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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-10 mutants display elongation and body morphology defects. Differential interference contrast micrographs of terminal-stage vab-10 mutants. (A) Wild-type twofold embryo (mid-embryogenesis). (B) vab-10(h1356) embryo; the body (demarcated by arrowheads) failed to elongate. (C) vab-10A(ju281) embryo with a localized detachment of the epidermis from the cuticle (arrow); all vab-10A(ju281) embryos raised at 20°C and 79% of those raised at 25°C (n = 149) elongated 2.5-fold like this embryo, and occasionally hatched to generate kinked and paralyzed larvae, whereas 21% of those raised at 25°C looked like h1356 embryos. (D) vab-10A(RNAi) embryo; 95% of these embryos (n = 135) resembled h1356 embryos. (E) Arrested L1 vab-10B(mc44) larva (65%, n = 403, could hatch), and (F) hatching L1 vab-10B(RNAi) larva; the body morphology is very irregular. Embryos laid after eliciting an RNAi response against vab-10A– or vab-10B–specific exons are denoted vab-10A(RNAi) or vab-10B(RNAi). Here (as in Figs. 4, 6, and 8), dorsal is up, anterior is left, and bars represent 10 μm.
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fig1: vab-10 mutants display elongation and body morphology defects. Differential interference contrast micrographs of terminal-stage vab-10 mutants. (A) Wild-type twofold embryo (mid-embryogenesis). (B) vab-10(h1356) embryo; the body (demarcated by arrowheads) failed to elongate. (C) vab-10A(ju281) embryo with a localized detachment of the epidermis from the cuticle (arrow); all vab-10A(ju281) embryos raised at 20°C and 79% of those raised at 25°C (n = 149) elongated 2.5-fold like this embryo, and occasionally hatched to generate kinked and paralyzed larvae, whereas 21% of those raised at 25°C looked like h1356 embryos. (D) vab-10A(RNAi) embryo; 95% of these embryos (n = 135) resembled h1356 embryos. (E) Arrested L1 vab-10B(mc44) larva (65%, n = 403, could hatch), and (F) hatching L1 vab-10B(RNAi) larva; the body morphology is very irregular. Embryos laid after eliciting an RNAi response against vab-10A– or vab-10B–specific exons are denoted vab-10A(RNAi) or vab-10B(RNAi). Here (as in Figs. 4, 6, and 8), dorsal is up, anterior is left, and bars represent 10 μm.

Mentions: Previously, we performed a genetic screen to identify loci required for embryonic morphogenesis, and reported that embryos homozygous for the chromosomal deficiency hDf17 arrest with severe morphogenic defects (Labouesse, 1997). We could identify an embryonic lethal mutation, h1356, that recapitulates some aspects of the hDf17 mutant phenotype (Fig. 1 B), and then found that h1356 is allelic to the viable mutation vab-10(e698). This allele was originally identified for its variable head morphogenesis defects (vab, variably abnormal), and was later observed to cause muscle attachments to be fragile in larvae (Hodgkin, 1983; Plenefisch et al., 2000). In an independent screen for lethal mutants, we identified the vab-10 allele ju281 (Fig. 1 C). Finally, after cloning vab-10, we recovered the small deletion mc44 using a molecular approach (Fig. 1 E; see Materials and methods).


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-10 mutants display elongation and body morphology defects. Differential interference contrast micrographs of terminal-stage vab-10 mutants. (A) Wild-type twofold embryo (mid-embryogenesis). (B) vab-10(h1356) embryo; the body (demarcated by arrowheads) failed to elongate. (C) vab-10A(ju281) embryo with a localized detachment of the epidermis from the cuticle (arrow); all vab-10A(ju281) embryos raised at 20°C and 79% of those raised at 25°C (n = 149) elongated 2.5-fold like this embryo, and occasionally hatched to generate kinked and paralyzed larvae, whereas 21% of those raised at 25°C looked like h1356 embryos. (D) vab-10A(RNAi) embryo; 95% of these embryos (n = 135) resembled h1356 embryos. (E) Arrested L1 vab-10B(mc44) larva (65%, n = 403, could hatch), and (F) hatching L1 vab-10B(RNAi) larva; the body morphology is very irregular. Embryos laid after eliciting an RNAi response against vab-10A– or vab-10B–specific exons are denoted vab-10A(RNAi) or vab-10B(RNAi). Here (as in Figs. 4, 6, and 8), dorsal is up, anterior is left, and bars represent 10 μm.
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fig1: vab-10 mutants display elongation and body morphology defects. Differential interference contrast micrographs of terminal-stage vab-10 mutants. (A) Wild-type twofold embryo (mid-embryogenesis). (B) vab-10(h1356) embryo; the body (demarcated by arrowheads) failed to elongate. (C) vab-10A(ju281) embryo with a localized detachment of the epidermis from the cuticle (arrow); all vab-10A(ju281) embryos raised at 20°C and 79% of those raised at 25°C (n = 149) elongated 2.5-fold like this embryo, and occasionally hatched to generate kinked and paralyzed larvae, whereas 21% of those raised at 25°C looked like h1356 embryos. (D) vab-10A(RNAi) embryo; 95% of these embryos (n = 135) resembled h1356 embryos. (E) Arrested L1 vab-10B(mc44) larva (65%, n = 403, could hatch), and (F) hatching L1 vab-10B(RNAi) larva; the body morphology is very irregular. Embryos laid after eliciting an RNAi response against vab-10A– or vab-10B–specific exons are denoted vab-10A(RNAi) or vab-10B(RNAi). Here (as in Figs. 4, 6, and 8), dorsal is up, anterior is left, and bars represent 10 μm.
Mentions: Previously, we performed a genetic screen to identify loci required for embryonic morphogenesis, and reported that embryos homozygous for the chromosomal deficiency hDf17 arrest with severe morphogenic defects (Labouesse, 1997). We could identify an embryonic lethal mutation, h1356, that recapitulates some aspects of the hDf17 mutant phenotype (Fig. 1 B), and then found that h1356 is allelic to the viable mutation vab-10(e698). This allele was originally identified for its variable head morphogenesis defects (vab, variably abnormal), and was later observed to cause muscle attachments to be fragile in larvae (Hodgkin, 1983; Plenefisch et al., 2000). In an independent screen for lethal mutants, we identified the vab-10 allele ju281 (Fig. 1 C). Finally, after cloning vab-10, we recovered the small deletion mc44 using a molecular approach (Fig. 1 E; see Materials and methods).

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