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Biomedical subjects

A C Bell

Publications and source records attributed to A C Bell.

30 records · Page 2Linked to original sources
PubMed1997

Characterization of the chicken beta-globin insulator.

Insulators, first identified in Drosophila, are DNA sequence elements that shield a promoter from nearby regulatory elements. We have previously reported that a DNA sequence at the 5' end of the chicken beta-globin locus can function as an insulator. It is capable of shielding a reporter gene from the activating effects of a nearby mouse beta-globin locus control region element in the human erythroleukemic cell line K562. In this report, we show that most of the insulating activity lies in a 250-bp CpG island (core element), which contains the constitutive DNase I-hypersensitive site (5'HS4). DNA binding assays with the core sequence reveal a complex protein binding pattern. The insulating activity of the core element is multiplied when tandem copies are used. Although CpG islands are often associated with promoters of housekeeping genes, we find little evidence that the core element is a promoter. Furthermore, the insulator differs from a promoter in its ability to block the locus control region effect directionally.

Animals↗
PubMed1996

Nutrient intakes of Tongan and Tokelauan children living in New Zealand.

AIMS: To assess the adequacy of nutrient intakes of 10- to 13-year-old Tongan and Tokelauan children living in New Zealand and to compare these data with data from nonPacific Islands children of the same age. METHODS: A 24-hour diet record was used to assess the nutrient intakes of Tongan and Tokelauan school children (n = 162), aged 10- to 13-years, living in Auckland and Wellington. Nutrient intakes using the same methodology were compared with those from a nationally representative sample of nonPacific Islands, Form 1 children and also with Australian recommended dietary intakes for children aged 12- to 15-years. RESULTS: Data were collected from 162 (68 boys and 94 girls) of 220 children eligible to participate in the study (74%). Mean energy intakes for both the Tongan (8855 kJ for boys, 8610 kJ for girls) and the Tokelauan (9872 kJ for boys, 8826 kJ for girls) children were above the range of intake recommended by the World Health Organisation. The combined average energy intake of the two groups was higher than that of nonPacific Islands children for both boys and girls although not statistically significantly. Total fat intake was significantly higher (p < 0.05) for Tongan and Tokelauan boys, protein intake significantly higher for Tongan and Tokelauan boys (p < 0.01) and girls (p < 0.01), and carbohydrate intake significantly lower (p < 0.01) for Tongan and Tokelauan girls than for nonPacific Islands children. Compared with nonPacific Islands children micronutrient intakes were generally lower for Tongan and Tokelauan children with intakes of calcium, riboflavin, thiamin, niacin, folate and vitamin A being significantly lower for both sexes. Vitamin C was also significantly lower for girls (p < 0.05). Tongan and Tokelauan children obtain most of their nutrients from meat, bakery products, fast foods and dairy products. Fruit and vegetables were not significant contributors to nutrient intakes. CONCLUSIONS: Tongan and Tokelauan children living in New Zealand consume a diet that is larger in amount but lower in nutrient density compared to that of nonPacific Islands New Zealand children. Their relatively high dietary energy intakes allow them to meet the recommended intake requirements for most nutrients although if current intakes of fat and energy are maintained this may put them at risk of heart disease and other diseases later in life.

Adolescent↗
PubMed1995

How 434 repressor discriminates between OR1 and OR3. The influence of contacted and noncontacted base pairs.

The sequence of the bacteriophage 434 OR1 (ACAAAACTTTCTTGT) differs from its OR3 (ACAGTTTTCTTGT) at positions 4-6. X-ray analysis shows that the side chain of Gln33 of the 434 repressor makes van der Waals' and H-bond contacts with the T at position 4' in complex with OR1, but no specific contact is observed at this position in 434 repressor-OR3 complexes. No contacts are made by repressor to the bases at positions 5 or 6 in either binding site. The significance of the sequence differences between OR1 and OR3 in determining the operator affinity for repressor were examined by constructing synthetic variants of these operators. Measurements of the affinity of these operators for repressor as a function of ionic strength revealed that although base pairs 5 and 6 are not contacted by 434 repressor, they can nonetheless influence operator affinity for repressor by modulating the degree to which ionic interactions contribute to the overall binding energy. Both the magnitude and direction of their effect depends on the status of repressor's contacts to the bases at position 4. The role of contact made by Gln33 to position 4 was examined by mutating this amino acid to Ala and by examining the affinity of wild type repressor for an operator bearing a 5-methylcytosine at position 4' in an OR1-4G mutant. These experiments showed that repressor's preferences at operator positions 5 and 6 are linked to its position 4 preference via a van der Waals' contact between amino acid 33 and a methyl group on the base at operator position 4'. Together, the results of the experiments shown here reveal that bases that do not contact the protein alter its preferences for bases at the contacted operator position 4.

Amino Acids↗
PubMed1995

Mechanical effects of rear-wheel camber on wheelchairs.

Giving the rear wheels of manually propelled wheelchairs negative camber (by angling them such that the bottoms of the wheels are farther apart than the tops) has become increasingly popular, especially among active users. This study's purpose was to evaluate how changing camber affects a wheelchair's mechanics and the extent of these changes. Using a representative wheelchair occupied by an anthropomorphic dummy, we altered the camber from +15 degrees to -15 degrees and measured the effects on nine selected variables. In addition to increasing the wheelchair's track width, negative camber increases the wheelchair's wheelbase and decreases the height of the frame. With negative camber, the center of gravity (CG) of the occupied wheelchair moves backwards. Negative camber causes a backwards tilt of the frame which, in turn, causes toe-out of the rear wheels, a positive caster-inclination angle and an increase in the caster-trail distance. It is apparent that a change in one component of a wheelchair can affect many others, which should be taken into consideration and, where appropriate, compensated for when changing the camber of the wheelchair.

Biomechanical Phenomena↗
PubMed1994

Embryo transfer in fallow deer (Dama dama): superovulation, embryo recovery and laparoscopic transfer of fresh and cryopreserved embryos.

Multiple ovulation-embryo transfer (MOET) protocols for farmed fallow deer (Dama dama) were investigated in a series of 3 experiments. A total of 37 donors, of either European (D.d. dama ; n = 30) or Mesopotamian hybrid (D.d. mesopotamica x D.d. dama ; n =7) genotype, each received an intravaginal silastic device containing 0.3 g progesterone (CIDR-type G device) for 14 d and injections of 0.5 units ovine FSH (8 x 0.06 unit injections from Days 10 to 14 of device insertion) and 100 IU PMSG (either with the first or last FSH injection). All donors received laparoscopic intrauterine inseminations of fresh semen (50 x 10(6) spermatozoa) from a Mesopotamian sire 36 h after withdrawal of CIDR devices. Embryos were recovered by laparotomy on Day 6 (Day 0 = estrus). Mean ovulation rates for the 3 experiments were 8.1, 9.8 and 7.0, with no effect of PMSG timing (P>0.10). However, embryo recovery rates, albeit low throughout the study (29.6%), were significantly improved with later PMSG administration (33.9 vs 20.1%; P<0.05). Hybrid and European donors performed in a similar manner. A range of embryo development stages was recovered throughout the study. In 2 experiments laparoscopic transfer of embryos to 48 recipient does treated previously with intravaginal CIDR devices for 14 d yielded a total pregnancy rate of 37.5%. In the experiment with fresh embryos, the use of clenbuterol to reduce uterine turgidity resulted in a higher proportion of does conceiving (3/4 ; 75%) compared with that of the untreated does (0/6 , 0%; P<0.05). In the second experiment, in which all the does routinely received clenbuterol, 10/19 (53%) and 5 19 (26%) does conceived following the transfer of fresh and cryopreserved embryos, respectively (P<0.05). While the overall efficiency of the MOET program was low (equivalent of 0.9 to 1.0 surrogate pregnancies per donor), improvements in the recovery rate of transferable embryos have considerable potential for genetic improvement of farm stock and captive propagation of endangered Mesopotamian fallow deer through maternal surrogacy programs.

Journal Article↗
PubMed1993

Operator sequence context influences amino acid-base-pair interactions in 434 repressor-operator complexes.

The 434 repressor binds more tightly to OR1 than it does to OR3. The repressor makes several specific contacts with the symmetrically arrayed outer four base-pairs of the 14 base-pair site, and no specific contacts to the central six base-pairs. The sequence of the outer base-pairs of OR1 and OR3 differs only by an A-->G substitution at position 4 in one half-site of OR3, while that of central bases is very different. As expected from sequence analysis of wild-type operators, the data show repressor prefers an A.T base-pair at position 4. The magnitude of this preference depends on operator sequence context and solution conditions. Position 4 changes in the context of OR1 have a greater effect on operator affinity for 434 repressor than do similar changes in OR3. Although OR1 and OR3 display different affinities for 434 repressor, their repressor-operator complexes are similarly insensitive to changes in salt concentration and temperature. By contrast, complexes formed between repressor and position 4 mutant OR1, bearing an A.T-->G.C change, and OR3, which bears a G.C-->A.T change, are affected greatly, and to similar extents, by changes in ionic strength and temperature. Nuclease protection experiments show that 434 repressor protects the DNA phosphate backbone of wild-type operators from cleavage more efficiently than those of mutant operators. These data show that the biochemical and structural properties of a repressor-operator complex, while affected by position 4 base sequence, are independent of the identity of this base. The ability of repressor to recognize the base at position 4 depends on the sequence context at operator positions 5 to 7. Apparently there is an interplay between the bases at operator positions 4 to 7 which has a global effect on the structure of the repressor-operator complex.

Base Composition↗
PubMed1993

Metabolism of pyruvate by pre-elongation sheep embryos and effect of pyruvate and lactate concentrations during culture in vitro.

In the first of two experiments, utilization of [1-14C]pyruvate by 8-cell and blastocyst-stage embryos derived in vivo was examined during a 3-h incubation in HEPES-buffered synthetic oviduct fluid (SOF) medium in the presence or absence of other substrates. In the second, a factorial design examined the effect of pyruvate (0, 0.33, 1.0 and 3.3 mM) and lactate (3.3, 10 and 33 mM) on development of 1- and 2-cell sheep embryos cultured in vitro in a modified SOF medium (containing glucose, glutamine and modified Eagle's medium non-essential amino acids). Peak utilization of [1-14C]pyruvate was unaffected by the presence or absence of other energy substrates. In contrast, rate of utilization was affected by the addition of other energy substrates, with half maximal utilization occurring at either 0.4 +/- 0.2 mM or 1.2 +/- 0.2 mM for 8-cells and either 0.2 +/- 0.2 mM or 1.3 +/- 0.3 mM for blastocysts when incubated in the absence or presence of other energy substrates respectively. In the second experiment the proportion of embryos developing to blastocysts was inhibited by high lactate levels (P < 0.001), but was generally not affected by pyruvate concentration. However, there was a significant interaction (P < 0.001) between pyruvate and lactate when both were present in the medium. At 0.33 mM pyruvate, 3.3 mM lactate supported good development (83 +/- 8% blastocysts) whereas 10 mM lactate supported less development (50 +/- 11%). However, at the higher levels of pyruvate this effect was lost.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1978

Fluid dynamics of coronary artery stenosis.

A large-scale model of the coronary circulation, instrumented to permit detailed pressure and velocity measurements, has been used to study flow through isolated stenotic elements in large coronary arteries. Pulsatile aortic and instantaneous peripheral resistance were stimulated with servovalves. A variety of axisymmetric and asymmetric stenoses were studied and flow separation was found to occur for all but very mild stenoses. Pressure recovery downstream of the stenosis throat was limited and, in some cases, no recovery was observed. Pressure drop was primarily dependent upon the minimum area of the stenosis and relatively independent of stenosis geometry. Flow was quasi-steady at normal heart rates, and simple steady flow theory proved adequate to describe the pressure drop through the stenosis. The theory yielded results that agreed well with published data for dogs and appears promising for predicting effects of hemodynamic variables on a given stenotic lesion. Thus, principal findings of the study are that a relatively severe stenosis behaves essentially like an orifice and that a simple quasi-steady theory appears adequate to predict effects of a stenosis on coronary flow.

Blood Pressure↗