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Mar Carmena

Publications and source records attributed to Mar Carmena.

9 recordsLinked to original sources
PubMed2006

Drosophila Incenp is required for cytokinesis and asymmetric cell division during development of the nervous system.

The chromosomal passenger protein complex has emerged as a key player in mitosis, with important roles in chromatin modifications, kinetochore-microtubule interactions, chromosome bi-orientation and stability of the bipolar spindle, mitotic checkpoint function, assembly of the central spindle and cytokinesis. The inner centromere protein (Incenp; a subunit of this complex) is thought to regulate the Aurora B kinase and target it to its substrates. To explore the roles of the passenger complex in a developing multicellular organism, we have performed a genetic screen looking for new alleles and interactors of Drosophila Incenp. We have isolated a new null allele of Incenp that has allowed us for the first time to study the functions of the chromosomal passengers during development. Homozygous incenp(EC3747) embryos show absence of phosphorylation of histone H3 in mitosis, failure of cytokinesis and polyploidy, and defects in peripheral nervous system development. These defects are consistent with depletion of Aurora B kinase activity. In addition, the segregation of the cell-fate determinant Prospero in asymmetric neuroblast division is abnormal, suggesting a role for the chromosomal passenger complex in the regulation of this process.

Animals↗
PubMed2006

INCENP and Aurora B promote meiotic sister chromatid cohesion through localization of the Shugoshin MEI-S332 in Drosophila.

The chromosomal passenger complex protein INCENP is required in mitosis for chromosome condensation, spindle attachment and function, and cytokinesis. Here, we show that INCENP has an essential function in the specialized behavior of centromeres in meiosis. Mutations affecting Drosophila incenp profoundly affect chromosome segregation in both meiosis I and II, due, at least in part, to premature sister chromatid separation in meiosis I. INCENP binds to the cohesion protector protein MEI-S332, which is also an excellent in vitro substrate for Aurora B kinase. A MEI-S332 mutant that is only poorly phosphorylated by Aurora B is defective in localization to centromeres. These results implicate the chromosomal passenger complex in directly regulating MEI-S332 localization and, therefore, the control of sister chromatid cohesion in meiosis.

Animals↗
PubMed2003

RNAi analysis reveals an unexpected role for topoisomerase II in chromosome arm congression to a metaphase plate.

DNA topoisomerase II (Topo II) is a major component of mitotic chromosomes and an important drug target in cancer chemotherapy, however, its role in chromosome structure and dynamics remains controversial. We have used RNAi to deplete Topo II in Drosophila S2 cells in order to carry out a detailed functional analysis of the role of the protein during mitosis. We find that Topo II is not required for the assembly of a functional kinetochore or the targeting of chromosomal passenger proteins, nonetheless, it is essential for anaphase sister chromatid separation. In response to a long-running controversy, we show that Topo II does have some role in mitotic chromatin condensation. Chromosomes formed in its absence have a 2.5-fold decrease in the level of chromatin compaction, and are morphologically abnormal. However, it is clear that the overall programme of mitotic chromosome condensation can proceed without Topo II. Surprisingly, in metaphase cells depleted of Topo II, one or more chromosome arms frequently stretch out from the metaphase plate to the vicinity of the spindle pole. This is not kinetochore-based movement, as the centromere of the affected chromosome is located on the plate. This observation raises the possibility that further unexpected functions for Topo II may remain to be discovered.

Anaphase↗
PubMed2003

Survivin is required for stable checkpoint activation in taxol-treated HeLa cells.

Survivin is an essential chromosomal passenger protein whose function remains unclear. Here, we have used RNA interference to specifically repress Survivin in cultured HeLa cells. Immunoblot analysis showed that Survivin was no longer detectable in cultures 60 hours after transfection with Survivin-specific siRNA. Live cell analysis showed that many Survivin-depleted cells were delayed in mitosis, and immunofluorescence analysis of fixed specimens revealed that Survivin-depleted cells accumulated in prometaphase with misaligned chromosomes. The chromosomal passenger proteins, INCENP and Aurora-B, which can interact directly with Survivin, were absent from the centromeres of Survivin-depleted cells. These data contribute to the emerging picture that Survivin operates together with INCENP and Aurora-B to perform its mitotic duties. Some Survivin-depleted cells eventually exited mitosis without completing cytokinesis. This resulted in a gradual increase in the percentage of multinucleated cells in the culture. Time-lapse imaging of synchronized cultures revealed that control and Survivin-depleted cells arrested in mitosis in the presence of nocodazole; however, the latter failed to arrest in mitosis when treated with taxol. Immunofluorescence studies revealed that Survivin-depleted cells were unable to stably maintain BubR1 at the kinetochores in the presence of either taxol or nocodazole. Our data reveal that Survivin is not required for the spindle assembly checkpoint when it is activated by the loss of microtubules. However, Survivin is required for the maintenance of the checkpoint when it is activated by taxol, which is generally thought to cause a loss of spindle tension.

Antineoplastic Agents↗
PubMed2003

A perfect funeral with no corpse.

"Indeed, the role in mitosis of the chromosome arms, which carry most of the genetic material, may be compared with that of a corpse at a funeral: they provide the reason for the proceedings but do not take an active part in them." (Mazia, 1961)

Animals↗
PubMed2003

Dynamic relocalization of the chromosomal passenger complex proteins inner centromere protein (INCENP) and aurora-B kinase during male mouse meiosis.

INCENP and aurora-B kinase are two chromosomal passenger proteins that are thought to play key roles in coordinating chromosome segregation with cytokinesis in somatic cells. Here we have analyzed their subcellular distribution, and that of phosphorylated histone H3, and the timing of their relative appearance in mouse spermatocytes during both meiotic divisions. Our results show that in mitotic spermatogonial cells, INCENP and aurora-B show the same pattern of distribution as they do in cultured somatic cells. INCENP labels the synaptonemal complex central element from zygotene up to late pachytene when it begins to relocalize to heterochromatic chromocentres. Aurora-B first appears at chromocentres in late diplotene before the initial phosphorylation of histone H3. INCENP and aurora-B concentrate at centromeres during diakinesis and appear during metaphase I as T-shaped signals at their inner domains, just below associated sister kinetochores. During late anaphase I both proteins relocalize to the spindle midzone. Both proteins colocalize at a connecting strand traversing the centromere region and joining sister kinetochores, in metaphase II centromeres. This strand disappears at the metaphase II/anaphase II transition and relocalizes to the spindle midzone. We discuss the complex dynamic relocalization of the chromosomal passenger complex during prophase I. Additionally, we suggest that this complex may regulate sister-chromatid centromere cohesion during both meiotic divisions.

3T3 Cells↗
PubMed2002

MAST/Orbit has a role in microtubule-kinetochore attachment and is essential for chromosome alignment and maintenance of spindle bipolarity.

Multiple asters (MAST)/Orbit is a member of a new family of nonmotor microtubule-associated proteins that has been previously shown to be required for the organization of the mitotic spindle. Here we provide evidence that MAST/Orbit is required for functional kinetochore attachment, chromosome congression, and the maintenance of spindle bipolarity. In vivo analysis of Drosophila mast mutant embryos undergoing early mitotic divisions revealed that chromosomes are unable to reach a stable metaphase alignment and that bipolar spindles collapse as centrosomes move progressively closer toward the cell center and eventually organize into a monopolar configuration. Similarly, soon after depletion of MAST/Orbit in Drosophila S2 cells by double-stranded RNA interference, cells are unable to form a metaphase plate and instead assemble monopolar spindles with chromosomes localized close to the center of the aster. In these cells, kinetochores either fail to achieve end-on attachment or are associated with short microtubules. Remarkably, when microtubule dynamics is suppressed in MAST-depleted cells, chromosomes localize at the periphery of the monopolar aster associated with the plus ends of well-defined microtubule bundles. Furthermore, in these cells, dynein and ZW10 accumulate at kinetochores and fail to transfer to microtubules. However, loss of MAST/Orbit does not affect the kinetochore localization of D-CLIP-190. Together, these results strongly support the conclusion that MAST/Orbit is required for microtubules to form functional attachments to kinetochores and to maintain spindle bipolarity.

Alleles↗