The MEK Kinase Ssk2p Promotes Actin Cytoskeleton Recovery After Osmotic Stress

Saccharomyces cerevisiae adapts to osmotic stress through the activation of a conserved high-osmolarity growth (HOG) mitogen-activated protein (MAP) kinase pathway. Transmission through the HOG pathway is very well understood, yet other aspects of the cellular response to osmotic stress remain poorly understood, most notably regulation of actin organization. The actin cytoskeleton rapidly disassembles in response to osmotic insult and is induced to reassemble only after osmotic balance with the environment is reestablished. Here, we show that one of three MEK kinases of the HOG pathway, Ssk2p, is specialized to facilitate actin cytoskeleton reassembly after osmotic stress. Within minutes of cells' experiencing osmotic stress or catastrophic disassembly of the actin cytoskeleton through latrunculin A treatment, Ssk2p concentrates in the neck of budding yeast cells and concurrently forms a 1:1 complex with actin. These observations suggest that Ssk2p has a novel, previously undescribed function in sensing damage to the actin cytoskeleton. We also describe a second function for Ssk2p in facilitating reassembly of a polarized actin cytoskeleton at the end of the cell cycle, a prerequisite for efficient cell cycle completion. Loss of Ssk2p, its kinase activity, or its ability to localize and interact with actin led to delays in actin recovery and a resulting delay in cell cycle completion. These unique capabilities of Ssk2p are activated by a novel mechanism that does not involve known components of the HOG pathway

Uranus Pathfinder: exploring the origins and evolution of Ice Giant planets

The “Ice Giants” Uranus and Neptune are a different class of planet compared to Jupiter and Saturn. Studying these objects is important for furthering our understanding of the formation and evolution of the planets, and unravelling the fundamental physical and chemical processes in the Solar System. The importance of filling these gaps in our knowledge of the Solar System is particularly acute when trying to apply our understanding to the numerous planetary systems that have been discovered around other stars. The Uranus Pathfinder (UP) mission thus represents the quintessential aspects of the objectives of the European planetary community as expressed in ESA’s Cosmic Vision 2015–2025. UP was proposed to the European Space Agency’s M3 call for medium-class missions in 2010 and proposed to be the first orbiter of an Ice Giant planet. As the most accessible Ice Giant within the M-class mission envelope Uranus was identified as the mission target. Although not selected for this call the UP mission concept provides a baseline framework for the exploration of Uranus with existing low-cost platforms and underlines the need to develop power sources suitable for the outer Solar System. The UP science case is based around exploring the origins, evolution, and processes at work in Ice Giant planetary systems. Three broad themes were identified: (1) Uranus as an Ice Giant, (2) An Ice Giant planetary system, and (3) An asymmetric magnetosphere. Due to the long interplanetary transfer from Earth to Uranus a significant cruise-phase science theme was also developed. The UP mission concept calls for the use of a Mars Express/Rosetta-type platform to launch on a Soyuz–Fregat in 2021 and entering into an eccentric polar orbit around Uranus in the 2036–2037 timeframe. The science payload has a strong heritage in Europe and beyond and requires no significant technology developments