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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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Analysis of mesodermal derivatives in mbc mutant embryos. Tissues were visualized with a monoclonal antibody to MHC. All  embryos are oriented with anterior to the left. A and B are lateral views with dorsal to the top, C and D are ventral views, and E and F  are dorsal views. A, C, and E are wild-type embryos; B, D, and F are mbcF12.7/Df(3R)mbc-30 transheterozygotes. (A and B) Somatic  muscle pattern of stage 16 embryos. Defects in myoblast fusion, as previously described by Rushton et al. (1995), are evident in B. (C  and D) Visceral musculature and gut formation in late stage 16 embryos. Note the midgut constrictions in C and the absence of these  constrictions in D. (E and F) Dorsal vessel of stage 17 embryos. At this level, there are no obvious defects. Bars, 50 μm.
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Figure 7: Analysis of mesodermal derivatives in mbc mutant embryos. Tissues were visualized with a monoclonal antibody to MHC. All embryos are oriented with anterior to the left. A and B are lateral views with dorsal to the top, C and D are ventral views, and E and F are dorsal views. A, C, and E are wild-type embryos; B, D, and F are mbcF12.7/Df(3R)mbc-30 transheterozygotes. (A and B) Somatic muscle pattern of stage 16 embryos. Defects in myoblast fusion, as previously described by Rushton et al. (1995), are evident in B. (C and D) Visceral musculature and gut formation in late stage 16 embryos. Note the midgut constrictions in C and the absence of these constrictions in D. (E and F) Dorsal vessel of stage 17 embryos. At this level, there are no obvious defects. Bars, 50 μm.

Mentions: Given the broad expression pattern of mbc, it was of interest to examine mbc mutant embryos for defects in other tissues. For this purpose we used mbcF12.7, since the protein is truncated at amino acid 492, and analyzed embryos that were genetically mbcF12.7/Df(3R)mbc-30. These embryos exhibited the severe somatic muscle phenotype previously reported (Rushton et al., 1995) and shown in Fig. 7 B. By comparison, although the visceral musculature appeared to be present, as evidenced by myosin-staining cells, obvious defects in midgut constriction and orientation were observed in ∼25% of the embryos (Fig. 7, C and D). However, these defects may be an indirect consequence of the lack of somatic muscles rather than a direct effect of the loss of MBC in either the visceral mesoderm or the endoderm. The overall structure of the heart, which expresses MBC late in development, appeared to be normal at this level of analysis (Fig. 7, E and F).


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)

Analysis of mesodermal derivatives in mbc mutant embryos. Tissues were visualized with a monoclonal antibody to MHC. All  embryos are oriented with anterior to the left. A and B are lateral views with dorsal to the top, C and D are ventral views, and E and F  are dorsal views. A, C, and E are wild-type embryos; B, D, and F are mbcF12.7/Df(3R)mbc-30 transheterozygotes. (A and B) Somatic  muscle pattern of stage 16 embryos. Defects in myoblast fusion, as previously described by Rushton et al. (1995), are evident in B. (C  and D) Visceral musculature and gut formation in late stage 16 embryos. Note the midgut constrictions in C and the absence of these  constrictions in D. (E and F) Dorsal vessel of stage 17 embryos. At this level, there are no obvious defects. Bars, 50 μm.
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Related In: Results  -  Collection

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Figure 7: Analysis of mesodermal derivatives in mbc mutant embryos. Tissues were visualized with a monoclonal antibody to MHC. All embryos are oriented with anterior to the left. A and B are lateral views with dorsal to the top, C and D are ventral views, and E and F are dorsal views. A, C, and E are wild-type embryos; B, D, and F are mbcF12.7/Df(3R)mbc-30 transheterozygotes. (A and B) Somatic muscle pattern of stage 16 embryos. Defects in myoblast fusion, as previously described by Rushton et al. (1995), are evident in B. (C and D) Visceral musculature and gut formation in late stage 16 embryos. Note the midgut constrictions in C and the absence of these constrictions in D. (E and F) Dorsal vessel of stage 17 embryos. At this level, there are no obvious defects. Bars, 50 μm.
Mentions: Given the broad expression pattern of mbc, it was of interest to examine mbc mutant embryos for defects in other tissues. For this purpose we used mbcF12.7, since the protein is truncated at amino acid 492, and analyzed embryos that were genetically mbcF12.7/Df(3R)mbc-30. These embryos exhibited the severe somatic muscle phenotype previously reported (Rushton et al., 1995) and shown in Fig. 7 B. By comparison, although the visceral musculature appeared to be present, as evidenced by myosin-staining cells, obvious defects in midgut constriction and orientation were observed in ∼25% of the embryos (Fig. 7, C and D). However, these defects may be an indirect consequence of the lack of somatic muscles rather than a direct effect of the loss of MBC in either the visceral mesoderm or the endoderm. The overall structure of the heart, which expresses MBC late in development, appeared to be normal at this level of analysis (Fig. 7, E and F).

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