Chromosome distribution of intracisternal A-particle sequences in the Syrian hamster and mouse

Metaphase chromosomes of Syrian hamster and BALB/c mice were hybridized in situ with radiolabeled probes derived from cloned intracisternal A-particle (IAP) genes of the corresponding species. The DNAs of these species are known to contain about 900 and 1,000 copies, respectively, of the retrovirus-like IAP sequence elements per haploid genome. Multiple IAP sequences were found on all chromosomes of both hamster and mouse. In the hamster, more than half of the IAP sequences were located in regions of non-centromeric constitutive heterochromatin, at an average concentration per unit chromosome length 5 times greater than in the euchromatic regions. The other dispersed sequences showed marked local variations in concentration along the chromosome lengths; both discrete foci and large grain clusters were observed as well as regions apparently lacking IAP sequences. Within the resolution of the techniques, IAP sequences appeared to be more evenly distributed over the mouse chromosomes; however, some prominent variations in concentration were seen. The number of potentially active IAP genes in the Syrian hamster, and by extension in the mouse, may be restricted by the preferential location of IAP sequences in genetically inert regions of the genome.     

Influence of sleep on the cardiovascular and metabolic responses to a decrease in ambient temperature in lambs

Experiments were done on seven lambs between the ages of 10 and 24 days to investigate the effects of sleep on the cardiovascular and metabolic responses to a decrease in ambient temperature. Each lamb was anesthetized and instrumented for recordings of electrocorticogram, electro-oculogram, and nuchal electromyograms and measurements of cardiac output, systemic and pulmonic pressures and hemoglobin oxygen saturations as well as body core temperature. No sooner than three days after surgery, measurements were made during periods of quiet wakefulness, quiet sleep and active sleep at ambient temperatures of 25 degrees C and 18 degrees C. Decreasing the environmental temperature from 25 degrees C to 18 degrees C elicited a similar thermogenic response during quiet wakefulness, quiet sleep and active sleep as evidenced by an increase in total body oxygen consumption. The increased metabolic oxygen demand was met by an increase in systemic oxygen transport as well as by an increase in total body oxygen extraction. Since shivering was absent during active sleep, it is likely that nonshivering thermogenesis played a major role in the metabolic response. Our data provide evidence that sleep does not significantly alter the cardiovascular and metabolic responses to a modest decrease in ambient temperature in young lambs.     

Detecting non-neutral heterogeneity across a region of DNA sequence in the ratio of polymorphism to divergence

Natural selection, in the form of balancing selection or selective sweeps, can result in a decoupling of the amounts of molecular polymorphism and divergence. Thus natural selection can cause some areas of DNA sequence to have greater silent polymorphism, relative to divergence between species, than other areas. It would be useful to have a statistical test for heterogeneity in the polymorphism to divergence ratio across a region of DNA sequence, one that could identify heterogeneity greater than that expected from the neutral processes of mutation, drift, and recombination. The only currently available test requires that a region be arbitrarily divided into sections that are compared with each other, and the subjectivity of this division could be problematic. Here a test is proposed in which runs of polymorphic and fixed sites are counted, where a "run" is a set of one or more sites of one type preceded and followed by the other type. The number of runs is smaller than otherwise expected if polymorphisms are clumped together. By simulating neutral evolution and comparing the observed number of runs to the simulations, a statistical test is possible which does not require any a priori decisions about subdivision.      

Thermoregulatory control during pregnancy and lactation in rats

Eliason, Heather L., and James E. Fewell.Thermoregulatory control during pregnancy and lactation in rats.J. Appl. Physiol. 83(3): 837-844, 1997.Although the mechanisms remain unknown, maternal coretemperature (T_c) decreases nearterm of pregnancy and is increased throughout lactation in rats. Thepurpose of our present experiments was to determine whether pregnancy and lactation shift the thermoneutral zone of rats and to investigate whether the changes in maternal T_cduring pregnancy and lactation result from "forced" or"regulated" thermoregulatory responses. Conscious, chronicallyinstrumented nonpregnant and pregnant and lactating rats were studiedboth in a thermocline (a chamber with a linear temperature gradientfrom 12 to 36°C) and in a metabolic chamber to determine theinfluence of pregnancy and lactation on selected ambient temperature aswell as the thermoregulatory response to changes in ambienttemperature. We found that selected ambient temperature, oxygenconsumption, and thermal conductance did not change in rats studied ina thermocline as T_c decreased nearterm of pregnancy. There was, however, a downward shift in thethermoneutral zone of rats studied in a metabolic chamber near term ofpregnancy. During lactation, selected ambient temperature decreased inrats studied in a thermocline as oxygen consumption andT_c increased. The thermoneutralzone of lactating rats was not different from that of nonpregnantanimals. Thus our data provide evidence that the decrease inT_c near term of pregnancy in ratsresults from a regulated thermoregulatory response,whereas the increase in T_c duringlactation results from a forced thermoregulatory response.

     

Induction of neural-like cells and acetylcholinesterase activity in cultures of F9 teratocarcinoma treated with retinoic acid and dibutyryl cyclic adenosine monophosphate

Cultures of F9 embryonal carcinoma cells treated with retinoic acid showed partial differentiation to endoderm cells as previously reported [Strickland, S., and Mahdavi, V. (1978).Cell15, 393–403]. Addition of dibutyryl cAMP to cultures pretreated with retinoic acid led to a second distinctive change in the cell population, with the formation of many neural-like cells. The appearance of these cells coincided with large increases in specific acetylcholinesterase activity of the cultures. Provided the cultures had been exposed to retinoic acid for at least 48 hr beforehand, the morphological and enzymatic changes became apparent between 24 and 48 hr after the addition of dibutyryl cAMP. The changes proceeded more abruptly and extensively when cells were grown in nongelatinized culture dishes. On gelatin-coated surfaces, the differentiated cells occasionally showed local areas of ordered arrangements. It is suggested that this system may be useful in analyzing early events in neural differentiation.     

Factor VIII complex in uraemia and effects of haemodialysis.

Levels of the factor VIII complex were found to be raised in patients with chronic renal failure and further raised by regular dialysis. Increased fibrinogen concentrations were also found. These results suggest the existence of a prothrombotic state in uraemia that is exacerbated by haemodialysis. Ristocetin-induced platelet agglutination, however, was depressed in uraemia and worsened by dialysis. This defect may be transferred to normal platelets from dialysed uraemic plasma, suggesting the existence of an inhibitor of the interaction between factor VIII and platelet glycoprotein. These results may help to explain the anomaly of a prolonged bleeding time together with accelerated atherogenesis that is found in patients with uraemia receiving dialysis.