Induction of functional Fc receptors in P388 leukemia cells : Requirement for multiple differentiation signals

The development of functional Fc receptors (FcR) during induced differentiation with the tumor promoter, phorbol myristate acetate (PMA), was studied in the murine tumor cell line, P388. PMA induced the appearance of FcR on the membranes of P388 cells as indicated by the binding of IgG-coated sheep red blood cells (IgG-SRBC). Concentrations of PMA as low as 1 ng/ml were sufficient to induce the expression of FcR as well as to inhibit cellular division and to induce adherence in the P388 tumor cell line; however, optimal FcR induction occurred at PMA concentrations of 10-100 ng/ml. Immunofluorescent analysis with heat-aggregated myeloma proteins indicated that PMA induced FcR which were capable of binding IgG2a and IgG2b immunoglobulins, but not IgG1. Adherence to a substratum was determined to be a second required signal for expression of FcR, since PMA induction of P388 tumor cells in teflon dishes failed to fully develop FcR and adherence of P388 cells to poly-L-lysine-coated culture dishes in the absence of PMA was insufficient for FcR expression. FcR which appeared after PMA induction were non-functional in the sense that membrane-bound IgG-SRBC were not ingested to any significant extent by the tumor cells. However, if FcR induction occurred in the presence conA-induced rat spleen cell culture supernatants, phagocytosis of membrane-bound erythrocytes occurred. These findings suggest that for the expression of FcR which are capable of particle internalization, at least three identifiable membrane-transmitted signals are required during differentiation.     

Heparin binding to lipoprotein lipase and low density lipoproteins

Heparin was fractionated on an affinity column of bovine milk lipoprotein lipase (LpL) immobilized to Affi-Gel-15. The bound heparin, designated high-reactive heparin (HRH), enhanced LpL activity, presumably by stabilizing the enzyme against denaturation. The unbound heparin fraction had no observable effect on the initial rate of enzyme activity. However, at longer times of incubation there was inhibition of LpL activity. LpL-specific HRH also showed a high, Ca²⁺-dependent precipitating activity towards human plasma low density lipoproteins (LDL). Since LpL and LDL both bind to heparin-like molecules at the surface of the arterial wall, we suggest that their similar heparin-binding specificity may have physiological consequences as it relates to the development of atherosclerosis.

Heparin binding Lipoprotein lipase LDL Apolipoprotein Lipolysis     

Stable Equilibria at Two Loci in Populations with Large Selfing Rates

The equilibrium structure of two-locus, two-allele models with very large selfing rates is found using perturbation techniques. For free recombination, r = 1/2, the following results hold. If the heterozygotes do not have at least an approximate 30% advantage in fitness relative to homozygotes, a stable equilibrium with all alleles present is possible only if all of the homozygote fitnesses differ at most by approximately the outcrossing rate, t, and all stable polymorphic equilibria have disequilibrium values, D, that are at most on the order of the outcrossing rate. Once the heterozygote fitnesses are above the threshold, there are stable equilibria possible with D near its maximum possible value. The results show that the observed disequilibria in highly selfed plant populations are not likely to result from selection leading to an equilibrium.     

The Molecular through Ecological Genetics of Abnormal Abdomen in DROSOPHILA MERCATORUM. I. Basic Genetics

The abnormal abdomen syndrome (aa) in Drosophila mercatorum is characterized by the persistence of juvenilized cuticle on the adult abdomen. The aa phenotype is shown to depend on at least two X-linked genetic elements that are about one map unit apart near the centromeric end of the X chromosome. These two genetic elements are necessary for aa expression; one behaves as a dominant element and the other as a recessive. Overlaying these genetic studies upon molecular work reported elsewhere, it is argued that the dominant element is the presence of a 5 kb insertion in a majority of the X-linked repeats coding for the 28S ribosomal RNA. The recessive element appears to be a locus controlling differential replication of noninserted over inserted 28S genes during polytenization. The aa syndrome requires both the presence of the inserted repeats and the failure to preferentially amplify noninserted repeats. Given the necessary X-linked elements for aa, a variety of modifiers are revealed. First, aa expression in males is Y-linked, apparently corresponding to a deletion of the 18S/28S rDNA gene cluster normally found on the Y. Moreover, all major autosomes can modify the penetrance of aa.     

Desipramine Binding: Relationship to Central and Sympathetic Noradrenergic Activity

We examined the effects of treatments affecting norepinephrine release on the number of norepinephrine reuptake recognition sites as reflected by desipramine binding. To do this, we used manipulations having similar presynaptic but contrasting postsynaptic effects. Presynaptic inhibition by 6-hydroxydopamine lesion or by clonidine, and postsynaptic receptor stimulation by isoproterenol, reduced desipramine binding. Presynaptic stimulation by d-amphetamine and postsynaptic receptor blockade by prazosin increased desipramine binding. Similar effects and binding properties were seen in cerebral cortex, heart, and soleus muscle. After unilateral noradrenergic lesions, reduction in desipramine binding correlated with reduction in norepinephrine uptake. These results show that norepinephrine reuptake appears to be regulated by transmitter release regardless of effects on postsynaptic transmission, and that this regulation is analogous in the central and sympathetic nervous systems.     

Quinolinic Acid Phosphoribosyltransferase in Rat Brain

Because of the possible participation of quinolinic acid in brain function and/or dysfunction, the characteristics of its catabolic enzyme, quinolinic acid phosphoribosyltransferase (QPRTase; EC 2.4.2.19), were examined in rat brain tissue. For this purpose, a sensitive radiochemical assay method, based on the conversion of quinolinic acid to nicotinic acid mononucleotide (NAMN), was developed. For brain QPRTase, the Mg2+ dependency, substrate specificity, and optimal assay conditions were virtually identical to those of the liver enzyme. Kinetic analyses of brain QPRTase revealed a Km of 3.17 +/- 0.30 microM for quinolinic acid and Km = 65.13 +/- 13.74 microM for the cosubstrate phosphoribosylpyrophosphate. The respective Vmax values were: 0.91 +/- 0.08 pmol NAMN/h/mg tissue for quinolinic acid and 11.65 +/- 1.55 fmol NAMN/h/mg tissue for phosphoribosylpyrophosphate. All kinetic parameters measured for the brain enzyme were significantly different from those determined for liver QPRTase, indicating structural differences or distinct regulatory processes for the brain and liver enzymes. Phthalic acid was a potent competitive inhibitor of brain QPRTase. Examination of the regional distribution of QPRTase in the rat CNS and retina indicated a greater than 20-fold difference between the area displaying the highest activity (olfactory bulb) and those of only moderate activity (frontal cortex, striatum, retina, hippo-campus). Enzyme activity was present at the earliest age tested, 2 days, and tended to increase in older animals. Brain QPRTase activity was preferentially located in the nerve-ending (synaptosomal) fraction. Enzyme activity was stable over extensive periods of storage at -80 degrees C.(ABSTRACT TRUNCATED AT 250 WORDS)     

A glycophospholipid covalently attached to the C-terminus of the Thy-1 glycoprotein

The Thy-1 glycoprotein is a very abundant cell surface molecule of rat thymocytes and neuronal cells with the properties of a molecule that inserts into the lipid bilayer. The hydrophobicity is due to a glycophospholipid component covalently attached to the carboxy group of the C-terminal cysteine residue. The mature glycoprotein does not contain a stretch of hydrophobic amino acids that could traverse the membrane bilayer. These findings present a new mode of membrane attachment for a cell surface molecule that can mediate lymphokine release and cell division after cross-linking by antibodies.     

Allometries of the durations of torpid and euthermic intervals during mammalian hibernation: A test of the theory of metabolic control of the timing of changes in body temperature

Summary The durations of the intervals of torpor and euthermia during mammalian hibernation were found to be dependent on body mass. These relationships support the concept that the timing of body temperature changes is controlled by some metabolic process. Data were obtained from species spanning nearly three orders of magnitude in size, that were able to hibernate for over six months without food at 5°C. The timing of body temperature changes was determined from the records of copper-constantan thermocouples placed directly underneath each animal. Because all species underwent seasonal changes in their patterns of hibernation, animals were compared in midwinter when the duration of euthermic intervals was short and relatively constant and when the duration of torpid intervals was at its longest. Large hibernators remained euthermic longer than small hibernators (Fig. 2). This was true among and within species. The duration of euthermic intervals increased with mass at the same rate (mass^0.38) that mass-specific rates of euthermic metabolism decrease, suggesting that hibernators remain at high body temperatures until a fixed amount of metabolism has been completed. These data are consistent with the theory that each interval of euthermia is necessary to restore some metabolic imbalance that developed during the previous bout of torpor. In addition, small species remained torpid for longer intervals, than large species (Fig. 3). The absolute differences between different-sized species were large, but, on a proportional basis, they were comparatively slight. Mass-specific rates of metabolism during torpor also appear to be much less dependent on body mass than those during euthermia, but the precision of these metabolic measurements is insufficient for them to provide a conclusive test of the metabolic theory. Finally, small species with high mass-specific rates of euthermic metabolism are under tighter energetic constraints during dormancy than large species. The data presented here show that, in midwinter, small species compensate both by spending less time at high body temperatures following each arousal episode and by arousing less frequently, although the former is far more important energetically than the latter.     

Mapping X-linked ophthalmic diseases: II. Linkage relationship of X-linked retinitis pigmentosa to X chromosomal short arm markers

Summary X-linked retinitis pigmentosa (XLRP) is a series of hereditary dystrophic diseases of the retina that occur in three clinically distinguishable variants: the classic form (McK-31360), a type known as choroidoretinal dystrophy (McK-30330), and a variant with golden-metallic or tapetal reflex in the heterozygote (McK30320). Controversy exists as to whether these phenotypic differences are due to clinical variability in disease expression, heterogeneity in disease alleles at a single locus, or a multiplicity of loci for XLRP. We have studied a single large kindred segregating for XLRP with the metallic fundus reflex in the heterozygote with restriction fragment length polymorphisms (RFLPs) from the short arm of the human X chromosome, and found measurable linkage to DXS7 (=12.5 cMorgans at LOD=2.5), the same RFLP previously shown by others to be tightly linked to the other forms of XLRP at =3cM. Although these estimates appeared to be different, each fell just within the 95% probability interval of the other and, therefore, were insufficient to prove or disprove that the metallic sheen form of XLRP is allelic with other forms of XLRP. Additional RFLPs at the DXS43 and the ornithine transcarbamoylase loci provided three-point crosses for determining the relative positions of DXS7 and XLRP, and supported an order that placed this form of XLRP distal to DXS7 on the Xp. Until the question of genetic heterogeneity is resolved, careful phenotypic characterization of the clinical type of XLRP present in families being used for linkage analyses is advisable.Presented in part at the American Society of Human Genetics meeting, Toronto, Canada, November 1, 1984     

Maturation of pig and rat oocytes transplanted into surrogate pig follicles in vitro

Pig oocytes obtained from slaughterhouse material and rat oocytes obtained from PMSG-treated immature females were incubated as isolated oocytes or injected into explanted pig follicles (5–8 mm). Free oocytes of both species, with or without their cumulus investment or gonadotropins during culture, matured at high rates after 30 hr or 9–10 hr of culture, respectively. Gonadotropic stimulation was necessary for maturation of both the native and injected cumulus-intact pig oocytes in follicle culture. Cumulus-free pig oocytes injected into follicle failed to mature in response to gonadotropic stimulation, suggesting an inability to perceive or respond to stimulation. Injected rat oocytes, however, matured irrespective of cumulus investment or gonadotropic stimulation. Their maturation was delayed and reduced at 9 hr. These results in the rat suggest that the pig follicular environment is incapable of regulating rat oocyte maturation but rather presents a permissive or supportive environment for their maturation. The explanted surrogate follicles from the pig or other species may provide a useful model for the study of oocyte-follicle interactions in oocyte maturation within or between species.