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Essential role of Gab1 for signaling by the c-Met receptor in vivo.

Sachs M, Brohmann H, Zechner D, Müller T, Hülsken J, Walther I, Schaeper U, Birchmeier C, Birchmeier W - J. Cell Biol. (2000)

Bottom Line: Moreover, Gab1-/- embryos die in a broad time window between E13.5 and E18.5, and display reduced liver size and placental defects.The labyrinth layer, but not the spongiotrophoblast layer, of the placenta is severely reduced, resulting in impaired communication between maternal and fetal circulation.This is genetic evidence that Gab1 is essential for c-Met signaling in vivo.

View Article: PubMed Central - PubMed

Affiliation: Department of Growth and Differentiation, Max-Delbrueck-Center for Molecular Medicine, 13092 Berlin, Germany.

ABSTRACT
The docking protein Gab1 binds phosphorylated c-Met receptor tyrosine kinase directly and mediates signals of c-Met in cell culture. Gab1 is phosphorylated by c-Met and by other receptor and nonreceptor tyrosine kinases. Here, we report the functional analysis of Gab1 by targeted mutagenesis in the mouse, and compare the phenotypes of the Gab1 and c-Met mutations. Gab1 is essential for several steps in development: migration of myogenic precursor cells into the limb anlage is impaired in Gab1-/- embryos. As a consequence, extensor muscle groups of the forelimbs are virtually absent, and the flexor muscles reach less far. Fewer hindlimb muscles exist, which are smaller and disorganized. Muscles in the diaphragm, which also originate from migratory precursors, are missing. Moreover, Gab1-/- embryos die in a broad time window between E13.5 and E18.5, and display reduced liver size and placental defects. The labyrinth layer, but not the spongiotrophoblast layer, of the placenta is severely reduced, resulting in impaired communication between maternal and fetal circulation. Thus, extensive similarities between the phenotypes of c-Met and HGF/SF mutant mice exist, and the muscle migration phenotype is even more pronounced in Gab1-/-:c-Met+/- embryos. This is genetic evidence that Gab1 is essential for c-Met signaling in vivo. Analogy exists to signal transmission by insulin receptors, which require IRS1 and IRS2 as specific docking proteins.

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Immunohistologi-cal analysis of muscle groups in Gab+/− (a) and Gab1−/− embryos (b), as visualized by staining with anti–skeletal fast myosin heavy chain antibodies and HRP. Sagittal sections of E13.5 embryos show the muscle of the diaphragm, which is split by the esophagus (dotted line). Note the strong reduction of the size of diaphragm muscles in Gab1−/− embryos. Bar, 250 μm.
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Figure 5: Immunohistologi-cal analysis of muscle groups in Gab+/− (a) and Gab1−/− embryos (b), as visualized by staining with anti–skeletal fast myosin heavy chain antibodies and HRP. Sagittal sections of E13.5 embryos show the muscle of the diaphragm, which is split by the esophagus (dotted line). Note the strong reduction of the size of diaphragm muscles in Gab1−/− embryos. Bar, 250 μm.

Mentions: We analyzed differentiated muscle groups in the limbs of E14.5 embryos; at this stage, skeletal muscle cells in the limbs express muscle-specific proteins such as fast myosin heavy chain, which was visualized by immunohistochemistry. The extensor muscle groups of the proximal lower forelimbs are either absent or very small in Gab1−/− mice compared with control mice; flexor muscles are present (Fig. 4, a and c, arrows mark extensors, arrowhead, flexors). In the distal lower forelimb, the phenotype is more pronounced, and only traces of muscle cells can be detected at this site in Gab1−/− embryos; both extensor and flexor muscles groups are strongly affected (Fig. 4b and Fig. d). In the proximal lower hindlimb, some muscle groups are present but reduced in size; distally, the size reduction is again more pronounced (Fig. 4, a′–d′). We also set up cross-breedings of Gab1 and c-Met (Bladt et al. 1995) mutant mice to obtain compound Gab1−/−:c-Met+/− embryos. Remarkably, virtual absence of all muscles was observed in the lower limbs of these embryos (Fig. 4, e–f′). The diaphragm muscle, which is also colonized by migrating muscle precursor cells, was examined. Sagittal sections of wild-type embryos at E13.5 reveal the diaphragm muscle (Fig. 5 a), which is split by the esophagus in this particular section plane. In Gab1 mutant embryos, the diaphragm muscle is strongly reduced in size (Fig. 5 b). No change was observed in the internal tongue muscle also generated by migrating cells (not shown). Note that other muscle groups that do not develop from migrating cells, like intercostal or body wall muscle, are well developed in the Gab1 mutants (Fig. 4 and data not shown). Thus, specific muscle groups that derive from migrating precursor cells are severely impaired in their development in Gab1 mutants. In HGF/SF−/−, c-Met−/−, and Gab1−/−: c-Met+/− embryos, these muscle groups are completely absent (Bladt et al. 1995; Dietrich et al. 1998). Interestingly, the reduced colonization of limbs and diaphragm with muscle precursor cells in Gab1−/− embryos is not markedly compensated at later stages in development.


Essential role of Gab1 for signaling by the c-Met receptor in vivo.

Sachs M, Brohmann H, Zechner D, Müller T, Hülsken J, Walther I, Schaeper U, Birchmeier C, Birchmeier W - J. Cell Biol. (2000)

Immunohistologi-cal analysis of muscle groups in Gab+/− (a) and Gab1−/− embryos (b), as visualized by staining with anti–skeletal fast myosin heavy chain antibodies and HRP. Sagittal sections of E13.5 embryos show the muscle of the diaphragm, which is split by the esophagus (dotted line). Note the strong reduction of the size of diaphragm muscles in Gab1−/− embryos. Bar, 250 μm.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2150711&req=5

Figure 5: Immunohistologi-cal analysis of muscle groups in Gab+/− (a) and Gab1−/− embryos (b), as visualized by staining with anti–skeletal fast myosin heavy chain antibodies and HRP. Sagittal sections of E13.5 embryos show the muscle of the diaphragm, which is split by the esophagus (dotted line). Note the strong reduction of the size of diaphragm muscles in Gab1−/− embryos. Bar, 250 μm.
Mentions: We analyzed differentiated muscle groups in the limbs of E14.5 embryos; at this stage, skeletal muscle cells in the limbs express muscle-specific proteins such as fast myosin heavy chain, which was visualized by immunohistochemistry. The extensor muscle groups of the proximal lower forelimbs are either absent or very small in Gab1−/− mice compared with control mice; flexor muscles are present (Fig. 4, a and c, arrows mark extensors, arrowhead, flexors). In the distal lower forelimb, the phenotype is more pronounced, and only traces of muscle cells can be detected at this site in Gab1−/− embryos; both extensor and flexor muscles groups are strongly affected (Fig. 4b and Fig. d). In the proximal lower hindlimb, some muscle groups are present but reduced in size; distally, the size reduction is again more pronounced (Fig. 4, a′–d′). We also set up cross-breedings of Gab1 and c-Met (Bladt et al. 1995) mutant mice to obtain compound Gab1−/−:c-Met+/− embryos. Remarkably, virtual absence of all muscles was observed in the lower limbs of these embryos (Fig. 4, e–f′). The diaphragm muscle, which is also colonized by migrating muscle precursor cells, was examined. Sagittal sections of wild-type embryos at E13.5 reveal the diaphragm muscle (Fig. 5 a), which is split by the esophagus in this particular section plane. In Gab1 mutant embryos, the diaphragm muscle is strongly reduced in size (Fig. 5 b). No change was observed in the internal tongue muscle also generated by migrating cells (not shown). Note that other muscle groups that do not develop from migrating cells, like intercostal or body wall muscle, are well developed in the Gab1 mutants (Fig. 4 and data not shown). Thus, specific muscle groups that derive from migrating precursor cells are severely impaired in their development in Gab1 mutants. In HGF/SF−/−, c-Met−/−, and Gab1−/−: c-Met+/− embryos, these muscle groups are completely absent (Bladt et al. 1995; Dietrich et al. 1998). Interestingly, the reduced colonization of limbs and diaphragm with muscle precursor cells in Gab1−/− embryos is not markedly compensated at later stages in development.

Bottom Line: Moreover, Gab1-/- embryos die in a broad time window between E13.5 and E18.5, and display reduced liver size and placental defects.The labyrinth layer, but not the spongiotrophoblast layer, of the placenta is severely reduced, resulting in impaired communication between maternal and fetal circulation.This is genetic evidence that Gab1 is essential for c-Met signaling in vivo.

View Article: PubMed Central - PubMed

Affiliation: Department of Growth and Differentiation, Max-Delbrueck-Center for Molecular Medicine, 13092 Berlin, Germany.

ABSTRACT
The docking protein Gab1 binds phosphorylated c-Met receptor tyrosine kinase directly and mediates signals of c-Met in cell culture. Gab1 is phosphorylated by c-Met and by other receptor and nonreceptor tyrosine kinases. Here, we report the functional analysis of Gab1 by targeted mutagenesis in the mouse, and compare the phenotypes of the Gab1 and c-Met mutations. Gab1 is essential for several steps in development: migration of myogenic precursor cells into the limb anlage is impaired in Gab1-/- embryos. As a consequence, extensor muscle groups of the forelimbs are virtually absent, and the flexor muscles reach less far. Fewer hindlimb muscles exist, which are smaller and disorganized. Muscles in the diaphragm, which also originate from migratory precursors, are missing. Moreover, Gab1-/- embryos die in a broad time window between E13.5 and E18.5, and display reduced liver size and placental defects. The labyrinth layer, but not the spongiotrophoblast layer, of the placenta is severely reduced, resulting in impaired communication between maternal and fetal circulation. Thus, extensive similarities between the phenotypes of c-Met and HGF/SF mutant mice exist, and the muscle migration phenotype is even more pronounced in Gab1-/-:c-Met+/- embryos. This is genetic evidence that Gab1 is essential for c-Met signaling in vivo. Analogy exists to signal transmission by insulin receptors, which require IRS1 and IRS2 as specific docking proteins.

Show MeSH
Related in: MedlinePlus