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Embryonic frog epidermis: a model for the study of cell-cell interactions in the development of mucociliary disease.

Dubaissi E, Papalopulu N - Dis Model Mech (2010)

Bottom Line: These cells express high levels of ion channels and transporters; therefore, we suggest that they are analogous to ionocytes found in transporting epithelia such as the mammalian kidney.Depletion of ionocytes by foxi1e knockdown has detrimental effects on the development of multiciliated cells, which show fewer and aberrantly beating cilia.These results reveal a newly identified role for ionocytes and suggest that the frog embryonic skin is a model system that is particularly suited to studying the interactions of different cell types in mucociliary, as well as in secretory and transporting, epithelia.

View Article: PubMed Central - PubMed

Affiliation: Faculty of Life Sciences, University of Manchester, Manchester, UK.

ABSTRACT
Specialised epithelia such as mucociliary, secretory and transporting epithelia line all major organs, including the lung, gut and kidney. Malfunction of these epithelia is associated with many human diseases. The frog embryonic epidermis possesses mucus-secreting and multiciliated cells, and has served as an excellent model system for the biogenesis of cilia. However, ionic regulation is important for the function of all specialised epithelia and it is not clear how this is achieved in the embryonic frog epidermis. Here, we show that a third cell type develops alongside ciliated and mucus-secreting cells in the tadpole skin. These cells express high levels of ion channels and transporters; therefore, we suggest that they are analogous to ionocytes found in transporting epithelia such as the mammalian kidney. We show that frog ionocytes express the transcription factor foxi1e, which is required for the development of these cells. Depletion of ionocytes by foxi1e knockdown has detrimental effects on the development of multiciliated cells, which show fewer and aberrantly beating cilia. These results reveal a newly identified role for ionocytes and suggest that the frog embryonic skin is a model system that is particularly suited to studying the interactions of different cell types in mucociliary, as well as in secretory and transporting, epithelia.

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Ionocytes express the transcription factor foxi1e. (A) Whole-mount in situ hybridisation and cross-sections of stage 14 and stage 25 embryos hybridised with foxi1e probe. foxi1e is expressed in a spotted pattern and the location of the expressing cells changes from the inner to outer layer between the neurula and tailbud stages. Sections are on fluorescent in situ samples with foxi1e in red and DAPI staining in blue. Scale bars: 250 μm (whole mounts); 50 μm (sections). (B) Whole-mount double immunostaining of stage 27 tadpoles with anti-foxi1e, anti-acetylated tubulin and anti-xeel, as indicated. foxi1e-expressing cells (green) are distinct from ciliated (CC) and goblet (GC) cells. Scale bars: 50 μm. (C) Whole-mount in situ hybridisation with foxi1e probe and immunostaining with anti-ca12 and anti-v1a, in the combinations indicated. Upper and lower panels represent the same field of imaging, with upper panels showing the in situ probes and lower panels showing antibody staining overlaying the in situ probes. In the foxi1e/ca12 combination, arrows point to three cells that express foxi1e but not ca12, and arrowhead points to a cell that expresses both. In the foxi1e/v1a combination, complete overlap is detected. In the v1a/ca12 combination, arrows point to three cells that express v1a but not ca12, and arrowhead points to a cell that expresses both. Scale bars: 40 μm.
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f4-0040179: Ionocytes express the transcription factor foxi1e. (A) Whole-mount in situ hybridisation and cross-sections of stage 14 and stage 25 embryos hybridised with foxi1e probe. foxi1e is expressed in a spotted pattern and the location of the expressing cells changes from the inner to outer layer between the neurula and tailbud stages. Sections are on fluorescent in situ samples with foxi1e in red and DAPI staining in blue. Scale bars: 250 μm (whole mounts); 50 μm (sections). (B) Whole-mount double immunostaining of stage 27 tadpoles with anti-foxi1e, anti-acetylated tubulin and anti-xeel, as indicated. foxi1e-expressing cells (green) are distinct from ciliated (CC) and goblet (GC) cells. Scale bars: 50 μm. (C) Whole-mount in situ hybridisation with foxi1e probe and immunostaining with anti-ca12 and anti-v1a, in the combinations indicated. Upper and lower panels represent the same field of imaging, with upper panels showing the in situ probes and lower panels showing antibody staining overlaying the in situ probes. In the foxi1e/ca12 combination, arrows point to three cells that express foxi1e but not ca12, and arrowhead points to a cell that expresses both. In the foxi1e/v1a combination, complete overlap is detected. In the v1a/ca12 combination, arrows point to three cells that express v1a but not ca12, and arrowhead points to a cell that expresses both. Scale bars: 40 μm.

Mentions: To find out whether ionocytes have a role in the development of the epidermis, first we sought to find out how their formation is regulated. We cloned and characterised the transcription factor foxi1e in Xenopus tropicalis, because members of this family have been shown to be important in ionocyte development in zebrafish and other systems. In Xenopus laevis, the closest homologue is foxi1e (also known as xema) (supplementary material Fig. S1). Earlier studies in the frog showed that the expression of foxi1e is controlled by interaction of vegT, bmp and notch signalling, and, in turn, foxi1e is needed to form both neural and epidermal ectoderm (Mir et al., 2008; Mir et al., 2007; Suri et al., 2005). foxi1e was shown to be expressed in scattered cells in the epidermis that were distinct from ciliated cells; however, the expression was not characterised further (Mir et al., 2008; Mir et al., 2007; Suri et al., 2005). In the X. tropicalis tadpole, foxi1e was also found to be expressed in a scattered pattern (Fig. 4A). Cross-section analysis showed that foxi1e-expressing cells intercalate from the inner to the outer layer of the epidermis, suggesting that they are either ciliated cells or ionocytes (Fig. 4A).


Embryonic frog epidermis: a model for the study of cell-cell interactions in the development of mucociliary disease.

Dubaissi E, Papalopulu N - Dis Model Mech (2010)

Ionocytes express the transcription factor foxi1e. (A) Whole-mount in situ hybridisation and cross-sections of stage 14 and stage 25 embryos hybridised with foxi1e probe. foxi1e is expressed in a spotted pattern and the location of the expressing cells changes from the inner to outer layer between the neurula and tailbud stages. Sections are on fluorescent in situ samples with foxi1e in red and DAPI staining in blue. Scale bars: 250 μm (whole mounts); 50 μm (sections). (B) Whole-mount double immunostaining of stage 27 tadpoles with anti-foxi1e, anti-acetylated tubulin and anti-xeel, as indicated. foxi1e-expressing cells (green) are distinct from ciliated (CC) and goblet (GC) cells. Scale bars: 50 μm. (C) Whole-mount in situ hybridisation with foxi1e probe and immunostaining with anti-ca12 and anti-v1a, in the combinations indicated. Upper and lower panels represent the same field of imaging, with upper panels showing the in situ probes and lower panels showing antibody staining overlaying the in situ probes. In the foxi1e/ca12 combination, arrows point to three cells that express foxi1e but not ca12, and arrowhead points to a cell that expresses both. In the foxi1e/v1a combination, complete overlap is detected. In the v1a/ca12 combination, arrows point to three cells that express v1a but not ca12, and arrowhead points to a cell that expresses both. Scale bars: 40 μm.
© Copyright Policy - open-access
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC3046089&req=5

f4-0040179: Ionocytes express the transcription factor foxi1e. (A) Whole-mount in situ hybridisation and cross-sections of stage 14 and stage 25 embryos hybridised with foxi1e probe. foxi1e is expressed in a spotted pattern and the location of the expressing cells changes from the inner to outer layer between the neurula and tailbud stages. Sections are on fluorescent in situ samples with foxi1e in red and DAPI staining in blue. Scale bars: 250 μm (whole mounts); 50 μm (sections). (B) Whole-mount double immunostaining of stage 27 tadpoles with anti-foxi1e, anti-acetylated tubulin and anti-xeel, as indicated. foxi1e-expressing cells (green) are distinct from ciliated (CC) and goblet (GC) cells. Scale bars: 50 μm. (C) Whole-mount in situ hybridisation with foxi1e probe and immunostaining with anti-ca12 and anti-v1a, in the combinations indicated. Upper and lower panels represent the same field of imaging, with upper panels showing the in situ probes and lower panels showing antibody staining overlaying the in situ probes. In the foxi1e/ca12 combination, arrows point to three cells that express foxi1e but not ca12, and arrowhead points to a cell that expresses both. In the foxi1e/v1a combination, complete overlap is detected. In the v1a/ca12 combination, arrows point to three cells that express v1a but not ca12, and arrowhead points to a cell that expresses both. Scale bars: 40 μm.
Mentions: To find out whether ionocytes have a role in the development of the epidermis, first we sought to find out how their formation is regulated. We cloned and characterised the transcription factor foxi1e in Xenopus tropicalis, because members of this family have been shown to be important in ionocyte development in zebrafish and other systems. In Xenopus laevis, the closest homologue is foxi1e (also known as xema) (supplementary material Fig. S1). Earlier studies in the frog showed that the expression of foxi1e is controlled by interaction of vegT, bmp and notch signalling, and, in turn, foxi1e is needed to form both neural and epidermal ectoderm (Mir et al., 2008; Mir et al., 2007; Suri et al., 2005). foxi1e was shown to be expressed in scattered cells in the epidermis that were distinct from ciliated cells; however, the expression was not characterised further (Mir et al., 2008; Mir et al., 2007; Suri et al., 2005). In the X. tropicalis tadpole, foxi1e was also found to be expressed in a scattered pattern (Fig. 4A). Cross-section analysis showed that foxi1e-expressing cells intercalate from the inner to the outer layer of the epidermis, suggesting that they are either ciliated cells or ionocytes (Fig. 4A).

Bottom Line: These cells express high levels of ion channels and transporters; therefore, we suggest that they are analogous to ionocytes found in transporting epithelia such as the mammalian kidney.Depletion of ionocytes by foxi1e knockdown has detrimental effects on the development of multiciliated cells, which show fewer and aberrantly beating cilia.These results reveal a newly identified role for ionocytes and suggest that the frog embryonic skin is a model system that is particularly suited to studying the interactions of different cell types in mucociliary, as well as in secretory and transporting, epithelia.

View Article: PubMed Central - PubMed

Affiliation: Faculty of Life Sciences, University of Manchester, Manchester, UK.

ABSTRACT
Specialised epithelia such as mucociliary, secretory and transporting epithelia line all major organs, including the lung, gut and kidney. Malfunction of these epithelia is associated with many human diseases. The frog embryonic epidermis possesses mucus-secreting and multiciliated cells, and has served as an excellent model system for the biogenesis of cilia. However, ionic regulation is important for the function of all specialised epithelia and it is not clear how this is achieved in the embryonic frog epidermis. Here, we show that a third cell type develops alongside ciliated and mucus-secreting cells in the tadpole skin. These cells express high levels of ion channels and transporters; therefore, we suggest that they are analogous to ionocytes found in transporting epithelia such as the mammalian kidney. We show that frog ionocytes express the transcription factor foxi1e, which is required for the development of these cells. Depletion of ionocytes by foxi1e knockdown has detrimental effects on the development of multiciliated cells, which show fewer and aberrantly beating cilia. These results reveal a newly identified role for ionocytes and suggest that the frog embryonic skin is a model system that is particularly suited to studying the interactions of different cell types in mucociliary, as well as in secretory and transporting, epithelia.

Show MeSH
Related in: MedlinePlus