Polo-like kinase 4 controls centriole duplication but does not directly regulate cytokinesis

Centrioles organize the centrosome, and accurate control of their number is critical for the maintenance of genomic integrity. Centrioles duplicate once per cell cycle, and duplication is coordinated by Polo-like kinase 4 (Plk4). We previously demonstrated that Plk4 accumulation is autoregulated by its own kinase activity. However, loss of heterozygosity of Plk4 in mouse embryonic fibroblasts has been proposed to cause cytokinesis failure as a primary event, leading to centrosome amplification and gross chromosomal abnormalities. Using targeted gene disruption, we show that human epithelial cells with one inactivated Plk4 allele undergo neither cytokinesis failure nor increase in centrosome amplification. Plk4 is shown to localize exclusively at the centrosome, with none in the spindle midbody. Substantial depletion of Plk4 by small interfering RNA leads to loss of centrioles and subsequent spindle defects that lead to a modest increase in the rate of cytokinesis failure. Therefore, Plk4 is a centriole-localized kinase that does not directly regulate cytokinesis.

Environmental controls on the Emiliania huxleyi calcite mass

Although ocean acidification is expected to impact (bio)calcification by decreasing the seawater carbonate ion concentration, [CO3]2-, there exists evidence of non-uniform response of marine calcifying plankton to low seawater [CO3]2-. This raises questions on the role of environmental factors other than acidification and on the complex physiological responses behind calcification. Here we investigate the synergistic effect of multiple environmental parameters, including temperature, nutrient (nitrate and phosphate) availability, and seawater carbonate chemistry on the coccolith calcite mass of the cosmopolitan coccolithophore Emiliania huxleyi, the most abundant species in the world ocean. We use a suite of surface (late Holocene) sediment samples from the South Atlantic and southwestern Indian Ocean taken from depths lying well above the modern lysocline. The coccolith calcite mass in our results presents a latitudinal distribution pattern that mimics the main oceanographic features, thereby pointing to the potential importance of phosphorus and temperature in determining coccolith mass by affecting primary calcification and possibly driving the E. huxleyi morphotype distribution. This evidence does not necessarily argue against the potentially important role of the rapidly changing seawater carbonate chemistry in the future, when unabated fossil fuel burning will likely perturb ocean chemistry beyond a critical point. Rather our study highlights the importance of evaluating the combined effect of several environmental stressors on calcifying organisms to project their physiological response(s) in a high CO2 world and improve interpretation of paleorecords.

[Economic controls and commercial policies in the Latin American republics]

Reproduced from type-written copy.

Aviation security : improved controls needed to prevent unauthorized access at key airports : report to the Secretary of Transportation.

"B-226652"--P. 1.

Controls over vocational rehabilitation training services need improvement, Rehabilitation Services Administration, Department of Health, Education and Welfare : report to the Congress /

Date on cover: May 5, 1977.

Naval shipyards: management of borrowed labor can be enhanced by stronger internal controls.

Mode of access: Internet.

Traffic controls for construction and maintenance worksites: a research reference report. Volume I - project report. Final report.

Federal Highway Administration, Office of Research and Development, Washington, D.C.

Development of recommendations to improve controls operability. Final report.

National Highway Traffic Safety Administration, Washington, D.C.

Nuclear nonproliferation : DOE needs better controls to identify contractors having foreign interests : report to the Chairman, Committee on Governmental Affairs, U.S. Senate /

"B-221179.10"--p.1

Analysis of vegetation controls on bank erosion rates, Clark Fork of the Columbia River, Deer Lodge Valley, Montana /

"U.S. Geological Survey, U.S. Department of the Interior"--P. [1].