Increased proliferation of B cells and auto-immunity in mice lacking protein kinase Cdelta

Protein kinase C (PKC), which comprises 11 closely related isoforms, has been implicated in a wide variety of cellular processes, such as growth, differentiation, secretion, apoptosis and tumour development. Among the PKC isotypes, PKC-delta is unique in that its overexpression results in inhibition of cell growth. Here we show that mice that lack PKC-delta exhibit expansion of the B-lymphocyte population with the formation of numerous germinal centres in the absence of stimulation. The rate of proliferation in response to stimulation was greater for B cells from PKC-delta-deficient mice than for those from wild-type mice. Adoptive transfer experiments suggested that the hyperproliferation phenotype is B-cell autonomous. Production of interleukin-6 was markedly increased in B cells of PKC-delta-null mice as a result of an increase in the DNA-binding activity of NF-IL6. Furthermore, the PKC-delta-deficient mice contain circulating autoreactive antibodies and display immune-complex-type glomerulonephritis, as well as lymphocyte infiltration in many organs. These results suggest that PKC-delta has an indispensable function in negative regulation of B-cell proliferation, and is particularly important for the establishment of B-cell tolerance.     

CDK-dependent phosphorylation of Sld2 and Sld3 initiates DNA replication in budding yeast

In eukaryotic cells, cyclin-dependent kinases (CDKs) have an important involvement at various points in the cell cycle. At the onset of S phase, active CDK is essential for chromosomal DNA replication, although its precise role is unknown. In budding yeast (Saccharomyces cerevisiae), the replication protein Sld2 (ref. 2) is an essential CDK substrate, but its phospho-mimetic form (Sld2-11D) alone neither affects cell growth nor promotes DNA replication in the absence of CDK activity, suggesting that other essential CDK substrates promote DNA replication. Here we show that both an allele of CDC45 (JET1) and high-copy DPB11, in combination with Sld2-11D, separately confer CDK-independent DNA replication. Although Cdc45 is not an essential CDK substrate, CDK-dependent phosphorylation of Sld3, which associates with Cdc45 (ref. 5), is essential and generates a binding site for Dpb11. Both the JET1 mutation and high-copy DPB11 by-pass the requirement for Sld3 phosphorylation in DNA replication. Because phosphorylated Sld2 binds to the carboxy-terminal pair of BRCT domains in Dpb11 (ref. 4), we propose that Dpb11 connects phosphorylated Sld2 and Sld3 to facilitate interactions between replication proteins, such as Cdc45 and GINS. Our results demonstrate that CDKs regulate interactions between BRCT-domain-containing replication proteins and other phosphorylated proteins for the initiation of chromosomal DNA replication; similar regulation may take place in higher eukaryotes.     

Detection of a radio counterpart to the 27 December 2004 giant flare from SGR 1806-20

It was established over a decade ago that the remarkable high-energy transients known as soft gamma-ray repeaters (SGRs) are located in our Galaxy and originate from neutron stars with intense (< or = 10(15)G) magnetic fields-so-called 'magnetars'. On 27 December 2004, a giant flare with a fluence exceeding 0.3 erg cm(-2) was detected from SGR 1806-20. Here we report the detection of a fading radio counterpart to this event. We began a monitoring programme from 0.2 to 250 GHz and obtained a high-resolution 21-cm radio spectrum that traces the intervening interstellar neutral hydrogen clouds. Analysis of the spectrum yields the first direct distance measurement of SGR 1806-20: the source is located at a distance greater than 6.4 kpc and we argue that it is nearer than 9.8 kpc. If correct, our distance estimate lowers the total energy of the explosion and relaxes the demands on theoretical models. The energetics and the rapid decay of the radio source are not compatible with the afterglow model that is usually invoked for gamma-ray bursts. Instead, we suggest that the rapidly decaying radio emission arises from the debris ejected during the explosion.     

Sex-specific peptides from exocrine glands stimulate mouse vomeronasal sensory neurons

In mammals, social and reproductive behaviours are modulated by pheromones, which are chemical signals that convey information about sex and strain. The vomeronasal organ, located at the base of the nasal septum, is responsible for mediating pheromone information in mice. Two classes of putative pheromone receptor gene families, V1R and V2R, are expressed by vomeronasal sensory neurons in mutually segregated epithelial zones of the vomeronasal organ. Although numerous studies have suggested that pheromones originate from urine, direct recordings of behaving mice have shown that neuronal firing in the vomeronasal system is modulated by physical contact with the facial area. Here we identify a male-specific 7-kDa peptide secreted from the extraorbital lacrimal gland. This peptide, which we named exocrine gland-secreting peptide 1 (ESP1), is encoded by a gene from a previously unrecognized large family clustered in proximity to the class I major histocompatibility complex (MHC) region. ESP1 is secreted from the eyes and is transferred to the female vomeronasal organ, where it stimulates V2R-expressing vomeronasal sensory neurons and elicits an electrical response. Our results indicate that mice respond to sex-specific peptides released from exocrine glands through the vomeronasal system during direct contact.     

Carbon-Carbon Bond Formation Reactions in the Preparation of Hydrindanones

1 Introduction Carbon-carbon bond formation reactions are highly important in organic chemistry, because these reactions may be used to construct complicated molecules. Samarium diiodide is known to be a one-electron reducing agent and recently used in many organic reactions. A radicals is postulated as an intermediate, which may be formed by direct reduction of halides, carbonyls and other functional groups.1IntroductionCarbon-carbon bond formation reactions are highly i mportant in organic …     

Genome sequence of the ultrasmall unicellular red alga Cyanidioschyzon merolae 10D

Small, compact genomes of ultrasmall unicellular algae provide information on the basic and essential genes that support the lives of photosynthetic eukaryotes, including higher plants. Here we report the 16,520,305-base-pair sequence of the 20 chromosomes of the unicellular red alga Cyanidioschyzon merolae 10D as the first complete algal genome. We identified 5,331 genes in total, of which at least 86.3% were expressed. Unique characteristics of this genomic structure include: a lack of introns in all but 26 genes; only three copies of ribosomal DNA units that maintain the nucleolus; and two dynamin genes that are involved only in the division of mitochondria and plastids. The conserved mosaic origin of Calvin cycle enzymes in this red alga and in green plants supports the hypothesis of the existence of single primary plastid endosymbiosis. The lack of a myosin gene, in addition to the unexpressed actin gene, suggests a simpler system of cytokinesis. These results indicate that the C. merolae genome provides a model system with a simple gene composition for studying the origin, evolution and fundamental mechanisms of eukaryotic cells.     

Radixin deficiency causes conjugated hyperbilirubinemia with loss of Mrp2 from bile canalicular membranes

The ezrin-radixin-moesin (ERM) family of proteins crosslink actin filaments and integral membrane proteins. Radixin (encoded by Rdx) is the dominant ERM protein in the liver of wildtype mice and is concentrated at bile canalicular membranes (BCMs). Here we show that Rdx(-/-) mice are normal at birth, but their serum concentrations of conjugated bilirubin begin to increase gradually around 4 weeks, and they show mild liver injury after 8 weeks. This phenotype is similar to human conjugated hyperbilirubinemia in Dubin-Johnson syndrome, which is caused by mutations in the multidrug resistance protein 2 (MRP2, gene symbol ABCC2), although this syndrome is not associated with overt liver injury. In wildtype mice, Mrp2 concentrates at BCMs to secrete conjugated bilirubin into bile. In the BCMs of Rdx(-/-) mice, Mrp2 is decreased compared with other BCM proteins such as dipeptidyl peptidase IV (CD26) and P-glycoproteins. In vitro binding studies show that radixin associates directly with the carboxy-terminal cytoplasmic domain of human MRP2. These findings indicate that radixin is required for secretion of conjugated bilirubin through its support of Mrp2 localization at BCMs.     

Actomyosin structure in contracting muscle detected by rapid freezing

It is now widely accepted that the ATP-induced active sliding of adjacent thin and thick filaments mediated by myosin heads (cross-bridges) is responsible for muscle contraction. Despite intensive studies, the behaviour of the myosin heads during muscle contraction is still unclear. Recent progress in the rapid freezing electron microscope technique has greatly improved the temporal resolution of the images that can be obtained. Here, we report a new type of actomyosin structure captured by rapid freezing. We have analysed images from thin sections of freeze-substituted rabbit skeletal muscle rapidly frozen during isometric contraction. For comparison, we also studied relaxed and rigor muscles. Our results show that, during isometric contraction, most myosin heads are regularly arrayed along the helix of the actin filaments and that this actomyosin structure appears to be distinct from that observed in rigor muscle.