Differential proliferative response of cultured fetal and regenerating hepatocytes to growth factors and hormones

Upon epidermal growth factor (EGF) stimulation, fetal (20 days of gestation) and regenerating (44-48 h after partial hepatectomy) rat hepatocytes, isolated and cultured under identical conditions, increased DNA synthesis and entered into S-phase and mitosis, measured as [3H]thymidine incorporation and DNA content per nucleus in a flow cytometer, respectively. Fetal hepatocytes consisted of a homogeneous population of diploid (2C) cells. Two different populations of cells were present in regenerating liver, diploid (2C) and tetraploid (4C) cells, that responded to EGF. Glucagon or norepinephrine did not affect EGF stimulation of DNA synthesis in fetal liver cells, but they potentiated EGF response in regenerating hepatocyte cultures. Glucocorticoid hormones (dexamethasone) inhibited DNA synthesis in fetal hepatocyte cultures, an effect potentiated by the presence of glucagon or norepinephrine. In contrast, in regenerating hepatocytes, dexamethasone increased EGF-induced proliferation. EGF-dependent DNA synthesis was inhibited by TGF-beta in both fetal and regenerating cultured hepatocytes. TGF-beta action was partially suppressed by norepinephrine in regenerating hepatocytes, but was without effect in fetal hepatocyte cultures, whereas a synergistic action between TGF-beta and dexamethasone inhibiting growth in fetal but not in regenerating hepatocytes was found. Taken together, these results may suggest that there are significant differences between fetal and regenerating hepatocyte growth in their response to various hormones.     

Deoxyribose 5-phosphate aldolase of Bacillus cereus: purification and properties.

Deoxyribose 5-phosphate aldolase was purified 41 times from Bacillus cereus induced by growth on deoxyribonucleosides. The purification procedure includes ammonium sulphate fractionation, gel filtration on Sephadex G-100, ion-exchange chromatography on DEAE-Sephacel and preparative electrophoresis on 10% polyacrylamide gel. The enzyme is stable above pH 6.5, but is rapidly inactivated by sulfhydryl reagents. Being insensitive to EDTA, it may be considered as a Class I aldolase. Among a number of compounds tested (including some carboxylic acids, free and phosphorylated pentoses, nucleotides and nucleosides), none has been found to affect the enzyme activity. The enzyme appears to be dimeric, with a subunit Mr of 23,600. A Km of 4.4 x 10(-4) M was calculated for dRib 5-P.     

Identification and purification of a calcium-binding protein from Bacillus subtilis

A Ca(2+)-binding protein was identified in Bacillus subtilis in the log phase of growth. The molecular mass of this protein is about 38 kDa as estimated by polyacrylamide gel electrophoresis in the presence of SDS and by gel filtration. The protein was found to be resistant 10 min at 65 degrees C and was purified about 400 times, starting from heated crude extract, by conventional procedures. This novel protein is able to bind Ca2+ in the presence of an excess of MgCl2 and KCl both in solution and after SDS gel electrophoresis and electrotransfer. Since an impairment of the Ca2+ intake, in Bacillus subtilis, results in an impairment of chemotactic behavior (Matsushita, T. et al (1988) FEBS lett. 236, 437-440), 38 kDa protein may be involved in the regulation of chemotaxis.     

Ecological aspects of Sargassum muticum (Fucales,Phaeophyta) in Baja California,Mexico: reproductive phenology and epiphytes

The reproductive phenology and epiphytic macroalgae of Sargassum muticum were studied through an annual cycle (September 1987 to November 1988) at two sites on the northwestern coast of Baja California, Mexico, which were subjected to different degrees of wave exposure. Sargassum muticum is a brown alga of Japanese origin, now considered a permanent member of the marine flora of Baja California. A similar reproductive development was observed at both sites, with a maximum percentage of reproductive plants from May to July (spring–summer) and minimum from December to March (winter). Reproductive plants were found throughout the year. A total of 48 species of epiphytes were identified and seasonal variation in their diversity was observed. The greatest diversity was found at the more protected site.     

Biosynthesis of 1α,2α,3β-trihydroxy-p-menthane by Fusicoccum amygdali

Measurement of isotope ratios in 1α,2α,3β-trihydroxy-p-menthane, which has been biosynthesized in Fusicoccum amygdali from ³H- and ¹⁴C-labelled mevalonate and in its degradation product diosphenol indicates that: (a) four tritium atoms arising from [5-³H₂, 2-¹⁴C]MVA are retained, one more than suggested from the hydroxylation pattern, (b) menth-2-ene-1-ol is generated from an α-terpinyl cation through a 1,3-hydride shift and (c) trans-cleavage of an α-epoxide by hydrolysis gives 1α,2α,3β-trihydroxy-p-menthane.     

Amino acid transport in pig lymphocytes Enhanced activity of transport system asc following mitogenic stimulation

Changes in neutral amino acid transport activity caused by addition of phytohaemagglutinin-P to quiescent peripheral pig lymphocytes have been evaluated by measurements of ¹⁴C-labelled neutral and analogue amino acids under conditions approaching initial entry rates. Utilizing methylaminoisobutyric acid, the best model substrate of System A, we confirmed our previous report (Borghetti, A.F., Kay, J.E. and Wheeler, K.P. (1979) Biochem. J. 182, 27–32) on the absence of this transport system in quiescent cells and its emergence following stimulation. Furthermore, we demonstrated the presence in quiescent cells of an Na⁺-dependent transport system for neutral amino acids that has been characterized as System ASC by several criteria including intolerance to methylaminoisobutyric acid, strict Na⁺-dependence, the property of transtimulation and specificity for pertinent substrates such as alanine, serine, cysteine and threonine. Analysis of the relationship between influx and substrate concentration revealed that two independent saturable components contribute to entry of alanine in quiescent cells: a low affinity ($\text{K}{}_{\mathrm{<mtext>m</mtext>}}\text{= ≈4}\text{mM}$) and a high affinity ($\text{K}{}_{\mathrm{<mtext>m</mtext>}}\text{= ≈0.2}\text{mM}$) component. The high affinity component could be inhibited in a competitive way by serine, cysteine and threonine, but methylaminoisobutyric acid did not change appreciably its constants. The enhanced activity of alanine transport through the ASC system observed in activated cells resulted from a large increase in the capacity ($\text{V}$) of the high affinity component without any substantial change in the apparent affinity constant ($\text{K}{}_{\mathrm{<mtext>m</mtext>}}$).     

Autosomal synaptonemal complexes and sex chromosomes without axes in Triatoma infestans (Reduviidae; Hemiptera)

Meiotic and somatic cells at interphase in Triatoma infestans are characterized by the formation of a large chromocenter, which was assumed to contain the whole of the three large pairs of autosomes and the sex chromosomes. Observations with C-banding techniques show that the chromocenter is formed only by the terminal and subterminal heterochromatic blocks of the three large pairs of autosomes and the sex chromosomes. During pachytene the two largest autosomal pairs loop on themselves and their condensed ends form the chromocenter, together with the single heterochromatic end of the third autosomal pair. The X and Y chromosomes seem to associate with these condensed ends by their affinity for C-heterochromatin. During a very short pachytene stage, bivalents and synaptonemal complexes (SCs) are observed. Pachytene is followed by a very long diffuse stage, during which SCs are disassembled, multiple complexes aggregate on the inner face of the chromocenter and finally all complexes disappear and a dense material is extruded to the cytoplasm through the annuli. The 3-dimensional reconstruction of early pachytene chromocenters show 3 SCs entering and tunnelling the chromocenter, while during mid-pachytene 4 SCs enter this mass and a 5th SC is in a separate small mass. The looping of a whole SC which has both ends in the chromocenter was shown by the reconstructions. These data are interpreted as the progressive looping of the two largest bivalents during pachytene, forming finally the association of 5 bivalent ends corresponding to the 5 C-banding blocks of the large autosomal pairs. No single axis or SC that could be ascribed to the sex chromosomes was found. This agrees with the pachytene microspreads, which show only 10 SCs corresponding to the autosomal bivalents. The X and Y chromosomes are enclosed in the chromocenter, as shown by the unravelling chromocenters at diplotene-diakinesis. Thus the sex chromosomes do not form axial condensations, and this fact may be related to the ability of the X and Y chromosomes to divide equationally at metaphase I. SCsThis paper is dedicated to the memory of the late Professor Francisco A. Saez     

The “High Irradiance Responses” of plant photomorphogenesis

Plants growing in the natural environment are exposed daily to prolonged periods of high intensity irradiation. Many plant photomorphogenic responses are fully expressed only under prolonged exposures to high irradiances of light. The intensive study of these responses, the “High Irradiance Responses” (HIR) of plant photomorphogenesis, which started about 20 years ago, has been essentially directed—so far—toward the identification of the HIR photoreceptor, or photoreceptors, a problem that has not been satisfactorily and definitively solved, as yet. There is a great deal of evidence in support of the hypothesis that phytochrome, the pigment mediating the redfar red reversible plant photo-responses to low fluences of light, is involved in the photocontrol of the HIR. It seems likely that phytochrome may be the only photomorphogenic receptor responsible for the photocontrol of HIR responses brought about by irradiation at wavelengths longer than 600 nm. Phytochrome is probably also involved in the photocontrol of the HIR effects brought about by irradiation in the 350 to 500 nm region of the spectrum, but it cannot be excluded that other photochemical systems may also be involved. From a theoretical point of view, it does not seem unreasonable that the final expression of an HIR response may involve an interaction between phytochrome and other photochemical systems, with phytochrome probably playing the primary role and being responsible for the control of the activity of the other systems. Numerous “phytochrome only” interpretations (models) of the HIR have been proposed. Some of them have been developed to a fairly high degree of elaboration and have allowed the prediction of at least some of the features of the HIR. These “models,” although not rigorously and completely tested yet, seem to provide a reasonable interpretation for the HIR effects displayed under prolonged far red irradiation and for those HIR responses for which far red is the most effective spectral region. However, they do not provide a satisfactory explanation for the HIR responses for which blue is the most or the only effective spectral region, nor for the high effectiveness of white light. But, in spite of these problems, the “phytochrome only” interpretations of the HIR can be considered more satisfactory than those based on an interaction between phytochrome and other photochemical systems, especially in relation to the fact that the identity of these other photochemical systems has not been defined yet.