The RHG motifs of Drosophila Reaper and Grim are important for their distinct cell death-inducing abilities.

Reaper, Hid, and Grim are three Drosophila cell death activators that each contain a conserved NH(2)-terminal Reaper, Hid, Grim (RHG) motif. We have analyzed the importance of the RHG motifs in Reaper and Grim for their different abilities to activate cell death during development. Analysis of chimeric R/Grim and G/Reaper proteins indicated that the Reaper and Grim RHG motifs are functionally distinct and help to determine specific cell death activation properties. A truncated GrimC protein lacking the RHG motif retained an ability to induce cell death, and unlike Grim, R/Grim, or G/Reaper, its actions were not efficiently blocked by the cell death inhibitors, Diap1, Diap2, p35, or a dominant/negative Dronc caspase. Finally, we identified a second region of sequence similarity in Reaper, Hid, and Grim, that may be important for shared RHG motif-independent activities.

Distinct cell killing properties of the Drosophila reaper, head involution defective, and grim genes.

The Drosophila reaper, head involution defective (hid), and grim genes play key roles in regulating the activation of programmed cell death. Two useful systems for studying the functions of these genes are the embryonic CNS midline and adult eye. In this study we use the Gal4/UAS targeted gene expression system to demonstrate that unlike reaper or hid, expression of grim alone is sufficient to induce ectopic CNS midline cell death. We also show that in both the midline and eye, grim-induced cell death is not blocked by the Drosophila anti-apoptosis protein Diap2, which does block both reaper- and hid-induced cell death. grim can also function synergistically with reaper or hid to induce higher levels of midline cell death than observed for any of the genes individually. Finally we analyzed the function of a truncated Reaper-C protein which lacks the NH2-terminal 14 amino acids that are conserved between Reaper, Hid, and Grim. Ectopic expression of Reaper-C revealed cell killing activities distinct from full length Reaper, and indicated that the conserved NH2-terminal domain acts in part to modulate Reaper activity.

cul-1 is required for cell cycle exit in C. elegans and identifies a novel gene family.

The gene cul-1 (formerly lin-19) is a negative regulator of the cell cycle in C. elegans. Null mutations cause hyperplasia of all tissues. cul-1 is required for developmentally programmed transitions from the G1 phase of the cell cycle to the GO phase or the apoptotic pathway. Moreover, the mutant phenotype suggests that G1-to-S phase progression is accelerated, overriding mechanisms for mitotic arrest and producing abnormally small cells. Significantly, diverse aspects of cell fate and differentiation are unaffected in cul-1 mutants. cul-1 represents a conserved family of genes, designated cullins, with at least five members in nematodes, six in humans, and three in budding yeast.

ICE-LAP3, a novel mammalian homologue of the Caenorhabditis elegans cell death protein Ced-3 is activated during Fas- and tumor necrosis factor-induced apoptosis.

Members of the ICE/ced-3 gene family have been implicated as components of the cell death pathway. Based on similarities with the structural prototype interleukin-1 beta-converting enzyme (ICE), family members are synthesized as proenzymes that are proteolytically processed to form active heterodimeric enzymes. In this report, we describe a novel member of this growing gene family, ICE-LAP3, which is closely related to the death effector Yama/CPP32/Apopain. Pro-ICE-LAP3 is a 35-kDa protein localized to the cytoplasm and expressed in a variety of tissues and cell lines. Overexpression of a truncated version of ICE-LAP3 (missing the pro-domain) induces apoptosis in MCF7 breast carcinoma cells. Importantly, upon receipt of a death stimulus, endogenous ICE-LAP3 is processed to its subunit forms, suggesting a physiological role in cell death. This is the first report to demonstrate processing of a native ICE/ced-3 family member during execution of the death program and the first description of the subcellular localization of an ICE/ced-3 family member.

The differential diagnosis of bigeminal rhythms.

Bigeminal rhythms may arise from ectopic firing or from failure of impulse generation or conduction. In atrial bigeminy a premature atrial beat beat follows each sinus beat. If the PAC is not conducted bradycardia may result; if it is symptomatic treatment with digitalis or quinidine is indicated. Junctional bigeminy may be coupled to sinus beats or may accompany atrial fibrillation. Ventricular bigeminy, the most common type of bigeminy involving ectopic firing, usually requires treatment with suppressive drugs. Concealed bigeminy manifested as PVCs separated by an odd number of sinus beats has the same clinical implications as ventricular bigeminy. Re-entrant premature beats may also be triggered by an artificial ventricular pacemaker. Bigeminy associated with delayed impulse conduction is most often caused by a 3:2 Wenckebach block at the A-V junction but the block may also be at the S-A node or around an ectopic pacemaker. Conduction or production delay may produce "escape-capture" bigeminy in which successive beats are produced by the dominant pacemaker and an alternate one. Implantation of an artificial pacemaker may be appropriate. It is important for the observer to be able to identify the mechanism of any bigeminal rhythm since crucial clinical decisions may attend such identification.

Integration and induction of phage P22 in a recombination-deficient mutant of Salmonella typhimurium.

Phage P22 can integrate as prophage into a recombination-deficient (Rec(-)) strain of Salmonella typhimurium. At 37 C, the integration efficiency is only 10% that in Rec(+) infection, but at 25 C the efficiencies in Rec(-) and Rec(+) hosts are similar. Rec(-) lysogens cannot be induced by ultraviolet irradiation or by treatments with the chemical inducing agents streptonigrin or mitomycin C. Heat induction of Rec(-) cells lysogenic for a temperature-sensitive c(2) mutant (ts c(2)) is normal, showing that the Rec(-) cell has the machinery necessary for prophage excision. Ultraviolet irradiation of Rec(-) (ts c(2)) lysogens prior to heat induction does not prevent the formation of infective centers after temperature shift. Thus, the noninducibility of Rec(-) lysogens is not due to destruction of the prophage as a result of ultraviolet irradiation. Deoxyribonucleic acid-ribonucleic acid (RNA) hybridization experiments demonstrate that no increase in phage-specific RNA synthesis occurs after ultraviolet irradiation of a Rec(-) (c(+)) lysogen. The Rec(-) mutant appears to lack part of the mechanism required to destroy the phage repressor and allow the initiation of early phage functions such as messenger RNA synthesis. A similar conclusion was reached previously for an Escherichia coli Rec(-) strain.

Recombination-deficient mutant of Salmonella typhimurium.

A recombination-deficient (Rec(-)) ultraviolet-sensitive mutant of Salmonella typhimurium was isolated. The mutant grows more slowly than the wild-type strain and degrades its deoxyribonucleic acid extensively both during normal growth and after ultraviolet irradiation. Evidence is presented that a growing Rec(-) population consists of two types of cells, one which can divide and one which cannot.