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The function of a spindle checkpoint gene bub-1 in C. elegans development.

Wang X, Liu M, Li W, Suh CD, Zhu Z, Jin Y, Fan Q - PLoS ONE (2009)

Bottom Line: In addition, bub-1(fw5 and fw8) mutants showed widespread effects on postembryonic development in many cell lineages.We found that bub-1 functioned maternally in several developmental lineages at the embryonic stage in C. elegans.Our results demonstrate a conserved role of bub-1 in cell-cycle regulation and reveal that C. elegans bub-1 is required both maternally and zygotically.

View Article: PubMed Central - PubMed

Affiliation: School of Life Sciences, Peking University, Beijing, China.

ABSTRACT

Background: The serine/threonine kinase BUB1 (Budding Uninhibited by Benzimidazole 1) was originally identified in yeast as a checkpoint protein, based on its mutant's incapacity of delaying the cell cycle in response to loss of microtubules. Our understanding of its function is primarily from studies carried out in yeast S. cerevisiae. It has been shown that it is a component of the mitotic spindle checkpoint and regulates the separation of sister chromatids through its downstream molecules. However, its roles in multi-cellular organisms remain unclear.

Methods and findings: In nematode C. elegans, rapid cell divisions primarily occur in embryos and in germline of postembryonic larvae and adults. In addition, a select set of cells undergo a few rounds of cell division postembryonically. One common phenotype associated with impaired cell division is described as Stu (Sterile and Uncoordinated) [1], [2]. We conducted a genetic screen for zygotic mutants that displayed Stu phenotype in C. elegans. We isolated seven Stu mutants that fell into five complementation groups. We report here that two mutations, FanWang5 (fw5) and FanWang8 (fw8) affect the bub-1 gene, a homolog of yeast BUB1. Both mutant alleles of fw5 and fw8 exhibited variable behavioral defects, including developmental arrest, uncoordination and sterility. The number of postembryonically born neurons in the ventral cord decreased and their axon morphology was abnormal. Also, the decrease of neurons in the ventral cord phenotype could not be suppressed by a caspase-3 loss-of-function mutant. In addition, bub-1(fw5 and fw8) mutants showed widespread effects on postembryonic development in many cell lineages. We found that bub-1 functioned maternally in several developmental lineages at the embryonic stage in C. elegans. Studies in yeast have shown that BUB1 functions as a spindle checkpoint protein by regulating the anaphase promoting complex/cyclosome (APC/C). We performed double mutant analysis and observed that bub-1 genetically interacted with several downstream genes, including fzy-1/CDC20, mat-2/APC1 and emb-27/APC6.

Conclusions: Our results demonstrate a conserved role of bub-1 in cell-cycle regulation and reveal that C. elegans bub-1 is required both maternally and zygotically. Further, our genetic analysis is consistent with that the function of bub-1 in C. elegans is likely similar to its yeast and mammalian homologs.

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Nomarski and DTC Marked GFP (qIs56) Images of bub-1 Mutants.(A) The DIC and (C) the DTC GFP picture of the same N2. (B) The DIC and (D) the DTC GFP picture of the same bub-1(fw8) mutant. The DTC GFP cells showed that the bub-1(fw8) mutant gonad arm could not grow to form the U shape gonad. Anterior is to the left and ventral side is down. One gonad in each animal in (A) and (B) was outlined in a dotted line. Dorsal is up in 7a and 7c; and dorsal is facing out the paper in 7b and 7d. The scale bar represents 25 µm.
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pone-0005912-g007: Nomarski and DTC Marked GFP (qIs56) Images of bub-1 Mutants.(A) The DIC and (C) the DTC GFP picture of the same N2. (B) The DIC and (D) the DTC GFP picture of the same bub-1(fw8) mutant. The DTC GFP cells showed that the bub-1(fw8) mutant gonad arm could not grow to form the U shape gonad. Anterior is to the left and ventral side is down. One gonad in each animal in (A) and (B) was outlined in a dotted line. Dorsal is up in 7a and 7c; and dorsal is facing out the paper in 7b and 7d. The scale bar represents 25 µm.

Mentions: The transgenic GFP line qIs56 allowed us to visualize the two distal tip cells (DTCs) of the U-shaped gonads [42] (Figure 7A and 7C). The gonad arms acquire their U-shape by directed migration of the DTC. The arm elongation begins at the L2 stage and continues until the L4 molt [38]. We observed that about half of bub-1(fw8) animals showed only one gonad arm, and most of them stopped development prematurely (n = 32) (Figure 7B and 7D). Among the 48 gonad arms scored, 9 grew one quarter or less of the normal gonad length; 15 gonad arms grew less than one half of the normal length; and 10 gonad arms grew about three quarters of the normal length. Furthermore, the number of germ cells in bub-1(fw8) was decreased to about 117 per arm (n = 11) (compared to about 1000 in wild type). In the abnormal gonads, we did not observe any eggs. Sperms, however, formed only in 2 of the 9 bub-1 mutant animals observed by DAPI staining (Figure 5D).


The function of a spindle checkpoint gene bub-1 in C. elegans development.

Wang X, Liu M, Li W, Suh CD, Zhu Z, Jin Y, Fan Q - PLoS ONE (2009)

Nomarski and DTC Marked GFP (qIs56) Images of bub-1 Mutants.(A) The DIC and (C) the DTC GFP picture of the same N2. (B) The DIC and (D) the DTC GFP picture of the same bub-1(fw8) mutant. The DTC GFP cells showed that the bub-1(fw8) mutant gonad arm could not grow to form the U shape gonad. Anterior is to the left and ventral side is down. One gonad in each animal in (A) and (B) was outlined in a dotted line. Dorsal is up in 7a and 7c; and dorsal is facing out the paper in 7b and 7d. The scale bar represents 25 µm.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2691579&req=5

pone-0005912-g007: Nomarski and DTC Marked GFP (qIs56) Images of bub-1 Mutants.(A) The DIC and (C) the DTC GFP picture of the same N2. (B) The DIC and (D) the DTC GFP picture of the same bub-1(fw8) mutant. The DTC GFP cells showed that the bub-1(fw8) mutant gonad arm could not grow to form the U shape gonad. Anterior is to the left and ventral side is down. One gonad in each animal in (A) and (B) was outlined in a dotted line. Dorsal is up in 7a and 7c; and dorsal is facing out the paper in 7b and 7d. The scale bar represents 25 µm.
Mentions: The transgenic GFP line qIs56 allowed us to visualize the two distal tip cells (DTCs) of the U-shaped gonads [42] (Figure 7A and 7C). The gonad arms acquire their U-shape by directed migration of the DTC. The arm elongation begins at the L2 stage and continues until the L4 molt [38]. We observed that about half of bub-1(fw8) animals showed only one gonad arm, and most of them stopped development prematurely (n = 32) (Figure 7B and 7D). Among the 48 gonad arms scored, 9 grew one quarter or less of the normal gonad length; 15 gonad arms grew less than one half of the normal length; and 10 gonad arms grew about three quarters of the normal length. Furthermore, the number of germ cells in bub-1(fw8) was decreased to about 117 per arm (n = 11) (compared to about 1000 in wild type). In the abnormal gonads, we did not observe any eggs. Sperms, however, formed only in 2 of the 9 bub-1 mutant animals observed by DAPI staining (Figure 5D).

Bottom Line: In addition, bub-1(fw5 and fw8) mutants showed widespread effects on postembryonic development in many cell lineages.We found that bub-1 functioned maternally in several developmental lineages at the embryonic stage in C. elegans.Our results demonstrate a conserved role of bub-1 in cell-cycle regulation and reveal that C. elegans bub-1 is required both maternally and zygotically.

View Article: PubMed Central - PubMed

Affiliation: School of Life Sciences, Peking University, Beijing, China.

ABSTRACT

Background: The serine/threonine kinase BUB1 (Budding Uninhibited by Benzimidazole 1) was originally identified in yeast as a checkpoint protein, based on its mutant's incapacity of delaying the cell cycle in response to loss of microtubules. Our understanding of its function is primarily from studies carried out in yeast S. cerevisiae. It has been shown that it is a component of the mitotic spindle checkpoint and regulates the separation of sister chromatids through its downstream molecules. However, its roles in multi-cellular organisms remain unclear.

Methods and findings: In nematode C. elegans, rapid cell divisions primarily occur in embryos and in germline of postembryonic larvae and adults. In addition, a select set of cells undergo a few rounds of cell division postembryonically. One common phenotype associated with impaired cell division is described as Stu (Sterile and Uncoordinated) [1], [2]. We conducted a genetic screen for zygotic mutants that displayed Stu phenotype in C. elegans. We isolated seven Stu mutants that fell into five complementation groups. We report here that two mutations, FanWang5 (fw5) and FanWang8 (fw8) affect the bub-1 gene, a homolog of yeast BUB1. Both mutant alleles of fw5 and fw8 exhibited variable behavioral defects, including developmental arrest, uncoordination and sterility. The number of postembryonically born neurons in the ventral cord decreased and their axon morphology was abnormal. Also, the decrease of neurons in the ventral cord phenotype could not be suppressed by a caspase-3 loss-of-function mutant. In addition, bub-1(fw5 and fw8) mutants showed widespread effects on postembryonic development in many cell lineages. We found that bub-1 functioned maternally in several developmental lineages at the embryonic stage in C. elegans. Studies in yeast have shown that BUB1 functions as a spindle checkpoint protein by regulating the anaphase promoting complex/cyclosome (APC/C). We performed double mutant analysis and observed that bub-1 genetically interacted with several downstream genes, including fzy-1/CDC20, mat-2/APC1 and emb-27/APC6.

Conclusions: Our results demonstrate a conserved role of bub-1 in cell-cycle regulation and reveal that C. elegans bub-1 is required both maternally and zygotically. Further, our genetic analysis is consistent with that the function of bub-1 in C. elegans is likely similar to its yeast and mammalian homologs.

Show MeSH
Related in: MedlinePlus