Host discrimination byChelonus insularis [Hym.: Braconidae], telenomus heliothidis [Hym.: Scelionidae], andTrichogramma pretiosum [Hym.: Trichogrammatidae]

The ability of female parasitoids (Chelonus insularis Cresson,Telenomus heliothidis Ashmead, andTrichogramma pretiosum Riley) to distinguish between parasitized and unparasitized tobacco budworm,Heliothis virescens (F.), eggs was determined in laboratory studies. All 3 species were relatively efficient at detecting eggs that were previously parasitized by conspecific females.T. heliothidis andT. pretiosum were able to discriminate on the basis of external examination of host eggs, whereasC. insularis appeared to examine hosts internally as well as externally. In interspecific tests, no species readily rejected eggs parasitized by the other 2 species.     

Vitamin D metabolism and expression in rats fed on low-calcium and low-phosphorus diets

1. Cholecalciferol, radioactively labelled with both (14)C and (3)H, was administered weekly for 7 weeks to rats that had been depleted of vitamin D for 4 weeks before repletion with the radioactive vitamin. This permitted measurement of the steady-state effect on vitamin D metabolism of low-calcium and low-phosphorus regimens, as compared with a normal mineral intake. These dietary manoeuvres were carried out during the last 3 weeks of repletion. Cholecalciferol, 25-hydroxycholecalciferol and 1,25-dihydroxycholecalciferol were determined in plasma, intestine, kidney and bone. Ca(2+)-binding-protein content was measured in intestine and kidneys of comparable animals. 2. In rats on the low-calcium diets, 1,25-dihydroxycholecalciferol concentration was elevated in plasma, bone, kidney and intestine, and intestinal Ca(2+)-binding protein was increased to over twice the concentration found in the control animals. 3. The low-phosphorus regimens led to a decrease in plasma phosphate and 1,25-dihydroxycholecalciferol in all tissues studied, for the latter to the point where it was undetectable in plasma and bone. Intestinal and renal concentrations of Ca(2+)-binding protein were unchanged in the low-phosphate-intake group and decreased in the very-low-phosphate-intake group. 4. It is concluded that in the rat, unlike in the chick, hypophosphataemia is not associated with a stimulation of the production of 1,25-dihydroxycholecalciferol or its expression in the synthesis of Ca(2+)-binding protein. Therefore the plasma phosphate concentration does not appear to be directly involved in the regulation of the functional metabolism of vitamin D.     

Assignment of murine cellular Harvey ras gene to chromosome 7

Mouse-Chinese hamster somatic cell hybrids containing various combinations of mouse chromosomes were analyzed for the presence of the mouse c-Ha-ras (1) sequences after restriction endonuclease digestion and hybridization with a 32P-labeled Ha-ras specific probe according to the procedure of Southern (2). The presence of the mouse c-Ha-ras containing fragment was correlated with the presence of mouse chromosome 7 in the hybrids.     

Genetics of social behaviour in charrs (Salvelinus species)

Juvenile brook charr (Salvelinus fontinalis) are territorial and have high levels of agonistic behaviour. Juvenile lake charr (S. namaycush) rarely show any indication of territoriality and have very low levels of agonistic behaviour. The inheritance of behaviour in their reciprocal hybrids was investigated by multivariate stepwise discriminant analysis. Lateral display, charge, chase, and forage composed the first canonical axis (87.2% of total dispersion). Pooled hybrid means were closer to that of brook charr, suggesting either directional dominance or modification of the behaviour of hybrids in response to water flow. The mean values of reciprocal hybrids were skewed towards the maternal parent, suggesting a maternal effect in the phenotypic expression of behaviour in these fish.     

Deletion of approximately 10 kDa from the carboxyl terminus of a soluble approximately 48-kDa insulin receptor protein-tyrosine kinase results in slower rates of diphosphorylation of a series of dodecapeptide substrates. An assessment by 1H NMR.

Autophosphorylation of a soluble approximately 48-kDa derivative of the insulin receptor protein-tyrosine kinase is accompanied by an increase in its specific activity towards exogenous substrates. In the present study, we have utilized 1H NMR to compare the order and rate of mono- and diphosphorylation of multiple tyrosine residues in a series of synthetic dodecapeptide substrates (based on the receptor sequence, which includes major sites of autophosphorylation (RRDIYETDYYRK), with substitution(s) at positions 6 and/or 7 based on residue size and/or charge) by the approximately 48-kDa enzyme and by a approximately 38-kDa enzyme generated by tryptic deletion of approximately 10 kDa from the carboxyl terminus of the approximately 48-kDa protein. Both enzymes exhibit a marked order and progression of phosphorylation of peptide tyrosine residues; for each peptide, phosphorylation initiates and proceeds to completion first on tyrosine 9, followed by phosphorylation on tyrosine 10. Although removal of the carboxyl terminus does not affect the rate of monophosphorylation of these peptides on tyrosine 9, the smaller enzyme exhibits a slower rate of diphosphorylation (at tyrosine 10), as compared with the approximately 48-kDa enzyme.     

Plasminogen activation by receptor-bound urokinase. A kinetic study with both cell-associated and isolated receptor

The specific cellular receptor for urokinase-type plasminogen activator (uPA) is found on a variety of cell types and has been postulated to play a central role in the mediation of pericellular proteolytic activity. We have studied the kinetics of plasminogen (Plg) activation catalyzed by uPA specifically bound to its receptor on the human monocytoid cell-line U937 and demonstrate this process to have properties differing widely from those observed for uPA in solution. The solution-phase reaction was characterized by a Km of 25 microM and for the cell-associated reaction this fell 40-fold to 0.67 microM, below the physiological Plg concentration of 2 microM. A concomitant 6-fold reduction in kcat resulted in an increase in the overall catalytic efficiency, kcat/Km, of 5.7-fold. This high affinity Plg activation was abolished in the presence of a Plg-binding antagonist. In contrast to intact cells, purified uPA receptor (isolated from phorbol 12-myristate 13-acetate-stimulated U937 cells) was observed to partially inhibit uPA-catalyzed Plg activation, although activity against low molecular weight substrates was retained. Therefore, the cellular binding of Plg appears to be of critical importance for the efficient activation of Plg by receptor-bound uPA. Plasmin generated in the cell-surface Plg activation system described here was also observed to be protected from its principal physiological inhibitor alpha-2-antiplasmin. Together, these data demonstrate that the cell surface constitutes the preferential site for Plg activation when uPA is bound to its specific cellular receptor, which therefore has the necessary characteristics to play an efficient role in the generation of pericellular proteolytic activity.     

The role of EGF in testosterone-induced reproductive tract differentiation

EGF is known to modulate a variety of cellular functions including differentiation. The aim of this investigation was to determine the role of EGF in androgen-induced masculine differentiation. Accordingly, a series of experiments were designed and the results are summarized as described below. (1) We found that the specific deprivation of EGF using anti-EGF serum during the period of masculine differentiation in an organ culture bioassay system resulted in the disintegration of the Wolffian system in a dose-dependent manner. (2) Exogenous EGF supplemented in the above experiment corrected the anti-EGF effect, suggesting a specific role of EGF. (3) Anti-EGF serum was also found to disrupt the differentiation even in the presence of exogenous testosterone, suggesting an effect independent of testosterone synthesis. (4) EGF was found to have a direct masculinizing effect both in vivo and in vitro; however, it was not able to mimic all masculinizing effects of testosterone. The mesonephric segment of the Wolffian duct was retained by EGF in the female fetal tract under in vitro conditions, and under in vivo conditions EGF was able to increase anogenital distance and to induce epididymis in some female fetal mice. (5) We were able to detect an EGF-like material in the fetal genital tract during differentiation and found that the level of this material increased with advancement of differentiation. Thus, it appears from the above results that EGF plays a role in testosterone-induced reproductive tract differentiation.