The C. elegans genes ced-2, ced-5, and ced-10, and their mammalian homologs crkII, dock180, and rac1, mediate cytoskeletal rearrangements during phagocytosis of apoptotic cells and cell motility. Here, we describe an additional member of this signaling pathway, ced-12, and its mammalian homologs, elmo1 and elmo2. In C. elegans, CED-12 is required for engulfment of dying cells and for cell migrations. In mammalian cells, ELMO1 functionally cooperates with CrkII and Dock180 to promote phagocytosis and cell shape changes. CED-12/ELMO-1 binds directly to CED-5/Dock180; this evolutionarily conserved complex stimulates a Rac-GEF, leading to Rac1 activation and cytoskeletal rearrangements. These studies identify CED-12/ELMO as an upstream regulator of Rac1 that affects engulfment and cell migration from C. elegans to mammals.

The Ran guanosine triphosphatase (GTPase) controls nucleocytoplasmic transport, mitotic spindle formation, and nuclear envelope assembly. These functions rely on the association of the Ran-specific exchange factor, RCC1 (regulator of chromosome condensation 1), with chromatin. We find that RCC1 binds directly to mononucleosomes and to histones H2A and H2B. RCC1 utilizes these histones to bind Xenopus sperm chromatin, and the binding of RCC1 to nucleosomes or histones stimulates the catalytic activity of RCC1. We propose that the docking of RCC1 to H2A/H2B establishes the polarity of the Ran-GTP gradient that drives nuclear envelope assembly, nuclear transport, and other nuclear events.

RCC1, the only known guanine-nucleotide exchange factor for the Ran GTPase, is an ∼45-kD nuclear protein that can bind chromatin. An important question concerns how RCC1 traverses the nuclear envelope. We now show that nuclear RCC1 is not exported readily in interphase cells and that the import of RCC1 into the nucleoplasm is extremely rapid. Import can proceed by at least two distinct mechanisms. The first is a classic import pathway mediated by basic residues within the NH2-terminal domain (NTD) of RCC1. This pathway is dependent upon both a preexisting Ran gradient and energy, and preferentially uses the importin-α3 isoform of importin-α. The second pathway is not mediated by the NTD of RCC1. This novel pathway does not require importin-α or importin-β or the addition of any other soluble factor in vitro; however, this pathway is saturable and sensitive only to a subset of inhibitors of classical import pathways. Furthermore, the nuclear import of RCC1 does not require a preexisting Ran gradient or energy. We speculate that this second import pathway evolved to ensure that RCC1 never accumulates in the cytoplasm.

Patients with malignant hyperthermia experience an exaggerated metabolic response when exposed to volatile anesthetic gases and succinylcholine. The minimum concentration of anesthetic gas needed to trigger a malignant hyperthermia crisis in humans is unknown and may remain so because of the inherent risks associated with studying the complex nature of this rare and lethal genetic disorder. The Malignant Hyperthermia Association of the United States provides specific instructions on purging anesthesia machines of volatile agents to reduce the risk of exposure. However, these recommendations were developed from studies of older generation machines. Modern anesthesia workstations are more complex and contain more gas absorbing materials. A review of the literature found the current guidelines inadequate to prepare newer generation workstations, which require more time for purging anesthetic gases, autoclaving or replacement of parts, and modifications to the gas delivery system. Protocols must be developed to prepare newer generation anesthesia machines.