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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

Analyses of endothelial cell nuclei during pruning.Analyses of the nuclei number and behavior in double transgenic embryos Tg(BAC:kdrl:mKate2-CAAX)UBS16; Tg(kdrl:EGFPnls) UBS1. Nuclei were marked and quantified within a region of interest around the pruning segments (nuclei are encircled in dark blue, and green arrows point to a regressing branch). New nuclei derived from cell divisions happening between the time points are marked with light-blue circles and connected to the mother nuclei with a blue line (B–D). Nuclei that leave the field of view in the next time point are marked with asterisks (B–D). The nuclei changed positions in a way corresponding to cell rearrangements. The number of nuclei increased over time because of cell divisions. Nuclei numbers are indicated in the bottom right corner: in dark blue is the number of counted nuclei, in light blue the number of new nuclei (B–D), and in white the nuclei in view. No apoptotic nuclei were observed. See also S6 Movie and S2 Table. Scale bar: 20 μm.
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pbio.1002126.g002: Analyses of endothelial cell nuclei during pruning.Analyses of the nuclei number and behavior in double transgenic embryos Tg(BAC:kdrl:mKate2-CAAX)UBS16; Tg(kdrl:EGFPnls) UBS1. Nuclei were marked and quantified within a region of interest around the pruning segments (nuclei are encircled in dark blue, and green arrows point to a regressing branch). New nuclei derived from cell divisions happening between the time points are marked with light-blue circles and connected to the mother nuclei with a blue line (B–D). Nuclei that leave the field of view in the next time point are marked with asterisks (B–D). The nuclei changed positions in a way corresponding to cell rearrangements. The number of nuclei increased over time because of cell divisions. Nuclei numbers are indicated in the bottom right corner: in dark blue is the number of counted nuclei, in light blue the number of new nuclei (B–D), and in white the nuclei in view. No apoptotic nuclei were observed. See also S6 Movie and S2 Table. Scale bar: 20 μm.

Mentions: Previous reports suggest that in certain cases pruning is accompanied by endothelial cell apoptosis [12,20]. We used a transgenic line labeling cell nuclei to verify whether apoptotic cells are present during the SIV plexus remodeling. In our time-lapse movies (S6 Movie, n = 10), we did not observe dying cells near the pruning vessels, and we noted an increase in nuclei number in analyzed pruning regions—a result of observed cell divisions (Fig 2 and S2 Table). The nuclei movements suggested that cell rearrangements, rather than apoptosis, account for vessel regression. The nuclei moved away from the pruning segments and incorporated into the remaining major SIV branches (Fig 2 and S6 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)

Analyses of endothelial cell nuclei during pruning.Analyses of the nuclei number and behavior in double transgenic embryos Tg(BAC:kdrl:mKate2-CAAX)UBS16; Tg(kdrl:EGFPnls) UBS1. Nuclei were marked and quantified within a region of interest around the pruning segments (nuclei are encircled in dark blue, and green arrows point to a regressing branch). New nuclei derived from cell divisions happening between the time points are marked with light-blue circles and connected to the mother nuclei with a blue line (B–D). Nuclei that leave the field of view in the next time point are marked with asterisks (B–D). The nuclei changed positions in a way corresponding to cell rearrangements. The number of nuclei increased over time because of cell divisions. Nuclei numbers are indicated in the bottom right corner: in dark blue is the number of counted nuclei, in light blue the number of new nuclei (B–D), and in white the nuclei in view. No apoptotic nuclei were observed. See also S6 Movie and S2 Table. Scale bar: 20 μm.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4401649&req=5

pbio.1002126.g002: Analyses of endothelial cell nuclei during pruning.Analyses of the nuclei number and behavior in double transgenic embryos Tg(BAC:kdrl:mKate2-CAAX)UBS16; Tg(kdrl:EGFPnls) UBS1. Nuclei were marked and quantified within a region of interest around the pruning segments (nuclei are encircled in dark blue, and green arrows point to a regressing branch). New nuclei derived from cell divisions happening between the time points are marked with light-blue circles and connected to the mother nuclei with a blue line (B–D). Nuclei that leave the field of view in the next time point are marked with asterisks (B–D). The nuclei changed positions in a way corresponding to cell rearrangements. The number of nuclei increased over time because of cell divisions. Nuclei numbers are indicated in the bottom right corner: in dark blue is the number of counted nuclei, in light blue the number of new nuclei (B–D), and in white the nuclei in view. No apoptotic nuclei were observed. See also S6 Movie and S2 Table. Scale bar: 20 μm.
Mentions: Previous reports suggest that in certain cases pruning is accompanied by endothelial cell apoptosis [12,20]. We used a transgenic line labeling cell nuclei to verify whether apoptotic cells are present during the SIV plexus remodeling. In our time-lapse movies (S6 Movie, n = 10), we did not observe dying cells near the pruning vessels, and we noted an increase in nuclei number in analyzed pruning regions—a result of observed cell divisions (Fig 2 and S2 Table). The nuclei movements suggested that cell rearrangements, rather than apoptosis, account for vessel regression. The nuclei moved away from the pruning segments and incorporated into the remaining major SIV branches (Fig 2 and S6 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