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Transdifferentiation is a driving force of regeneration in Halisarca dujardini (Demospongiae, Porifera).

Borisenko IE, Adamska M, Tokina DB, Ereskovsky AV - PeerJ (2015)

Bottom Line: Epithelial cells from damaged and adjacent intact choanocyte chambers and aquiferous canals assume mesenchymal phenotype and migrate into the mesohyl.After the blastema is formed, MET becomes the principal mechanism of regeneration.Further studies will be needed to uncover the molecular mechanisms governing regeneration in sponges.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Embryology, Faculty of Biology, Saint-Petersburg State University , Saint-Petersburg , Russia.

ABSTRACT
The ability to regenerate is widespread in the animal kingdom, but the regenerative capacities and mechanisms vary widely. To understand the evolutionary history of the diverse regeneration mechanisms, the regeneration processes must be studied in early-evolved metazoans in addition to the traditional bilaterian and cnidarian models. For this purpose, we have combined several microscopy techniques to study mechanisms of regeneration in the demosponge Halisarca dujardini. The objectives of this work are to detect the cells and morphogenetic processes involved in Halisarca regeneration. We show that in Halisarca there are three main sources of the new exopinacoderm during regeneration: choanocytes, archaeocytes and (rarely) endopinacocytes. Here we show that epithelial-to-mesenchymal transition (EMT) and mesenchymal-to-epithelial transition (MET) occur during Halisarca regeneration. EMT is the principal mechanism during the first stages of regeneration, soon after the injury. Epithelial cells from damaged and adjacent intact choanocyte chambers and aquiferous canals assume mesenchymal phenotype and migrate into the mesohyl. Together with archaeocytes, these cells form an undifferentiated cell mass beneath of wound, which we refer to as a blastema. After the blastema is formed, MET becomes the principal mechanism of regeneration. Altogether, we demonstrate that regeneration in demosponges involves a variety of processes utilized during regeneration in other animals (e.g., cell migration, dedifferentiation, blastema formation) and points to the particular importance of transdifferentiation in this process. Further studies will be needed to uncover the molecular mechanisms governing regeneration in sponges.

No MeSH data available.


Related in: MedlinePlus

Halisarca dujardini 6 h after injury.(A) SEM of a wound surface (show with dotted line) with debris (de) and marginal zone, surrounding a wound with dense ECM of the cortex and the exopinacocytes. (B) SEM of intact exopinacoderm, marginal zone and the wound (show with dotted line), covered with debris. (C) Semi thin section of wounded ectosome (1) and adjacent area of choanosome (2). (D) TEM of external part of the wound with cell debris and dense ECM. (E) TEM of dedifferentiating choanocyte in the wound area. (F) TEM of amoebocyte of mesohyl, filled with phagosomes. (G) Endopinacocyte from the wound area filled with big phagosomes. Scale bars: A, B—30 µm; C—25 µm; D–G—2 µm. de, debris; ECM, extra cellular matrix; iex, intact exopinacoderm; mv, microvilli; mz, marginal zone; n, nucleus, pd, pseudopodia; ph, phagosome.
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fig-3: Halisarca dujardini 6 h after injury.(A) SEM of a wound surface (show with dotted line) with debris (de) and marginal zone, surrounding a wound with dense ECM of the cortex and the exopinacocytes. (B) SEM of intact exopinacoderm, marginal zone and the wound (show with dotted line), covered with debris. (C) Semi thin section of wounded ectosome (1) and adjacent area of choanosome (2). (D) TEM of external part of the wound with cell debris and dense ECM. (E) TEM of dedifferentiating choanocyte in the wound area. (F) TEM of amoebocyte of mesohyl, filled with phagosomes. (G) Endopinacocyte from the wound area filled with big phagosomes. Scale bars: A, B—30 µm; C—25 µm; D–G—2 µm. de, debris; ECM, extra cellular matrix; iex, intact exopinacoderm; mv, microvilli; mz, marginal zone; n, nucleus, pd, pseudopodia; ph, phagosome.

Mentions: Sections of ectosome together with the directly adjacent choanosome were surgically removed at the beginning of the experiment (Fig. 2). Immediately after the injury, the wound surface retracts, leaving the surface of the intact ectosome protruding around the edges of the wound (Figs. 3A and 3B). The ectosome and the upper areas of choanosome are destroyed (Fig. 3C). However, the structure of the aquiferous system in the deeper zone of choanosome is preserved. The wound surface is covered with exudate and cell debris. A number of amoeboid cells can be identified among the extracellular matrix fibers (ECM) (Figs. 3A–3D). Choanocyte chambers and aquiferous canals in the damaged zone disintegrate: cells of these structures lose contacts with adjacent cells and change their shape from trapeziform (choanocytes) and flat (endopinacocytes) to spherical or amoeboid (Figs. 3E–3G). These changes mark the beginning of dedifferentiation (followed by transdifferentiation, see next section), which is accompanied by migration of the cells into the mesohyl. The de- and trans-differentiating cells can be tracked thanks to preservation of their characteristic organelles. The natural label of dedifferentiated choanocytes is the flagellar apparatus (basal body and accessory centriole situated next to the nucleus), which remains in the cell. The collar of microvilli is reduced and disappears, and the flagellum resorbs (Fig. 3E), although some dedifferentiated choanocytes keep their flagella up to the last stage of transdifferentiation into an exopinacocyte (see: Fig. 9H). Endopinacocytes, which are flat in their intact state, assume spherical to amoeboid shapes and can be identified by their small anucleolated nuclei.


Transdifferentiation is a driving force of regeneration in Halisarca dujardini (Demospongiae, Porifera).

Borisenko IE, Adamska M, Tokina DB, Ereskovsky AV - PeerJ (2015)

Halisarca dujardini 6 h after injury.(A) SEM of a wound surface (show with dotted line) with debris (de) and marginal zone, surrounding a wound with dense ECM of the cortex and the exopinacocytes. (B) SEM of intact exopinacoderm, marginal zone and the wound (show with dotted line), covered with debris. (C) Semi thin section of wounded ectosome (1) and adjacent area of choanosome (2). (D) TEM of external part of the wound with cell debris and dense ECM. (E) TEM of dedifferentiating choanocyte in the wound area. (F) TEM of amoebocyte of mesohyl, filled with phagosomes. (G) Endopinacocyte from the wound area filled with big phagosomes. Scale bars: A, B—30 µm; C—25 µm; D–G—2 µm. de, debris; ECM, extra cellular matrix; iex, intact exopinacoderm; mv, microvilli; mz, marginal zone; n, nucleus, pd, pseudopodia; ph, phagosome.
© Copyright Policy - open-access
Related In: Results  -  Collection

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Show All Figures
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fig-3: Halisarca dujardini 6 h after injury.(A) SEM of a wound surface (show with dotted line) with debris (de) and marginal zone, surrounding a wound with dense ECM of the cortex and the exopinacocytes. (B) SEM of intact exopinacoderm, marginal zone and the wound (show with dotted line), covered with debris. (C) Semi thin section of wounded ectosome (1) and adjacent area of choanosome (2). (D) TEM of external part of the wound with cell debris and dense ECM. (E) TEM of dedifferentiating choanocyte in the wound area. (F) TEM of amoebocyte of mesohyl, filled with phagosomes. (G) Endopinacocyte from the wound area filled with big phagosomes. Scale bars: A, B—30 µm; C—25 µm; D–G—2 µm. de, debris; ECM, extra cellular matrix; iex, intact exopinacoderm; mv, microvilli; mz, marginal zone; n, nucleus, pd, pseudopodia; ph, phagosome.
Mentions: Sections of ectosome together with the directly adjacent choanosome were surgically removed at the beginning of the experiment (Fig. 2). Immediately after the injury, the wound surface retracts, leaving the surface of the intact ectosome protruding around the edges of the wound (Figs. 3A and 3B). The ectosome and the upper areas of choanosome are destroyed (Fig. 3C). However, the structure of the aquiferous system in the deeper zone of choanosome is preserved. The wound surface is covered with exudate and cell debris. A number of amoeboid cells can be identified among the extracellular matrix fibers (ECM) (Figs. 3A–3D). Choanocyte chambers and aquiferous canals in the damaged zone disintegrate: cells of these structures lose contacts with adjacent cells and change their shape from trapeziform (choanocytes) and flat (endopinacocytes) to spherical or amoeboid (Figs. 3E–3G). These changes mark the beginning of dedifferentiation (followed by transdifferentiation, see next section), which is accompanied by migration of the cells into the mesohyl. The de- and trans-differentiating cells can be tracked thanks to preservation of their characteristic organelles. The natural label of dedifferentiated choanocytes is the flagellar apparatus (basal body and accessory centriole situated next to the nucleus), which remains in the cell. The collar of microvilli is reduced and disappears, and the flagellum resorbs (Fig. 3E), although some dedifferentiated choanocytes keep their flagella up to the last stage of transdifferentiation into an exopinacocyte (see: Fig. 9H). Endopinacocytes, which are flat in their intact state, assume spherical to amoeboid shapes and can be identified by their small anucleolated nuclei.

Bottom Line: Epithelial cells from damaged and adjacent intact choanocyte chambers and aquiferous canals assume mesenchymal phenotype and migrate into the mesohyl.After the blastema is formed, MET becomes the principal mechanism of regeneration.Further studies will be needed to uncover the molecular mechanisms governing regeneration in sponges.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Embryology, Faculty of Biology, Saint-Petersburg State University , Saint-Petersburg , Russia.

ABSTRACT
The ability to regenerate is widespread in the animal kingdom, but the regenerative capacities and mechanisms vary widely. To understand the evolutionary history of the diverse regeneration mechanisms, the regeneration processes must be studied in early-evolved metazoans in addition to the traditional bilaterian and cnidarian models. For this purpose, we have combined several microscopy techniques to study mechanisms of regeneration in the demosponge Halisarca dujardini. The objectives of this work are to detect the cells and morphogenetic processes involved in Halisarca regeneration. We show that in Halisarca there are three main sources of the new exopinacoderm during regeneration: choanocytes, archaeocytes and (rarely) endopinacocytes. Here we show that epithelial-to-mesenchymal transition (EMT) and mesenchymal-to-epithelial transition (MET) occur during Halisarca regeneration. EMT is the principal mechanism during the first stages of regeneration, soon after the injury. Epithelial cells from damaged and adjacent intact choanocyte chambers and aquiferous canals assume mesenchymal phenotype and migrate into the mesohyl. Together with archaeocytes, these cells form an undifferentiated cell mass beneath of wound, which we refer to as a blastema. After the blastema is formed, MET becomes the principal mechanism of regeneration. Altogether, we demonstrate that regeneration in demosponges involves a variety of processes utilized during regeneration in other animals (e.g., cell migration, dedifferentiation, blastema formation) and points to the particular importance of transdifferentiation in this process. Further studies will be needed to uncover the molecular mechanisms governing regeneration in sponges.

No MeSH data available.


Related in: MedlinePlus