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Tre1, a G protein-coupled receptor, directs transepithelial migration of Drosophila germ cells.

Kunwar PS, Starz-Gaiano M, Bainton RJ, Heberlein U, Lehmann R - PLoS Biol. (2003)

Bottom Line: In tre1 mutant embryos, most germ cells do not exit the PMG.Recently, the chemokine receptor CXCR4 was shown to direct migration in vertebrate germ cells.Thus, germ cells may more generally use GPCR signaling to navigate the embryo toward their target.

View Article: PubMed Central - PubMed

Affiliation: Howard Hughes Medical Institute, Developmental Genetics Program, New York University School of Medicine, New York, New York, USA.

ABSTRACT
In most organisms, germ cells are formed distant from the somatic part of the gonad and thus have to migrate along and through a variety of tissues to reach the gonad. Transepithelial migration through the posterior midgut (PMG) is the first active step during Drosophila germ cell migration. Here we report the identification of a novel G protein-coupled receptor (GPCR), Tre1, that is essential for this migration step. Maternal tre1 RNA is localized to germ cells, and tre1 is required cell autonomously in germ cells. In tre1 mutant embryos, most germ cells do not exit the PMG. The few germ cells that do leave the midgut early migrate normally to the gonad, suggesting that this gene is specifically required for transepithelial migration and that mutant germ cells are still able to recognize other guidance cues. Additionally, inhibiting small Rho GTPases in germ cells affects transepithelial migration, suggesting that Tre1 signals through Rho1. We propose that Tre1 acts in a manner similar to chemokine receptors required during transepithelial migration of leukocytes, implying an evolutionarily conserved mechanism of transepithelial migration. Recently, the chemokine receptor CXCR4 was shown to direct migration in vertebrate germ cells. Thus, germ cells may more generally use GPCR signaling to navigate the embryo toward their target.

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Germ Cell-Specific Requirement of tre1 by Germ Cell Transplantation(A), (C), and (E) depict the experimental scheme for germ cell transplantation. Germ cells (yellow) were transplanted from wild-type (A) or tre1 (C) stage 6 embryos to same stage embryos from tudor mothers, which do not have germ cells. In (E), germ cells (blue) labeled with LacZ (faf–LacZ) transgene were transplanted to the same stage tre1 embryos, to distinguish donor and host germ cells by β-galactosidase activity. (B), (D), and (F) are examples of transplanted, fixed, and stained embryos. Anterior is left in all embryos. Embryos in (B) and (F) are at stage 13; embryo in (D) is at stage 14. Embryos in (B) and (D) are stained with anti-Vasa (brown), and the embryo in (F) is stained with anti-β-galactosidase (brown). Arrow points to transplanted germ cells. (G–H) Summary of transplantation experiments. The bar graph in (G) summarizes the position of germ cells in embryos with successful transplantation (n = 36 for wild-type germ cells, n = 38 for tre1 mutant germ cells, and n = 48 for faf–LacZ-labeled wild-type germ cells). The bar graph in (H) summarizes the number of germ cells from successful transplantations at particular locations (n = 115 for wild-type germ cells, n = 87 for tre1 mutant germ cells, and n = 184 for faf–LacZ-labeled wild-type germ cells). Note that even in wild-type control transplantations, most germ cells, which do not reach the gonad, remain associated with the gut.
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pbio.0000080-g005: Germ Cell-Specific Requirement of tre1 by Germ Cell Transplantation(A), (C), and (E) depict the experimental scheme for germ cell transplantation. Germ cells (yellow) were transplanted from wild-type (A) or tre1 (C) stage 6 embryos to same stage embryos from tudor mothers, which do not have germ cells. In (E), germ cells (blue) labeled with LacZ (faf–LacZ) transgene were transplanted to the same stage tre1 embryos, to distinguish donor and host germ cells by β-galactosidase activity. (B), (D), and (F) are examples of transplanted, fixed, and stained embryos. Anterior is left in all embryos. Embryos in (B) and (F) are at stage 13; embryo in (D) is at stage 14. Embryos in (B) and (D) are stained with anti-Vasa (brown), and the embryo in (F) is stained with anti-β-galactosidase (brown). Arrow points to transplanted germ cells. (G–H) Summary of transplantation experiments. The bar graph in (G) summarizes the position of germ cells in embryos with successful transplantation (n = 36 for wild-type germ cells, n = 38 for tre1 mutant germ cells, and n = 48 for faf–LacZ-labeled wild-type germ cells). The bar graph in (H) summarizes the number of germ cells from successful transplantations at particular locations (n = 115 for wild-type germ cells, n = 87 for tre1 mutant germ cells, and n = 184 for faf–LacZ-labeled wild-type germ cells). Note that even in wild-type control transplantations, most germ cells, which do not reach the gonad, remain associated with the gut.

Mentions: tre1 mutants affect germ cell migration maternally, and tre1 RNA is present in early germ cells; we therefore hypothesized that tre1 may act specifically in germ cells to mediate their migration through the PMG. We used two experimental approaches to test whether tre1 is required in the germ cells in a cell-autonomous manner. In the first approach, germ cells from wild-type or tre1 mutant females were transplanted into tudor embryos (embryos produced by homozygous tudor mothers that lack germ cells) (Boswell and Mahowald 1985; Lehmann and Nüsslein-Volhard 1986, 1987). In the control experiments, wild-type germ cells migrated to the gonad in 41.6% (total number of embryos, n = 36) (Figure 5A–5B and 5G–5H). In total, 34% of all transplanted germ cells migrated successfully to the gonad (total number of germ cells transplanted, n = 115). In contrast, tre1 germ cells transplanted into tudor embryos rarely migrated to the gonad. Only 11% of embryos had transplanted tre1 germ cells in the gonad (n = 38) (Figure 5C–5D and 5G–5H), and only 9.1% of all transplanted germ cells successfully migrated to the gonad (n = 87). To test for a somatic role of tre1, we transplanted wild-type germ cells into tre1 mutant embryos. We marked the transplanted germ cells with a P[faf–LacZ] transgene, to distinguish the transplanted from the endogenous germ cells by the presence of β-galactosidase activity (Fischer-Vize et al. 1992). In 54.4% (n = 48) of embryos examined, germ cells migrated to the gonad (Figure 5E–5F and 5G–5H) and 40.2% of the transplanted germ cells successfully migrated to the gonad (n = 184). These experiments suggest that tre1 function is required within the germ cells for their normal migration.


Tre1, a G protein-coupled receptor, directs transepithelial migration of Drosophila germ cells.

Kunwar PS, Starz-Gaiano M, Bainton RJ, Heberlein U, Lehmann R - PLoS Biol. (2003)

Germ Cell-Specific Requirement of tre1 by Germ Cell Transplantation(A), (C), and (E) depict the experimental scheme for germ cell transplantation. Germ cells (yellow) were transplanted from wild-type (A) or tre1 (C) stage 6 embryos to same stage embryos from tudor mothers, which do not have germ cells. In (E), germ cells (blue) labeled with LacZ (faf–LacZ) transgene were transplanted to the same stage tre1 embryos, to distinguish donor and host germ cells by β-galactosidase activity. (B), (D), and (F) are examples of transplanted, fixed, and stained embryos. Anterior is left in all embryos. Embryos in (B) and (F) are at stage 13; embryo in (D) is at stage 14. Embryos in (B) and (D) are stained with anti-Vasa (brown), and the embryo in (F) is stained with anti-β-galactosidase (brown). Arrow points to transplanted germ cells. (G–H) Summary of transplantation experiments. The bar graph in (G) summarizes the position of germ cells in embryos with successful transplantation (n = 36 for wild-type germ cells, n = 38 for tre1 mutant germ cells, and n = 48 for faf–LacZ-labeled wild-type germ cells). The bar graph in (H) summarizes the number of germ cells from successful transplantations at particular locations (n = 115 for wild-type germ cells, n = 87 for tre1 mutant germ cells, and n = 184 for faf–LacZ-labeled wild-type germ cells). Note that even in wild-type control transplantations, most germ cells, which do not reach the gonad, remain associated with the gut.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC300690&req=5

pbio.0000080-g005: Germ Cell-Specific Requirement of tre1 by Germ Cell Transplantation(A), (C), and (E) depict the experimental scheme for germ cell transplantation. Germ cells (yellow) were transplanted from wild-type (A) or tre1 (C) stage 6 embryos to same stage embryos from tudor mothers, which do not have germ cells. In (E), germ cells (blue) labeled with LacZ (faf–LacZ) transgene were transplanted to the same stage tre1 embryos, to distinguish donor and host germ cells by β-galactosidase activity. (B), (D), and (F) are examples of transplanted, fixed, and stained embryos. Anterior is left in all embryos. Embryos in (B) and (F) are at stage 13; embryo in (D) is at stage 14. Embryos in (B) and (D) are stained with anti-Vasa (brown), and the embryo in (F) is stained with anti-β-galactosidase (brown). Arrow points to transplanted germ cells. (G–H) Summary of transplantation experiments. The bar graph in (G) summarizes the position of germ cells in embryos with successful transplantation (n = 36 for wild-type germ cells, n = 38 for tre1 mutant germ cells, and n = 48 for faf–LacZ-labeled wild-type germ cells). The bar graph in (H) summarizes the number of germ cells from successful transplantations at particular locations (n = 115 for wild-type germ cells, n = 87 for tre1 mutant germ cells, and n = 184 for faf–LacZ-labeled wild-type germ cells). Note that even in wild-type control transplantations, most germ cells, which do not reach the gonad, remain associated with the gut.
Mentions: tre1 mutants affect germ cell migration maternally, and tre1 RNA is present in early germ cells; we therefore hypothesized that tre1 may act specifically in germ cells to mediate their migration through the PMG. We used two experimental approaches to test whether tre1 is required in the germ cells in a cell-autonomous manner. In the first approach, germ cells from wild-type or tre1 mutant females were transplanted into tudor embryos (embryos produced by homozygous tudor mothers that lack germ cells) (Boswell and Mahowald 1985; Lehmann and Nüsslein-Volhard 1986, 1987). In the control experiments, wild-type germ cells migrated to the gonad in 41.6% (total number of embryos, n = 36) (Figure 5A–5B and 5G–5H). In total, 34% of all transplanted germ cells migrated successfully to the gonad (total number of germ cells transplanted, n = 115). In contrast, tre1 germ cells transplanted into tudor embryos rarely migrated to the gonad. Only 11% of embryos had transplanted tre1 germ cells in the gonad (n = 38) (Figure 5C–5D and 5G–5H), and only 9.1% of all transplanted germ cells successfully migrated to the gonad (n = 87). To test for a somatic role of tre1, we transplanted wild-type germ cells into tre1 mutant embryos. We marked the transplanted germ cells with a P[faf–LacZ] transgene, to distinguish the transplanted from the endogenous germ cells by the presence of β-galactosidase activity (Fischer-Vize et al. 1992). In 54.4% (n = 48) of embryos examined, germ cells migrated to the gonad (Figure 5E–5F and 5G–5H) and 40.2% of the transplanted germ cells successfully migrated to the gonad (n = 184). These experiments suggest that tre1 function is required within the germ cells for their normal migration.

Bottom Line: In tre1 mutant embryos, most germ cells do not exit the PMG.Recently, the chemokine receptor CXCR4 was shown to direct migration in vertebrate germ cells.Thus, germ cells may more generally use GPCR signaling to navigate the embryo toward their target.

View Article: PubMed Central - PubMed

Affiliation: Howard Hughes Medical Institute, Developmental Genetics Program, New York University School of Medicine, New York, New York, USA.

ABSTRACT
In most organisms, germ cells are formed distant from the somatic part of the gonad and thus have to migrate along and through a variety of tissues to reach the gonad. Transepithelial migration through the posterior midgut (PMG) is the first active step during Drosophila germ cell migration. Here we report the identification of a novel G protein-coupled receptor (GPCR), Tre1, that is essential for this migration step. Maternal tre1 RNA is localized to germ cells, and tre1 is required cell autonomously in germ cells. In tre1 mutant embryos, most germ cells do not exit the PMG. The few germ cells that do leave the midgut early migrate normally to the gonad, suggesting that this gene is specifically required for transepithelial migration and that mutant germ cells are still able to recognize other guidance cues. Additionally, inhibiting small Rho GTPases in germ cells affects transepithelial migration, suggesting that Tre1 signals through Rho1. We propose that Tre1 acts in a manner similar to chemokine receptors required during transepithelial migration of leukocytes, implying an evolutionarily conserved mechanism of transepithelial migration. Recently, the chemokine receptor CXCR4 was shown to direct migration in vertebrate germ cells. Thus, germ cells may more generally use GPCR signaling to navigate the embryo toward their target.

Show MeSH