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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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Rho GTPase Is Required for Transepithelial Migration of Germ Cells(A–F) Wild-type, constitutively active, and dominant-negative Rho1 constructs under UAS promoter control were expressed in germ cells using the nos-GAL4 driver. Embryos are stained with anti-Vasa (brown) to mark germ cells. Anterior is left. Embryos in (A), (C), and (E) are lateral views at stage 11. Embryos in (B), (D), and (F) are top views, stage 13.(A and B) Germ cells expressing wild-type Rho1 (Rho1wt) migrate normally.(C and D) Germ cells expressing constitutively active Rho1 (Rho1V14) successfully transmigrated the PMG (C), but some germ cells fail to move from the PMG into the mesoderm and remain associated with the PMG (D).(E and F) Germ cells expressing dominant-negative Rho1 (Rho1N19) are still inside the PMG at stage 11 (E), and most germ cells remain “clumped” inside the gut (F).
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pbio.0000080-g008: Rho GTPase Is Required for Transepithelial Migration of Germ Cells(A–F) Wild-type, constitutively active, and dominant-negative Rho1 constructs under UAS promoter control were expressed in germ cells using the nos-GAL4 driver. Embryos are stained with anti-Vasa (brown) to mark germ cells. Anterior is left. Embryos in (A), (C), and (E) are lateral views at stage 11. Embryos in (B), (D), and (F) are top views, stage 13.(A and B) Germ cells expressing wild-type Rho1 (Rho1wt) migrate normally.(C and D) Germ cells expressing constitutively active Rho1 (Rho1V14) successfully transmigrated the PMG (C), but some germ cells fail to move from the PMG into the mesoderm and remain associated with the PMG (D).(E and F) Germ cells expressing dominant-negative Rho1 (Rho1N19) are still inside the PMG at stage 11 (E), and most germ cells remain “clumped” inside the gut (F).

Mentions: GPCR signal transduction is often mediated by members of the Rho family of small GTPases. These GTPases play major roles in the reorganization of the actin cytoskeleton to promote adhesion and movement (Mitchell et al. 1998; Fukuhara et al. 1999; Ridley 2001; Neves et al. 2002; Pierce et al. 2002). To test the involvement of these proteins in transepithelial migration, we used the UAS/nos-GAL4 system to express wild-type, constitutively active, or dominant-negative forms of small GTPases in the germ cells. Rac, RhoL, and Cdc42 expression had no effects on transepithelial migration of germ cells, while later aspects of germ cell migration were affected by expression of constitutively active and dominant-negative forms of Rac in germ cells (data not shown; Starz-Gaiano 2002). Interference with normal Rho1 function, on the other hand, caused a consistent and penetrant transepithelial migration phenotype (Figure 8A–8F). Overexpression of a dominant-negative form of Rho1, Rho1N19, in germ cells caused many of them to remain inside the PMG of stage 10 embryos, closely resembling the phenotype observed in tre1 mutant embryos (Figure 8E) (Barrett et al. 1997). Rho1N19-expressing germ cells were clumped in the middle of embryos at stage 13 (Figure 8F). At stages 13–14, when wild-type germ cells assemble into gonads, very few germ cells expressing the Rho1N19 transgene had successfully reached the gonad. Dominant-active Rho had a different effect. RhoV14-expressing germ cells successfully transmigrated the PMG during stages 9 and 10 of embryogenesis, but subsequently some germ cells failed to move from the PMG into the mesoderm (Figure 8C) (Lee et al. 2000). As a consequence, these germ cells also remained associated with the PMG (Figure 8D). Expression of wild-type Rho1 had no effect on germ cell migration (Figure 8A–8B) (Prokopenko et al. 1999). The fact that a dominant-negative form of Rho1 caused a similar migration defect as that observed in tre1 mutant embryos and that expression of other GTPases either showed no or a different migration defect strongly suggest that Tre1-dependent transepithelial migration is mediated by Rho GTPase in germ cells.


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)

Rho GTPase Is Required for Transepithelial Migration of Germ Cells(A–F) Wild-type, constitutively active, and dominant-negative Rho1 constructs under UAS promoter control were expressed in germ cells using the nos-GAL4 driver. Embryos are stained with anti-Vasa (brown) to mark germ cells. Anterior is left. Embryos in (A), (C), and (E) are lateral views at stage 11. Embryos in (B), (D), and (F) are top views, stage 13.(A and B) Germ cells expressing wild-type Rho1 (Rho1wt) migrate normally.(C and D) Germ cells expressing constitutively active Rho1 (Rho1V14) successfully transmigrated the PMG (C), but some germ cells fail to move from the PMG into the mesoderm and remain associated with the PMG (D).(E and F) Germ cells expressing dominant-negative Rho1 (Rho1N19) are still inside the PMG at stage 11 (E), and most germ cells remain “clumped” inside the gut (F).
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC300690&req=5

pbio.0000080-g008: Rho GTPase Is Required for Transepithelial Migration of Germ Cells(A–F) Wild-type, constitutively active, and dominant-negative Rho1 constructs under UAS promoter control were expressed in germ cells using the nos-GAL4 driver. Embryos are stained with anti-Vasa (brown) to mark germ cells. Anterior is left. Embryos in (A), (C), and (E) are lateral views at stage 11. Embryos in (B), (D), and (F) are top views, stage 13.(A and B) Germ cells expressing wild-type Rho1 (Rho1wt) migrate normally.(C and D) Germ cells expressing constitutively active Rho1 (Rho1V14) successfully transmigrated the PMG (C), but some germ cells fail to move from the PMG into the mesoderm and remain associated with the PMG (D).(E and F) Germ cells expressing dominant-negative Rho1 (Rho1N19) are still inside the PMG at stage 11 (E), and most germ cells remain “clumped” inside the gut (F).
Mentions: GPCR signal transduction is often mediated by members of the Rho family of small GTPases. These GTPases play major roles in the reorganization of the actin cytoskeleton to promote adhesion and movement (Mitchell et al. 1998; Fukuhara et al. 1999; Ridley 2001; Neves et al. 2002; Pierce et al. 2002). To test the involvement of these proteins in transepithelial migration, we used the UAS/nos-GAL4 system to express wild-type, constitutively active, or dominant-negative forms of small GTPases in the germ cells. Rac, RhoL, and Cdc42 expression had no effects on transepithelial migration of germ cells, while later aspects of germ cell migration were affected by expression of constitutively active and dominant-negative forms of Rac in germ cells (data not shown; Starz-Gaiano 2002). Interference with normal Rho1 function, on the other hand, caused a consistent and penetrant transepithelial migration phenotype (Figure 8A–8F). Overexpression of a dominant-negative form of Rho1, Rho1N19, in germ cells caused many of them to remain inside the PMG of stage 10 embryos, closely resembling the phenotype observed in tre1 mutant embryos (Figure 8E) (Barrett et al. 1997). Rho1N19-expressing germ cells were clumped in the middle of embryos at stage 13 (Figure 8F). At stages 13–14, when wild-type germ cells assemble into gonads, very few germ cells expressing the Rho1N19 transgene had successfully reached the gonad. Dominant-active Rho had a different effect. RhoV14-expressing germ cells successfully transmigrated the PMG during stages 9 and 10 of embryogenesis, but subsequently some germ cells failed to move from the PMG into the mesoderm (Figure 8C) (Lee et al. 2000). As a consequence, these germ cells also remained associated with the PMG (Figure 8D). Expression of wild-type Rho1 had no effect on germ cell migration (Figure 8A–8B) (Prokopenko et al. 1999). The fact that a dominant-negative form of Rho1 caused a similar migration defect as that observed in tre1 mutant embryos and that expression of other GTPases either showed no or a different migration defect strongly suggest that Tre1-dependent transepithelial migration is mediated by Rho GTPase in germ cells.

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