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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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Phylogenetic Tree of Tre1 and Expression Patterns of CG3171 (tre1)(A) Phylogenetic tree of Tre1 protein with other closely related GPCRs (drawn using ClustalW of MegAlign program from DNA-STAR). Tre1 (indicated by arrow) is closely related to a group of fly, Anopheles, and vertebrate GPCRs. Among known ligand–receptor pairs, this novel receptor group is most closely related to melatonin, histamine, and serotonin receptors. Abbreviations: Ag, Anopheles gambiae; Dm, Drosophila melanogaster; Dr, Danio rerio; Fr, Fugu rubripes; Hs, Homo sapiens; Mm, Mus musculus; Xl, Xenopus laevis.(B–G) RNA expression pattern of CG3171 (tre1). Anterior is to the left in all embryos. All embryos are in lateral views. (B–E) Expression pattern of tre1 (CG3171) RNA in wild-type embryos.(B) In a stage 3 embryo, tre1 transcript is provided maternally and enriched at the posterior pole (arrow).(C) At stage 6, tre1 transcript is degraded in somatic tissues, but protected in the germ cells (arrow).(D) At stage 9, tre1 transcript is still detected in germ cells (arrow), but is also expressed broadly throughout the soma.(E) By stage 13, tre1 transcript is highly expressed in several somatic tissues, including the midline glial, cuprophilic cells, glial cells, and CNS.(F) In a stage 6 M− Z− tre1 embryo, no specific tre1 transcript is detected in germ cells (arrow). Weak staining in somatic tissues represents the background as it is also seen with sense control RNA probe. At stage 13, weak but specific tre1 expression is detected in cuprophilic cells and CNS (data not shown).(G) M− Z+ tre1 embryo. tre1 transcript is detected weakly in the germ cells at stage 9, indicating zygotic expression in the germ cells (arrow). Note the broad zygotic tre1 expression similar to (D).
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pbio.0000080-g002: Phylogenetic Tree of Tre1 and Expression Patterns of CG3171 (tre1)(A) Phylogenetic tree of Tre1 protein with other closely related GPCRs (drawn using ClustalW of MegAlign program from DNA-STAR). Tre1 (indicated by arrow) is closely related to a group of fly, Anopheles, and vertebrate GPCRs. Among known ligand–receptor pairs, this novel receptor group is most closely related to melatonin, histamine, and serotonin receptors. Abbreviations: Ag, Anopheles gambiae; Dm, Drosophila melanogaster; Dr, Danio rerio; Fr, Fugu rubripes; Hs, Homo sapiens; Mm, Mus musculus; Xl, Xenopus laevis.(B–G) RNA expression pattern of CG3171 (tre1). Anterior is to the left in all embryos. All embryos are in lateral views. (B–E) Expression pattern of tre1 (CG3171) RNA in wild-type embryos.(B) In a stage 3 embryo, tre1 transcript is provided maternally and enriched at the posterior pole (arrow).(C) At stage 6, tre1 transcript is degraded in somatic tissues, but protected in the germ cells (arrow).(D) At stage 9, tre1 transcript is still detected in germ cells (arrow), but is also expressed broadly throughout the soma.(E) By stage 13, tre1 transcript is highly expressed in several somatic tissues, including the midline glial, cuprophilic cells, glial cells, and CNS.(F) In a stage 6 M− Z− tre1 embryo, no specific tre1 transcript is detected in germ cells (arrow). Weak staining in somatic tissues represents the background as it is also seen with sense control RNA probe. At stage 13, weak but specific tre1 expression is detected in cuprophilic cells and CNS (data not shown).(G) M− Z+ tre1 embryo. tre1 transcript is detected weakly in the germ cells at stage 9, indicating zygotic expression in the germ cells (arrow). Note the broad zygotic tre1 expression similar to (D).

Mentions: The specific effect of CG4322 misexpression on germ cell migratory behavior suggested to us that GPCR signaling may be important for normal germ cell migration in Drosophila, as was recently shown for zebrafish and mouse (Doitsidou et al. 2002; Ara et al. 2003; Knaut et al. 2003; Kunwar and Lehmann 2003; Molyneaux et al. 2003). However, as CG4322 mutations did not affect germ cell migration, we reasoned that other, perhaps related GPCRs may play a role in germ cells either in concert with CG4322 or on their own. To identify such a putative GPCR, we searched the Drosophila genome database for genes closely related to homologs of CG4322. CG4322 belongs to the Rhodopsin receptor class of GPCRs. The closest homologs of CG4322 in the fly genome are CG4313, the neighboring gene 2.5 kb upstream of CG4322, which has not yet been further characterized, and CG3171, which was previously thought to encode the receptor for Trehalose, tre1 (see below) (Ishimoto et al. 2000; Dahanukar et al. 2001; Ueno et al. 2001). The National Center for Biotechnology Information (NCBI) database analysis identified three Anopheles proteins of unknown function, each most closely related to the respective fly GPCRs (Figure 2A). Several uncharacterized proteins from vertebrates, such as the human EX33 protein, which was found in a neutrophil cDNA library, the mouse GPR84 receptor, and a zebrafish (ENSDARG07201) and Fugu (FuguGenscan31921) putative GPCR, are the closest homologs to CG3171, CG4322, and CG4313. Our phylogenetic analysis suggests that this group may represent a new subclass of GPCRs. Among known ligand–receptor pairs, this group is most closely related to the vertebrate melatonin and histamine receptors and, more distantly, to vertebrate chemokine receptors (Figure 2A; data not shown).


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)

Phylogenetic Tree of Tre1 and Expression Patterns of CG3171 (tre1)(A) Phylogenetic tree of Tre1 protein with other closely related GPCRs (drawn using ClustalW of MegAlign program from DNA-STAR). Tre1 (indicated by arrow) is closely related to a group of fly, Anopheles, and vertebrate GPCRs. Among known ligand–receptor pairs, this novel receptor group is most closely related to melatonin, histamine, and serotonin receptors. Abbreviations: Ag, Anopheles gambiae; Dm, Drosophila melanogaster; Dr, Danio rerio; Fr, Fugu rubripes; Hs, Homo sapiens; Mm, Mus musculus; Xl, Xenopus laevis.(B–G) RNA expression pattern of CG3171 (tre1). Anterior is to the left in all embryos. All embryos are in lateral views. (B–E) Expression pattern of tre1 (CG3171) RNA in wild-type embryos.(B) In a stage 3 embryo, tre1 transcript is provided maternally and enriched at the posterior pole (arrow).(C) At stage 6, tre1 transcript is degraded in somatic tissues, but protected in the germ cells (arrow).(D) At stage 9, tre1 transcript is still detected in germ cells (arrow), but is also expressed broadly throughout the soma.(E) By stage 13, tre1 transcript is highly expressed in several somatic tissues, including the midline glial, cuprophilic cells, glial cells, and CNS.(F) In a stage 6 M− Z− tre1 embryo, no specific tre1 transcript is detected in germ cells (arrow). Weak staining in somatic tissues represents the background as it is also seen with sense control RNA probe. At stage 13, weak but specific tre1 expression is detected in cuprophilic cells and CNS (data not shown).(G) M− Z+ tre1 embryo. tre1 transcript is detected weakly in the germ cells at stage 9, indicating zygotic expression in the germ cells (arrow). Note the broad zygotic tre1 expression similar to (D).
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Related In: Results  -  Collection

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pbio.0000080-g002: Phylogenetic Tree of Tre1 and Expression Patterns of CG3171 (tre1)(A) Phylogenetic tree of Tre1 protein with other closely related GPCRs (drawn using ClustalW of MegAlign program from DNA-STAR). Tre1 (indicated by arrow) is closely related to a group of fly, Anopheles, and vertebrate GPCRs. Among known ligand–receptor pairs, this novel receptor group is most closely related to melatonin, histamine, and serotonin receptors. Abbreviations: Ag, Anopheles gambiae; Dm, Drosophila melanogaster; Dr, Danio rerio; Fr, Fugu rubripes; Hs, Homo sapiens; Mm, Mus musculus; Xl, Xenopus laevis.(B–G) RNA expression pattern of CG3171 (tre1). Anterior is to the left in all embryos. All embryos are in lateral views. (B–E) Expression pattern of tre1 (CG3171) RNA in wild-type embryos.(B) In a stage 3 embryo, tre1 transcript is provided maternally and enriched at the posterior pole (arrow).(C) At stage 6, tre1 transcript is degraded in somatic tissues, but protected in the germ cells (arrow).(D) At stage 9, tre1 transcript is still detected in germ cells (arrow), but is also expressed broadly throughout the soma.(E) By stage 13, tre1 transcript is highly expressed in several somatic tissues, including the midline glial, cuprophilic cells, glial cells, and CNS.(F) In a stage 6 M− Z− tre1 embryo, no specific tre1 transcript is detected in germ cells (arrow). Weak staining in somatic tissues represents the background as it is also seen with sense control RNA probe. At stage 13, weak but specific tre1 expression is detected in cuprophilic cells and CNS (data not shown).(G) M− Z+ tre1 embryo. tre1 transcript is detected weakly in the germ cells at stage 9, indicating zygotic expression in the germ cells (arrow). Note the broad zygotic tre1 expression similar to (D).
Mentions: The specific effect of CG4322 misexpression on germ cell migratory behavior suggested to us that GPCR signaling may be important for normal germ cell migration in Drosophila, as was recently shown for zebrafish and mouse (Doitsidou et al. 2002; Ara et al. 2003; Knaut et al. 2003; Kunwar and Lehmann 2003; Molyneaux et al. 2003). However, as CG4322 mutations did not affect germ cell migration, we reasoned that other, perhaps related GPCRs may play a role in germ cells either in concert with CG4322 or on their own. To identify such a putative GPCR, we searched the Drosophila genome database for genes closely related to homologs of CG4322. CG4322 belongs to the Rhodopsin receptor class of GPCRs. The closest homologs of CG4322 in the fly genome are CG4313, the neighboring gene 2.5 kb upstream of CG4322, which has not yet been further characterized, and CG3171, which was previously thought to encode the receptor for Trehalose, tre1 (see below) (Ishimoto et al. 2000; Dahanukar et al. 2001; Ueno et al. 2001). The National Center for Biotechnology Information (NCBI) database analysis identified three Anopheles proteins of unknown function, each most closely related to the respective fly GPCRs (Figure 2A). Several uncharacterized proteins from vertebrates, such as the human EX33 protein, which was found in a neutrophil cDNA library, the mouse GPR84 receptor, and a zebrafish (ENSDARG07201) and Fugu (FuguGenscan31921) putative GPCR, are the closest homologs to CG3171, CG4322, and CG4313. Our phylogenetic analysis suggests that this group may represent a new subclass of GPCRs. Among known ligand–receptor pairs, this group is most closely related to the vertebrate melatonin and histamine receptors and, more distantly, to vertebrate chemokine receptors (Figure 2A; data not shown).

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