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A spindle-independent cleavage pathway controls germ cell formation in Drosophila.

Cinalli RM, Lehmann R - Nat. Cell Biol. (2013)

Bottom Line: The primordial germ cells (PGCs) are the first cells to form during Drosophila melanogaster embryogenesis.In addition to using core regulators of cleavage, including the small GTPase RhoA (Drosophila rho1) and the Rho-associated kinase, ROCK (Drosophila drok), we show that this pathway requires Germ cell-less (GCL), a conserved BTB-domain protein not previously implicated in cleavage mechanics.This alternative form of cell formation suggests that organisms have evolved multiple molecular strategies for regulating the cytoskeleton during cleavage.

View Article: PubMed Central - PubMed

Affiliation: HHMI and Kimmel Center for Biology and Medicine at the Skirball Institute, Department of Cell Biology, New York University School of Medicine, New York, New York 10016, USA.

ABSTRACT
The primordial germ cells (PGCs) are the first cells to form during Drosophila melanogaster embryogenesis. Whereas the process of somatic cell formation has been studied in detail, the mechanics of PGC formation are poorly understood. Here, using four-dimensional multi-photon imaging combined with genetic and pharmacological manipulations, we find that PGC formation requires an anaphase spindle-independent cleavage pathway. In addition to using core regulators of cleavage, including the small GTPase RhoA (Drosophila rho1) and the Rho-associated kinase, ROCK (Drosophila drok), we show that this pathway requires Germ cell-less (GCL), a conserved BTB-domain protein not previously implicated in cleavage mechanics. This alternative form of cell formation suggests that organisms have evolved multiple molecular strategies for regulating the cytoskeleton during cleavage.

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Mis-expression of Germ cell-less together with Anillin is sufficient for ectopic cell formation(a) Surface micrographs of wt and Gcl mis-expressing embryos (gcl-bcd) during somatic cellularization (Anillin (green), and DNA (blue)). Note mis-expression disrupts somatic cell formation by inducing the premature constriction of the cellularization furrow. Insets are representative micrographs depicting lateral views of the cellularization furrow in wt and Gcl mis-expressing embryos.(b) Micrographs of the anterior pole of Oskar mis-expressing (osk-bcd), gcl-bcd, and gcl-bcd, anillin-GFP embryos (Vasa, germ plasm marker (green) and Actin (red)). Note Oskar is sufficient to ectopically recruit germ plasm (Vasa) and instruct cell formation, while gcl-bcd, anillin-GFP embryos instruct cell formation but do not recruit germ plasm. Arrows mark ectopic cells in gcl-bcd, anillin-GFP embryos prior to somatic cell formation. (c) Micrographs of the anterior pole of embryos from females expressing gcl-bcd, anillin-GFP and gcl-bcd, anillin-GFP transgenes (Anillin-GFP (green) GCL-Actin (red) and DNA (blue)). Arrows mark ectopic cells in gcl-bcd, anillin-GFP embryos at the start of somatic cell formation. Scale bars = 5 μm
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Figure 5: Mis-expression of Germ cell-less together with Anillin is sufficient for ectopic cell formation(a) Surface micrographs of wt and Gcl mis-expressing embryos (gcl-bcd) during somatic cellularization (Anillin (green), and DNA (blue)). Note mis-expression disrupts somatic cell formation by inducing the premature constriction of the cellularization furrow. Insets are representative micrographs depicting lateral views of the cellularization furrow in wt and Gcl mis-expressing embryos.(b) Micrographs of the anterior pole of Oskar mis-expressing (osk-bcd), gcl-bcd, and gcl-bcd, anillin-GFP embryos (Vasa, germ plasm marker (green) and Actin (red)). Note Oskar is sufficient to ectopically recruit germ plasm (Vasa) and instruct cell formation, while gcl-bcd, anillin-GFP embryos instruct cell formation but do not recruit germ plasm. Arrows mark ectopic cells in gcl-bcd, anillin-GFP embryos prior to somatic cell formation. (c) Micrographs of the anterior pole of embryos from females expressing gcl-bcd, anillin-GFP and gcl-bcd, anillin-GFP transgenes (Anillin-GFP (green) GCL-Actin (red) and DNA (blue)). Arrows mark ectopic cells in gcl-bcd, anillin-GFP embryos at the start of somatic cell formation. Scale bars = 5 μm

Mentions: While increased Gcl levels in the germ plasm result in supernumerary PGCs, mis-expression of gcl alone is not sufficient to cause ectopic cell formation38. However, ectopic expression of gcl at the anterior pole (gcl-bcd) causes defects in somatic cellularization38. To determine how Gcl activity disrupts somatic cell formation, we immunostained control and Gcl mis-expressing embryos using an antibody against a somatic contractile ring component, Anillin. While constriction of the somatic contractile ring normally occurs only after membranes have surrounded the nuclei, we found that this Anillin-stained structure prematurely constricted in gcl-bcd embryos (Fig. 5a). Premature constriction of the contractile ring displaced somatic nuclei from the embryonic cortex and caused disruption of somatic cell organization. Thus, we conclude that Gcl is sufficient to promote constriction of the contractile ring independent of other germ plasm components. Because Gcl can influence the constriction behavior of both the BF and somatic contractile ring, we suggest that Gcl activity directly or indirectly regulates a core contractile component during cleavage.


A spindle-independent cleavage pathway controls germ cell formation in Drosophila.

Cinalli RM, Lehmann R - Nat. Cell Biol. (2013)

Mis-expression of Germ cell-less together with Anillin is sufficient for ectopic cell formation(a) Surface micrographs of wt and Gcl mis-expressing embryos (gcl-bcd) during somatic cellularization (Anillin (green), and DNA (blue)). Note mis-expression disrupts somatic cell formation by inducing the premature constriction of the cellularization furrow. Insets are representative micrographs depicting lateral views of the cellularization furrow in wt and Gcl mis-expressing embryos.(b) Micrographs of the anterior pole of Oskar mis-expressing (osk-bcd), gcl-bcd, and gcl-bcd, anillin-GFP embryos (Vasa, germ plasm marker (green) and Actin (red)). Note Oskar is sufficient to ectopically recruit germ plasm (Vasa) and instruct cell formation, while gcl-bcd, anillin-GFP embryos instruct cell formation but do not recruit germ plasm. Arrows mark ectopic cells in gcl-bcd, anillin-GFP embryos prior to somatic cell formation. (c) Micrographs of the anterior pole of embryos from females expressing gcl-bcd, anillin-GFP and gcl-bcd, anillin-GFP transgenes (Anillin-GFP (green) GCL-Actin (red) and DNA (blue)). Arrows mark ectopic cells in gcl-bcd, anillin-GFP embryos at the start of somatic cell formation. Scale bars = 5 μm
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Figure 5: Mis-expression of Germ cell-less together with Anillin is sufficient for ectopic cell formation(a) Surface micrographs of wt and Gcl mis-expressing embryos (gcl-bcd) during somatic cellularization (Anillin (green), and DNA (blue)). Note mis-expression disrupts somatic cell formation by inducing the premature constriction of the cellularization furrow. Insets are representative micrographs depicting lateral views of the cellularization furrow in wt and Gcl mis-expressing embryos.(b) Micrographs of the anterior pole of Oskar mis-expressing (osk-bcd), gcl-bcd, and gcl-bcd, anillin-GFP embryos (Vasa, germ plasm marker (green) and Actin (red)). Note Oskar is sufficient to ectopically recruit germ plasm (Vasa) and instruct cell formation, while gcl-bcd, anillin-GFP embryos instruct cell formation but do not recruit germ plasm. Arrows mark ectopic cells in gcl-bcd, anillin-GFP embryos prior to somatic cell formation. (c) Micrographs of the anterior pole of embryos from females expressing gcl-bcd, anillin-GFP and gcl-bcd, anillin-GFP transgenes (Anillin-GFP (green) GCL-Actin (red) and DNA (blue)). Arrows mark ectopic cells in gcl-bcd, anillin-GFP embryos at the start of somatic cell formation. Scale bars = 5 μm
Mentions: While increased Gcl levels in the germ plasm result in supernumerary PGCs, mis-expression of gcl alone is not sufficient to cause ectopic cell formation38. However, ectopic expression of gcl at the anterior pole (gcl-bcd) causes defects in somatic cellularization38. To determine how Gcl activity disrupts somatic cell formation, we immunostained control and Gcl mis-expressing embryos using an antibody against a somatic contractile ring component, Anillin. While constriction of the somatic contractile ring normally occurs only after membranes have surrounded the nuclei, we found that this Anillin-stained structure prematurely constricted in gcl-bcd embryos (Fig. 5a). Premature constriction of the contractile ring displaced somatic nuclei from the embryonic cortex and caused disruption of somatic cell organization. Thus, we conclude that Gcl is sufficient to promote constriction of the contractile ring independent of other germ plasm components. Because Gcl can influence the constriction behavior of both the BF and somatic contractile ring, we suggest that Gcl activity directly or indirectly regulates a core contractile component during cleavage.

Bottom Line: The primordial germ cells (PGCs) are the first cells to form during Drosophila melanogaster embryogenesis.In addition to using core regulators of cleavage, including the small GTPase RhoA (Drosophila rho1) and the Rho-associated kinase, ROCK (Drosophila drok), we show that this pathway requires Germ cell-less (GCL), a conserved BTB-domain protein not previously implicated in cleavage mechanics.This alternative form of cell formation suggests that organisms have evolved multiple molecular strategies for regulating the cytoskeleton during cleavage.

View Article: PubMed Central - PubMed

Affiliation: HHMI and Kimmel Center for Biology and Medicine at the Skirball Institute, Department of Cell Biology, New York University School of Medicine, New York, New York 10016, USA.

ABSTRACT
The primordial germ cells (PGCs) are the first cells to form during Drosophila melanogaster embryogenesis. Whereas the process of somatic cell formation has been studied in detail, the mechanics of PGC formation are poorly understood. Here, using four-dimensional multi-photon imaging combined with genetic and pharmacological manipulations, we find that PGC formation requires an anaphase spindle-independent cleavage pathway. In addition to using core regulators of cleavage, including the small GTPase RhoA (Drosophila rho1) and the Rho-associated kinase, ROCK (Drosophila drok), we show that this pathway requires Germ cell-less (GCL), a conserved BTB-domain protein not previously implicated in cleavage mechanics. This alternative form of cell formation suggests that organisms have evolved multiple molecular strategies for regulating the cytoskeleton during cleavage.

Show MeSH
Related in: MedlinePlus