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MTM-6, a phosphoinositide phosphatase, is required to promote synapse formation in Caenorhabditis elegans.

Ericson VR, Spilker KA, Tugizova MS, Shen K - PLoS ONE (2014)

Bottom Line: We found that loss of function of the phosphoinositide phosphatase mtm-6 results in a reduction in the number of synaptic puncta.The reduction in synapses is partially the result of MTM-6 regulation of the secretion of the Wnt ligand EGL-20 from cells in the tail and partially the result of neuronal action.We conclude that regulation of secretion of different Wnt ligands can use different components.

View Article: PubMed Central - PubMed

Affiliation: Department of Biology, Howard Hughes Medical Institute, Stanford University, Stanford, California, United States of America.

ABSTRACT
Forming the proper number of synapses is crucial for normal neuronal development. We found that loss of function of the phosphoinositide phosphatase mtm-6 results in a reduction in the number of synaptic puncta. The reduction in synapses is partially the result of MTM-6 regulation of the secretion of the Wnt ligand EGL-20 from cells in the tail and partially the result of neuronal action. MTM-6 shows relative specificity for EGL-20 over the other Wnt ligands. We suggest that the ability of MTM-6 to regulate EGL-20 secretion is a function of its expression pattern. We conclude that regulation of secretion of different Wnt ligands can use different components. Additionally, we present a novel neuronal function for MTM-6.

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Loss of mtm-6 enhances the Wnt phenotype in DA9 in an egl-20 dependent manner.(A) Schematic of DA9. GFP::RAB-3 puncta were quantified in the commissural region, the dorsal asynaptic region and the total dorsal region. lin-44(n1792) shows a stereotyped shift of GFP::RAB-3 into the dorsal asynaptic region of DA9 (B). lin-44(n1792); mtm-6(ok330) animals have GFP::RAB-3 puncta in the commissure (C,D). (E) Quantification of the number of commissural puncta to measure the enhancement of the Wnt phenotype by mtm-6 and to measure the cell-autonomous rescue experiments. n = 40, **** is p<0.0001, n.s is not significant, and error bars are SD. Arrows in (A-D) mark the DA9 dorsal commissure turn. Scale bar is 10 µm.
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pone-0114501-g006: Loss of mtm-6 enhances the Wnt phenotype in DA9 in an egl-20 dependent manner.(A) Schematic of DA9. GFP::RAB-3 puncta were quantified in the commissural region, the dorsal asynaptic region and the total dorsal region. lin-44(n1792) shows a stereotyped shift of GFP::RAB-3 into the dorsal asynaptic region of DA9 (B). lin-44(n1792); mtm-6(ok330) animals have GFP::RAB-3 puncta in the commissure (C,D). (E) Quantification of the number of commissural puncta to measure the enhancement of the Wnt phenotype by mtm-6 and to measure the cell-autonomous rescue experiments. n = 40, **** is p<0.0001, n.s is not significant, and error bars are SD. Arrows in (A-D) mark the DA9 dorsal commissure turn. Scale bar is 10 µm.

Mentions: If MTM-6 primarily regulates EGL-20 secretion, then there should be no enhancement between the egl-20 and mtm-6 mutants. Indeed, we found that the mtm-6; egl-20 double mutant shows no significant enhancement of the synaptic number phenotype (Fig. 5C-E, H and Table S1, 16.1+/−2.3, n = 40, SD, p>0.9998). In contrast, the mtm-6; lin-44 double mutant shows enhanced phenotypes with puncta appearing in the commissure (Fig. 6C-E and Table S1, 3.6+/−3.1, n = 40, SD). From prior reports, the appearance of puncta in the commissure is typical of loss of the frizzled receptor lin-17 or loss of the combination of egl-20 and lin-44 (Fig. 6B-D and Table S1) [56], [60]. As previously mentioned, it represents a more severe loss of inhibitory positional cues. The enhancement of the misolocalization phenotype in the lin-44 background by mtm-6 is not significantly different from lin-17(n671) or the lin-44; egl-20 double mutant (Fig. 6E and Table S1). There is no enhancement of the lin-44 mutant by either the cwn-1 or cwn-2 mutants, suggesting that cwn-1 and cwn-2 are not involved (Fig. S5 and Table S1). The fact that the mtm-6 and egl-20 mutants enhance the lin-44 mutant in a similar manner supports the hypothesis that MTM-6 regulates EGL-20 secretion.


MTM-6, a phosphoinositide phosphatase, is required to promote synapse formation in Caenorhabditis elegans.

Ericson VR, Spilker KA, Tugizova MS, Shen K - PLoS ONE (2014)

Loss of mtm-6 enhances the Wnt phenotype in DA9 in an egl-20 dependent manner.(A) Schematic of DA9. GFP::RAB-3 puncta were quantified in the commissural region, the dorsal asynaptic region and the total dorsal region. lin-44(n1792) shows a stereotyped shift of GFP::RAB-3 into the dorsal asynaptic region of DA9 (B). lin-44(n1792); mtm-6(ok330) animals have GFP::RAB-3 puncta in the commissure (C,D). (E) Quantification of the number of commissural puncta to measure the enhancement of the Wnt phenotype by mtm-6 and to measure the cell-autonomous rescue experiments. n = 40, **** is p<0.0001, n.s is not significant, and error bars are SD. Arrows in (A-D) mark the DA9 dorsal commissure turn. Scale bar is 10 µm.
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pone-0114501-g006: Loss of mtm-6 enhances the Wnt phenotype in DA9 in an egl-20 dependent manner.(A) Schematic of DA9. GFP::RAB-3 puncta were quantified in the commissural region, the dorsal asynaptic region and the total dorsal region. lin-44(n1792) shows a stereotyped shift of GFP::RAB-3 into the dorsal asynaptic region of DA9 (B). lin-44(n1792); mtm-6(ok330) animals have GFP::RAB-3 puncta in the commissure (C,D). (E) Quantification of the number of commissural puncta to measure the enhancement of the Wnt phenotype by mtm-6 and to measure the cell-autonomous rescue experiments. n = 40, **** is p<0.0001, n.s is not significant, and error bars are SD. Arrows in (A-D) mark the DA9 dorsal commissure turn. Scale bar is 10 µm.
Mentions: If MTM-6 primarily regulates EGL-20 secretion, then there should be no enhancement between the egl-20 and mtm-6 mutants. Indeed, we found that the mtm-6; egl-20 double mutant shows no significant enhancement of the synaptic number phenotype (Fig. 5C-E, H and Table S1, 16.1+/−2.3, n = 40, SD, p>0.9998). In contrast, the mtm-6; lin-44 double mutant shows enhanced phenotypes with puncta appearing in the commissure (Fig. 6C-E and Table S1, 3.6+/−3.1, n = 40, SD). From prior reports, the appearance of puncta in the commissure is typical of loss of the frizzled receptor lin-17 or loss of the combination of egl-20 and lin-44 (Fig. 6B-D and Table S1) [56], [60]. As previously mentioned, it represents a more severe loss of inhibitory positional cues. The enhancement of the misolocalization phenotype in the lin-44 background by mtm-6 is not significantly different from lin-17(n671) or the lin-44; egl-20 double mutant (Fig. 6E and Table S1). There is no enhancement of the lin-44 mutant by either the cwn-1 or cwn-2 mutants, suggesting that cwn-1 and cwn-2 are not involved (Fig. S5 and Table S1). The fact that the mtm-6 and egl-20 mutants enhance the lin-44 mutant in a similar manner supports the hypothesis that MTM-6 regulates EGL-20 secretion.

Bottom Line: We found that loss of function of the phosphoinositide phosphatase mtm-6 results in a reduction in the number of synaptic puncta.The reduction in synapses is partially the result of MTM-6 regulation of the secretion of the Wnt ligand EGL-20 from cells in the tail and partially the result of neuronal action.We conclude that regulation of secretion of different Wnt ligands can use different components.

View Article: PubMed Central - PubMed

Affiliation: Department of Biology, Howard Hughes Medical Institute, Stanford University, Stanford, California, United States of America.

ABSTRACT
Forming the proper number of synapses is crucial for normal neuronal development. We found that loss of function of the phosphoinositide phosphatase mtm-6 results in a reduction in the number of synaptic puncta. The reduction in synapses is partially the result of MTM-6 regulation of the secretion of the Wnt ligand EGL-20 from cells in the tail and partially the result of neuronal action. MTM-6 shows relative specificity for EGL-20 over the other Wnt ligands. We suggest that the ability of MTM-6 to regulate EGL-20 secretion is a function of its expression pattern. We conclude that regulation of secretion of different Wnt ligands can use different components. Additionally, we present a novel neuronal function for MTM-6.

Show MeSH