The Structure of the Mitotic Spindle and Nucleolus during Mitosis in the Amebo-Flagellate Naegleria

Mitosis in the amebo-flagellate Naegleria pringsheimi is acentrosomal and closed (the nuclear membrane does not break down). The large central nucleolus, which occupies about 20% of the nuclear volume, persists throughout the cell cycle. At mitosis, the nucleolus divides and moves to the poles in association with the chromosomes. The structure of the mitotic spindle and its relationship to the nucleolus are unknown. To identify the origin and structure of the mitotic spindle, its relationship to the nucleolus and to further understand the influence of persistent nucleoli on cellular division in acentriolar organisms like Naegleria, three-dimensional reconstructions of the mitotic spindle and nucleolus were carried out using confocal microscopy. Monoclonal antibodies against three different nucleolar regions and α-tubulin were used to image the nucleolus and mitotic spindle. Microtubules were restricted to the nucleolus beginning with the earliest prophase spindle microtubules. Early spindle microtubules were seen as short rods on the surface of the nucleolus. Elongation of the spindle microtubules resulted in a rough cage of microtubules surrounding the nucleolus. At metaphase, the mitotic spindle formed a broad band completely embedded within the nucleolus. The nucleolus separated into two discreet masses connected by a dense band of microtubules as the spindle elongated. At telophase, the distal ends of the mitotic spindle were still completely embedded within the daughter nucleoli. Pixel by pixel comparison of tubulin and nucleolar protein fluorescence showed 70% or more of tubulin co-localized with nucleolar proteins by early prophase. These observations suggest a model in which specific nucleolar binding sites for microtubules allow mitotic spindle formation and attachment. The fact that a significant mass of nucleolar material precedes the chromosomes as the mitotic spindle elongates suggests that spindle elongation drives nucleolar division

Elizabeth Ann Barson et al v. E. R. Squibb & Sons, Inc. : Reply Brief of Appellant

Appeal from the District Court of the First Judicial District of the State of Utah. Sat Below: Hon. VeNoy Christofferson, District Judge, and a Jury

Corporate Compliance and the Antitrust Agencies’ Bi-Modal Penalties

Calkins discusses individual compared with entity penalties as tools for encouraging corporate law compliance and comments on the relationship between monetary payments as compensation and deterrence

Two Mistakes Behavioralists Make: A Response to Professors Feigenson et al. and Professor Slovic

This article provides a critique of Professors Feigenson and Slovic\u27s submissions to the Interdisciplinary Perspectives on Fear and Risk Perception in Times of Democratic Crisis Symposium. Examined are two common mistakes that behaviorists make; 1) discounting the rational account too quickly and 2) reflexively advocating a governmental fix

Two Mistakes Behavioralists Make: A Reply to Professor Feigenson et al. and Professor Slovic

First, the growing catalog of cognitive quirks may lead behavioralists to hastily adopt “non-rational” explanations for otherwise rational behavior. Second, because their evidence seems to undermine the rationality assumption of Chicago school law and economics, behavioralists may improperly assume that their work also undermines that school\u27s default policy prescription--i.e., laissez faire. Consequently, they may advocate inappropriately paternalistic government policies