Demonstration of the capacity of nacre to induce bone formation by human osteoblasts maintained in vitro.

Nacre implanted in vivo in bone is osteogenic suggesting that it may possess factor(s) which stimulate bone formation. The present study was undertaken to test the hypothesis that nacre can induce mineralization by human osteoblasts in vitro. Nacre chips were placed on a layer of first passage human osteoblasts. None of the chemical inducers generally required to obtain bone formation in vitro was added to the cultures. Osteoblasts proliferated and were clearly attracted by nacre chips to which they attached. Induction of mineralization appeared preferentially in bundles of osteoblasts surrounding the nacre chips. Three-dimensional nodules were formed by a dense osteoid matrix with cuboidal osteoblasts at the periphery and osteocytic-like cells in the center. These nodules contained foci with features of mineralized structures and bone-like structures, both radiodense to X-ray. Active osteoblasts (e.m.) with abundant rough endoplasmic reticulum, extrusion of collagen fibrils and budding of vesicles were observed. Matrix vesicles induced mineral deposition. Extracellular collagen fibrils appeared cross-banded and electrodense indicating mineralization. These results demonstrate that a complete sequence of bone formation is reproduced when human osteoblasts are cultured in the presence of nacre. This model provides a new approach to study the steps of osteoblastic differentiation and the mechanisms of induction of mineralization.     

Inhibition by L-arginine of the endothelin-mediated increase in cytosolic calcium in human neutrophils

The effect of endothelin (ET) on the cytosolic-free calcium [(Ca2+]i) changes in polymorphonuclear leukocytes (PMN) from normal humans and Wistar rats was investigated. ET induced a dose-related [Ca2+]i peak. This [Ca2+]i transient was blunted by TMB-8 (10(-5)M) and by Ca(2+)-free EGTA medium, therefore suggesting a role of both intracellular Ca2+ release and Ca2+ influx in the generation of the [Ca2+]i peak. Preincubation of PMN with the nitric oxide (NO)-donor L-arginine (L-Arg) markedly blocked the ET-induced [Ca2+]i transient in an enantiomerically-specific manner. A similar blunting effect of L-Arg on the fMLP (10(-7)M)-induced [Ca2+]i transient was detected. The L-Arg antagonist, NG-monomethyl-L-arginine (L-NMMA), reverted the L-Arg blocking effect on both ET- and fMLP-induced [Ca2+]i transients. These data suggest that ET has a potential role in activating Ca2+ mobilization in PMN, an effect that can be inhibited by L-Arg.     

Persistence of Cell Division Synchrony in Spirogyra Insignis (Gamophyceae): Membrane Proteoglycans Transmitting Synchronizing Information Throughout Generations

Spirogyra insignis shows a long-term persistence of cell division synchrony in the absence of the synchronizing Zeitgeber, so that at least six generations are involved in the process. This tentatively suggests that a mechanism of transmission throughout generations of synchronizing information could maintain this synchrony. Apparently, a vital part of the molecular basis of this mechanism is a membrane proteoglycan complex. This complex could obtain temporal information from a synchronizing Zeitgeber and be transmitted to the progeny by distribution of plasma membrane between daughter cells.     

Sequence of the Streptococcus pneumoniae bacteriophage HB-3 amidase reveals high homology with the major host autolysin.

We have sequenced a DNA fragment containing the pneumococcal bacteriophage HB-3 hbl gene, which codes for the phage lytic amidase. A remarkable nucleotide similarity (87.1%) between the lytA gene, coding for the pneumococcal amidase, the major autolysin of Streptococcus pneumoniae, and the hbl gene was found. This similarity completely disappeared outside the open reading frames coding for both amidases. The hbl gene transformed amidase-deficient strains of S. pneumoniae to the wild-type phenotype, and Southern blotting experiments provided evidence for recombination between donor and recipient genes. A comprehensive evaluation of these and previous results on the peptidoglycan hydrolases of S. pneumoniae and its bacteriophages suggested that recombination mechanisms participate in the evolution of the genes coding for these enzymes.     

Trehalose in yeast,stress protectant rather than reserve carbohydrate

Trehalose and glycogen are generally regarded as the two main reserve carbohydrates in yeast. However, several lines of evidence suggest that trehalose does not primarily function as a reserve but as a highly efficient protecting agent to maintain strutural integrity of the cytoplasm under environmental stress conditions.     

Growth of rural and urban children in the Valley of Oaxaca,Mexico

Weight, stature, arm circumference, and the triceps skinfold were measured in 1,410 school children, 6 through 14 years of age, from two urban colonias in the city of Oaxaca de Juarez (n = 479), and from two rural Ladino (n = 467) and two rural Zapotec (n = 464) communities in the Valley of Oaxaca in southern Mexico. Children from rural Ladino communities and urban colonias are significantly taller, heavier, and more muscular than children in rural Zapotec communities. The differences between rural Ladino and urban colonia children favor the former, particularly for weight and stature. These observations thus suggest (1) that children in the rural, indigenous communities in the Valley of Oaxaca are relatively undernourished compared to children in Ladinoized and urban communities, and (2) that rural-to-urban migration does not necessarily result in improved growth status.     

Growth of rural and urban children in the valley of Oaxaca,Mexico

Weight, stature, arm circumference, and the triceps skinfold were measured in 1,410 school children, 6 through 14 years of age, from two urban colonias in the city of Oaxaca de Juarez (n = 479), and from two rural Ladino (n = 467) and two rural Zapotec (n = 464) communities in the Valley of Oaxaca in southern Mexico. Children from rural Ladino communities and urban colonias are significantly taller, heavier, and more muscular than children in rural Zapotec communities. The differences between rural Ladino and urban colonia children favor the former, particularly for weight and stature. These observations thus suggest (1) that children in the rural, indigenous communities in the Valley of Oaxaca are relatively undernourished compared to children in Ladinoized and urban communities, and (2) that rural-to-urban migration does not necessarily result in improved growth status.     

In vitro metabolism of C19 steroids in human endometrium

In order to quantitate the extent of intracellular metabolic conversions of C19 steroids in human endometrium, specimens of proliferative and secretory tissue were superfused at a constant rate with several pairs of labeled compounds at low concentrations. About 16% of dehydroepiandrosterone sulfate interacting with endometrial cells was converted to dehydroepiandrosterone and about 3% of this compound was converted to androstenedione. Androstenedione was reversibly reduced to testosterone and the extent of this conversion was shown to be several-fold higher in secretory than in proliferative tissue. About 1% of testosterone entering the cells was reduced to 5 alpha-dihydrotestosterone. These results demonstrate that the conversion of the main circulating C19 steroids in women, i.e. dehydroepiandrosterone sulfate and androstenedione, to 5 alpha-dihydrotestosterone, the compound considered to be the true intracellular androgen, is very small. In contrast, formation of testosterone from androstenedione is extensive and increases during the luteal phase under the influence of progesterone, a hormone known to stimulate the activity of 17 beta-hydroxysteroid dehydrogenase in human endometrium.