Ribozyme déjà vu

A nuclear protein, PfMORC confers melatonin dependent synchrony of the human malaria parasite P. falciparum in the asexual stage

The host hormone melatonin is known to modulate the asexual cell-cycle of the human malaria parasite Plasmodium falciparum and the kinase PfPK7 is fundamental in the downstream signaling pathways. The nuclear protein PfMORC displays a histidine kinase domain and is involved in parasite cell cycle control. By using a real-time assay, we show a 24 h (h) rhythmic expression of PfMORC at the parasite asexual cycle and the expression is dramatically changed when parasites were treated with 100 nM melatonin for 17 h. Moreover, PfMORC expression was severely affected in PfPK7 knockout (PfPK7⁻) parasites following melatonin treatment. Parasites expressing 3D7^morc-GFP shows nuclear localization of the protein during the asexual stage of parasite development. Although the PfMORC knockdown had no significant impact on the parasite proliferation in vitro it significantly changed the ratio of the different asexual intraerythrocytic stages of the parasites upon the addition of melatonin. Our data reveal that in addition to the upstream melatonin signaling pathways such as IP₃ generation, calcium, and cAMP rise, a nuclear protein, PfMORC is essential for the hormone response in parasite synchronization.

Synthetic RNA circuits

Natural and engineered RNA 'parts' can perform a variety of functions, including hybridizing to targets, binding ligands and undergoing programmed conformational changes, and catalyzing reactions. These RNA parts can in turn be assembled into synthetic genetic circuits that regulate gene expression by acting either in cis or in trans on mRNAs. As more parts are discovered and engineered, it should be increasingly possible to create synthetic RNA circuits that are able to carry out complex logical operations in cells, either superimposed on or autonomous to extant gene regulation.

Aptamers against extracellular targets for in vivo applications

Oligonucleotides are multifunctional molecules which can interfere with gene expression by different mechanism such as antisense, RNA interference, ribozymes, etc. For most in vivo diagnostic and therapeutic applications, oligonucleotides need to be delivered to the intracellular compartment of a specific organ, a difficult task which limits considerably their use. However, aptamer oligonucleotides which target extracellular markers obviate this problem. Aptamers are short oligonucleotides (<100 bases) selected from large combinatorial pools of sequences for their capacity to bind to many types of different targets, ranging from small molecules (amino acids, antibiotics...) to proteins or nucleic acid structures. Aptamers present the same high specificity and affinity for their targets as antibodies. In addition to efficient binding, aptamers have been shown in many cases to display an inhibitory activity on their targets. Moreover, they seem to lack immunogenicity and can be chemically modified in order to improve their stability against nucleases or extend their blood circulation time, two properties which are particularly useful for in vivo applications. Recently, aptamers have been selected against whole living cells, opening a new avenue which presents three major advantages 1) direct selection without prior purification of the targets; 2) conservation of membrane proteins in their native conformation similar to the in vivo conditions and 3) identification of (new) targets for a specific phenotype. Many aptamers are now being developed against biomedical relevant extracellular targets: membrane receptor proteins, hormones, neuropeptides, coagulation factors... Among them, one aptamer that inhibits the human VEGF165 has recently been approved by FDA for the treatment of age-related macular degeneration. Here we discuss the recent developments of aptamers against extracellular targets for in vivo therapy and as tools for diagnosis using molecular imaging.