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AIR-2: An Aurora/Ipl1-related protein kinase associated with chromosomes and midbody microtubules is required for polar body extrusion and cytokinesis in Caenorhabditis elegans embryos.

Schumacher JM, Golden A, Donovan PJ - J. Cell Biol. (1998)

Bottom Line: Unlike other Aurora/Ipl1-related kinases, the Caenorhabditis elegans orthologue, AIR-2, is associated with meiotic and mitotic chromosomes.AIR-2 also remains associated with both extruded polar bodies.In the embryo, AIR-2 is found on metaphase chromosomes, moves to midbody microtubules at anaphase, and then persists at the cytokinesis remnant.

View Article: PubMed Central - PubMed

Affiliation: Cell Biology of Development and Differentiation Group, ABL-Basic Research Program, NCI-Frederick Cancer Research and Development Center, Frederick, Maryland 21702, USA.

ABSTRACT
An emerging family of kinases related to the Drosophila Aurora and budding yeast Ipl1 proteins has been implicated in chromosome segregation and mitotic spindle formation in a number of organisms. Unlike other Aurora/Ipl1-related kinases, the Caenorhabditis elegans orthologue, AIR-2, is associated with meiotic and mitotic chromosomes. AIR-2 is initially localized to the chromosomes of the most mature prophase I-arrested oocyte residing next to the spermatheca. This localization is dependent on the presence of sperm in the spermatheca. After fertilization, AIR-2 remains associated with chromosomes during each meiotic division. However, during both meiotic anaphases, AIR-2 is present between the separating chromosomes. AIR-2 also remains associated with both extruded polar bodies. In the embryo, AIR-2 is found on metaphase chromosomes, moves to midbody microtubules at anaphase, and then persists at the cytokinesis remnant. Disruption of AIR-2 expression by RNA- mediated interference produces entire broods of one-cell embryos that have executed multiple cell cycles in the complete absence of cytokinesis. The embryos accumulate large amounts of DNA and microtubule asters. Polar bodies are not extruded, but remain in the embryo where they continue to replicate. The cytokinesis defect appears to be late in the cell cycle because transient cleavage furrows initiate at the proper location, but regress before the division is complete. Additionally, staining with a marker of midbody microtubules revealed that at least some of the components of the midbody are not well localized in the absence of AIR-2 activity. Our results suggest that during each meiotic and mitotic division, AIR-2 may coordinate the congression of metaphase chromosomes with the subsequent events of polar body extrusion and cytokinesis.

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The cleavage furrow is unstable in air-2  (RNAi) embryos. Wild-type and air-2(RNAi)  embryos were dissected from adult hermaphrodites, fixed, and then stained with DAPI (A, E, I,  and M), NMY-2 (B, F, J, and N), actin (C, G, and  K), and α-tubulin antibodies (O). Merged images  are shown in D, H, L, and P. (A–D) A wild-type  two-cell embryo in prophase. (B) NMY-2 is  faintly seen on the cell membrane and at the cytokinesis remnant. (C) Actin is apparent at the  cell membrane. (D) Both proteins overlap at the  cell membrane. (E–H) A wild-type two-cell embryo where the AB cell (left) is in anaphase and  the P1 (right) is in metaphase. (F) NMY-2 and  (G) actin colocalize at the cell membrane (H).  (I–L) An air-2(RNAi) embryo undergoing the  first cell cycle. (J) NMY-2 and (K) actin colocalize to an incomplete cleavage furrow (L). (M–P)  An air-2(RNAi) embryo undergoing the first cell  cycle. A transient cleavage furrow bisecting the  cell is apparent by (N) NMY-2 and (O) α-tubulin  staining that overlaps (P). Bar, 10 μm.
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Figure 9: The cleavage furrow is unstable in air-2 (RNAi) embryos. Wild-type and air-2(RNAi) embryos were dissected from adult hermaphrodites, fixed, and then stained with DAPI (A, E, I, and M), NMY-2 (B, F, J, and N), actin (C, G, and K), and α-tubulin antibodies (O). Merged images are shown in D, H, L, and P. (A–D) A wild-type two-cell embryo in prophase. (B) NMY-2 is faintly seen on the cell membrane and at the cytokinesis remnant. (C) Actin is apparent at the cell membrane. (D) Both proteins overlap at the cell membrane. (E–H) A wild-type two-cell embryo where the AB cell (left) is in anaphase and the P1 (right) is in metaphase. (F) NMY-2 and (G) actin colocalize at the cell membrane (H). (I–L) An air-2(RNAi) embryo undergoing the first cell cycle. (J) NMY-2 and (K) actin colocalize to an incomplete cleavage furrow (L). (M–P) An air-2(RNAi) embryo undergoing the first cell cycle. A transient cleavage furrow bisecting the cell is apparent by (N) NMY-2 and (O) α-tubulin staining that overlaps (P). Bar, 10 μm.

Mentions: To specifically address the cytokinesis defects seen in air-2 (RNAi) embryos, we stained wild-type and air-2(RNAi) embryos with antibodies specific for the cleavage furrow. Both actin and the C. elegans nonmuscle myosin protein NMY-2 localize to the cleavage furrow in wild-type cells (Fig. 9, A–H) (Guo and Kemphues, 1996). In air-2(RNAi) embryos, we have occasionally found staining indicative of cleavage furrow formation with both the NMY-2 and actin antibodies (Fig. 9, I–P). However, we have never seen multicellular air-2(RNAi) embryos. This suggests that although cleavage furrows form, they regress before the cell membrane is established. To confirm this, we videorecorded several wild-type and air-2(RNAi) embryos undergoing the first few cleavages. Whereas wild-type cleavage furrows persisted, those in air-2(RNAi) embryos formed transiently and then regressed, leaving a multinucleate or polyploid one cell embryo (data not shown). After the first cell cycle, cytokinesis furrows began to form and regress in very dynamic patterns indicative of the tri- and tetrapolar spindles found in air-2(RNAi) embryos by α-tubulin staining (data not shown and Fig. 10 G). Thus, the cytokinesis defects seen in air-2(RNAi) embryos do not arise from a failure in initiating a cleavage furrow, but instead appear to be due to a failure in the completion of or stabilization of the newly formed cell membrane.


AIR-2: An Aurora/Ipl1-related protein kinase associated with chromosomes and midbody microtubules is required for polar body extrusion and cytokinesis in Caenorhabditis elegans embryos.

Schumacher JM, Golden A, Donovan PJ - J. Cell Biol. (1998)

The cleavage furrow is unstable in air-2  (RNAi) embryos. Wild-type and air-2(RNAi)  embryos were dissected from adult hermaphrodites, fixed, and then stained with DAPI (A, E, I,  and M), NMY-2 (B, F, J, and N), actin (C, G, and  K), and α-tubulin antibodies (O). Merged images  are shown in D, H, L, and P. (A–D) A wild-type  two-cell embryo in prophase. (B) NMY-2 is  faintly seen on the cell membrane and at the cytokinesis remnant. (C) Actin is apparent at the  cell membrane. (D) Both proteins overlap at the  cell membrane. (E–H) A wild-type two-cell embryo where the AB cell (left) is in anaphase and  the P1 (right) is in metaphase. (F) NMY-2 and  (G) actin colocalize at the cell membrane (H).  (I–L) An air-2(RNAi) embryo undergoing the  first cell cycle. (J) NMY-2 and (K) actin colocalize to an incomplete cleavage furrow (L). (M–P)  An air-2(RNAi) embryo undergoing the first cell  cycle. A transient cleavage furrow bisecting the  cell is apparent by (N) NMY-2 and (O) α-tubulin  staining that overlaps (P). Bar, 10 μm.
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Related In: Results  -  Collection

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Figure 9: The cleavage furrow is unstable in air-2 (RNAi) embryos. Wild-type and air-2(RNAi) embryos were dissected from adult hermaphrodites, fixed, and then stained with DAPI (A, E, I, and M), NMY-2 (B, F, J, and N), actin (C, G, and K), and α-tubulin antibodies (O). Merged images are shown in D, H, L, and P. (A–D) A wild-type two-cell embryo in prophase. (B) NMY-2 is faintly seen on the cell membrane and at the cytokinesis remnant. (C) Actin is apparent at the cell membrane. (D) Both proteins overlap at the cell membrane. (E–H) A wild-type two-cell embryo where the AB cell (left) is in anaphase and the P1 (right) is in metaphase. (F) NMY-2 and (G) actin colocalize at the cell membrane (H). (I–L) An air-2(RNAi) embryo undergoing the first cell cycle. (J) NMY-2 and (K) actin colocalize to an incomplete cleavage furrow (L). (M–P) An air-2(RNAi) embryo undergoing the first cell cycle. A transient cleavage furrow bisecting the cell is apparent by (N) NMY-2 and (O) α-tubulin staining that overlaps (P). Bar, 10 μm.
Mentions: To specifically address the cytokinesis defects seen in air-2 (RNAi) embryos, we stained wild-type and air-2(RNAi) embryos with antibodies specific for the cleavage furrow. Both actin and the C. elegans nonmuscle myosin protein NMY-2 localize to the cleavage furrow in wild-type cells (Fig. 9, A–H) (Guo and Kemphues, 1996). In air-2(RNAi) embryos, we have occasionally found staining indicative of cleavage furrow formation with both the NMY-2 and actin antibodies (Fig. 9, I–P). However, we have never seen multicellular air-2(RNAi) embryos. This suggests that although cleavage furrows form, they regress before the cell membrane is established. To confirm this, we videorecorded several wild-type and air-2(RNAi) embryos undergoing the first few cleavages. Whereas wild-type cleavage furrows persisted, those in air-2(RNAi) embryos formed transiently and then regressed, leaving a multinucleate or polyploid one cell embryo (data not shown). After the first cell cycle, cytokinesis furrows began to form and regress in very dynamic patterns indicative of the tri- and tetrapolar spindles found in air-2(RNAi) embryos by α-tubulin staining (data not shown and Fig. 10 G). Thus, the cytokinesis defects seen in air-2(RNAi) embryos do not arise from a failure in initiating a cleavage furrow, but instead appear to be due to a failure in the completion of or stabilization of the newly formed cell membrane.

Bottom Line: Unlike other Aurora/Ipl1-related kinases, the Caenorhabditis elegans orthologue, AIR-2, is associated with meiotic and mitotic chromosomes.AIR-2 also remains associated with both extruded polar bodies.In the embryo, AIR-2 is found on metaphase chromosomes, moves to midbody microtubules at anaphase, and then persists at the cytokinesis remnant.

View Article: PubMed Central - PubMed

Affiliation: Cell Biology of Development and Differentiation Group, ABL-Basic Research Program, NCI-Frederick Cancer Research and Development Center, Frederick, Maryland 21702, USA.

ABSTRACT
An emerging family of kinases related to the Drosophila Aurora and budding yeast Ipl1 proteins has been implicated in chromosome segregation and mitotic spindle formation in a number of organisms. Unlike other Aurora/Ipl1-related kinases, the Caenorhabditis elegans orthologue, AIR-2, is associated with meiotic and mitotic chromosomes. AIR-2 is initially localized to the chromosomes of the most mature prophase I-arrested oocyte residing next to the spermatheca. This localization is dependent on the presence of sperm in the spermatheca. After fertilization, AIR-2 remains associated with chromosomes during each meiotic division. However, during both meiotic anaphases, AIR-2 is present between the separating chromosomes. AIR-2 also remains associated with both extruded polar bodies. In the embryo, AIR-2 is found on metaphase chromosomes, moves to midbody microtubules at anaphase, and then persists at the cytokinesis remnant. Disruption of AIR-2 expression by RNA- mediated interference produces entire broods of one-cell embryos that have executed multiple cell cycles in the complete absence of cytokinesis. The embryos accumulate large amounts of DNA and microtubule asters. Polar bodies are not extruded, but remain in the embryo where they continue to replicate. The cytokinesis defect appears to be late in the cell cycle because transient cleavage furrows initiate at the proper location, but regress before the division is complete. Additionally, staining with a marker of midbody microtubules revealed that at least some of the components of the midbody are not well localized in the absence of AIR-2 activity. Our results suggest that during each meiotic and mitotic division, AIR-2 may coordinate the congression of metaphase chromosomes with the subsequent events of polar body extrusion and cytokinesis.

Show MeSH
Related in: MedlinePlus