Katanin, kinesin-13, and ataxin-2 inhibit premature interaction between maternal and paternal genomes in zygotes.

Fertilization occurs before the completion of oocyte meiosis in the majority of animal species and sperm contents move long distances within the zygotes of mouse and . If incorporated into the meiotic spindle, paternal chromosomes could be expelled into a polar body resulting in lethal monosomy. Through live imaging of fertilization in , we found that the microtubule disassembling enzymes, katanin and kinesin-13 limit long-range movement of sperm contents and that maternal ataxin-2 maintains paternal DNA and paternal mitochondria as a cohesive unit that moves together.

Roles of Tubulin Concentration during Prometaphase and Ran-GTP during Anaphase of Meiosis.

In many animal species, the oocyte meiotic spindle, which is required for chromosome segregation, forms without centrosomes. In some systems, Ran-GEF on chromatin initiates spindle assembly. We found that in oocytes, endogenously-tagged Ran-GEF dissociates from chromatin during spindle assembly but re-associates during meiotic anaphase.

Roles of Tubulin Concentration during Prometaphase and Ran-GTP during Anaphase of meiosis.

In many animal species, the oocyte meiotic spindle, which is required for chromosome segregation, forms without centrosomes. In some systems, Ran-GEF on chromatin initiates spindle assembly. We found that in oocytes, endogenously-tagged Ran-GEF dissociates from chromatin during spindle assembly but re-associates during meiotic anaphase.

Katanin, kinesin-13 and ataxin-2 inhibit premature interaction between maternal and paternal genomes in zygotes.

Fertilization occurs before completion of oocyte meiosis in the majority of animal species and sperm contents move long distances within zygotes of mouse and . If incorporated into the meiotic spindle, paternal chromosomes could be expelled into a polar body resulting in lethal monosomy. Through live imaging of fertilization in , we found that the microtubule disassembling enzymes, katanin and kinesin-13 limit long range movement of sperm contents and that maternal ataxin-2 maintains paternal DNA and paternal mitochondria as a cohesive unit that moves together.

Auxin-induced degradation of the aurora A kinase, AIR-1, in does not prevent assembly of bipolar meiotic spindles.

Chromosome segregation during mitosis and male meiosis is mediated by centrosomal spindles that require the activity of the aurora A kinase, whereas female meiotic spindles of many species are acentrosomal. We addressed the role of the aurora A kinase, AIR-1 , in acentrosomal spindle assembly by generating a strain in which AIR-1 is tagged with both an auxin-induced degron and HALO tag. The meiotic spindle pole marker, MEI-1 , and chromosomes were labeled with GFP and mCH::histone respectively.

Cohesin is required for meiotic spindle assembly independent of its role in cohesion in C. elegans.

Accurate chromosome segregation requires a cohesin-mediated physical attachment between chromosomes that are to be segregated apart, and a bipolar spindle with microtubule plus ends emanating from exactly two poles toward the paired chromosomes. We asked whether the striking bipolar structure of C. elegans meiotic chromosomes is required for bipolarity of acentriolar female meiotic spindles by time-lapse imaging of mutants that lack cohesion between chromosomes.

Evidence for anaphase pulling forces during C. elegans meiosis.

Anaphase chromosome movement is thought to be mediated by pulling forces generated by end-on attachment of microtubules to the outer face of kinetochores. However, it has been suggested that during C. elegans female meiosis, anaphase is mediated by a kinetochore-independent pushing mechanism with microtubules only attached to the inner face of segregating chromosomes.

Spherical spindle shape promotes perpendicular cortical orientation by preventing isometric cortical pulling on both spindle poles during female meiosis.

Meiotic spindles are positioned perpendicular to the oocyte cortex to facilitate segregation of chromosomes into a large egg and a tiny polar body. In , spindles are initially ellipsoid and parallel to the cortex before shortening to a near-spherical shape with flattened poles and then rotating to the perpendicular orientation by dynein-driven cortical pulling. The mechanistic connection between spindle shape and rotation has remained elusive.

Autosomal Trisomy and Triploidy Are Corrected During Female Meiosis in .

Trisomy and triploidy, defined as the presence of a third copy of one or all chromosomes, respectively, are deleterious in many species including humans. Previous studies have demonstrated that with a third copy of the X chromosome are viable and fertile. However, the extra X chromosome was shown to preferentially segregate into the first polar body during oocyte meiosis to produce a higher frequency of euploid offspring than would be generated by random segregation.

A novel chromosome segregation mechanism during female meiosis.

In a wide range of eukaryotes, chromosome segregation occurs through anaphase A, in which chromosomes move toward stationary spindle poles, anaphase B, in which chromosomes move at the same velocity as outwardly moving spindle poles, or both. In contrast, Caenorhabditis elegans female meiotic spindles initially shorten in the pole-to-pole axis such that spindle poles contact the outer kinetochore before the start of anaphase chromosome separation. Once the spindle pole-to-kinetochore contact has been made, the homologues of a 4-μm-long bivalent begin to separate.

Dynactin-dependent cortical dynein and spherical spindle shape correlate temporally with meiotic spindle rotation in Caenorhabditis elegans.

Oocyte meiotic spindles orient with one pole juxtaposed to the cortex to facilitate extrusion of chromosomes into polar bodies. In Caenorhabditis elegans, these acentriolar spindles initially orient parallel to the cortex and then rotate to the perpendicular orientation. To understand the mechanism of spindle rotation, we characterized events that correlated temporally with rotation, including shortening of the spindle in the pole-to pole axis, which resulted in a nearly spherical spindle at rotation.

The asymmetry of female meiosis reduces the frequency of inheritance of unpaired chromosomes.

Trisomy, the presence of a third copy of one chromosome, is deleterious and results in inviable or defective progeny if passed through the germ line. Random segregation of an extra chromosome is predicted to result in a high frequency of trisomic offspring from a trisomic parent. Caenorhabditis elegans with trisomy of the X chromosome, however, have far fewer trisomic offspring than expected.

Katanin maintains meiotic metaphase chromosome alignment and spindle structure in vivo and has multiple effects on microtubules in vitro.

Assembly of Caenorhabditis elegans female meiotic spindles requires both MEI-1 and MEI-2 subunits of the microtubule-severing ATPase katanin. Strong loss-of-function mutants assemble apolar intersecting microtubule arrays, whereas weaker mutants assemble bipolar meiotic spindles that are longer than wild type. To determine whether katanin is also required for spindle maintenance, we monitored metaphase I spindles after a fast-acting mei-1(ts) mutant was shifted to a nonpermissive temperature.

Kinesin-1 prevents capture of the oocyte meiotic spindle by the sperm aster.

Centrioles are lost during oogenesis and inherited from the sperm at fertilization. In the zygote, the centrioles recruit pericentriolar proteins from the egg to form a mature centrosome that nucleates a sperm aster. The sperm aster then captures the female pronucleus to join the maternal and paternal genomes.

The spindle assembly function of Caenorhabditis elegans katanin does not require microtubule-severing activity.

Katanin is a heterodimeric microtubule-severing protein that is conserved among eukaryotes. Loss-of-function mutations in the Caenorhabditis elegans katanin catalytic subunit, MEI-1, cause specific defects in female meiotic spindles. To determine the relationship between katanin's microtubule-severing activity and its role in meiotic spindle formation, we analyzed the MEI-1(A338S) mutant.

Kinesin-dependent transport results in polarized migration of the nucleus in oocytes and inward movement of yolk granules in meiotic embryos.

During female meiosis, meiotic spindles are positioned at the oocyte cortex to allow expulsion of chromosomes into polar bodies. In C. elegans, kinesin-dependent translocation of the entire spindle to the cortex precedes dynein-dependent rotation of one spindle pole toward the cortex.

Levels of the ubiquitin ligase substrate adaptor MEL-26 are inversely correlated with MEI-1/katanin microtubule-severing activity during both meiosis and mitosis.

The MEI-1/MEI-2 microtubule-severing complex, katanin, is required for oocyte meiotic spindle formation and function in C. elegans, but the microtubule-severing activity must be quickly downregulated so that it does not interfere with formation of the first mitotic spindle. Post-meiotic MEI-1 inactivation is accomplished by two parallel protein degradation pathways, one of which requires MEL-26, the substrate-specific adaptor that recruits MEI-1 to a CUL-3 based ubiquitin ligase.

Katanin controls mitotic and meiotic spindle length.

Accurate control of spindle length is a conserved feature of eukaryotic cell division. Lengthening of mitotic spindles contributes to chromosome segregation and cytokinesis during mitosis in animals and fungi. In contrast, spindle shortening may contribute to conservation of egg cytoplasm during female meiosis.

Fertilization initiates the transition from anaphase I to metaphase II during female meiosis in C. elegans.

Oocytes from most animals arrest twice during the meiotic cell cycle. The universally conserved prophase I arrest is released by a maturation hormone that allows progression to a second arrest point, typically metaphase I or II. This second arrest allows for short-term storage of fertilization-competent eggs and is released by signaling that occurs during fertilization.

MEI-1/katanin is required for translocation of the meiosis I spindle to the oocyte cortex in C elegans.

In most animals, successful segregation of female meiotic chromosomes involves sequential associations of the meiosis I and meiosis II spindles with the cell cortex so that extra chromosomes can be deposited in polar bodies. The resulting reduction in chromosome number is essential to prevent the generation of polyploid embryos after fertilization. Using time-lapse imaging of living Caenorhabditis elegans oocytes containing fluorescently labeled chromosomes or microtubules, we have characterized the movements of meiotic spindles relative to the cell cortex.

Nursing home physician educational intervention improves end-of-life outcomes.

Context: Nursing homes are the setting for one of five deaths in the United States. Unfortunately these deaths are often accompanied by pain and symptoms of discomfort.

Objective: To determine if an educational intervention designed for nursing home physicians improves the quality of dying for nursing home residents.

Katanin-mediated microtubule severing can be regulated by multiple mechanisms.

Microtubules are essential for a wide range of cellular processes that vary between cell types. Katanin is a microtubule-severing protein that carries out an essential role in meiotic spindles in Caenorhabditis elegans and a non-essential role in mitotic spindles of vertebrates. In contrast to these M-phase associated roles, katanin is also essential for post-mitotic differentiation events in vertebrate neurons and in Arabidopsis.

Katanin inhibition prevents the redistribution of gamma-tubulin at mitosis.

Katanin is a microtubule-severing protein that is concentrated at mitotic spindle poles but katanin's function in the mitotic spindle has not been previously reported. Inhibition of katanin with either of two dominant-negative proteins or a subunit-specific antibody prevented the redistribution of gamma-tubulin from the centrosome to the spindle in prometaphase CV-1 cells as assayed by immunofluorescence microscopy. Because gamma-tubulin complexes can bind to pre-existing microtubule minus ends, these results could be explained by a model in which the broad distribution of gamma-tubulin in the mitotic spindle is in part due to cytosolic gamma-tubulin ring complexes binding to microtubule minus ends generated by katanin-mediated microtubule severing.