The potential of annexin-labelling for the diagnosis and follow-up of glaucoma

Glaucoma is one of the leading causes of blindness in developed countries and is mainly attributable to the apoptosis of retinal ganglion cells (RGCs). Although several diagnostic tools have been developed to detect and monitor this disease, none has the requisite sensitivity to identify it at a preclinical stage or to perceive small changes in retinal health over short periods. Specifically, irreversible visual changes occur before neuronal damage is discovered. The most widely accepted in vitro assay for apoptotic cells involves the use of fluorescent annexin A5. The radiolabelling of this marker makes it possible to assess, in vivo and non-invasively, various diseases in which the apoptotic process is pivotal, such as myocardial infarction or tumour response to chemotherapy. Recently, a new technique has been developed to visualise directly individual RGCs undergoing apoptosis in the living eye. This DARC (detection of apoptosing retinal cells) technology uses fluorescently labelled annexin A5 to bind apoptosing retinal neurons and confocal scanning laser ophthalmoscopy to detect the marked dying cells. Based on experimental models, DARC has been suggested to offer a direct and quantitative assessment of the retinal condition of patients. A Phase I clinical trial in glaucoma patients is scheduled to start shortly. This technology has the potential to pre-empt the diagnosis of glaucoma prior to visual deterioration, to provide an accurate numeric evaluation highlighting even small retinal changes and to allow the rapid judgement of the efficacy of both current and new therapeutic strategies.     

Tight intramolecular regulation of the human Upf1 helicase by its N- and C-terminal domains

The RNA helicase Upf1 is a multifaceted eukaryotic enzyme involved in DNA replication, telomere metabolism and several mRNA degradation pathways. Upf1 plays a central role in nonsense-mediated mRNA decay (NMD), a surveillance process in which it links premature translation termination to mRNA degradation with its conserved partners Upf2 and Upf3. In human, both the ATP-dependent RNA helicase activity and the phosphorylation of Upf1 are essential for NMD. Upf1 activation occurs when Upf2 binds its N-terminal domain, switching the enzyme to the active form. Here, we uncovered that the C-terminal domain of Upf1, conserved in higher eukaryotes and containing several essential phosphorylation sites, also inhibits the flanking helicase domain. With different biochemical approaches we show that this domain, named SQ, directly interacts with the helicase domain to impede ATP hydrolysis and RNA unwinding. The phosphorylation sites in the distal half of the SQ domain are not directly involved in this inhibition. Therefore, in the absence of multiple binding partners, Upf1 is securely maintained in an inactive state by two intramolecular inhibition mechanisms. This study underlines the tight and intricate regulation pathways required to activate multifunctional RNA helicases like Upf1.     

Reproductive system morphology of Lightiella magdalenina (Crustacea,Cephalocarida): functional and adaptive implications

The reproductive systems of adults and larvae of Lightiella magdalenina were examined. Lightiella magdalenina, similar to the best-known cephalocarida species Hutchinsoniella macracantha, is a simultaneous hermaphrodite. Although the morphology of their reproductive system is similar, L. magdalenina differs from H. macracantha in exhibiting reduced fecundity: it lays one egg, not two, per reproductive event. This is due to asynchronous development of the oocytes inside the paired female reproductive structures, which determines the maturation of a single egg at a time. The reduced fecundity of L. magdalenina could be offset by the precocious release of oocytes from the germarium, which begins the vitellogenetic process during the last larval stages. Due to this process, after their last moult, reproductive adults can have a large number of advanced vitellogenic oocytes, reducing the time required for their maturation. A possible adaptive relationship between the halved fecundity with pre- and post-hatching parental care is discussed.     

Short-term dynamics of physico-chemical and biological features in a shallow, evaporative antarctic lake

Lakes are among the most productive and biodiverse ecosystems in Antarctica, and they behave as important indicators of local climatic and environmental changes. However, few studies have focused on the local drivers of short-term temporal variability in lacustrine biogeochemical variables. In the present study, measurements of physical, chemical, biological and optical characteristics of the shallow endorheic Lake 14 at Edmonson Point (74.33° S, 165.13° E) were made over the ice-free period in December 2006. A significant variation in most variables was observed. Possible drivers for these changes were the loss of the ice cover, an increase in solar irradiance, a change in photosynthetic activity and the evaporative loss of water. By removing relative changes due to evaporative losses, new insights were gained into the driving factors controlling the biogeochemistry and primary productivity in the shallow Antarctic lake. In particular, a decrease in phytoplankton biomass was observed and was probably linked to photoinhibition as revealed by an increase in photoprotective pigments. The absorbance by dissolved organic matter, when weighted with respect to evaporative loss, shows an overall reduction in humic-like absorption, most likely linked to photodegradation.