Compartmental Analysis Suggests Macropinocytosis at the Onset of Diatom Valve Formation

During valve formation of the siliceous frustules of diatoms, bulk uptake of silicic acid and its subsequent transport through the cell is required before it can be deposited in the silica deposition vesicle (SDV). It has been assumed that transport takes place via silicon transporters (SITs), but if that were the case a control mechanism would have to exist for stabilization of the large amounts of reactive silicon species during their passage through the cell on the way to the SDV. There is, however, no reason to assume that classical silica chemistry does not apply at elevated levels of silicic acid, and therefore autopolymerization could reasonably be expected to occur. In order to find alternative ways of Si transport that correspond with the high speed of valve formation at the earliest stages of cell division we followed 31Si(OH)4 uptake in synchronously dividing cells of the diatoms Coscinodiscus wailesii, Navicula pelliculosa, N. salinarum, and Pleurosira laevis. The results were related to systematically derived mathematical models for a compartmental analysis of 5 possible uptake/transport pathways, including one involving SITs and one involving (macro)pinocytosis-mediated uptake from the extracellular environment. Our study indicates that the uptake of radioactive silicic acid matches best with the model that describes macropinocytosis-mediated silicon uptake. This process is well in line with the observed ‘surge uptake’ at the start of valve formation when the demand for silicon is high; it infers that in diatoms a pathway of uptake and transport exists in which SITs are not involved.Radiation, Radionuclides and ReactorsApplied Science

The role of fetal autopsy and placental examination in the causes of fetal death: a retrospective study of 132 cases of stillbirths.

PURPOSE: To investigate the most plausible cause of stillbirth by evaluating clinical records and postmortem examination findings including placental analysis. METHODS: A retrospective cohort study concerning 132 stillbirths from 124 pregnancies occurred in the Mother-Infant Department of the University Hospital of Modena, Italy, from January 2000 to December 2004. Collected data were reviewed and classified according to the Gardosi ReCoDe system. RESULTS: A reasonable cause of fetal death was identified in 99/124 pregnancies (79.84\%). No associated relevant factors were disclosed in 25 fetuses (20.16\%) classified as unexplained stillbirths. A succeeding scrupulous analysis of the placenta and an accurate clinical record review were useful to detect other conditions in 82 cases, including 5 cases of unexplained stillbirth. The major relevant conditions associated to stillbirths were feto-placental infection especially in the early fetal gestation age, under the 24th week of gestation, and placental insufficiency occurred both in early and late gestation age fetuses and mainly associated with a IUGR (<10th customized percentile). The main frequent secondary conditions were represented by placental anomalies including cluster of avascular villi with stromal fibrosis associated to thrombosis in minor and/or major vessel(s). Through the further analysis of the placenta, we were able to reduce the unexplained stillbirth rate from 20.16 to 15\%. CONCLUSION: Accurate fetal autopsy and placental examination related to meticulous clinical collecting data are requisites in the valuation of stillbirth and could play an important role in reduction of unexplained stillbirth rate