Mitotic spindle assembly by two different pathways in vitro

Abstract. We have used Xenopus egg extracts to study spindle morphogenesis in a cell-free system and have identified two pathways of spindle assembly in vitro using methods of fluorescent analogue cytochemistry. When demembranated sperm nuclei are added to egg extracts arrested in a mitotic state, individual nuclei direct the assembly of polarized microtubule arrays, which we term half-spindles; half-spindles then fuse pairwise to form bipolar spindles. In contrast, when sperm nuclei are added to extracts that are induced to enter interphase and arrested in the following mitosis, a single sperm nucleus can direct the assembly of a complete spindle. We find that microtubule arrays in vitro are strongly biased towards chromatin, but this does not depend on specific kinetochore-microtubul

Microtubule flux in mitosis is independent of chromosomes, centrosomes, and antiparallel microtubules

We investigated the mechanism of poleward microtubule flux in the mitotic spindle by generating spindle subassemblies in Xenopus egg extracts in vitro and assaying their ability to flux by photoactivation of fluorescence and low-light multichannel fluorescence video-microscopy. We find that monopolar intermediates of in vitro spindle assembly (half-spindles) exhibit normal poleward flux, as do astral microtubule arrays induced by the addition of dimethyl sulfoxide to egg extracts in the absence of both chromosomes and conventional centrosomes. Immunodepletion of the kinesin-related microtubule motor protein Eg5, a candidate flux motor, suggests that Eg5 is not required for flux. These results suggest that poleward flux is a basic element of microtubule behavior exhibited by even simple self-organized microtubule arrays and presumably underlies the most elementary levels of spindle morphogenesis

Mutations in the kinesin-like protein Eg5 disrupting localization to the mitotic spindle

Eg5, a member of the bimC subfamily of kinesin-like microtubule motor proteins, localizes to spindle microtubules in mitosis but not to interphase microtubules. We investigated the molecular basis for spindle localization by transient transfection of Xenopus A6 cells with myc-tagged derivatives of Eg5. Expressed at constitutively high levels from a cytomegalovirus promoter, mycEg5 protein is cytoplasmic throughout interphase, begins to bind microtubules in early prophase, and remains localized to spindle and/or midbody microtubules through mitosis to the end of telophase. Both N- and C-terminal regions of Eg5 are required for this cell-cycle-regulated targeting. Eg5 also contains within its C-terminal domain a sequence conserved among bimC subfamily proteins that includes a potential p34cdc2 phosphorylation site. We show that mutation of a single threonine (T937) within this site to nonphosphorylatable alanine abolishes localization of the mutant protein to the spindle, whereas mutation of T937 to serine preserves spindle localization. We hypothesize that phosphorylation of Eg5 may regulate its localization to the spindle in the cell cycle

Precambrian nomenclature in Kansas

The informal stratigraphic term “Precambrian” is replaced by formal nomenclature—Proterozoic and Archean Eonothems/Eons—and the informal term Hadean. The Phanerozoic Eonothem/Eon, representing all rocks younger than the Proterozoic, is added. The Proterozoic is further divided into Paleoproterozoic, Mesoproterozoic, and Neoproterozoic Erathems/Eras. The name Rice Formation (Scott, 1966) is abandoned, and the use of the informal term “Rice unit” is recommended. The proposed name Rice Series (Berendsen, 1994) is not accepted. These changes are adopted by the Kansas Geological Survey (KGS) and the stratigraphic nomenclature of Zeller (1968) has been revised accordingly

Clarification and Changes in Permian Stratigraphic Nomenclature in Kansas

This paper outlines Permian nomenclature changes to Zeller (1968) that have been adopted by the Kansas Geological Survey. The Permian System/Period, Cisuralian Series/Epoch, and Asselian Stage/Age are established at the base of the Bennett Shale Member of the Red Eagle Limestone. Series/epoch names Wolfcampian, Leonardian, and Guadalupian are retained and usage of Gearyan, Cimarronian, and Custerian is abandoned. The repositioned Carboniferous-Permian boundary divides the Council Grove Group into Carboniferous (Upper Pennsylvanian Series/Epoch; Virgilian Stage/Age) and Permian (Wolfcampian Series/Epoch) segments

Carboniferous–Permian Boundary in Kansas, Midcontinent, U.S.A.

The placement of the Carboniferous (Pennsylvanian)-Permian boundary in Kansas has been debated since the rocks of this age were first described and named. With the ratification of the Global Stratotype Section and Point (GSSP) for the base of the Permian System in the southern Ural Mountains, the Carboniferous-Permian boundary in Kansas can now be confidently defined. Based on the identification of the first occurrence of the conodont Streptognathodus isolatus that definitively correlates the Kansas rock section to the basal Permian GSSP, the Carboniferous-Permian boundary in Kansas can be placed at the base of the Bennett Shale Member of the Red Eagle Limestone. The Kansas Geological Survey proposes that the Tuttle Creek Lake Spillway section, located in northeast Kansas, be considered for the Carboniferous-Permian boundary stratotype in Kansas. It is further suggested that the stratigraphic position of the Carboniferous-Permian boundary in the Tuttle Creek Lake Spillway section be considered as a potential North American stratotype. In addition to being a significant biostratigraphic boundary, the Carboniferous-Permian boundary and enclosing strata also have significance because they reflect important geologic events and changes that occurred on a regional and global scale

New Stratigraphic Rank for the Carboniferous, Mississippian, and Pennsylvanian in Kansas

A new classification for the Carboniferous System/Period is formally adopted by the Kansas Geological Survey (KGS), and Zeller (1968) is modified accordingly. The Carboniferous is the system/period between the Devonian and Permian, and the Mississippian and Pennsylvanian are subsystems/subperiods of the Carboniferous. The Mississippian is subdivided into Lower, Middle, and Upper Mississippian Series and the Pennsylvanian is subdivided into Lower, Middle, and Upper Pennsylvanian Series. Regional stage names remain unchanged

Mississippian Stratigraphic Nomenclature Revisions in Kansas

This paper reviews proposed Mississippian nomenclature changes in Kansas and outlines the changes to Zeller (1968) that have been adopted by the Kansas Geological Survey. The Sedalia Dolomite is changed to the Sedalia Formation and the Northview Shale is changed to Northview Formation due to lateral lithology changes. The Short Creek Oolite Member as originally defined and described by Smith and Siebenthal (1907) at the type section in Kansas is reinstated. The Cowley Formation as originally defined and described by Lee (1940) in Kansas is reinstated. The Ste. Genevieve Limestone is placed as the basal formation of the Chesteran Stage

A Review of the Stratigraphy of the Ogallala Formation and Revision of Neogene (“Tertiary”) Nomenclature in Kansas

The member names for the Ogallala Formation (including the Valentine, Ash Hollow, and Kimball) in Kansas of Zeller (1968) are abandoned. The Ogallala Formation in Kansas includes strata of Miocene and earliest Pliocene age, revising earlier correlation to the Pliocene only (Zeller, 1968). The Kansas Geological Survey is abandoning use of the term "Tertiary," to be replaced by the term "Neogene." International stage boundaries for the Neogene have not been established in Kansas