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Systemic bud induction and retinoic acid signaling underlie whole body regeneration in the urochordate Botrylloides leachi.

Rinkevich Y, Paz G, Rinkevich B, Reshef R - PLoS Biol. (2007)

Bottom Line: We found that retinoic acid (RA) regulates diverse developmental aspects in WBR.The administration of all-trans RA to blood vessel fragments resulted in doubly accelerated regeneration and multibud formation, leading to restored colonies with multiple zooids.This unique Botrylloides WBR process could serve as a new in vivo model system for regeneration, suggesting that RA signaling may have had ancestral roles in body restoration events.

View Article: PubMed Central - PubMed

Affiliation: Faculty of Biology, Technion-Israel Institute of Technology, Haifa, Israel.

ABSTRACT
Regeneration in adult chordates is confined to a few model cases and terminates in restoration of restricted tissues and organs. Here, we study the unique phenomenon of whole body regeneration (WBR) in the colonial urochordate Botrylloides leachi in which an entire adult zooid is restored from a miniscule blood vessel fragment. In contrast to all other documented cases, regeneration is induced systemically in blood vessels. Multiple buds appear simultaneously in newly established regeneration niches within vasculature fragments, stemming from composites of pluripotent blood cells and terminating in one functional zooid. We found that retinoic acid (RA) regulates diverse developmental aspects in WBR. The homologue of the RA receptor and a retinaldehyde dehydrogenase-related gene were expressed specifically in blood cells within regeneration niches and throughout bud development. The addition of RA inhibitors as well as RNA interference knockdown experiments resulted in WBR arrest and bud malformations. The administration of all-trans RA to blood vessel fragments resulted in doubly accelerated regeneration and multibud formation, leading to restored colonies with multiple zooids. The Botrylloides system differs from known regeneration model systems by several fundamental criteria, including epimorphosis without the formation of blastema and the induction of a "multifocal regeneration niche" system. This is also to our knowledge the first documented case of WBR from circulating blood cells that restores not only the soma, but also the germ line. This unique Botrylloides WBR process could serve as a new in vivo model system for regeneration, suggesting that RA signaling may have had ancestral roles in body restoration events.

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All-trans RA Leads to Accelerated Regeneration and Multibud FormationRA-treated regenerating fragments that were sectioned at different final stages of the regeneration process show a remarkable accelerated regeneration. By days 6–7 postseparation, most of the regenerating buds reached these final stages (compared to 10–14 days in control experiments), exhibiting complete organogenesis. The regenerating zooids manifested fully differentiated organ systems such as stigmata with cilia (A, arrows). Different from normal blastogenic buds or control experiments, blood cells extensively colonized these regenerating buds between atrial folds and throughout internal cavities (B, arrows). The acceleration of the process was also exemplified in the subsequent blastogenesis. At day 7, the regenerating bud progressed to the stage where secondary buds were formed on the primary palleal buds (C, arrow and arrowhead, respectively). In marked contrast to control regenerating fragments, where only a single bud was developed, numerous buds at different regeneration niches simultaneously reached the final stages of organogenesis (2–5 functional zooids) (D, arrows, compare to Figure 2G). Scale bar represents 100 μm.
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pbio-0050071-g007: All-trans RA Leads to Accelerated Regeneration and Multibud FormationRA-treated regenerating fragments that were sectioned at different final stages of the regeneration process show a remarkable accelerated regeneration. By days 6–7 postseparation, most of the regenerating buds reached these final stages (compared to 10–14 days in control experiments), exhibiting complete organogenesis. The regenerating zooids manifested fully differentiated organ systems such as stigmata with cilia (A, arrows). Different from normal blastogenic buds or control experiments, blood cells extensively colonized these regenerating buds between atrial folds and throughout internal cavities (B, arrows). The acceleration of the process was also exemplified in the subsequent blastogenesis. At day 7, the regenerating bud progressed to the stage where secondary buds were formed on the primary palleal buds (C, arrow and arrowhead, respectively). In marked contrast to control regenerating fragments, where only a single bud was developed, numerous buds at different regeneration niches simultaneously reached the final stages of organogenesis (2–5 functional zooids) (D, arrows, compare to Figure 2G). Scale bar represents 100 μm.

Mentions: On day 6, all RA-treated fragments were sacrificed for histological examinations. Results showed further accelerated regeneration throughout the entire vasculature. Haemocytes aggregated systemically along blood vessels and not only near the vessel epithelium. Buds were present in many blood vessels and revealed extremely high variation in developmental states, from cell aggregates to well-developed zooids. The regenerating zooids manifested fully differentiated organ systems (Figure 7; Table 1), including stigmata with cilia (Figure 7A, arrows), a completed digestive system, and a pair of contracting siphons carrying normally developed tentacles. Different from normal blastogenic buds, blood cells colonized extensively these regenerating buds between atrial folds and throughout internal cavities (Figure 7B, arrows). The consecutive generation of palleal buds, at progressive developmental stages, had already started to grow from both sides of the regenerating zooids. In one case, the regenerating bud progressed to the stage where secondary buds formed on the primary palleal buds (Figure 7C, arrow and arrowhead, respectively). In marked contrast to control regenerating fragments where only a single bud developed, numerous buds at different regeneration niches had simultaneously reached the final stages of organogenesis (2–5 functional zooids) (Figure 7D, arrows), exhibiting fully differentiated organ systems that reproduced asexually through palleal budding. At high concentrations of RA (50 μM), buds developed abnormally with an enlarged digestive tract, pyloric gland, and swelling of the atrial folds (unpublished data).


Systemic bud induction and retinoic acid signaling underlie whole body regeneration in the urochordate Botrylloides leachi.

Rinkevich Y, Paz G, Rinkevich B, Reshef R - PLoS Biol. (2007)

All-trans RA Leads to Accelerated Regeneration and Multibud FormationRA-treated regenerating fragments that were sectioned at different final stages of the regeneration process show a remarkable accelerated regeneration. By days 6–7 postseparation, most of the regenerating buds reached these final stages (compared to 10–14 days in control experiments), exhibiting complete organogenesis. The regenerating zooids manifested fully differentiated organ systems such as stigmata with cilia (A, arrows). Different from normal blastogenic buds or control experiments, blood cells extensively colonized these regenerating buds between atrial folds and throughout internal cavities (B, arrows). The acceleration of the process was also exemplified in the subsequent blastogenesis. At day 7, the regenerating bud progressed to the stage where secondary buds were formed on the primary palleal buds (C, arrow and arrowhead, respectively). In marked contrast to control regenerating fragments, where only a single bud was developed, numerous buds at different regeneration niches simultaneously reached the final stages of organogenesis (2–5 functional zooids) (D, arrows, compare to Figure 2G). Scale bar represents 100 μm.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC1808485&req=5

pbio-0050071-g007: All-trans RA Leads to Accelerated Regeneration and Multibud FormationRA-treated regenerating fragments that were sectioned at different final stages of the regeneration process show a remarkable accelerated regeneration. By days 6–7 postseparation, most of the regenerating buds reached these final stages (compared to 10–14 days in control experiments), exhibiting complete organogenesis. The regenerating zooids manifested fully differentiated organ systems such as stigmata with cilia (A, arrows). Different from normal blastogenic buds or control experiments, blood cells extensively colonized these regenerating buds between atrial folds and throughout internal cavities (B, arrows). The acceleration of the process was also exemplified in the subsequent blastogenesis. At day 7, the regenerating bud progressed to the stage where secondary buds were formed on the primary palleal buds (C, arrow and arrowhead, respectively). In marked contrast to control regenerating fragments, where only a single bud was developed, numerous buds at different regeneration niches simultaneously reached the final stages of organogenesis (2–5 functional zooids) (D, arrows, compare to Figure 2G). Scale bar represents 100 μm.
Mentions: On day 6, all RA-treated fragments were sacrificed for histological examinations. Results showed further accelerated regeneration throughout the entire vasculature. Haemocytes aggregated systemically along blood vessels and not only near the vessel epithelium. Buds were present in many blood vessels and revealed extremely high variation in developmental states, from cell aggregates to well-developed zooids. The regenerating zooids manifested fully differentiated organ systems (Figure 7; Table 1), including stigmata with cilia (Figure 7A, arrows), a completed digestive system, and a pair of contracting siphons carrying normally developed tentacles. Different from normal blastogenic buds, blood cells colonized extensively these regenerating buds between atrial folds and throughout internal cavities (Figure 7B, arrows). The consecutive generation of palleal buds, at progressive developmental stages, had already started to grow from both sides of the regenerating zooids. In one case, the regenerating bud progressed to the stage where secondary buds formed on the primary palleal buds (Figure 7C, arrow and arrowhead, respectively). In marked contrast to control regenerating fragments where only a single bud developed, numerous buds at different regeneration niches had simultaneously reached the final stages of organogenesis (2–5 functional zooids) (Figure 7D, arrows), exhibiting fully differentiated organ systems that reproduced asexually through palleal budding. At high concentrations of RA (50 μM), buds developed abnormally with an enlarged digestive tract, pyloric gland, and swelling of the atrial folds (unpublished data).

Bottom Line: We found that retinoic acid (RA) regulates diverse developmental aspects in WBR.The administration of all-trans RA to blood vessel fragments resulted in doubly accelerated regeneration and multibud formation, leading to restored colonies with multiple zooids.This unique Botrylloides WBR process could serve as a new in vivo model system for regeneration, suggesting that RA signaling may have had ancestral roles in body restoration events.

View Article: PubMed Central - PubMed

Affiliation: Faculty of Biology, Technion-Israel Institute of Technology, Haifa, Israel.

ABSTRACT
Regeneration in adult chordates is confined to a few model cases and terminates in restoration of restricted tissues and organs. Here, we study the unique phenomenon of whole body regeneration (WBR) in the colonial urochordate Botrylloides leachi in which an entire adult zooid is restored from a miniscule blood vessel fragment. In contrast to all other documented cases, regeneration is induced systemically in blood vessels. Multiple buds appear simultaneously in newly established regeneration niches within vasculature fragments, stemming from composites of pluripotent blood cells and terminating in one functional zooid. We found that retinoic acid (RA) regulates diverse developmental aspects in WBR. The homologue of the RA receptor and a retinaldehyde dehydrogenase-related gene were expressed specifically in blood cells within regeneration niches and throughout bud development. The addition of RA inhibitors as well as RNA interference knockdown experiments resulted in WBR arrest and bud malformations. The administration of all-trans RA to blood vessel fragments resulted in doubly accelerated regeneration and multibud formation, leading to restored colonies with multiple zooids. The Botrylloides system differs from known regeneration model systems by several fundamental criteria, including epimorphosis without the formation of blastema and the induction of a "multifocal regeneration niche" system. This is also to our knowledge the first documented case of WBR from circulating blood cells that restores not only the soma, but also the germ line. This unique Botrylloides WBR process could serve as a new in vivo model system for regeneration, suggesting that RA signaling may have had ancestral roles in body restoration events.

Show MeSH
Related in: MedlinePlus