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C. elegans FOG-3/Tob can either promote or inhibit germline proliferation, depending on gene dosage and genetic context.

Snow JJ, Lee MH, Verheyden J, Kroll-Conner PL, Kimble J - Oncogene (2012)

Bottom Line: Thus, fog-3 mutants possess fewer germ cells than normal, a modest but reproducible decrease observed for each of two distinct fog-3 alleles.Finally, we show that FOG-3 and FBF work together to promote tumor formation in animals carrying oncogenic Notch mutations.A similar effect was not observed when germline tumors were induced by manipulation of other regulators; therefore, this FOG-3 tumor-promoting effect is context dependent.

View Article: PubMed Central - PubMed

Affiliation: Program in Cellular and Molecular Biology, University of Wisconsin-Madison, Madison, WI, USA.

ABSTRACT
Vertebrate Tob/BTG proteins inhibit cell proliferation when overexpressed in tissue-culture cells, and they can function as tumor suppressors in mice. The single Caenorhabditis elegans Tob/BTG ortholog, FOG-3, by contrast, was identified from its loss-of-function phenotype as a regulator of sperm fate specification. Here we report that FOG-3 also regulates proliferation in the germline tissue. We first demonstrate that FOG-3 is a positive regulator of germline proliferation. Thus, fog-3 mutants possess fewer germ cells than normal, a modest but reproducible decrease observed for each of two distinct fog-3 alleles. A similar decrease also occurred in fog-3/+ heterozygotes, again for both fog-3 alleles, revealing a haplo-insufficient effect on proliferation. Therefore, FOG-3 normally promotes proliferation, and two copies of the fog-3 gene are required for this function. We next overexpressed FOG-3 by removal of FBF, the collective term for FBF-1 and FBF-2, two nearly identical PUF RNA-binding proteins. We find that overexpressed FOG-3 blocks proliferation in fbf-1 fbf-2 mutants; whereas germ cells stop dividing and instead differentiate in fbf-1 fbf-2 double mutants, they continue to proliferate in fog-3; fbf-1 fbf-2 triple mutants. Therefore, like its vertebrate Tob/BTG cousins, overexpressed FOG-3 is 'antiproliferative'. Indeed, some fog-3; fbf-1 fbf-2 mutants possess small tumors, suggesting that FOG-3 can act as a tumor suppressor. Finally, we show that FOG-3 and FBF work together to promote tumor formation in animals carrying oncogenic Notch mutations. A similar effect was not observed when germline tumors were induced by manipulation of other regulators; therefore, this FOG-3 tumor-promoting effect is context dependent. We conclude that FOG-3 can either promote or inhibit proliferation in a manner that is sensitive to both genetic context and gene dosage. The discovery of these FOG-3 effects on proliferation has implications for our understanding of vertebrate Tob/BTG proteins and their influence on normal development and tumorigenesis.

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FOG-3 and FBF can promote tumor formation. (a) Effects of fog-3, fbf-1 and fbf-2 depletion on tumor formation in animals homozygous for an oncogenic Notch mutation, glp-1(gf). Tum, tumorous; *, some fog-3(RNAi) tumorous germlines made a few oocytes; n, number of germlines scored; a Berry et al. (27). (b–d) Young adult gonads in intact animals, 1 day past L4. Dotted line, outline of gonadal tissue. Scale bar, 50 μM. Empty arrowheads, distal end. (b) Tumorous germline with no apparent differentiation. (c) Tumorous germline with oocytes (solid arrowheads) after fog-3 depletion. (d) Germline tumor abolished after fog-3 and fbf depletion.
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Figure 4: FOG-3 and FBF can promote tumor formation. (a) Effects of fog-3, fbf-1 and fbf-2 depletion on tumor formation in animals homozygous for an oncogenic Notch mutation, glp-1(gf). Tum, tumorous; *, some fog-3(RNAi) tumorous germlines made a few oocytes; n, number of germlines scored; a Berry et al. (27). (b–d) Young adult gonads in intact animals, 1 day past L4. Dotted line, outline of gonadal tissue. Scale bar, 50 μM. Empty arrowheads, distal end. (b) Tumorous germline with no apparent differentiation. (c) Tumorous germline with oocytes (solid arrowheads) after fog-3 depletion. (d) Germline tumor abolished after fog-3 and fbf depletion.

Mentions: We explored the idea that FOG-3 might influence tumor formation in mutants that normally generate very large germline tumors. We first used animals that harbor an oncogenic gain-of-function (gf) mutation in the gene encoding the GLP-1 Notch receptor (27). All glp-1(gf) homozygotes make germline tumors and are sterile, but they can be propagated from glp-1(gf)/+ heterozygotes, which are often fertile as young adults (27). We used RNAi to deplete fog-3 in glp-1(gf)/+ L4 larvae and examined their glp-1(gf) homozygous progeny in the next generation. The fog-3(RNAi); glp-1(gf) animals formed large germline tumors, similar to those in glp-1(gf) controls (Figures 4a-c, white asterisks). However, unlike glp-1(gf) germlines, the fog-3(RNAi); glp-1(gf) germline tumors sometimes made one or a few oocytes, confirming RNAi efficacy (Figure 4c, arrowheads). Therefore, FOG-3 depletion had no major effect on glp-1(gf) tumor formation. We then removed both FOG-3 and FBF with a much more dramatic result. Whereas RNAi knockdown of fbf-1 and fbf-2 had no effect (Figure 4a), as previously shown (19), the simultaneous depletion of both FOG-3 and FBF could abolish germline tumors: essentially no germ cells remained in ~50% of the fog-3(RNAi); fbf-1(RNAi); fbf-2(RNAi); glp-1(gf) homozygotes (Figure 4a, 4d). This ~50% penetrance likely reflects the well-known character of RNAi to reduce rather than eliminate gene expression. The loss of glp-1(gf) tumor formation might result from either a decrease in proliferation or increase in cell death. Regardless, FBF and FOG-3 work together to promote glp-1(gf) tumor formation—an activity consistent with a role in proliferation, but that may involve other developmental mechanisms.


C. elegans FOG-3/Tob can either promote or inhibit germline proliferation, depending on gene dosage and genetic context.

Snow JJ, Lee MH, Verheyden J, Kroll-Conner PL, Kimble J - Oncogene (2012)

FOG-3 and FBF can promote tumor formation. (a) Effects of fog-3, fbf-1 and fbf-2 depletion on tumor formation in animals homozygous for an oncogenic Notch mutation, glp-1(gf). Tum, tumorous; *, some fog-3(RNAi) tumorous germlines made a few oocytes; n, number of germlines scored; a Berry et al. (27). (b–d) Young adult gonads in intact animals, 1 day past L4. Dotted line, outline of gonadal tissue. Scale bar, 50 μM. Empty arrowheads, distal end. (b) Tumorous germline with no apparent differentiation. (c) Tumorous germline with oocytes (solid arrowheads) after fog-3 depletion. (d) Germline tumor abolished after fog-3 and fbf depletion.
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Figure 4: FOG-3 and FBF can promote tumor formation. (a) Effects of fog-3, fbf-1 and fbf-2 depletion on tumor formation in animals homozygous for an oncogenic Notch mutation, glp-1(gf). Tum, tumorous; *, some fog-3(RNAi) tumorous germlines made a few oocytes; n, number of germlines scored; a Berry et al. (27). (b–d) Young adult gonads in intact animals, 1 day past L4. Dotted line, outline of gonadal tissue. Scale bar, 50 μM. Empty arrowheads, distal end. (b) Tumorous germline with no apparent differentiation. (c) Tumorous germline with oocytes (solid arrowheads) after fog-3 depletion. (d) Germline tumor abolished after fog-3 and fbf depletion.
Mentions: We explored the idea that FOG-3 might influence tumor formation in mutants that normally generate very large germline tumors. We first used animals that harbor an oncogenic gain-of-function (gf) mutation in the gene encoding the GLP-1 Notch receptor (27). All glp-1(gf) homozygotes make germline tumors and are sterile, but they can be propagated from glp-1(gf)/+ heterozygotes, which are often fertile as young adults (27). We used RNAi to deplete fog-3 in glp-1(gf)/+ L4 larvae and examined their glp-1(gf) homozygous progeny in the next generation. The fog-3(RNAi); glp-1(gf) animals formed large germline tumors, similar to those in glp-1(gf) controls (Figures 4a-c, white asterisks). However, unlike glp-1(gf) germlines, the fog-3(RNAi); glp-1(gf) germline tumors sometimes made one or a few oocytes, confirming RNAi efficacy (Figure 4c, arrowheads). Therefore, FOG-3 depletion had no major effect on glp-1(gf) tumor formation. We then removed both FOG-3 and FBF with a much more dramatic result. Whereas RNAi knockdown of fbf-1 and fbf-2 had no effect (Figure 4a), as previously shown (19), the simultaneous depletion of both FOG-3 and FBF could abolish germline tumors: essentially no germ cells remained in ~50% of the fog-3(RNAi); fbf-1(RNAi); fbf-2(RNAi); glp-1(gf) homozygotes (Figure 4a, 4d). This ~50% penetrance likely reflects the well-known character of RNAi to reduce rather than eliminate gene expression. The loss of glp-1(gf) tumor formation might result from either a decrease in proliferation or increase in cell death. Regardless, FBF and FOG-3 work together to promote glp-1(gf) tumor formation—an activity consistent with a role in proliferation, but that may involve other developmental mechanisms.

Bottom Line: Thus, fog-3 mutants possess fewer germ cells than normal, a modest but reproducible decrease observed for each of two distinct fog-3 alleles.Finally, we show that FOG-3 and FBF work together to promote tumor formation in animals carrying oncogenic Notch mutations.A similar effect was not observed when germline tumors were induced by manipulation of other regulators; therefore, this FOG-3 tumor-promoting effect is context dependent.

View Article: PubMed Central - PubMed

Affiliation: Program in Cellular and Molecular Biology, University of Wisconsin-Madison, Madison, WI, USA.

ABSTRACT
Vertebrate Tob/BTG proteins inhibit cell proliferation when overexpressed in tissue-culture cells, and they can function as tumor suppressors in mice. The single Caenorhabditis elegans Tob/BTG ortholog, FOG-3, by contrast, was identified from its loss-of-function phenotype as a regulator of sperm fate specification. Here we report that FOG-3 also regulates proliferation in the germline tissue. We first demonstrate that FOG-3 is a positive regulator of germline proliferation. Thus, fog-3 mutants possess fewer germ cells than normal, a modest but reproducible decrease observed for each of two distinct fog-3 alleles. A similar decrease also occurred in fog-3/+ heterozygotes, again for both fog-3 alleles, revealing a haplo-insufficient effect on proliferation. Therefore, FOG-3 normally promotes proliferation, and two copies of the fog-3 gene are required for this function. We next overexpressed FOG-3 by removal of FBF, the collective term for FBF-1 and FBF-2, two nearly identical PUF RNA-binding proteins. We find that overexpressed FOG-3 blocks proliferation in fbf-1 fbf-2 mutants; whereas germ cells stop dividing and instead differentiate in fbf-1 fbf-2 double mutants, they continue to proliferate in fog-3; fbf-1 fbf-2 triple mutants. Therefore, like its vertebrate Tob/BTG cousins, overexpressed FOG-3 is 'antiproliferative'. Indeed, some fog-3; fbf-1 fbf-2 mutants possess small tumors, suggesting that FOG-3 can act as a tumor suppressor. Finally, we show that FOG-3 and FBF work together to promote tumor formation in animals carrying oncogenic Notch mutations. A similar effect was not observed when germline tumors were induced by manipulation of other regulators; therefore, this FOG-3 tumor-promoting effect is context dependent. We conclude that FOG-3 can either promote or inhibit proliferation in a manner that is sensitive to both genetic context and gene dosage. The discovery of these FOG-3 effects on proliferation has implications for our understanding of vertebrate Tob/BTG proteins and their influence on normal development and tumorigenesis.

Show MeSH
Related in: MedlinePlus