Location of the isoleucine arrest point in CHO and 3T3 cells

An isoleucine arrest point in G1 was determined by two methods for CHO and 3T3 cells. In the first method the fraction of cells entering S after isoleucine deprivation was assessed by [³H]thymidine labelling and autoradiography. In the second method cells entering S after isoleucine deprivation were identified by double-label autoradiography using [³H] and [¹⁴C]thymidine. From the fraction of cells entering S, determined by the two methods, the arrest point in G1 (and entry into G0) is located within the last 40 min of G1.     

Three-dimensional reconstruction of a human metaphase chromosome from electron micrographs

A complete human metaphase chromosome has been reconstructed from a series of electron microscopical projections obtained by tilting the specimen stage at 3 degree intervals from –60 to +60 degrees. The reconstructed structure is about 3.0 m long, 1.6 m wide, and 0.8 m thick. The mass distribution was fairly homogeneous within the chromatids and neither a hollow nor a dense core was observed. The distribution and course of fibers observed are most consistent with a looping model of chromosome structure.     

The evolutionary history of Drosophila buzzatii. XXIII. High content of nonsatellite repetitive DNA in D. buzzatii and in its sibling D. koepferae.

The frequency and types of repetitive nonsatellite DNA of two sibling species of the repleta group of Drosophila, D. buzzatii, and D. koepferae have been determined. For each species, the analysis is based on a sample of more than 100 clones (400 kb) obtained from genomic DNA. A theoretical model has been developed to correct for the presence of a mixture of repetitive and unique DNA in these clones. After correction, a high content of repetitive DNA has been demonstrated for both species (D. buzzatii, 19-26%; D. koepferae, 27-32%). The repetitive sequences have been classified according to their hybridization pattern when used as probes against genomic DNA and by their in situ hybridization signals on polytene chromosomes. Data suggest that the main nonsatellite component of these species is simpler and more repetitive than that of D. melanogaster, pointing to a wide variability in content and class size distribution of repetitive DNA among Drosophila species.     

Mode de formation des inclusions lamellaires dans le poumon embryonnaire de poulet

Résumé Les pneumocytes granuleux, qui constituent l'un des principaux types cellulaires de l'épithélium pulmonaire, sont caractérisés par la présence de volumineuses inclusions osmiophiles lamellaires.Nous avons étudié l'apparition et l'origine de ces inclusions dans l'épithélium du poumon embryonnaire de Poulet, en l'examinant à différents stades du développement.Les premières inclusions lamellaires apparaissent dans le poumon de l'embryon de 16 jours. A ce stade, quelques lamelles concentriques entourent une zône centrale amorphe étendue; la périphérie des inclusions contient toujours de petites structures granulaires. Les jours suivants le nombre de cellules contenant des inclusions lamellaires augmente rapidement; en même temps, les lamelles deviennent plus nombreuses. A 19 jours, les inclusions lamellaires ont un aspect semblable à celui qu'elles ont dans les poumons d'animaux adultes.Dès l'apparition des ébauches pulmonaires, à 2 1/2 jours d'incubation, les cellules épithéliales contiennent des inclusions typiques: les inclusions granulaires. Ces organites sont caractérisés par un centre granulaire, qu'entouré un système membranaire. Ce système, simple chez le jeune embryon, évolue ensuite en se compliquant; chez l'embryon de 16 jours, il s'enroule en plusieurs couches autour de la masse centrale. Au moment où les premières inclusions lamellaires apparaissent, le nombre des inclusions granulaires augmente rapidement; on les trouve souvent étroitement associées à des vacuoles lipidiques.L'analyse des relations entre inclusions lamellaires, inclusions granulaires et vacuoles lipidiques suggère que l'inclusion lamellaire résulte de la collaboration entre une vacuole lipidique et plusieurs inclusions granulaires.

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Differentiation of lamellar inclusions in the chick embryonic lung

Summary The granular pneumocytes, one of the main cellular types of the lung epithelium, are characterized by the presence of large osmiophilic lamellar inclusions. The appearance and origin of these inclusions has been studied in the epithelium of chick embryonic lung at different developmental stages.Lamellar inclusions are first seen in the lung of 16 day old embryos. At this stage, few concentric lamellae surround a large amorphous center; the periphery of the inclusions always contains small granular structures. In the following days, the number of cells containing these lamellar inclusions increases rapidly, while their lamellae progressively become more numerous. In 19 day old embryos, the lamellar inclusions are similar to those in the lungs of adult animals.From the earliest formation of the bronchial primordia, their epithelial cells contain a number of typical granular inclusions. These organelles are characterized by a granular center, enclosed in a membranous system. This structure becomes more complex as the embryo develops; in the 16 day old embryo, the multilayered membranous system coils around the granular center. At the time when lamellar inclusions first appear, granular inclusions increase rapidly in number and are often found in close association with lipidic vacuoles.The relationships between lamellar inclusions, granular inclusions and lipidic vacuoles are discussed. The evidence suggests that a lamellar inclusion arises from the cooperation of several granular inclusions and a lipidic vacuole.

     

SDSE: A software package to simulate the evolution of a pair of DNA sequences

An algorithm to simulate DNA sequence evolution under a generalstochastic model, including as particular cases all the previouslyused schemes of nucleotide substitution, is described. The simulationis carried out on finite, variable length, DNA sequences througha strict stochastic process, according to the particular substitutionrates imposed by each scheme. Five FORTRAN programs, runningon an IBM PC and compatibles, carry out all the tasks neededfor the simulation. They are menu driven and interfaced to thesystem through a principal menu. All sequence data files usedand generated by the SDSE package conform to the standard GenBankdatabase format, thus allowing the use of any sequence retrievedfrom this databank, as well as the application of other packagesto analyse, manipulate or retrieve simulated sequences. Received on August 23, 1988; accepted on November 15, 1988     

Substrate-specific differences in the rate of bile acid carrier reorientation: studies on human placental basal vesicles.

The initial rate of transport of the bile acid glycocholic acid (GCA) has been measured in influx and efflux across placental basal membrane vesicles, and the mechanism of inhibition of its transport by the analogue taurochenodeoxycholic acid (TCDCA) analysed kinetically. This analogue, although trans-stimulating GCA efflux, inhibits influx in a way which does not depend upon substrate concentration; moreover, its potency as an inhibitor is markedly influenced by whether it is placed on one or on both sides of the vesicles membrane. These findings can be accounted for by postulating that both GCA and TCDCA are translocated through the carrier, but that the rate of loaded carrier reorientation is higher than that of the free carrier only when loaded with TCDCA and not with GCA.     

Factor affecting body mass of young fat dormics (Glis glis) at weaning and by hibernation

This paper describes the factors affecting body mass at weaning and by hibernation of young fat dormice (Glis glis) We studied a free-living population in 1991 and 1992 in a mixed forest where 100 nest-boxes were placed. In the two years, 128 females used the nest-boxes to give birth and rear their litters and more than 900 dormice have been individually marked. Body mass of young at weaning was positively correlated to body mass of the mother in both years and to birth date in 1991, while litter size was negatively correlated to body mass of the young in 1992 only, when birth took place about two weeks later than in 1991. On the contrary, by the time of hibernation, young born later weighed significantly less than those born earlier in the season, and heavier young at weaning remained heavier by hibernation, while maternal body mass and litter size did not significantly affect body mass of young at this stage. Body mass of the mother was negatively related to the date of parturition and early breeding females lost weight during lactation, while females that bred later did not. It seems, therefore, that early breeding carries a cost that only females in good condition can afford. It appears that females may follow two strategies: those in poor body condition will delay pregnancy so that lactation occurs when environmental feeding conditions are at their best; those in good condition will breed earlier, since they can afford to lose weight during lactation. Their young will have more time to grow before hibernation and the mothers themselves will have a longer period of time for restoring their fat reserves.     

Ouabain-insensitive Na+-stimulated ATPase activity of basolateral plasma membranes from guinea-pig kidney cortex cells: II. Effect of Ca2+

The ouabain-insensitive, Mg²⁺-dependent, Na⁺-stimulated ATPase activity present in fresh basolateral plasma membranes from guinea-pig kidney cortex cells (prepared at pH 7.2) can be increased by the addition of micromolar concentrations of Ca²⁺ to the assay medium. The Ca²⁺ involved in this effect seems to be associated with the membranes in two different ways: as a labile component, which can be quickly and easily ‘deactivated’ by reducing the free Ca²⁺ concentration of the assay medium to values lower than 1 μM; and as a stable component, which can be ‘deactivated’ by preincubating the membranes for periods of 3–4 h with 2 mM EDTA or EGTA. Both components are easily activated by micromolar concentrations of Ca²⁺. The $\text{K}{}_{\mathrm{<mtext>a</mtext>}}$ of the system for Na⁺ is the same, 8 mM, whether only the stable component or both components, stable and labile, are working. In other words, the activating effect of Ca²⁺ on the Na⁺-stimulated ATPase is on the $\text{V}{}_{\mathrm{<mtext>max</mtext>}}$, and not on the $\text{K}{}_{\mathrm{<mtext>a</mtext>}}$ of the system for Na⁺. The activating effect of Ca²⁺ may be related to some conformational change produced by the interaction of this ion with the membranes, since it can also be obtained by resuspending the membranes at pH 7.8 or by ageing the preparations. Changes in the Ca²⁺ concentration may modulate the ouabain-insensitive, Na⁺-stimulated ATPase activity. This modulation could regulate the magnitude of the extrusion of Na⁺ accompanied by Cl^? and water that these cells show, and to which the Na⁺-ATPase has been associated as being responsible for the energy supply of this mode of Na⁺ extrusion.     

Risk for AIDS in multiethnic neighborhoods in San Francisco,California. The population-based AMEN Study.

To examine the actual and potential spread of human immunodeficiency virus (HIV) from an acquired immunodeficiency syndrome (AIDS) epicenter to surrounding neighborhoods, we studied the prevalence of the viral infection and AIDS risk behaviors from 1988 to 1989 in a representative sample of unmarried whites, African Americans, and Hispanics living in San Francisco. We surveyed 1,770 single men and women aged 20 to 44 years (a 64% response rate) in a random household sample drawn from 3 neighborhoods of varying geographic and cultural proximity to the Castro District where the San Francisco epidemic began. Of 1,369 with blood tests, 69 (5%) had HIV antibodies; all but 5 of these reported either homosexual activity (32% HIV-positive; 95% confidence interval [CI] = 23%, 41%), injection drug use (5% HIV-positive; CI = 1%, 14%), or both (59% HIV-positive; CI 42%, 74%). Homosexual activity was more common among white men than among African-American or Hispanic men, but the proportion of those infected was similar in the 3 races. Both the prevalence of homosexually active men and the proportion infected were much lower in the 2 more outlying neighborhoods. Risk behaviors in the past year for acquiring HIV heterosexually--sex with an HIV-infected person or homosexually active man or injection drug user, unprotected sexual intercourse with more than 4 partners, and (as a proxy) having a sexually transmitted disease--were assessed in 1,573 neighborhood residents who were themselves neither homosexually active men nor injection drug users. The prevalence of reporting at least 1 of these risk behaviors was 12% overall, and race-gender estimates ranged from 5% among Hispanic women to 21% among white women. We conclude that in San Francisco, infection with HIV is rare among people who are neither homosexually active nor injection drug users, but the potential for the use spread of infection is substantial, as 12% of this group reported important risk behaviors for acquiring the virus heterosexually.