Immunological heterogeneity of rat apolipoprotein B epitope expression. A study using monoclonal antibodies to rat apolipoprotein B

Epitope expression of rat apolipoprotein B on lipoproteins was investigated with the help of six monoclonal antibodies produced from mice. Through a variety of techniques, which include cotitrations, ELISAs and quantitative immunoadsorption precipitation, we concluded that the six monoclonal antibodies recognize five different epitopes. LRB 110 and LRB 260 recognize epitopes that may be overlapping. LRB 240 and LRB 250 recognize epitopes that are preferentially expressed in triacylglycerol-rich particles. LRB 220 recognizes an epitope that is expressed by all apolipoprotein-B-containing lipoproteins. We have also determined that apolipoprotein B epitope expression in rat lipoproteins is very similar to its human counterpart. Both rat and human apolipoprotein B epitope expression on lipoproteins showed heterogeneities even in homologous lipoprotein preparations. We concluded that a variety of techniques are necessary to fully characterize monoclonal antibodies to apolipoproteins. The possible implications of epitope expression in pathophysiology are also discussed.     

High-pressure infrared spectroscopy of ether- and ester-linked phosphatidylcholine aqueous dispersions.

Infrared spectra of aqueous dispersions of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), and its ether-linked analogue, 1,2-dihexadecyl-sn-glycero-3-phosphocholine (DHPC), were measured in a diamond anvil cell at 28 degrees C as a function of pressure up to 20 kbar. Although these two lipids differ only in the linkages to the saturated hydrocarbon chains, significant differences were observed in their barotropic behavior. Most notable were the magnitudes of the pressure-induced correlation field splittings of the methylene scissoring and rocking modes, and the relative intensities of the corresponding component bands. In the case of the scissoring mode, not only can the correlation field component band be resolved at a lower pressure in DHPC (1.2 kbar, as compared with 2.2 kbar in DPPC), but the initial magnitude of the correlation field splitting in DHPC, particularly less than 9 kbar, is significantly greater than that observed in DPPC. These differences are attributed to the presence of an interdigitated lamellar gel phase in DHPC. At all pressures where the correlation field component band delta'CH2 can be resolved, the relative peak height/intensity ratio R = I delta'/I delta is greater in DPPC than in DHPC, suggesting that this parameter may be useful as a test of interdigitation.     

Intra-tree foraging behavior of Ceratitis capitata flies in relation to host fruit density and quality

We examined the intra-tree foraging behavior of individually-released, wild-population Mediterranean fruit flies (medflies), Ceratitis capitata (Wiedemann), on field-caged host trees bearing each of three different densities (0, 3, or 12 per tree) of non-infested host fruit (kumquat) or each of two levels of fruit quality (12 non-infested fruit or 12 fruit infested with eggs and covered with host marking pheromone). With increasing density of non-infested fruit, medflies tended to remain longer in trees, visit more fruit before leaving, oviposit more often, accept a proportionately smaller number of fruit visited, and emigrate sooner after the last egg was laid (i.e. have a shorter Giving-Up-Time). Medflies spent much less time, oviposited much less often, and exhibited a longer Giving-Up-Time on trees harboring pheromone-marked fruit than non-infested fruit. Variation in temperature within the range at which experiments were conducted (25–36°C) had little detectable influence on foraging behavior. We compare our findings with published findings on the intra-tree foraging behavior of another tephritid fly, Rhagoletis pomonella (Walsh), and with current foraging behavior theory. We discuss implications of our findings with respect to medfly management strategies, particularly fruit stripping in eradication programs and use of synthetic marking pheromone for control.

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Résumé Nous avons étudié le comportement de prospection dans un arbre, de femelles d'une population sauvage de C. capitata, libérées individuellement à l'intérieur de cages contenant des Eriobotrya japonica (kumquat), portant chacun 3 densités différentes de fruits no contaminés (0, 3, 12 par arbre) et chacun 2 niveaux de qualité de fruits: 12 fruits non infestés ou 12 fruits contaminés par des oeufs et recouverts de phéromone de marquage de l'hôte. C. capitata avait terndance à rester plus longtemps dans les arbres, à visiter plus de fruits avant le quitter, à pondre plus souvent, à accepter proportionnellement un nombre plus réduit de fruits déjà visités, à émigrer plus tôt après la ponte du dernier oeuf (c'est-à-dire à présenter un temps d'abandon plus bref), quand la densité des fruits non contaminés augmentait. C. capitata a dépensé beaucoup moins de temps, pondu beaucoup moins souvent, et présenté un temps d'abandon plus long sur les arbres portant des fruits marqués par la phéromone que sur ceux ayant des fruits non contaminés. Les variations de température dans la gamme de cells où les observations ont eu lieu (23–36°C) n'ont eu qu'une faible influence décelable sur le comportement de prospection. Nous avons comparé nos résultats avec ceux publiés sur la prospection à l'intérieur de l'arbre par une autre téphritide (Rhagoletis pomonella) et avec la théorie dominante sur le comportement de prospection. Nous discutons les conséquences de nos résultats sur les stratégies de lutte contre C. capitata, en particulier l'élimination des fruits dans les plans d'erradication et l'utilisation de phéromone synthétique de marquage.

     

Biogenesis of very-low-density lipoproteins in rat liver. Intracellular distribution of apolipoprotein B

The hepatic subcellular distribution of apolipoprotein B (apo B) was studied quantitatively by using an enzyme immunoassay developed for apo B and by immunoadsorption-precipitation of [3H]leucine-labelled apo B. Over 50% (of 0.59 microgram/mg protein) of the apo B was located in the microsomal fraction. Further subfractionation of the microsomes revealed that 47% of the microsomal apo B was in the Golgi apparatus, while another 43% was associated with the rough endoplasmic reticulum. The smooth endoplasmic reticulum accounted for only 4% of the total. When rat livers were labelled with [3H]leucine for 10 min, the rough endoplasmic reticulum accounted for 80% of the total immunoadsorbed precipitable apo B radioactivity while the smooth accounted for 20%, with no contribution from the Golgi. However, only 8.7% of the total radioactive immunoadsorbed precipitable apo B was lipoprotein-associated, the remainder being membrane-bound. Lipoprotein-associated apo B radioactivity in the smooth endoplasmic reticulum accounted for 40%, with the rough contribution attributed at 50% and the Golgi at 9%. We concluded that (a) there are two major pools of apo B in rat liver microsomes; (b) although the apo B mass may be negligible in the smooth endoplasmic reticulum, the latter does play a role in lipoprotein biogenesis. The possible function of apo B associated with membranes of the microsomes is also discussed.     

Unexpected thymic hyperplasia in transgenic mice harboring a neuronal promoter fused with simian virus 40 large T antigen.

The hypothalamic peptide growth hormone-releasing factor (GRF) regulates the secretion and production of growth hormone from the anterior pituitary (M. C. Gelato and G. R. Merriam, Annu. Rev. Physiol. 48:569-591). To study GRF gene regulation, transgenic mice were generated that harbor the human GRF promoter fused to the coding sequences from the simian virus 40 early region. These mice had normal hypothalamic functions but unexpectedly suffered from severe thymic hyperplasia. Immunohistochemical analysis revealed that large T antigen was expressed in the thymic epithelial cells. These cells have endocrine properties and are known to produce thymic hormones [corrected]. The thymic hyperplasia was the apparent consequence of inappropriate production of T-cell maturation factors by epithelial cells and could involve increased self renewal of apparently normal T stem cells in the thymus.     

A new approach to chromosome doubling for haploid rice plants

Summary Rice nodal segments from three flowering haploids were excised and treated for different lengths of time with 0.3% or 0.4% colchicine (dissolved in 2% DMSO) in an attempt to induce fertile seeds. A combination of higher colchicine concentration and longer hours of treatment reduced the survival rate of treated segments, but more fertile plants were transformed. Pooled data showed that of the 842 segments used, 42.2% survived the treatment and sprouted, but only 31.9% were successfully established and grown to maturity. Among the 269 mature plants, 29,4% produced fertile seeds (panicles) with an average of 146.2 seeds per diploidized plant.     

Determination of desmosine, isodesmosine, and other amino acids by liquid chromatography with electrochemical detection following precolumn derivatization with naphthalenedialdehyde/cyanide

Naphthalenedialdehyde (NDA) in the presence of cyanide (CN) reacts with primary amines to produce fluorescent cyano[f]benzoisoindole (CBI) derivatives. These derivatives have been shown to be substantially more stable than the corresponding o-phthalaldehyde derivatives. However, one drawback of this method is that compounds derivatized at more than one site exhibit quenching, precluding the use of fluorescence detection. The CBI derivatives have been found to be electroactive and are oxidized at a modest oxidation potential (+750 mV). Electrochemical detection is especially useful for the analysis of compounds containing more than one primary amine site because the response is not attenuated as it is in fluorescence detection. Desmosine and isodesmosine were of particular interest because of their importance in elastic fiber and the lack of highly sensitive HPLC methods for the determination of these compounds. Both of these compounds react with NDA/CN to produce electrochemically active derivatives. The combination of derivatization with NDA/CN and electrochemical detection was found to be linear over three orders of magnitude. Detection limits for CBI-lysine and CBI-desmosine were 100 fmol at a S/N of 2. Amino acids in elastin were quantitated using this method. The results correlate well with what has been reported previously in the literature. A significant advantage of the use of liquid chromatography with electrochemical detection with precolumn derivatization with NDA/CN for the analysis of desmosine and isodesmosine is that they can be separated and quantitated individually using this method. In addition, the unique voltammetry of multiderivatized CBI-amino acids can be used to verify peak purity.