Disproportionately elevated fasting proinsulin levels in normoglycemic patients with thalassemia major are correlated to the degree of iron overload

OBJECTIVE: To analyze the secretion of the insulin precursor proinsulin in patients with beta-thalassemia and its possible relation to iron overload. METHODS: We assessed fasting proinsulin, insulin, C-peptide and glucose levels from 34 patients with beta-thalassemia and 33 healthy controls. The correlation to age, body mass index, hepatic iron concentration, serum ferritin and serum AST was analyzed. RESULTS: Fasting proinsulin (p < 0.002) and proinsulin-to-insulin ratio (p < 0.02) were significantly increased in patients with thalassemia irrespective of the degree of glucose tolerance. They correlated positively to serum ferritin, liver iron, patient age and serum AST (all p < 0.05). CONCLUSIONS: Disproportionately elevated proinsulin levels in thalassemic patients indicate early beta-cell dysfunction due to siderosis. An additional biological significance of hyperproinsulinemia and its possible ability to predict long-term iron toxicity in these patients remain to be clarified.     

<Emphasis Type="Italic">ZWILLE</Emphasis> buffers meristem stability in<Emphasis Type="Italic"> Arabidopsis thaliana</Emphasis>

The shoot apical meristem of higher plants consists of a population of stem cells at the tip of the plant body that continuously gives rise to organs such as leaves and flowers. Cells that leave the meristem differentiate and must be replaced to maintain the integrity of the meristem. The balance between differentiation and maintenance is governed both by the environment and the developmental status of the plant. In order to respond to these different stimuli, the meristem has to be plastic thus ensuring the stereotypic shape of the plant body. Meristem plasticity requires the ZWILLE (ZLL) gene. In zll mutant embryos, the apical cells are misspecified causing a variability of the meristems size and function. Using specific antibodies against ZLL, we show that the zll phenotype is due to the complete absence of the ZLL protein. In immunohistochemical experiments we confirm the observation that ZLL is solely localized in vascular tissue. For a better understanding of the role of ZLL in meristem stability, we analysed the genetic interactions of ZLL with WUSCHEL (WUS) and the CLAVATA1, 2 and 3 (CLV) genes that are involved in size regulation of the meristem. In a zll loss-of-function background wus has a negative effect whereas clv mutations have a positive effect on meristem size. We propose that ZLL buffers meristem stability non-cell-autonomously by ensuring the critical number of apical cells required for proper meristem function.Edited by G. JürgensAn erratum to this article can be found at     

Arabidopsis phosphatidylglycerophosphate synthase 1 is essential for chloroplast differentiation,but is dispensable for mitochondrial function

Genetic dissection of the lipid bilayer composition provides essential in vivo evidence for the role of individual lipid species in membrane function. To understand the in vivo role of the anionic phospholipid, phosphatidylglycerol, the loss-of-function mutation was identified and characterized in the Arabidopsis thaliana gene coding for phosphatidylglycerophosphate synthase 1, PGP1. This mutation resulted in pigment-deficient plants of the xantha type in which the biogenesis of thylakoid membranes was severely compromised. The PGP1 gene coded for a precursor polypeptide that was targeted in vivo to both plastids and mitochondria. The activity of the plastidial PGP1 isoform was essential for the biosynthesis of phosphatidylglycerol in chloroplasts, whereas the mitochondrial PGP1 isoform was redundant for the accumulation of phosphatidylglycerol and its derivative cardiolipin in plant mitochondrial membranes. Together with findings in cyanobacteria, these data demonstrated that anionic phospholipids play an important, evolutionarily conserved role in the biogenesis and function of the photosynthetic machinery. In addition, mutant analysis suggested that in higher plants, mitochondria, unlike plastids, could import phosphatidylglycerol from the endoplasmic reticulum.     

Prey finding by larvae and adult females of shape Episyrphus balteatus

The prey-location behaviour of larvae of Episyrphus balteatus DeG. (Dipt.: Syrphidae) was investigated in two different experimental set-ups. First instar larvae exhibited directed search over short distances, guided by olfactory cues from aphids, but not from honeydew. However, second and third instars did not respond to aphid-plant-complex odours in a 4-arm-olfactometer. Aphid extracts, honeydew and sucrose were found to be feeding stimulants for the larvae. The oviposition behaviour of female syrphids was investigated in a series of two-choice experiments: females were able to evaluate aphid numbers and adjust oviposition rates accordingly, with higher prey numbers eliciting increased oviposition, even when the aphids were removed at the start of the experiment. The presence of conspecific syrphid larvae did not inhibit oviposition when the females were deprived of suitable oviposition sides before the experiments were conducted.