The Caenorhabditis elegans histone hairpin-binding protein is required for core histone gene expression and is essential for embryonic and postembryonic cell division.

As in all metazoans, the replication-dependent histone genes of Caenorhabditis elegans lack introns and contain a short hairpin structure in the 3' untranslated region. This hairpin structure is a key element for post-transcriptional regulation of histone gene expression and determines mRNA 3' end formation, nuclear export, translation and mRNA decay. All these steps contribute to the S-phase-specific expression of the replication-dependent histone genes. The hairpin structure is the binding site for histone hairpin-binding protein that is required for hairpin-dependent regulation. Here, we demonstrate that the C. elegans histone hairpin-binding protein gene is transcribed in dividing cells during embryogenesis and postembryonic development. Depletion of histone hairpin-binding protein (HBP) function in early embryos using RNA-mediated interference leads to an embryonic-lethal phenotype brought about by defects in chromosome condensation. A similar phenotype was obtained by depleting histones H3 and H4 in early embryos, indicating that the defects in hairpin-binding protein-depleted embryos are caused by reduced histone biosynthesis. We have confirmed this by showing that HBP depletion reduces histone gene expression. Depletion of HBP during postembryonic development also results in defects in cell division during late larval development. In addition, we have observed defects in the specification of vulval cell fate in animals depleted for histone H3 and H4, which indicates that histone proteins are required for cell fate regulation during vulval development.

Specificities of Caenorhabditis elegans and human hairpin binding proteins for the first nucleotide in the histone mRNA hairpin loop.

The 3' ends of animal replication-dependent histone mRNAs are formed by endonucleolytic cleavage of the primary transcripts downstream of a highly conserved RNA hairpin. The hairpin-binding protein (HBP) binds to this RNA element and is involved in histone RNA 3' processing. A minimal RNA-binding domain (RBD) of approximately 73 amino acids that has no similarity with other known RNA-binding motifs was identified in human HBP [Wang Z-F et al., Genes & Dev, 1996, 10:3028-3040]. The primary sequence identity between human and Caenorhabditis elegans RBDs is 55% compared to 38% for the full-length proteins. We analyzed whether differences between C. elegans and human HBP and hairpins are reflected in the specificity of RNA binding. The C. elegans HBP and its RBD recognize only their cognate RNA hairpins, whereas the human HBP or RBD can bind both the mammalian and the C. elegans hairpins. This selectivity of C. elegans HBP is mostly mediated by the first nucleotide in the loop, which is C in C. elegans and U in all other metazoans. By converting amino acids in the human RBD to the corresponding C. elegans residues at places where the latter deviates from the consensus, we could identify two amino acid segments that contribute to selectivity for the first nucleotide of the hairpin loop.

Monepantel irreversibly binds to and opens Haemonchus contortus MPTL-1 and Caenorhabditis elegans ACR-20 receptors.

Monepantel is a recently developed anthelmintic with a novel mode of action. Parasitic nematodes with reduced sensitivity to monepantel have led to the identification of MPTL-1, a ligand-gated ion-channel subunit of the parasitic nematode Haemonchus contortus, as a potential drug target. Homomeric MPTL-1 channels reconstituted in Xenopus oocytes are gated by µM concentrations of betaine and mM concentrations of choline. Measurement of reversal potentials indicated that the channel has a similar conductance for Na(+) and K(+) ions and does not permeate Ca(2+). Concentrations of monepantel (amino-acetonitrile derivative [AAD]-2225) >0.1 μM, but not its inactive enantiomer AAD-2224, induced channel opening in an irreversible manner. Currents elicited by monepantel alone were larger than the maximal current amplitudes achieved with betaine or choline, making monepantel a superagonist. Currents elicited by betaine or choline were allosterically potentiated by nM concentrations of monepantel and to a much smaller degree by AAD-2224. We have also reconstituted the Caenorhabditis elegans homomeric ACR-20 receptor in Xenopus oocytes. The acr-20 sequence has higher similarity to mptl-1 than acr-23, the primary target for monepantel mode of action in C. elegans. The ACR-20 channel is gated similarly as MPTL-1. Monepantel, but not AAD-2224, was able to induce channel opening in an irreversible manner at similar concentrations as for MPTL-1. Interestingly, the allosteric potentiation measured in the presence of betaine was much smaller than in MPTL-1 receptors. Together, these results establish the mode of action of monepantel in H. contortus and contribute to our understanding of the mode of action of this anthelmintic.

Zinnia elegans robusta grandiflora plenissima

anonym

Aristolochia elegans.

anonym

Aristolochia elegans

Anonym

Aristolochia elegans

AR

Aristolochia elegans

R. Anheisser

Früchte und Fruchtstände : Aristolochia elegans - Ptelea trifoliata - Details von Actaea und Aristolochia - Actaea alba - Prunella grandiflora (fällt weg)

AR

Früchte : Aristolochia elegans - Actaea alba - Ptelea trifoliata - Prunella incisa

AR

Blütenknospen : Aristolochia elegans - Stanhopea graveolens - Aristolochia tricandata - Bulbophyllum lobbii - Aristolochia tricandata - Nicotiana affinis

AR

Aristolochia elegans

AR

Blüten von Aristolochien : Aristolochia labiosa - Aristolochia elegans

AR

Caenorhabditis elegans germinal center kinase (Gck-1) is a p-body component that inhibits precocious ectopic MAP kinase dependent meiotic maturation

The Caenorhabditis elegans germline is an excellent model system for studying meiosis, as the gonad contains germ cells in all stages of meiosis I prophase in a linear temporal and spatial pattern. To form healthy gametes, many events must be coordinated. Failure of any step in the process can reduce fertility. Here, we describe a C. elegans Germinal Center Kinase, GCK-1, that is essential for the accurate progression of germ cells through meiosis I prophase. In the absence of GCK-1, germ cells undergo precocious maturation due to the activation of a specific MAP kinase isoform. Furthermore, GCK-1 localizes to P-bodies, RNP particles that have been implicated in RNA degradation and translational control. Like two other components of C. elegans germline P-bodies, GCK-1 functions to limit physiological germ cell apoptosis. This is the first study to identify a role for a GCK-III kinase in metazoan germ cell development and to link P-body function with MAP kinase activation and germ cell maturation. ^

Identification and analysis of novel mitotic inhibitors of the Caenorhabditis elegans Aurora B kinase

Proper execution of mitosis requires the accurate segregation of replicated DNA into each daughter cell. The highly conserved mitotic kinase AIR-2/Aurora B is a dynamic protein that interacts with subsets of cofactors and substrates to coordinate chromosome segregation and cytokinesis in Caenorhabdiris elegans. To identify components of the AIR-2 regulatory pathway, a genome-wide RNAi-based screen for suppressors of air-2 temperature-sensitive mutant lethality was conducted. Here, I present evidence that two classes of suppressors identified in this screen are bona fide regulators of the AIR-2 kinase. The strongest suppressor cdc-48.3, encodes an Afg2/Spaf-related Cdc48-like AAA+ ATPase that regulates AIR-2 kinase activity and stability during C. elegans embryogenesis. Loss of CDC-48.3 suppresses the lethality of air-2 mutant embryos, marked by the restoration of the dynamic behavior of AIR-2 and rescue of chromosome segregation and cytokinesis defects. Loss of CDC-48.3 leads to mitotic delays and abnormal accumulation of AIR-2 during late telophase/mitotic exit. In addition, AIR-2 kinase activity is significantly upregulated from metaphase through mitotic exit in CDC-48.3 depleted embryos. Inhibition of the AIR-2 kinase is dependent on (1) a direct physical interaction between CDC-48.3 and AIR-2, and (2) CDC-48.3 ATPase activity. Importantly, the increase in AIR-2 kinase activity does not correlate with the stabilization of AIR-2 in late mitosis. Hence, CDC-48.3 is a bi-functional inhibitor of AIR-2 that is likely to act via distinct mechanisms. The second class of suppressors consists of psy-2/smk-1 and pph-4.1, which encode two components of the conserved PP4 phosphatase complex that is essential for spindle assembly, chromosome segregation, and overall mitotic progression. AIR-2 and its substrates are likely to be targets of this complex since mitotic AIR-2 kinase activity is significantly increased during mitosis when either PSY-2/SMK-1 or PPH-4.l is depleted. Altogether, this study demonstrates that during the C. elegans embryonic cell cycle, regulators including the CDC-48.3 ATPase and PP4 phosphatase complex interact with and control the kinase activity, targeting behavior and protein stability of the Aurora B kinase to ensure accurate and timely progression of mitosis. ^