Protein Turnover in Brain of the Rat Fetus

Protein synthesis in vivo was studied in whole brain of rat fetuses using continuous intravenous infusion of L-[U-14C]tyrosine into unrestrained pregnant rats at 19 and 21 days gestation. Protein degradation (KD) was calculated by subtracting fractional growth rate of brain protein (KG) from the fractional synthesis rate (KS). KS was high at both gestational ages (0.42 +/- 0.03 days-1 at day 19, 0.47 +/- 0.029 days-1 at 21 days), comparable to values previously reported for newborn rat cerebral hemispheres, and threefold higher than is seen in adult animals. KD was similar at both 19 and 21 days gestation (0.19-0.24) and lower than that reported in neonatal rat brain using similar techniques. Protein accretion during the most rapid phase of brain growth (fetus) is accomplished by similar rates of protein synthesis, but decreased rates of degradation when compared with a slower growth phase (newborn). KD in the brain of the rapidly growing fetus is slightly higher than in adult cerebral hemispheres.     

Estimation of Individual Growth Curves by Empirically Weighted Least Squares

The simultaneous estimation of individual growth curves and a mean growth curve is accomplished by weighted least squares. A polynomial curve is fitted for each individual and the polynomial parameters are linear functions of parameters corresponding to covariates. A simple, computationally efficient variance-covariance estimator is derived. The resultant estimate is used in the weighted least squares estimation. The results are compared to empirical Bayes estimation.     

Spreading of non-transformed and transformed cells

Mechanisms of cellular reactions responsible for the spreading non-transformed cultured tissue cells on the surface of various substrata and relationships of these reactions to the control of cell proliferation are reviewed; the special role of the membrane-cystoskeleton interactions leading to extension and attachment of psuedopods is stressed.Transition of cells from non-transformed to transformed phenotype is characterized by decreased spreading and by decreased dependence of proliferation on spreading. Manifestations of both of these spreading-associated changes are reviewed and their possible mechanisms are discussed. It is suggested that cell transition to transformed phenotype involves shift of an equilibrium between the reactions induced by the two groups of membrane-bound ligands: those attached and those not attached to the substratum.     

Factors controlling embryonic heart cell proliferation in serum-free synthetic media

Summary Embryonic chick cardiac cell cultures, plated on collagen-coated dishes, containing serum-free synthetic media proliferate actively. The basic medium contained Ham's F12 nutrient mixture, fetuin, ascorbic acid, and bovine serum albumin. This medium was supplemented with various combinations of factors; endothelial cell growth supplement (ECGS), epidermal growth factor (EGF), insulin (I), transferrin (T), selenium (S), hydrocortisone, and thyroxine or supplemented alone. Basic medium supplemented with ECGS alone contributes to the highest final cell density among all other factors used in various combinations or alone. The final cell density of the control culture with 2% fetal bovine serum was higher than those of all experimental cultures and an additional control culture grown in the basic medium. Combinations of factors without ECGS do not promote significant cell proliferation. Thyroxine is required to induce optimal differentiation and contractility of cardiac myocytes in vitro. Fibronectin and laminin did not show any more influence than collagen did on the growth and maintenance of cardiac myocytes in serum-free media. The proportion of cardiac muscle cells in ECGS-containing media was higher than those in other experimental media and control media with the exception of ECGS and ITS-containing medium that showed lower proportion of cardiac myocytes than that of serum-containing medium on Days 3 and 5. The profiles of incorporation of [³H]thymidine into DNA of heart cells in experimental and control cultures showed a peak in incorporation values within the first week of culture and subsequently declined. Autoradiography studies revealed that cardiac myocytes in culture supplemented with ECGS alone attained a peak in labeling index on Day 1 with approximately 62% labeled cells. Subsequently, the labeling indices declined. Cardiac myocytes grown in media without ECGS showed significantly lower labeling indices than those in ECGS-containing media. This study has demonstrated the influence of ECGS, EGF and ITS in promoting the growth of cardiac myocytes and also in contributing to the maintenance of contractile cardiac myocytes in serum-free, long-term culture. The influence of ECGS on heart cell proliferation is considered to be superior to that of EGF and ITS. This study was supported in part by a grant HL-25482 from the National Heart Lung and Blood Institute and a grant from the American Heart Association of Michigan.     

Frequent,low‐amplitude disturbances drive high tree turnover rates on a remote,cyclone‐prone Polynesian island

Aim How important are frequent, low‐intensity disturbances to tree community dynamics of a cyclone‐prone forest? We tested the following hypotheses concerning the ‘inter‐cataclysm’ period on a remote Polynesian island: (1) tree turnover would be high and recruitment rates would be significantly higher than mortality; (2) low‐intensity disturbance would result in a marginal increase in tree mortality in the short term; (3) turnover would vary among species and would be associated with plant traits linked to differences in life history; and (4) mortality and recruitment events would be spatially non‐random. Location Tutuila, a volcanic island in the Samoan Archipelago, Polynesia. Methods We censused the tree (stem diameter ≥ 10 cm) community in 3.9 ha of tropical forest three times over a 10‐year period, 1998–2008. We calculated annual mortality, recruitment and turnover rates for 36 tree species. We tested for non‐random spatial patterns and predictors of mortality, and non‐random spatial patterns of tree recruitment. A 2004 cyclone passing within 400 km allowed us to measure the effects of a non‐cataclysmic disturbance on vital rates. Results Annual turnover was 2.8% and annual recruitment was 3.6%; these are some of the highest rates in the tropics, and likely to be a response to a cyclone that passed < 50 km from Tutuila in 1991. Species turnover rates over 10 years were negatively correlated with wood specific gravity, and positively correlated with annual stem diameter increment. Mortality was spatially aggregated, and a function of site, species and an individual’s growth rate. Recruitment was highest on ground with low slope. The low‐magnitude cyclone disturbance in 2004 defoliated 29% of all trees, but killed only 1.8% of trees immediately and increased annual mortality over 5 years by 0.7%. Main conclusions The inter‐cataclysm period on Tutuila is characterized by frequent, low‐amplitude disturbances that promote high rates of tree recruitment and create a dynamic, non‐equilibrium or disturbed island disequilibrium tree community. Species with low wood density and fast growth rates have enhanced opportunities for recruitment between cataclysms, but also higher probabilities of dying. Our results suggest that increases in the frequency of cyclone activity could shift relative abundances towards disturbance‐specialist species and new forest turnover rates.     

Determination of fetal biparietal diameter without the use of ultrasound in squirrel monkeys

This study evaluated manual caliper measurement of fetal BPD in Saimiri through the abdomen of the dam (TBPD) for correlation with paired ultrasound measurements, prediction of delivery date, subspecies variation, prediction of pregnancy outcome, and correlation between postpartum BPD and TBPD. Regression analysis revealed a close relationship between TBPD measurements and those obtained by ultrasound (P < 0.001). TBPD for Saimiri boliviensis boliviensis increased from a mean of 14.8 ± 0.3 mm for 11 weeks prepartum to a delivery week measurement of 33.2 ± 0.2mm. Delivery-week TBPD of Saimiri boliviensis peruviensis were significantly smaller than Saimiri sciureus sciureus (P < .05). Delivery week TBPD had a correlation coefficient of 0.64 with paired post-patrum measurements. No complications were associated with the technique. Delivery date could be predicted within two weeks. TBPD is an inexpensive, safe, rapid method of approximating fetal growth during the last half of pregnancy in Saimiri.     

A new sampler for extracting undisturbed surface peat cores for growth pot experiments

The sampler extracts uncompressed cores of 13·3 cm in diameter, up to 70 cm long, from the surface layers of peat. It has two close-fitting concentric cylindrical tubes, the outer one acting as a cutter and the inner one as a collector. As the outer tube is introduced by rotation into the peat, the cut core is collected in the inner tube which is maintained in a fixed position during the rotation phase and then pushed down stepwise. This limits friction between the peat core and the wall of the corer and prevents compression or distortion of the peat. These problems are also reduced by means of three skew cutters allowing the peat to be supported during the slicing action. Air can penetrate between the tubes to the lower end of the core, suppressing any suction effect during withdrawal. The sampler has been tested and has worked satisfactorily in many different peat types.