Differential effects of placental lactogen,growth hormone and prolactin on rat liver ornithine decarboxylase activity in the perinatal period

Ovine placental lactogen, (oPL), ovine growth hormone, (oGH), and ovine prolactin, (oPRL) are present in high concentrations in the fetal circulation late in gestation. To determine if these hormones stimulate the activity of ornithine decarboxylase (ODC), an enzyme widely implicated in the control of cellular growth, rat fetuses were injected $\text{in utero}$ with 100 μg of oPL, oGH, oPRL, rat growth hormone (rGH) or rat prolactin (rPRL) and ODC activity in the livers, hearts, and brains of the fetuses was measured 2, 4, and 6 hours after injection. OPL stimulated fetal liver ODC activity by 282 ± 45% (mean ± SEM) as compared to litter mates injected with buffer alone but oGH, oPRL, rGH and rPRL had no effect on fetal liver ODC activity. However, in neonatal rats 24–48 hours old all five hormones significantly increased liver ODC activity. ODC activities in the hearts and brains of the fetuses and neonates were unaffected by any of the five hormones. In other experiments 50 μg of oPL significantly stimulated fetal liver ODC activity while 250 μg of oGH were without effect. However 25 μg of oGH significantly stimulated liver ODC activity in rat pups 1–2 days after birth. These results suggest that oPL, by its stimulation of ODC activity, has somatotropic effects in the fetus and that rat liver ODC activity becomes responsive to growth hormone and prolactin in the perinatal period.     

The early ontogeny of hematopoietic cells studied by grafting cytogenetically labeled tissue anlagen: Localization of a prospective stem cell compartment

The relative contributions of ventral blood island mesoderm and dorsal anterior mesoderm to differentiated lineages of hematopoietic cells was assessed by reciprocal grafting of cytogenetically labeled tissues between 67- and 72-hr-old frog embryos (Shumway stages 15–16). Diploid (2N) and triploid (3N) cell populations from hematopoietic organs were distinguished by Feulgen-DNA microdensitometric analysis. Ventral blood island mesoderm appears to contribute an embryonic erythrocyte population that progressively declines during larval development. Dorsal anterior mesoderm appears to contribute a population of precursor cells that gives rise to differentiated lineages of hematopoietic cells found in the thymus, pronephros, mesonephros, spleen, and blood. Histological examination of the developing dorsal anterior area indicates that extensive vascularization is a prominent characteristic of this region. The dorsal aortae and vasculature surrounding the pronephros may be sites where at least one population of hematopoietic cells matures and subsequently enters circulation.     

Activation of human B lymphocytes: XVI. Cellular requirements,interactions, and immunoregulation of pokeweed mitogen-induced total-immunoglobulin producing plaque-forming cells in peripheral blood

The optimal culture and assay conditions for the detection of spontaneously occurring and pokeweed mitogen (PWM)-induced polyvalent Ig (IgG + IgM + IgA) and individual Ig class-specific plaque-forming cells (PFC) in human peripheral blood have been described in detail. Culture conditions are critical, particularly with regard to cell density and batches of supplemental serum. Fetal calf serum is a much more supportive serum supplement for PWM-induced PFC than is human serum. The assay system is a modified reverse hemolytic PFC assay using staphylococcal protein A coupled to sheep red blood cells by the chromic chloride method. PFC are developed by rabbit anti-human polyvalent Ig or anti-human individual Ig class antisera. Human peripheral blood contains 468 (±78) spontaneously occurring Ig secreting PFC per 10⁶ lymphocytes at Day 0 and 20,500(± 1971) PWM-induced Ig secreting PFC after 6 days in culture. The response is T-cell dependent; however, T cells can be replaced by a soluble T-cell factor prepared from a 48-hr allogeneic mixed lymphocyte reaction supernatant. The relative dependence on monocytes is a reflection of the culture conditions employed. Under the conditions of round-bottom tubes which promote cell-to-cell contact, depletion of monocytes to 0 to 2% does not result in a diminution of PFC responses. In fact, under such conditions, in certain individuals monocytes are markedly suppressive such that removal of monocytes results in a substantial enhancement of PFC responses. This system is simple and reproducible and should prove extremely useful in the delineation of the mechanisms of B-cell triggering and immunoregulation in normals and in disease states.     

Characterization of crystals of a cytochrome oxidase (nitrite reductase) from Pseudomonas aeruginosa by x-ray diffraction and electron microscopy

Cytochrome oxidase from Pseudomonas aeruginosa has been crystallized from 2 m-ammonium sulfate. The crystals occur principally as thin diamond-shaped plates of space group P2₁2₁2 with unit cell dimensions of 92 Å × 115 Å × 76 Å. Determination of the density of glutaraldehyde-fixed, water-equilibrated crystals (1.167 g/cm³), coupled with the unit cell volume (804,000 ų), indicates that there is one subunit (~63,000 Mr) per asymmetric unit. X-ray diffraction data which were limited to 12 Å resolution due to small crystal size were obtained for the hk0 and 0kl zones using precession photography. Amplitude and phase data for the hk0, 0kl, and h0l zones were obtained from computer-based Fourier analysis of appropriate micrographs recorded from negatively stained microplates and thin sections of larger crystals using minimal beam electron microscopy. For crystals embedded in the presence of tannic acid it was possible to achieve 20 Å resolution which is comparable to the resolution achieved with negative staining of thin crystalline arrays. In addition, unstained electron diffraction on glutaraldehyde-fixed, glucose-stabilized plates was recorded to a resolution of 9 Å. The three-dimensional packing of the cytochrome oxidase dimer in the unit cell has been deduced from computer reconstructed images of the three principal projections along the crystallographic axes. The cytochrome oxidase dimer is located in the unit cell with the dimer axis coincident with a crystallographic 2-fold axis; thus within the resolution of the present data in projection (9 Å) the two subunits are identical, in agreement with biochemical evidence. The crystals have been prepared with the enzyme in the fully oxidized state and upon reduction a progressive cracking of the crystals is observed, possibly due to a conformational change dependent on the oxidation state of the heme iron.     

Inverse correlation between species lifespan and capacity of cultured fibroblasts to convert benzo(a)pyrene to water-soluble metabolites

Diploid fibroblasts from lung and skin of eight mammalian species were cultured and the capacity of these cell strains to convert benzo(a)pyrene (BP) to water-soluble metabolites was determined. The rate of conversion is dependent upon culture density and varies widely among different species. There is a very good inverse correlation between species lifespan and the capacity of cultured fibroblasts from these species to metabolize BP to water-soluble forms. Since these cell systems have also shown a good inverse correlation between species lifespan and biological activity of 7,12-dimethylbenz(a)anthracene (DMBA), these data suggest that the capacity to metabolize polycyclic hydrocarbon carcinogens may be closely related to lifespan in mammalian species.     

A Chromosomal Translocation Causing Overproduction of Iso-2-Cytochrome c in Yeast

The CYC7–1 mutation in the yeast Saccharomyces cerevisiae causes the production of approximately 30 times the normal amount of iso-2-cytochrome c. Genetic analysis established that the CYC7–1 mutation is a reciprocal translocation involving the left arm of chromosome V and the right arm of chromosome XVI. The chromosome V arm was broken adjacent to the gene CYC7, which determines the primary structure of iso-2-cytochrome c, and this fragment containing the CYC7 gene was joined to the segment of chromosome XVI. It appears as though the elevation of iso-2-cytochrome c is caused by an abnormal controlling region adjacent to the structural region of the CYC7 gene.     

Auditory sensitivity of the saccule in the American toad (Bufo americanus)

Summary Single unit recordings in the posterior nerve branchlet from the saccule have shown that, in the American toad (Bufo americanus), approximately 30% of the fibers respond to airborne sounds in a way similar to fibers from the two known auditory organs, the amphibian and basilar papillae. In response to tones, saccule fibers have best excitatory frequencies which fall into two disjoint populations: units in the low-frequency-sensitive group (below 300 Hz) show tone-on-tone suppression while those in the high-frequency-sensitive group (700–1,200 Hz) show no evidence of peripheral inhibition. Saccule units have somewhat higher thresholds than those from the other auditory organs. It is suggested that the high-frequency-sensitive fibers might be useful for discriminating mating calls in an intense chorus while the low-frequency-sensitive units likely respond to other high intensity sounds in the environment.Research supported by the U.S. Public Health Service (NIH grant NS-09244).     

Mechanism of suppression in Drosophila. III. Phenol oxidase activity and the speck locus

A marked decrease in the amount of the A₂ component of phenol oxidase occurs in the speck locus of Drosophila melanogaster. The amount of A₂ in speck is restored to a normal amount in the presence of the suppressor mutant, su(s) ².     

Circular dichroism analysis of the ribosomal binding of initiation factor IF-3

The circular dichroism spectra of Escherichia coli 30 S ribosomal subunits have been determined between 200 and 320 nm in the presence and in the absence of initiation factor IF-3. The addition of IF-3 did not produce any major alteration of the circular dichroism spectrum of the 30 S subunits between 320 and 240 nm, but resulted in an increase of the negative ellipticity between 240 and 205 nm. The effect was maximal for an IF-3:30 S molar ratio of approximately one, and further addition of IF-3 did not lead to a further increase of ellipticity. A similar effect was not seen when the 30 S ribosomal subunits were previously heat-inactivated to destroy their IF-3 binding capacity. These data indicate that the ribosomal binding of IF-3 may be accompanied by an increase in the secondary structure of the ribosomal proteins, but does not involve any major net change in the secondary structure of the rRNA.