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Roles for laminin in embryogenesis: exencephaly, syndactyly, and placentopathy in mice lacking the laminin alpha5 chain.

Miner JH, Cunningham J, Sanes JR - J. Cell Biol. (1998)

Bottom Line: Previously described mutations in laminin chain genes result in diverse disorders that are manifested postnatally and therefore provide little insight into laminin's roles in embryonic development.Other laminin alpha chains accumulate in these BLs, but this compensation is apparently functionally inadequate.Our results identify new roles for laminins and BLs in diverse developmental processes.

View Article: PubMed Central - PubMed

Affiliation: Department of Medicine, Renal Division, St. Louis, Missouri, USA.

ABSTRACT
Laminins are the major noncollagenous glycoproteins of all basal laminae (BLs). They are alpha/beta/gamma heterotrimers assembled from 10 known chains, and they subserve both structural and signaling roles. Previously described mutations in laminin chain genes result in diverse disorders that are manifested postnatally and therefore provide little insight into laminin's roles in embryonic development. Here, we show that the laminin alpha5 chain is required during embryogenesis. The alpha5 chain is present in virtually all BLs of early somite stage embryos and then becomes restricted to specific BLs as development proceeds, including those of the surface ectoderm and placental vasculature. BLs that lose alpha5 retain or acquire other alpha chains. Embryos lacking laminin alpha5 die late in embryogenesis. They exhibit multiple developmental defects, including failure of anterior neural tube closure (exencephaly), failure of digit septation (syndactyly), and dysmorphogenesis of the placental labyrinth. These defects are all attributable to defects in BLs that are alpha5 positive in controls and that appear ultrastructurally abnormal in its absence. Other laminin alpha chains accumulate in these BLs, but this compensation is apparently functionally inadequate. Our results identify new roles for laminins and BLs in diverse developmental processes.

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Discontinuity of epidermis and BL in the distal limb.  (A–C) Toluidine blue–stained semithin sections of distal limb  from control (A) and mutant (B and C) E14.5 embryos. The surface ectoderm (se) is continuous in controls (A). In mutants, in  contrast, the ectoderm has been breached, and extruded mesenchymal cells (m) have migrated along the outer surface of the  limb (B). A nearby section from the same mutant limb shows a  thickened surface ectoderm (*) between the outer and inner mesenchymal populations (C). (D) Immunostaining of Lama5 −/−  limb with an antibody to laminin γ1 demonstrates the presence of  BL material on both sides of the thickened ectoderm (arrowheads), suggesting that the ectoderm has maintained a proper relationship with the displaced mesenchymal cells. (E and F) Ultrastructural analysis of distal limb BL at E14.5 shows a dense,  continuous BL (arrowhead) in the control (E) but a patchy, discontinuous BL in the mutant (F). Bars: (in D) 62.5 μm for A–C,  50 μm for D; (in F) 0.25 μm for E and F.
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Figure 4: Discontinuity of epidermis and BL in the distal limb. (A–C) Toluidine blue–stained semithin sections of distal limb from control (A) and mutant (B and C) E14.5 embryos. The surface ectoderm (se) is continuous in controls (A). In mutants, in contrast, the ectoderm has been breached, and extruded mesenchymal cells (m) have migrated along the outer surface of the limb (B). A nearby section from the same mutant limb shows a thickened surface ectoderm (*) between the outer and inner mesenchymal populations (C). (D) Immunostaining of Lama5 −/− limb with an antibody to laminin γ1 demonstrates the presence of BL material on both sides of the thickened ectoderm (arrowheads), suggesting that the ectoderm has maintained a proper relationship with the displaced mesenchymal cells. (E and F) Ultrastructural analysis of distal limb BL at E14.5 shows a dense, continuous BL (arrowhead) in the control (E) but a patchy, discontinuous BL in the mutant (F). Bars: (in D) 62.5 μm for A–C, 50 μm for D; (in F) 0.25 μm for E and F.

Mentions: As the limb bud elongates, cells are added to the ectoderm so that it completely covers the limb at all times. In mutants, however, ∼200-μm gaps appeared in the distal epidermis slightly ventral to the tip of each digit condensation (Fig. 4, A and B). Mesenchymal cells migrated or were extruded through these gaps. Some of these cells may have been sloughed into the amniotic fluid, but many remained associated with the external (peridermal) surface of the epithelium and migrated from the hole to form a continuous, multilayered coat over each digit tip (Fig. 4, B and C). As a result, the surface ectoderm thickened and became covered on both sides by a dermis at the limb tip (Fig. 4 C), and a second BL formed at the ectopic ectodermal/dermal interface (Fig. 4 D). Apparently, either the surface ectoderm “doubled back” on itself to maintain a basal relationship with the displaced mesenchymal cells, or, alternatively, the presence of displaced mesenchyme on the apical side of the epithelial cells induced a repolarization and/or a reorganization of some of these cells, producing a second epithelial/mesenchymal interface. In either case, the additional cells in the epithelium were clearly of epidermal lineage, as shown by immunostaining with an antibody to the keratinocyte-specific antigen keratin 14 (Stoler et al., 1988). This antibody stained all surface ectodermal cells as well as the full width of the thickened mutant epithelium at this stage (data not shown). Because the interdigital mesenchyme is intimately involved in digit septation (see Jiang et al., 1998 and references therein), its depletion from the interior might be expected to impede this process. Depleted mesenchyme could also lead to the observed digit fusion, and the doubled ectoderm could physically impede proper septation. Together, these abnormalities appear sufficient to account for the syndactyly observed in Lama5 −/− embryos.


Roles for laminin in embryogenesis: exencephaly, syndactyly, and placentopathy in mice lacking the laminin alpha5 chain.

Miner JH, Cunningham J, Sanes JR - J. Cell Biol. (1998)

Discontinuity of epidermis and BL in the distal limb.  (A–C) Toluidine blue–stained semithin sections of distal limb  from control (A) and mutant (B and C) E14.5 embryos. The surface ectoderm (se) is continuous in controls (A). In mutants, in  contrast, the ectoderm has been breached, and extruded mesenchymal cells (m) have migrated along the outer surface of the  limb (B). A nearby section from the same mutant limb shows a  thickened surface ectoderm (*) between the outer and inner mesenchymal populations (C). (D) Immunostaining of Lama5 −/−  limb with an antibody to laminin γ1 demonstrates the presence of  BL material on both sides of the thickened ectoderm (arrowheads), suggesting that the ectoderm has maintained a proper relationship with the displaced mesenchymal cells. (E and F) Ultrastructural analysis of distal limb BL at E14.5 shows a dense,  continuous BL (arrowhead) in the control (E) but a patchy, discontinuous BL in the mutant (F). Bars: (in D) 62.5 μm for A–C,  50 μm for D; (in F) 0.25 μm for E and F.
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Related In: Results  -  Collection

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Figure 4: Discontinuity of epidermis and BL in the distal limb. (A–C) Toluidine blue–stained semithin sections of distal limb from control (A) and mutant (B and C) E14.5 embryos. The surface ectoderm (se) is continuous in controls (A). In mutants, in contrast, the ectoderm has been breached, and extruded mesenchymal cells (m) have migrated along the outer surface of the limb (B). A nearby section from the same mutant limb shows a thickened surface ectoderm (*) between the outer and inner mesenchymal populations (C). (D) Immunostaining of Lama5 −/− limb with an antibody to laminin γ1 demonstrates the presence of BL material on both sides of the thickened ectoderm (arrowheads), suggesting that the ectoderm has maintained a proper relationship with the displaced mesenchymal cells. (E and F) Ultrastructural analysis of distal limb BL at E14.5 shows a dense, continuous BL (arrowhead) in the control (E) but a patchy, discontinuous BL in the mutant (F). Bars: (in D) 62.5 μm for A–C, 50 μm for D; (in F) 0.25 μm for E and F.
Mentions: As the limb bud elongates, cells are added to the ectoderm so that it completely covers the limb at all times. In mutants, however, ∼200-μm gaps appeared in the distal epidermis slightly ventral to the tip of each digit condensation (Fig. 4, A and B). Mesenchymal cells migrated or were extruded through these gaps. Some of these cells may have been sloughed into the amniotic fluid, but many remained associated with the external (peridermal) surface of the epithelium and migrated from the hole to form a continuous, multilayered coat over each digit tip (Fig. 4, B and C). As a result, the surface ectoderm thickened and became covered on both sides by a dermis at the limb tip (Fig. 4 C), and a second BL formed at the ectopic ectodermal/dermal interface (Fig. 4 D). Apparently, either the surface ectoderm “doubled back” on itself to maintain a basal relationship with the displaced mesenchymal cells, or, alternatively, the presence of displaced mesenchyme on the apical side of the epithelial cells induced a repolarization and/or a reorganization of some of these cells, producing a second epithelial/mesenchymal interface. In either case, the additional cells in the epithelium were clearly of epidermal lineage, as shown by immunostaining with an antibody to the keratinocyte-specific antigen keratin 14 (Stoler et al., 1988). This antibody stained all surface ectodermal cells as well as the full width of the thickened mutant epithelium at this stage (data not shown). Because the interdigital mesenchyme is intimately involved in digit septation (see Jiang et al., 1998 and references therein), its depletion from the interior might be expected to impede this process. Depleted mesenchyme could also lead to the observed digit fusion, and the doubled ectoderm could physically impede proper septation. Together, these abnormalities appear sufficient to account for the syndactyly observed in Lama5 −/− embryos.

Bottom Line: Previously described mutations in laminin chain genes result in diverse disorders that are manifested postnatally and therefore provide little insight into laminin's roles in embryonic development.Other laminin alpha chains accumulate in these BLs, but this compensation is apparently functionally inadequate.Our results identify new roles for laminins and BLs in diverse developmental processes.

View Article: PubMed Central - PubMed

Affiliation: Department of Medicine, Renal Division, St. Louis, Missouri, USA.

ABSTRACT
Laminins are the major noncollagenous glycoproteins of all basal laminae (BLs). They are alpha/beta/gamma heterotrimers assembled from 10 known chains, and they subserve both structural and signaling roles. Previously described mutations in laminin chain genes result in diverse disorders that are manifested postnatally and therefore provide little insight into laminin's roles in embryonic development. Here, we show that the laminin alpha5 chain is required during embryogenesis. The alpha5 chain is present in virtually all BLs of early somite stage embryos and then becomes restricted to specific BLs as development proceeds, including those of the surface ectoderm and placental vasculature. BLs that lose alpha5 retain or acquire other alpha chains. Embryos lacking laminin alpha5 die late in embryogenesis. They exhibit multiple developmental defects, including failure of anterior neural tube closure (exencephaly), failure of digit septation (syndactyly), and dysmorphogenesis of the placental labyrinth. These defects are all attributable to defects in BLs that are alpha5 positive in controls and that appear ultrastructurally abnormal in its absence. Other laminin alpha chains accumulate in these BLs, but this compensation is apparently functionally inadequate. Our results identify new roles for laminins and BLs in diverse developmental processes.

Show MeSH
Related in: MedlinePlus