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Drosophila myoblast city encodes a conserved protein that is essential for myoblast fusion, dorsal closure, and cytoskeletal organization.

Erickson MR, Galletta BJ, Abmayr SM - J. Cell Biol. (1997)

Bottom Line: It is also expressed in the pole cells and in ectodermally derived tissues, including the epidermis.Consistent with this latter expression, mbc mutant embryos exhibit defects in dorsal closure and cytoskeletal organization in the migrating epidermis.Both the mesodermal and ectodermal defects are reminiscent of those induced by altered forms of Drac1 and suggest that mbc may function in the same pathway.

View Article: PubMed Central - PubMed

Affiliation: Department of Biochemistry and Molecular Biology and Center for Gene Regulation, The Pennsylvania State University, University Park, Pennsylvania 16802, USA.

ABSTRACT
The Drosophila myoblast city (mbc) locus was previously identified on the basis of a defect in myoblast fusion (Rushton et al., 1995. Development [Camb.]. 121:1979-1988). We describe herein the isolation and characterization of the mbc gene. The mbc transcript and its encoded protein are expressed in a broad range of tissues, including somatic myoblasts, cardial cells, and visceral mesoderm. It is also expressed in the pole cells and in ectodermally derived tissues, including the epidermis. Consistent with this latter expression, mbc mutant embryos exhibit defects in dorsal closure and cytoskeletal organization in the migrating epidermis. Both the mesodermal and ectodermal defects are reminiscent of those induced by altered forms of Drac1 and suggest that mbc may function in the same pathway. MBC bears striking homology to human DOCK180, which interacts with the SH2-SH3 adapter protein Crk and may play a role in signal transduction from focal adhesions. Taken together, these results suggest the possibility that MBC is an intermediate in a signal transduction pathway from the rho/rac family of GTPases to events in the cytoskeleton and that this pathway may be used during myoblast fusion and dorsal closure.

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Spatial expression pattern of MBC in wild-type embryos. Anterior is to the left and dorsal to the top in all except A. (A) Stage  13 embryos from the progeny of mbcD11.2/TM3 lacZ-hg stained immunohistochemically for MBC. The embryo to the top left expressed  β-galactosidase and therefore carried TM3 lacZ-hg; the embryo to the bottom right (which is barely visible) did not express β-galactosidase (data not shown) and was therefore homozygous for mbcD11.2. As anticipated, no MBC expression is visible in the homozygous mutant embryo, establishing specificity of the antiserum. (B) Wild-type; Lateral view, stage 5. (C) Wild-type; Lateral view, stage 8. (D)  Wild-type; Lateral view, stage 14; arrow indicates the visceral musculature (vm). (E and F) Wild-type; Lateral views, stage 16; arrows in  E highlight somatic muscles 8, 12, and 19, using the nomenclature of Crossley (1978). Arrow in F marks the dorsal vessel (dv). Bars: (A– D and F) 100 μm; (E) 10 μm.
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Figure 5: Spatial expression pattern of MBC in wild-type embryos. Anterior is to the left and dorsal to the top in all except A. (A) Stage 13 embryos from the progeny of mbcD11.2/TM3 lacZ-hg stained immunohistochemically for MBC. The embryo to the top left expressed β-galactosidase and therefore carried TM3 lacZ-hg; the embryo to the bottom right (which is barely visible) did not express β-galactosidase (data not shown) and was therefore homozygous for mbcD11.2. As anticipated, no MBC expression is visible in the homozygous mutant embryo, establishing specificity of the antiserum. (B) Wild-type; Lateral view, stage 5. (C) Wild-type; Lateral view, stage 8. (D) Wild-type; Lateral view, stage 14; arrow indicates the visceral musculature (vm). (E and F) Wild-type; Lateral views, stage 16; arrows in E highlight somatic muscles 8, 12, and 19, using the nomenclature of Crossley (1978). Arrow in F marks the dorsal vessel (dv). Bars: (A– D and F) 100 μm; (E) 10 μm.

Mentions: The expression pattern of MBC was analyzed by fluorescent immunohistochemistry and confocal microscopy using an antiserum directed against the COOH-terminal portion of the protein. Examination of embryos homozygous for mbcD11.2 confirmed that the antiserum was specific (Fig. 5 A) since this allele encodes a severely truncated form of MBC that would not be detected. While slight temporal differences were evident between maximal levels of mRNA (stage 4; Fig. 4 A) and maximal levels of protein (stage 5; Fig. 5 B) in the pole cells, the expression of the protein essentially correlated with that of the mRNA. MBC appeared to be localized in the cytoplasm (Fig. 5 C), consistent with its human counterpart DOCK180. MBC is also present in the visceral musculature (Fig. 5 D, arrow) and the dorsal vessel (Fig. 5 F, arrow). Cross reactivity of the MBC antiserum was observed in the filtzkorper (Fig. 5 F) but does not correlate with the presence of transcript. Although mRNA was not evident in mature muscles, the protein could be detected at a low level (Fig. 5 E).


Drosophila myoblast city encodes a conserved protein that is essential for myoblast fusion, dorsal closure, and cytoskeletal organization.

Erickson MR, Galletta BJ, Abmayr SM - J. Cell Biol. (1997)

Spatial expression pattern of MBC in wild-type embryos. Anterior is to the left and dorsal to the top in all except A. (A) Stage  13 embryos from the progeny of mbcD11.2/TM3 lacZ-hg stained immunohistochemically for MBC. The embryo to the top left expressed  β-galactosidase and therefore carried TM3 lacZ-hg; the embryo to the bottom right (which is barely visible) did not express β-galactosidase (data not shown) and was therefore homozygous for mbcD11.2. As anticipated, no MBC expression is visible in the homozygous mutant embryo, establishing specificity of the antiserum. (B) Wild-type; Lateral view, stage 5. (C) Wild-type; Lateral view, stage 8. (D)  Wild-type; Lateral view, stage 14; arrow indicates the visceral musculature (vm). (E and F) Wild-type; Lateral views, stage 16; arrows in  E highlight somatic muscles 8, 12, and 19, using the nomenclature of Crossley (1978). Arrow in F marks the dorsal vessel (dv). Bars: (A– D and F) 100 μm; (E) 10 μm.
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Related In: Results  -  Collection

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Figure 5: Spatial expression pattern of MBC in wild-type embryos. Anterior is to the left and dorsal to the top in all except A. (A) Stage 13 embryos from the progeny of mbcD11.2/TM3 lacZ-hg stained immunohistochemically for MBC. The embryo to the top left expressed β-galactosidase and therefore carried TM3 lacZ-hg; the embryo to the bottom right (which is barely visible) did not express β-galactosidase (data not shown) and was therefore homozygous for mbcD11.2. As anticipated, no MBC expression is visible in the homozygous mutant embryo, establishing specificity of the antiserum. (B) Wild-type; Lateral view, stage 5. (C) Wild-type; Lateral view, stage 8. (D) Wild-type; Lateral view, stage 14; arrow indicates the visceral musculature (vm). (E and F) Wild-type; Lateral views, stage 16; arrows in E highlight somatic muscles 8, 12, and 19, using the nomenclature of Crossley (1978). Arrow in F marks the dorsal vessel (dv). Bars: (A– D and F) 100 μm; (E) 10 μm.
Mentions: The expression pattern of MBC was analyzed by fluorescent immunohistochemistry and confocal microscopy using an antiserum directed against the COOH-terminal portion of the protein. Examination of embryos homozygous for mbcD11.2 confirmed that the antiserum was specific (Fig. 5 A) since this allele encodes a severely truncated form of MBC that would not be detected. While slight temporal differences were evident between maximal levels of mRNA (stage 4; Fig. 4 A) and maximal levels of protein (stage 5; Fig. 5 B) in the pole cells, the expression of the protein essentially correlated with that of the mRNA. MBC appeared to be localized in the cytoplasm (Fig. 5 C), consistent with its human counterpart DOCK180. MBC is also present in the visceral musculature (Fig. 5 D, arrow) and the dorsal vessel (Fig. 5 F, arrow). Cross reactivity of the MBC antiserum was observed in the filtzkorper (Fig. 5 F) but does not correlate with the presence of transcript. Although mRNA was not evident in mature muscles, the protein could be detected at a low level (Fig. 5 E).

Bottom Line: It is also expressed in the pole cells and in ectodermally derived tissues, including the epidermis.Consistent with this latter expression, mbc mutant embryos exhibit defects in dorsal closure and cytoskeletal organization in the migrating epidermis.Both the mesodermal and ectodermal defects are reminiscent of those induced by altered forms of Drac1 and suggest that mbc may function in the same pathway.

View Article: PubMed Central - PubMed

Affiliation: Department of Biochemistry and Molecular Biology and Center for Gene Regulation, The Pennsylvania State University, University Park, Pennsylvania 16802, USA.

ABSTRACT
The Drosophila myoblast city (mbc) locus was previously identified on the basis of a defect in myoblast fusion (Rushton et al., 1995. Development [Camb.]. 121:1979-1988). We describe herein the isolation and characterization of the mbc gene. The mbc transcript and its encoded protein are expressed in a broad range of tissues, including somatic myoblasts, cardial cells, and visceral mesoderm. It is also expressed in the pole cells and in ectodermally derived tissues, including the epidermis. Consistent with this latter expression, mbc mutant embryos exhibit defects in dorsal closure and cytoskeletal organization in the migrating epidermis. Both the mesodermal and ectodermal defects are reminiscent of those induced by altered forms of Drac1 and suggest that mbc may function in the same pathway. MBC bears striking homology to human DOCK180, which interacts with the SH2-SH3 adapter protein Crk and may play a role in signal transduction from focal adhesions. Taken together, these results suggest the possibility that MBC is an intermediate in a signal transduction pathway from the rho/rac family of GTPases to events in the cytoskeleton and that this pathway may be used during myoblast fusion and dorsal closure.

Show MeSH
Related in: MedlinePlus