Light chains of sea urchin kinesin identified by immunoadsorption

Previous studies with monoclonal antibodies indicate that sea urchin kinesin contains two heavy chains arranged in parallel such that their N-terminal ends fold into globular mechanochemical heads attached to a thin stalk ending in a bipartite tail [Scholey et al., 1989]. In the present, complementary study, we have used the monoclonal antikinesin, SUK4, to probe the quaternary structure of sea urchin (Strongylocentrotus purpuratus) kinesin. Kinesin prepared from sea urchin cytosol sedimented at 9.6 S on sucrose density gradients and consisted of 130-kd heavy chains plus an 84-kd/78 kd doublet (1 mol heavy chain: 1 mol doublet determined by gel densitometry). Low levels of 110-kd and 90-kd polypeptides were sometimes present as well. The 84-kd/78 kd polypeptides are thought to be light chains because they were precipitated from the kinesin preparation at a stoichiometry of one mol doublet per 1 mol heavy chain using SUK4-Sepharose immunoaffinity resins. The 110-kd and 90-kd peptides, by contrast, were removed using this immunoadsorption method. SUK4-Sepharose immunoaffinity chromatography was also used to purify the 130-kd heavy chain and 84-kd/78-kd doublet (1 mol heavy chain: 1 mol doublet) directly from sea urchin egg cytosolic extracts, and from a MAP (microtubule-associated protein) fraction eluted by ATP from microtubules prepared in the presence of AMPPNP but not from microtubules prepared in ATP. The finding that sea urchin kinesin contains equimolar quantities of heavy and light chains, together with the aforementioned data on kinesin morphology, suggests that native sea urchin kinesin is a tetramer assembled from two light chains and two heavy chains.     

Human Cep192 is required for mitotic centrosome and spindle assembly

As cells enter mitosis, centrosomes dramatically increase in size and ability to nucleate microtubules. This process, termed centrosome maturation, is driven by the accumulation and activation of gamma-tubulin and other proteins that form the pericentriolar material on centrosomes during G2/prophase. Here, we show that the human centrosomal protein, Cep192 (centrosomal protein of 192 kDa), is an essential component of the maturation machinery. Specifically, we have found that siRNA depletion of Cep192 results in a complete loss of functional centrosomes in mitotic but not interphase cells. In mitotic cells lacking Cep192, microtubules become organized around chromosomes but rarely acquire stable bipolar configurations. These cells contain normal numbers of centrioles but cannot assemble gamma-tubulin, pericentrin, or other pericentriolar proteins into an organized PCM. Alternatively, overexpression of Cep192 results in the formation of multiple, extracentriolar foci of gamma-tubulin and pericentrin. Together, our findings support the hypothesis that Cep192 stimulates the formation of the scaffolding upon which gamma-tubulin ring complexes and other proteins involved in microtubule nucleation and spindle assembly become functional during mitosis.     

Drosophila katanin is a microtubule depolymerase that regulates cortical-microtubule plus-end interactions and cell migration

Regulation of microtubule dynamics at the cell cortex is important for cell motility, morphogenesis and division. Here we show that the Drosophila katanin Dm-Kat60 functions to generate a dynamic cortical-microtubule interface in interphase cells. Dm-Kat60 concentrates at the cell cortex of S2 Drosophila cells during interphase, where it suppresses the polymerization of microtubule plus-ends, thereby preventing the formation of aberrantly dense cortical arrays. Dm-Kat60 also localizes at the leading edge of migratory D17 Drosophila cells and negatively regulates multiple parameters of their motility. Finally, in vitro, Dm-Kat60 severs and depolymerizes microtubules from their ends. On the basis of these data, we propose that Dm-Kat60 removes tubulin from microtubule lattice or microtubule ends that contact specific cortical sites to prevent stable and/or lateral attachments. The asymmetric distribution of such an activity could help generate regional variations in microtubule behaviours involved in cell migration.     

MODERN TREATMENT OF PLACENTA PREVIA—A Study of 234 Cases

Study was made of 234 cases of placenta previa occurring in 48,752 deliveries at one hospital during the period 1947-1956. There was no maternal mortality. The uncorrected fetal mortality rate for all weight groups was 21.4 per cent. The rate varied from 88 per cent in babies under 1,500 grams to 5.7 per cent in babies over 2,500 grams. Initial conservative management to permit gestation to continue as close to term as possible is advisable.Ultimate termination of the pregnancy by cesarean section under spinal anesthesia gave the best results. The incidence of transverse and breech presentations in association with placenta previa was inordinately high. A progressive trend toward more conservative treatment of placenta previa was noted in the present series, with a concomitant reduction in fetal mortality rate.     

Expression of the mitotic kinesin Kif15 in postmitotic neurons: Implications for neuronal migration and development

Kif15 is a kinesin-related protein whose mitotic homologues are believed to crosslink and immobilize spindle microtubules. We have obtained rodent sequences of Kif15, and have studied their expression and distribution in the developing nervous system. Kif15 is indeed expressed in actively dividing fibroblasts, but is also expressed in terminally postmitotic neurons. In mitotic cells, Kif15 localizes to spindle poles and microtubules during prometaphase to early anaphase, but then to the actin-based cleavage furrow during cytokinesis. In interphase fibroblasts, Kif15 localizes to actin bundles but not to microtubules. In cultured neurons, Kif15 localizes to microtubules but shows no apparent co-localization with actin. Localization of Kif15 to microtubules is particularly good when the microtubules are bundled, and there is a notable enrichment of Kif15 in the microtubule bundles that occupy stalled growth cones and dendrites. Studies on developing rodent brain show a pronounced enrichment of Kif15 in migratory neurons compared to other neurons. Notably, migratory neurons have a cage-like configuration of microtubules around their nucleus that is linked to the microtubule array within the leading process, such that the entire array moves in unison as the cell migrates. Since the capacity of microtubules to move independently of one another is restricted in all of these cases, we propose that Kif15 opposes the capacity of other motors to generate independent microtubule movements within key regions of developing neurons.     

Individualized cosinor assessment of circadian hormonal variation in third trimester human pregnancy

Two clinically healthy pregnant women were studied in a single 24-h span during the third trimester. Blood drawn every 20 min was assayed for cortisol (F), dehydroepiandrosterone sulfate (DHEA-S), estriol (E3), and prolactin (PRL). Blood drawn hourly was assayed for progesterone (P), human placental lactogen (HPL) and 15alpha-hydroxyestriol (E4). Breast temperature (BT) was continuously monitored. Single cosinor analysis demonstrated statistically significant circadian rhythms for plasma concentrations of F, DHEA-S, and BT for both subjects, and of E3 for one subject. Statistically significant circadian rhythms in plasma concentrations of P, HPL, E4 or PRL could not be demonstrated in our third trimester subjects. However, analysis of data from subjects sampled at earlier gestational ages revealed highly significant PRL circadian rhythms. These results suggest that plasma concentrations of PRL show a progressive decrease in circadian amplitude despite a progressive increase in mesor with advancing gestational age. Frequent sampling and cosinor data analysis permit identification of circadian rhythms in BT. The use of BT as a potential marker for rhythms in plasma concentration of certain hormones awaits further scrutiny. The demonstration of several circadian endocrine rhythms in individual subjects in the third trimester of human pregnancy facilitates the usefulness of such marker rhythms.     

Pregnancy hormone concentrations in marijuana users

The maternal serum concentrations of human chorionic gonadotropin, pregnancy-specific beta-l-glycoprotein, placental lactogen, progesterone, 17-hydroxyprogesterone, estradiol and estriol were measured in 13 women who smoked marijuana regularly throughout pregnancy. Cannabinoid use in these women was confirmed by RIA measurements of their sum Δ ⁹- tetrahydrocannabinol (THC) concentrations. These THC using women were matched within $\text{2}\text{1}\text{2}$ weeks of gestational age with 13 pregnant non-THC using controls drawn from the same population. Placental protein and steroid hormone concentrations were within established normal ranges for gestational age and there were no significant differences between the groups in the concentrations of any of the protein and steroids measured. In addition, no significant differences between THC users were found following linear regression analysis of placental hormone concentrations as a function of gestational age. Thus, this study suggests that marijuana use during pregnancy does not significantly alter the circulating maternal concentrations of trophoblastic protein hormones or major fetoplacental steroid hormones.     

Drosophila Casein Kinase I Alpha Regulates Homolog Pairing and Genome Organization by Modulating Condensin II Subunit Cap-H2 Levels

The spatial organization of chromosomes within interphase nuclei is important for gene expression and epigenetic inheritance. Although the extent of physical interaction between chromosomes and their degree of compaction varies during development and between different cell-types, it is unclear how regulation of chromosome interactions and compaction relate to spatial organization of genomes. Drosophila is an excellent model system for studying chromosomal interactions including homolog pairing. Recent work has shown that condensin II governs both interphase chromosome compaction and homolog pairing and condensin II activity is controlled by the turnover of its regulatory subunit Cap-H2. Specifically, Cap-H2 is a target of the SCF^Slimb E3 ubiquitin-ligase which down-regulates Cap-H2 in order to maintain homologous chromosome pairing, chromosome length and proper nuclear organization. Here, we identify Casein Kinase I alpha (CK1α) as an additional negative-regulator of Cap-H2. CK1α-depletion stabilizes Cap-H2 protein and results in an accumulation of Cap-H2 on chromosomes. Similar to Slimb mutation, CK1α depletion in cultured cells, larval salivary gland, and nurse cells results in several condensin II-dependent phenotypes including dispersal of centromeres, interphase chromosome compaction, and chromosome unpairing. Moreover, CK1α loss-of-function mutations dominantly suppress condensin II mutant phenotypes in vivo. Thus, CK1α facilitates Cap-H2 destruction and modulates nuclear organization by attenuating chromatin localized Cap-H2 protein.     

The Drosophila Kinesin-13, KLP59D,Impacts Pacman- and Flux-based Chromosome Movement

Chromosome movements are linked to the active depolymerization of spindle microtubule (MT) ends. Here we identify the kinesin-13 family member, KLP59D, as a novel and uniquely important regulator of spindle MT dynamics and chromosome motility in Drosophila somatic cells. During prometaphase and metaphase, depletion of KLP59D, which targets to centrosomes and outer kinetochores, suppresses the depolymerization of spindle pole–associated MT minus ends, thereby inhibiting poleward tubulin Flux. Subsequently, during anaphase, loss of KLP59D strongly attenuates chromatid-to-pole motion by suppressing the depolymerization of both minus and plus ends of kinetochore-associated MTs. The mechanism of KLP59D''s impact on spindle MT plus and minus ends appears to differ. Our data support a model in which KLP59D directly depolymerizes kinetochore-associated plus ends during anaphase, but influences minus ends indirectly by localizing the pole-associated MT depolymerase KLP10A. Finally, electron microscopy indicates that, unlike the other Drosophila kinesin-13s, KLP59D is largely incapable of oligomerizing into MT-associated rings in vitro, suggesting that such structures are not a requisite feature of kinetochore-based MT disassembly and chromosome movements.     

Preparation of Drosophila S2 cells for Light Microscopy

The ideal experimental system would be cheap and easy to maintain, amenable to a variety of techniques, and would be supported by an extensive literature and genome sequence database. Cultured Drosophila S2 cells, the product of disassociated 20-24 hour old embryos¹, possess all these properties. Consequently, S2 cells are extremely well-suited for the analysis of cellular processes, including the discovery of the genes encoding the molecular components of the process or mechanism of interest. The features of S2 cells that are most responsible for their utility are the ease with which they are maintained, their exquisite sensitivity to double-stranded (ds)RNA-mediated interference (RNAi), and their tractability to fluorescence microscopy as either live or fixed cells.S2 cells can be grown in a variety of media, including a number of inexpensive, commercially-available, fully-defined, serum-free media². In addition, they grow optimally and quickly at 21-24°C and can be cultured in a variety of containers. Unlike mammalian cells, S2 cells do not require a regulated atmosphere, but instead do well with normal air and can even be maintained in sealed flasks.Complementing the ease of RNAi in S2 cells is the ability to readily analyze experimentally-induced phenotypes by phase or fluorescence microscopy of fixed or live cells. S2 cells grow in culture as a single monolayer but do not display contact inhibition. Instead, cells tend to grow in colonies in dense cultures. At low density, S2 cultures grown on glass or tissue culture-treated plastic are round and loosely-attached. However, the cytology of S2 cells can be greatly improved by inducing them to flatten extensively by briefly culturing them on a surface coated with the lectin, concanavalin A (ConA)³. S2 cells can also be stably transfected with fluorescently-tagged markers to label structures or organelles of interest in live or fixed cells. Therefore, the usual scenario for the microscopic analysis of cells is this: first, S2 cells (which can possess transgenes to express tagged markers) are treated by RNAi to eliminate a target protein(s). RNAi treatment time can be adjusted to allow for differences in protein turn-over kinetics and to minimize cell trauma/death if the target protein is important for viability. Next, the treated cells are transferred to a dish containing a coverslip pre-coated with conA to induce cells to spread and tightly adhere to the glass. Finally, cells are imaged with the researcher''s choice of microscopy modes. S2 cells are particularly good for studies requiring extended visualization of live cells since these cells stay healthy at room temperature and normal atmosphere.Download video file.^{(106M, mp4)}