Studies on the origin of milk fat. A further study of bovine serum lipoproteins and an estimation of their contribution to milk fat

1. Tritium-labelled palmitic acid combined in olive-oil triglycerides was introduced into the rumen of a lactating cow and the specific radioactivity of the lipids of milk and of the lipoproteins of both jugular and mammary venous serum was measured. 2. As previously found in a similar experiment with [(3)H]stearic acid, the specific radioactivity of the triglyceride fraction of the dextran sulphate-precipitable lipoproteins reached a maximum earlier and greater than that of the milk fat. 3. This fraction was the only lipid separated that had a significant arteriovenous difference in concentration, and is therefore identified as the main circulating lipid precursor of milk fat. 4. Although the non-esterified fatty acids showed no arteriovenous difference in concentration, they showed a negative difference in specific radioactivity that could have occurred only at the expense of the triglycerides of the precipitable lipoproteins. 5. The mean specific radioactivity of the triglycerides immediately after removal from the blood is calculated and shown to be very close in value to that of the corresponding fraction in mammary venous serum. 6. By comparison of the mean specific radioactivities of milk fat and of this precursor, its contribution is calculated as 36%. 7. This value is discussed with reference to the concentration of C(16) and C(18) fatty acids in milk fat and it is concluded that substantial amounts of these acids must have been derived from a source other than preformed circulating lipids.     

Neoplastic transformation by truncated alleles of human NOTCH1/TAN1 and NOTCH2.

The Notch genes of Drosophila melanogaster and vertebrates encode transmembrane receptors that help determine cell fate during development. Although ligands for Notch proteins have been identified, the signaling cascade downstream of the receptors remains poorly understood. In human acute lymphoblastic T-cell leukemia, a chromosomal translocation damages the NOTCH1 gene. The damage apparently gives rise to a constitutively activated version of NOTCH protein. Here we show that a truncated version of NOTCH1 protein resembling that found in the leukemic cells can transform rat kidney cells in vitro. The transformation required cooperation with the E1A oncogene of adenovirus. The transforming version of NOTCH protein was located in the nucleus. In contrast, neither wild-type NOTCH protein nor a form of the truncated protein permanently anchored to the plasma membrane produced transformation in vitro. We conclude that constitutive activation of NOTCH similar to that found in human leukemia can contribute to neoplastic transformation. Transformation may require that the NOTCH protein be translocated to the nucleus. These results sustain a current view of how Notch transduces a signal from the surface of the cell to the nucleus.     

Identification of a modifier gene locus on chromosome 1p35-36 in familial adenomatous polyposis

Phenotypic variability based on nonallelic heterogeneity is a characteristic feature of the dominantly inherited disease, familial adenomatous polyposis (FAP). A modifying locus, called Mom-1, which strongly influences disease expression has been mapped in the mouse model of FAP to the region of murine chromosome 4, which has synteny to human chromosome 1p35-36. In the present study, this chromosomal region was investigated by using 14 microsatellite markers within a large FAP kindred in which patients harbor the same germ-line mutation but show markedly different disease characteristics. The linkage program MLINK was used to determine whether any correlation exists between these markers and the development of extracolonic symptoms in polyposis coli patients. Depending on the mode of inheritance of the affected locus, a maximum lod score was observed for markers D1S211 and D1S197, reaching 2.08 and 1.77, respectively. The observed values obtained within one large FAP family are supportive of a phenotype-modifying locus within this chromosomal region. Received: 6 December 1996 / Revised: 23 December 1996     

Use of baculoviruses as biological insecticides

Naturally occurring baculoviruses can be used to control a wide range of insect pests. Most baculoviruses are used as biopesticides, that is, they are sprayed onto high-density pest populations in a manner akin to the use of synthetic chemical pesticides. However, other strategies that use the biological features of the viruses are also possible and should increase as we expand our knowledge of baculovirus ecology. In order to develop a baculovirus control program, several areas need to be studied before progressing to large scale field studies and commercialization. These range from laboratory efficacy testing and the development of production systems to detailed study of pest behavior and the development of appropriate application strategies.     

Binding of the estrogen receptor to DNA. The role of waters.

Molecular dynamics simulations are carried out to investigate the binding of the estrogen receptor, a member of the nuclear hormone receptor family, to specific and non-specific DNA. Two systems have been simulated, each based on the crystallographic structure of a complex of a dimer of the estrogen receptor DNA binding domain with DNA. One structure includes the dimer and a consensus segment of DNA, ds(CCAGGTCACAGTGACCTGG); the other structure includes the dimer and a nonconsensus segment of DNA, ds(CCAGAACACAGTGACCTGG). The simulations involve an atomic model of the protein-DNA complex, counterions, and a sphere of explicit water with a radius of 45 A. The molecular dynamics package NAMD was used to obtain 100 ps of dynamics for each system with complete long-range electrostatic interactions. Analysis of the simulations revealed differences in the protein-DNA interactions for consensus and nonconsensus sequences, a bending and unwinding of the DNA, a slight rearrangement of several amino acid side chains, and inclusion of water molecules at the protein-DNA interface region. Our results indicate that binding specificity and stability is conferred by a network of direct and water mediated protein-DNA hydrogen bonds. For the consensus sequence, the network involves three water molecules, residues Glu-25, Lys-28, Lys-32, Arg-33, and bases of the DNA. The binding differs for the nonconsensus DNA sequence in which case the fluctuating network of hydrogen bonds allows water molecules to enter the protein-DNA interface. We conclude that water plays a role in furnishing DNA binding specificity to nuclear hormone receptors.     

Analysis of mutation rates in the SMCY/SMCX genes shows that mammalian evolution is male driven

Mammalian evolution is believed to be male driven because the greater number of germ cell divisions per generation in males increases the opportunity for errors in DNA replication. Since the Y Chromosome (Chr) replicates exclusively in males, its genes should also evolve faster than X or autosomal genes. In addition, estimating the overall male-to-female mutation ratio (α_m) is of great importance as a large α_m implies that replication-independent mutagenic events play a relatively small role in evolution. A small α_m suggests that the impact of these factors may, in fact, be significant. In order to address this problem, we have analyzed the rates of evolution in the homologous X-Y common SMCX/SMCY genes from three different species—mouse, human, and horse. The SMC genes were chosen because the X and Y copies are highly homologous, well conserved in evolution, and in all probability functionally interchangeable. Sequence comparisons and analysis of synonymous substitutions in approximately 1kb of the 5′ coding region of the SMC genes reveal that the Y-linked copies are evolving approximately 1.8 times faster than their X homologs. The male-to-female mutation ratio α_m was estimated to be 3. These data support the hypothesis that mammalian evolution is male driven. However, the ratio value is far smaller than suggested in earlier works, implying significance of replication-independent mutagenic events in evolution. Received: 18 April 1996 / Accepted: 4 October 1996     

CO2 transport in normovolemic anemia: complete compensation and stability of blood CO2 tensions

Deem, Steven A., Michael K. Alberts, Michael J. Bishop,Akhil Bidani, and Erik R. Swenson.CO₂ transport in normovolemic anemia: complete compensation and stability of bloodCO₂ tensions. J. Appl. Physiol. 83(1): 240-246, 1997.Isovolemichemodilution does not appear to impairCO₂ elimination nor causeCO₂ retention despite theimportant role of red blood cells in bloodCO₂ transport. We studied thisphenomenon and its physiological basis in eight New Zealand Whiterabbits that were anesthetized, paralyzed, and mechanically ventilatedat a fixed minute ventilation. Isovolemic anemia was induced bysimultaneous blood withdrawal and infusion of 6% hetastarch insequential stages; exchange transfusions ranged from 15-30 ml involume. Variables measured after each hemodilution included hematocrit(Hct), arterial and venous blood gases, mixed expiredPCO₂ andPO₂, and blood pressure; also, O₂ consumption,CO₂ production, cardiac output(), and physiological dead space were calculated.Data were analyzed by comparison of changes in variables with changesin Hct and by using the model of capillary gas exchange described byBidani (J. Appl. Physiol. 70:1686-1699, 1991). There was complete compensation for anemia withstability of venous and arterial PCO₂between Hct values of 36 ± 3 and 12 ± 1%, which was predictedby the mathematical model. Over this range of hemodilution, rose 50%, and theO₂ extraction ratio increased 61%without a decline in CO₂production or a rise in alveolar ventilation. The dominantcompensations maintaining CO₂transport in normovolemic anemia include an increased and an augmented Haldane effect arising from theaccompanying greater O₂extraction.

     

Arterial baroreflex modulation of heat-induced vasodilation in the rabbit ear

Ryan, Kathy L., W. Fred Taylor, and Vernon S. Bishop.Arterial baroreflex modulation of heat-induced vasodilation in therabbit ear. J. Appl. Physiol. 83(6):2091-2097, 1997.The purpose of this study was to determinewhether nonthermal baroreflexes arising from cardiopulmonaryand/or arterial baroreceptors modulate rabbit ear blood flow(EBF) during hyperthermia. Intact and sinoaortic-denervated (SAD)rabbits were chronically instrumented with a Doppler ultrasonic flowprobe for measurement of EBF velocity (kHz). During whole body heatingin conscious rabbits, EBF and ear vascular conductance (EVC) increasedas core temperature increased until maximal plateau levels of EBF andEVC were reached. The maximal plateau level of EVC attained during heatstress was lower in SAD than in intact rabbits. Subsequentintrapericardial administration of procaine at maximal EBF blockedcardiac afferents but did not alter EVC in either animal group. In asecond experiment, ramp decreases in mean arterial pressure wereproduced by vena caval occlusion at maximal EBF. In intact rabbits, EBFand EVC decreased linearly as mean arterial pressure fell, but EBF andEVC did not decrease during vena caval occlusion in SAD rabbits. Thusneither pharmacological nor mechanical unloading of cardiacbaroreceptors results in reflex vasoconstriction in the heat-stressedrabbit ear. However, baroreflexes arising from arterial baroreceptorsmay modulate EBF in heat-stressed rabbits.