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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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Polar bodies are not extruded in air-2(RNAi) embryos.  (A–L) air-2(RNAi) embryos at various stages of development  were dissected from injected mothers, fixed, and then stained  with DAPI (left) and an antibody to α-tubulin (right). (A and B)  An air-2(RNAi) embryo completing meiosis. (A) The maternal  meiotic chromatin is apparent at the anterior (arrowhead),  whereas the sperm nucleus can be seen at the posterior of the embryo. (B) By tubulin staining, a morphologically normal meiotic  spindle is apparent surrounding the meiotic chromatin at the anterior of the embryo (arrowhead). (C and D) A one-cell air-2  (RNAi) embryo undergoing anaphase. (C) Note the chromatin  bridges and hypercondensation of the chromatin. The second  chromatin body appears to be a replicating unextruded polar  body (arrowhead). (D) The spindle is morphologically normal. (E  and F) An air-2(RNAi) embryo that has gone through multiple  rounds of DNA replication and centrosome duplication without  completing cytokinesis is shown. (E) The chromatin is condensed  and (F) multiple microtubule asters are apparent. (G and H) air-2  (RNAi) embryos cycle through interphase. (G) Chromosomes  are decondensed and (H) an “interphase array” of microtubules  is observed. (I–L) Polar bodies in some air-2(RNAi) embryos  proceed through the cell cycle asynchronously from the rest of  the chromatin in the embryo (arrowheads). (I) This polar body  appears to be in anaphase. (K) The polar body (arrowhead) has  microtubule asters surrounding it whereas the nuclear chromatin  appears to be interphase (L). Bar, 10 μm.
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Figure 8: Polar bodies are not extruded in air-2(RNAi) embryos. (A–L) air-2(RNAi) embryos at various stages of development were dissected from injected mothers, fixed, and then stained with DAPI (left) and an antibody to α-tubulin (right). (A and B) An air-2(RNAi) embryo completing meiosis. (A) The maternal meiotic chromatin is apparent at the anterior (arrowhead), whereas the sperm nucleus can be seen at the posterior of the embryo. (B) By tubulin staining, a morphologically normal meiotic spindle is apparent surrounding the meiotic chromatin at the anterior of the embryo (arrowhead). (C and D) A one-cell air-2 (RNAi) embryo undergoing anaphase. (C) Note the chromatin bridges and hypercondensation of the chromatin. The second chromatin body appears to be a replicating unextruded polar body (arrowhead). (D) The spindle is morphologically normal. (E and F) An air-2(RNAi) embryo that has gone through multiple rounds of DNA replication and centrosome duplication without completing cytokinesis is shown. (E) The chromatin is condensed and (F) multiple microtubule asters are apparent. (G and H) air-2 (RNAi) embryos cycle through interphase. (G) Chromosomes are decondensed and (H) an “interphase array” of microtubules is observed. (I–L) Polar bodies in some air-2(RNAi) embryos proceed through the cell cycle asynchronously from the rest of the chromatin in the embryo (arrowheads). (I) This polar body appears to be in anaphase. (K) The polar body (arrowhead) has microtubule asters surrounding it whereas the nuclear chromatin appears to be interphase (L). Bar, 10 μm.

Mentions: To analyze the progression of the air-2(RNAi) phenotype, embryos of varying ages were fixed and stained with DAPI and an antibody specific for α-tubulin (n > 200 embryos). In newly fertilized embryos, the meiotic spindle appeared to be normal and no obvious defects were observed (Fig. 8, A and B). However, external polar bodies were never found in the hundreds of air-2(RNAi) embryos we examined. Indeed, in pronuclear stage air-2(RNAi) embryos, we often observed maternal pronuclei that were clearly polyploid with respect to the paternal pronucleus (data not shown). In other cases, what appeared to be internal polar bodies remained separate from the zygotic chromatin and continued to replicate. Thus, although meiotic spindles were found in newly fertilized air-2(RNAi) embryos, polar bodies were not extruded but remained in the embryo where they either fused with the maternal pronucleus or remained separate from the zygotic chromatin.


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)

Polar bodies are not extruded in air-2(RNAi) embryos.  (A–L) air-2(RNAi) embryos at various stages of development  were dissected from injected mothers, fixed, and then stained  with DAPI (left) and an antibody to α-tubulin (right). (A and B)  An air-2(RNAi) embryo completing meiosis. (A) The maternal  meiotic chromatin is apparent at the anterior (arrowhead),  whereas the sperm nucleus can be seen at the posterior of the embryo. (B) By tubulin staining, a morphologically normal meiotic  spindle is apparent surrounding the meiotic chromatin at the anterior of the embryo (arrowhead). (C and D) A one-cell air-2  (RNAi) embryo undergoing anaphase. (C) Note the chromatin  bridges and hypercondensation of the chromatin. The second  chromatin body appears to be a replicating unextruded polar  body (arrowhead). (D) The spindle is morphologically normal. (E  and F) An air-2(RNAi) embryo that has gone through multiple  rounds of DNA replication and centrosome duplication without  completing cytokinesis is shown. (E) The chromatin is condensed  and (F) multiple microtubule asters are apparent. (G and H) air-2  (RNAi) embryos cycle through interphase. (G) Chromosomes  are decondensed and (H) an “interphase array” of microtubules  is observed. (I–L) Polar bodies in some air-2(RNAi) embryos  proceed through the cell cycle asynchronously from the rest of  the chromatin in the embryo (arrowheads). (I) This polar body  appears to be in anaphase. (K) The polar body (arrowhead) has  microtubule asters surrounding it whereas the nuclear chromatin  appears to be interphase (L). Bar, 10 μm.
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Figure 8: Polar bodies are not extruded in air-2(RNAi) embryos. (A–L) air-2(RNAi) embryos at various stages of development were dissected from injected mothers, fixed, and then stained with DAPI (left) and an antibody to α-tubulin (right). (A and B) An air-2(RNAi) embryo completing meiosis. (A) The maternal meiotic chromatin is apparent at the anterior (arrowhead), whereas the sperm nucleus can be seen at the posterior of the embryo. (B) By tubulin staining, a morphologically normal meiotic spindle is apparent surrounding the meiotic chromatin at the anterior of the embryo (arrowhead). (C and D) A one-cell air-2 (RNAi) embryo undergoing anaphase. (C) Note the chromatin bridges and hypercondensation of the chromatin. The second chromatin body appears to be a replicating unextruded polar body (arrowhead). (D) The spindle is morphologically normal. (E and F) An air-2(RNAi) embryo that has gone through multiple rounds of DNA replication and centrosome duplication without completing cytokinesis is shown. (E) The chromatin is condensed and (F) multiple microtubule asters are apparent. (G and H) air-2 (RNAi) embryos cycle through interphase. (G) Chromosomes are decondensed and (H) an “interphase array” of microtubules is observed. (I–L) Polar bodies in some air-2(RNAi) embryos proceed through the cell cycle asynchronously from the rest of the chromatin in the embryo (arrowheads). (I) This polar body appears to be in anaphase. (K) The polar body (arrowhead) has microtubule asters surrounding it whereas the nuclear chromatin appears to be interphase (L). Bar, 10 μm.
Mentions: To analyze the progression of the air-2(RNAi) phenotype, embryos of varying ages were fixed and stained with DAPI and an antibody specific for α-tubulin (n > 200 embryos). In newly fertilized embryos, the meiotic spindle appeared to be normal and no obvious defects were observed (Fig. 8, A and B). However, external polar bodies were never found in the hundreds of air-2(RNAi) embryos we examined. Indeed, in pronuclear stage air-2(RNAi) embryos, we often observed maternal pronuclei that were clearly polyploid with respect to the paternal pronucleus (data not shown). In other cases, what appeared to be internal polar bodies remained separate from the zygotic chromatin and continued to replicate. Thus, although meiotic spindles were found in newly fertilized air-2(RNAi) embryos, polar bodies were not extruded but remained in the embryo where they either fused with the maternal pronucleus or remained separate from the zygotic chromatin.

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