in higher time resolution. Inflated luminal compartments (1, arrows) are framed by apical membrane (marked by mKate2-CAAX) and separated by a thin bridge of cell body, most likely the nucleus (1, asterisk). The lumen expands and two apical membranes touch (2, arrow) and fuse (3), but the lumen does not completely inflate (4). The lumen breaks again (5–7) and reconnects in a similar fashion (8–11) within a short time. See also S15 Movie. (D) A schematic representing luminal instability, based on still pictures in C. The apical membrane is black, the cell body is dark gray, and the lumen is light gray.
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Related In: Results  -  Collection

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Show All Figures
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pbio.1002126.g005: Dynamic of lumen collapse in a unicellular tube.(A) Stills from a time-lapse movie illustrating lumen collapse in a unicellular tube in a transgenic embryo Tg(fliep:GFF)ubs3,(UAS:mRFP), (5xUAS:cdh5-EGFP)ubs12. A single lumenized “last link” cell connects two major branches (1). The white/black arrow marks lumen length. The asterisk marks the nucleus; the red arrow points to the narrowest lumen part (next to the nucleus). The lumen splits first next to the nucleus (2, red arrow), forming two distinct luminal compartments within the cell (2, white arrows) that are separated by a nonlumenized part (grey dotted line). The nonlumenized part increases in length as the lower luminal compartment collapses (3). The cell body (nucleus, asterisk) moves towards the upper major branch. The last cell extension (gray line) contacts the lower major branch with a spot-like junction (4, arrow). (B) Stills from a time-lapse movie showing lumen collapse in a unicellular tube in a transgenic embryo TgBAC(kdrl:mKate-CAAX)ubs16. Black arrows show continuous lumen, gray dotted lines show nonlumenized unicellular regions, the red arrow shows the point of lumen breakage, and asterisks mark the nucleus, where clearly distinguishable. Lumen breaks at the contact site to the lower major branch, next to the nucleus (1–3). The luminal compartment deflates and inflates again (4–5, arrows). After complete lumen collapse, the last connection is resolved (6–8). See also S14 Movie. (C) Stills from a time-lapse movie showing lumen collapse in higher time resolution. Inflated luminal compartments (1, arrows) are framed by apical membrane (marked by mKate2-CAAX) and separated by a thin bridge of cell body, most likely the nucleus (1, asterisk). The lumen expands and two apical membranes touch (2, arrow) and fuse (3), but the lumen does not completely inflate (4). The lumen breaks again (5–7) and reconnects in a similar fashion (8–11) within a short time. See also S15 Movie. (D) A schematic representing luminal instability, based on still pictures in C. The apical membrane is black, the cell body is dark gray, and the lumen is light gray.
Mentions: In type II regression, the vascular lumen collapses in a unicellular context. Here, the continuous apical compartment lining the luminal site of the cell was separated into two compartments when the opposing apical membranes collapsed on each other because of lumen deflation (Fig 5). Interestingly, in many cases the lumen split right next to the nucleus, where the cell body takes up the most space (Fig 5A and Fig 5C1, asterisks), thereby facilitating the separation of luminal compartments (Fig 5B and S14 Movie). Even though in several cases it took up to 12 hours to complete this step of the pruning process, the lumen collapse itself was very fast. When we analyzed luminal membrane using high-resolution time-lapse imaging, we found that the lumen broke and reconnected multiple times before completely separating the two remaining luminal compartments (Fig 5C and Fig 5D and S15 Movie).

Bottom Line: Because of the lack of an in vivo system suitable for high-resolution live imaging, the dynamics of the pruning process have not been described in detail.In pruning segments, endothelial cells first migrate toward opposing sides where they join the parental vascular branches, thus remodeling the multicellular segment into a unicellular connection.Often, the lumen is maintained throughout this process, and transient unicellular tubes form through cell self-fusion.

View Article: PubMed Central - PubMed

Affiliation: Biozentrum der Universität Basel, Basel, Switzerland.

ABSTRACT
During embryonic development, vascular networks remodel to meet the increasing demand of growing tissues for oxygen and nutrients. This is achieved by the pruning of redundant blood vessel segments, which then allows more efficient blood flow patterns. Because of the lack of an in vivo system suitable for high-resolution live imaging, the dynamics of the pruning process have not been described in detail. Here, we present the subintestinal vein (SIV) plexus of the zebrafish embryo as a novel model to study pruning at the cellular level. We show that blood vessel regression is a coordinated process of cell rearrangements involving lumen collapse and cell-cell contact resolution. Interestingly, the cellular rearrangements during pruning resemble endothelial cell behavior during vessel fusion in a reversed order. In pruning segments, endothelial cells first migrate toward opposing sides where they join the parental vascular branches, thus remodeling the multicellular segment into a unicellular connection. Often, the lumen is maintained throughout this process, and transient unicellular tubes form through cell self-fusion. In a second step, the unicellular connection is resolved unilaterally, and the pruning cell rejoins the opposing branch. Thus, we show for the first time that various cellular activities are coordinated to achieve blood vessel pruning and define two different morphogenetic pathways, which are selected by the flow environment.

No MeSH data available.


Related in: MedlinePlus