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The Caenorhabditis elegans vab-10 spectraplakin isoforms protect the epidermis against internal and external forces.

Bosher JM, Hahn BS, Legouis R, Sookhareea S, Weimer RM, Gansmuller A, Chisholm AD, Rose AM, Bessereau JL, Labouesse M - J. Cell Biol. (2003)

Bottom Line: We suggest that this isoform protects against forces external to the epidermis.In contrast, lack of VAB-10B leads to increased epidermal thickness during embryonic morphogenesis when epidermal cells change shape.We suggest that this isoform protects cells against tension that builds up within the epidermis.

View Article: PubMed Central - PubMed

Affiliation: Institut de Génétique et de Biologie Moléculaire et Cellulaire, CNRS/INSERM/ULP, BP10142, CU de Strasbourg, Illkirch Cedex F-67404, France.

ABSTRACT
Morphogenesis of the Caenorhabditis elegans embryo is driven by actin microfilaments in the epidermis and by sarcomeres in body wall muscles. Both tissues are mechanically coupled, most likely through specialized attachment structures called fibrous organelles (FOs) that connect muscles to the cuticle across the epidermis. Here, we report the identification of new mutations in a gene known as vab-10, which lead to severe morphogenesis defects, and show that vab-10 corresponds to the C. elegans spectraplakin locus. Our analysis of vab-10 reveals novel insights into the role of this plakin subfamily. vab-10 generates isoforms related either to plectin (termed VAB-10A) or to microtubule actin cross-linking factor plakins (termed VAB-10B). Using specific antibodies and mutations, we show that VAB-10A and VAB-10B have distinct distributions and functions in the epidermis. Loss of VAB-10A impairs the integrity of FOs, leading to epidermal detachment from the cuticle and muscles, hence demonstrating that FOs are functionally and molecularly related to hemidesmosomes. We suggest that this isoform protects against forces external to the epidermis. In contrast, lack of VAB-10B leads to increased epidermal thickness during embryonic morphogenesis when epidermal cells change shape. We suggest that this isoform protects cells against tension that builds up within the epidermis.

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VAB-10A–deficient mutants have nonfunctional FOs, VAB-10B–deficient mutants have an enlarged epidermis. EM analysis of cuticle–epidermis–muscle attachments of wild-type (A), vab-10A(RNAi) (B and F), vab-10A(ju281) (C), vab-10B(RNAi) (D), and vab-10(h1356) (E) embryos. B corresponds to a twofold enlargement of the area boxed in F. Sections are longitudinal to visualize FOs. The wild-type embryo (A) was at a stage when the muscle mass is not yet strongly developed (the fixation procedure used does not allow to visualize IFs). FOs were less numerous and/or not fully functional in VAB-10A–deficient embryos (B, C, and F), but appeared essentially normal in VAB-10B–deficient embryos (D), whereas the epidermal thickness was irregular and significantly increased in VAB-10B–deficient embryos (D); note that vab-10(h1356) embryos combined both defects (E). Black arrowheads, FO plaque at the apical plasma membrane; semi-open arrowheads, FO plaque at the basal plasma membrane; white open arrows, dense bodies at the muscle plasma membrane; capital S in white oval, sarcomeres; double arrows, epidermal layer. Bars, 1 μm.
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fig7: VAB-10A–deficient mutants have nonfunctional FOs, VAB-10B–deficient mutants have an enlarged epidermis. EM analysis of cuticle–epidermis–muscle attachments of wild-type (A), vab-10A(RNAi) (B and F), vab-10A(ju281) (C), vab-10B(RNAi) (D), and vab-10(h1356) (E) embryos. B corresponds to a twofold enlargement of the area boxed in F. Sections are longitudinal to visualize FOs. The wild-type embryo (A) was at a stage when the muscle mass is not yet strongly developed (the fixation procedure used does not allow to visualize IFs). FOs were less numerous and/or not fully functional in VAB-10A–deficient embryos (B, C, and F), but appeared essentially normal in VAB-10B–deficient embryos (D), whereas the epidermal thickness was irregular and significantly increased in VAB-10B–deficient embryos (D); note that vab-10(h1356) embryos combined both defects (E). Black arrowheads, FO plaque at the apical plasma membrane; semi-open arrowheads, FO plaque at the basal plasma membrane; white open arrows, dense bodies at the muscle plasma membrane; capital S in white oval, sarcomeres; double arrows, epidermal layer. Bars, 1 μm.

Mentions: The results described (along with Fig. 6) suggest that VAB-10A is essential to anchor muscle cells to the epidermis, and that VAB-10B is required to maintain the distance between the apical and basal plasma membranes of the epidermis. EM analysis allowed us to refine these conclusions. In wild-type embryos, sarcomeres are small relative to larvae and adults, and the dense bodies resemble electron-dense plaques at the plasma membrane instead of the elongated plaques spanning the sarcomeres of larvae and adults (Fig. 7 A). However, in the overlying epidermis, FOs had the same appearance as in adults, looking like regularly spaced electron-dense dots found between the developing cuticle or the basal lamina and the epidermis (Fig. 7 A). In vab-10(h1356) (Fig. 7 E) and vab-10A(RNAi) (Fig. 7 F), sarcomeres appeared severely disorganized and were not closely apposed to the epidermis. Some greyish material, which probably corresponds to ECM material, accumulated between muscles and the epidermis. Within epidermal cells, we observed fewer FOs than normal in vab-10A(ju281), vab-10A(RNAi), and vab-10(h1356) embryos with gaps between the cuticle and the epidermis (Fig. 7, B, C, and E). One reason why the cuticle–epidermis gap was not wider, except occasionally (Fig. 1 C, arrow), could be that once muscles have pulled away, there is no more tension exerted to widen it. Because we failed to observe similar defects in control embryos, we conclude that VAB-10A is essential to assemble or maintain FOs. In contrast, muscles remained closely apposed to epidermal cells in vab-10B(RNAi) embryos, but the thickness of epidermal cells was increased even in areas where the number of FOs was normal (Fig. 7 D).


The Caenorhabditis elegans vab-10 spectraplakin isoforms protect the epidermis against internal and external forces.

Bosher JM, Hahn BS, Legouis R, Sookhareea S, Weimer RM, Gansmuller A, Chisholm AD, Rose AM, Bessereau JL, Labouesse M - J. Cell Biol. (2003)

VAB-10A–deficient mutants have nonfunctional FOs, VAB-10B–deficient mutants have an enlarged epidermis. EM analysis of cuticle–epidermis–muscle attachments of wild-type (A), vab-10A(RNAi) (B and F), vab-10A(ju281) (C), vab-10B(RNAi) (D), and vab-10(h1356) (E) embryos. B corresponds to a twofold enlargement of the area boxed in F. Sections are longitudinal to visualize FOs. The wild-type embryo (A) was at a stage when the muscle mass is not yet strongly developed (the fixation procedure used does not allow to visualize IFs). FOs were less numerous and/or not fully functional in VAB-10A–deficient embryos (B, C, and F), but appeared essentially normal in VAB-10B–deficient embryos (D), whereas the epidermal thickness was irregular and significantly increased in VAB-10B–deficient embryos (D); note that vab-10(h1356) embryos combined both defects (E). Black arrowheads, FO plaque at the apical plasma membrane; semi-open arrowheads, FO plaque at the basal plasma membrane; white open arrows, dense bodies at the muscle plasma membrane; capital S in white oval, sarcomeres; double arrows, epidermal layer. Bars, 1 μm.
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC2199363&req=5

fig7: VAB-10A–deficient mutants have nonfunctional FOs, VAB-10B–deficient mutants have an enlarged epidermis. EM analysis of cuticle–epidermis–muscle attachments of wild-type (A), vab-10A(RNAi) (B and F), vab-10A(ju281) (C), vab-10B(RNAi) (D), and vab-10(h1356) (E) embryos. B corresponds to a twofold enlargement of the area boxed in F. Sections are longitudinal to visualize FOs. The wild-type embryo (A) was at a stage when the muscle mass is not yet strongly developed (the fixation procedure used does not allow to visualize IFs). FOs were less numerous and/or not fully functional in VAB-10A–deficient embryos (B, C, and F), but appeared essentially normal in VAB-10B–deficient embryos (D), whereas the epidermal thickness was irregular and significantly increased in VAB-10B–deficient embryos (D); note that vab-10(h1356) embryos combined both defects (E). Black arrowheads, FO plaque at the apical plasma membrane; semi-open arrowheads, FO plaque at the basal plasma membrane; white open arrows, dense bodies at the muscle plasma membrane; capital S in white oval, sarcomeres; double arrows, epidermal layer. Bars, 1 μm.
Mentions: The results described (along with Fig. 6) suggest that VAB-10A is essential to anchor muscle cells to the epidermis, and that VAB-10B is required to maintain the distance between the apical and basal plasma membranes of the epidermis. EM analysis allowed us to refine these conclusions. In wild-type embryos, sarcomeres are small relative to larvae and adults, and the dense bodies resemble electron-dense plaques at the plasma membrane instead of the elongated plaques spanning the sarcomeres of larvae and adults (Fig. 7 A). However, in the overlying epidermis, FOs had the same appearance as in adults, looking like regularly spaced electron-dense dots found between the developing cuticle or the basal lamina and the epidermis (Fig. 7 A). In vab-10(h1356) (Fig. 7 E) and vab-10A(RNAi) (Fig. 7 F), sarcomeres appeared severely disorganized and were not closely apposed to the epidermis. Some greyish material, which probably corresponds to ECM material, accumulated between muscles and the epidermis. Within epidermal cells, we observed fewer FOs than normal in vab-10A(ju281), vab-10A(RNAi), and vab-10(h1356) embryos with gaps between the cuticle and the epidermis (Fig. 7, B, C, and E). One reason why the cuticle–epidermis gap was not wider, except occasionally (Fig. 1 C, arrow), could be that once muscles have pulled away, there is no more tension exerted to widen it. Because we failed to observe similar defects in control embryos, we conclude that VAB-10A is essential to assemble or maintain FOs. In contrast, muscles remained closely apposed to epidermal cells in vab-10B(RNAi) embryos, but the thickness of epidermal cells was increased even in areas where the number of FOs was normal (Fig. 7 D).

Bottom Line: We suggest that this isoform protects against forces external to the epidermis.In contrast, lack of VAB-10B leads to increased epidermal thickness during embryonic morphogenesis when epidermal cells change shape.We suggest that this isoform protects cells against tension that builds up within the epidermis.

View Article: PubMed Central - PubMed

Affiliation: Institut de Génétique et de Biologie Moléculaire et Cellulaire, CNRS/INSERM/ULP, BP10142, CU de Strasbourg, Illkirch Cedex F-67404, France.

ABSTRACT
Morphogenesis of the Caenorhabditis elegans embryo is driven by actin microfilaments in the epidermis and by sarcomeres in body wall muscles. Both tissues are mechanically coupled, most likely through specialized attachment structures called fibrous organelles (FOs) that connect muscles to the cuticle across the epidermis. Here, we report the identification of new mutations in a gene known as vab-10, which lead to severe morphogenesis defects, and show that vab-10 corresponds to the C. elegans spectraplakin locus. Our analysis of vab-10 reveals novel insights into the role of this plakin subfamily. vab-10 generates isoforms related either to plectin (termed VAB-10A) or to microtubule actin cross-linking factor plakins (termed VAB-10B). Using specific antibodies and mutations, we show that VAB-10A and VAB-10B have distinct distributions and functions in the epidermis. Loss of VAB-10A impairs the integrity of FOs, leading to epidermal detachment from the cuticle and muscles, hence demonstrating that FOs are functionally and molecularly related to hemidesmosomes. We suggest that this isoform protects against forces external to the epidermis. In contrast, lack of VAB-10B leads to increased epidermal thickness during embryonic morphogenesis when epidermal cells change shape. We suggest that this isoform protects cells against tension that builds up within the epidermis.

Show MeSH
Related in: MedlinePlus