Reversal of X-inactivation in female mouse somatic cells hybridized with murine teratocarcinoma stem cells in vitro

A series of near-diploid embryonal carcinoma-like hybrid cells were obtained from polyethylene glycol mediated cell fusion between murine embryonal carcinoma cells (PSA-6TG1 or OTF9-63) having one X chromosome and thymocytes or bone marrow cells from female mice carrying Cattanach's or Searle's translocation. Prior to fusion with EC cells the somatic cells are presumed to contain only one active X chromosome. Following hybrid formation, the chronology of X chromosome replication and the expression of X-linked gene Pgk-1 indicated that all X chromosomes contributed by both parents were active in these hybrids. Experiments were performed to rule out the possibility that the hybrids were formed by fusion of EC cells with rare somatic cells in which both X chromosomes were active. Taken together the data indicate that within four days of fusion there is reactivation of the entire inactive X chromosome.     

Cortical vesicle exocytosis in isolated cortices of sea urchin eggs: Description of a turbidometric assay and its utilization in studying effects of different media on discharge

Cortices of unfertilized sea urchin eggs can be isolated in suspension and will discharge the attached cortical vesicles (CVs) in response to calcium. We describe a simple turbidometric assay for monitoring the Ca²⁺-induced discharge of these vesicles and also compare the discharge of vesicles isolated in a high salt medium (primarily KCl) with a medium more closely simulating the internal milieu of the cell (primarily potassium gluconate and glycine). Discharge in response to calcium is similar in both media, requiring approximately 6 μM calcium for one-half maximal discharge. There are, however, significant differences in morphology and protein composition of the two types of preparations (more proteins present in the glycine cortices) and also in the rate of discharge of the vesicles in response to calcium (KCl cortices with $\text{t}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ 6 sec as opposed to 30 sec in the glycine cortices). The glycine cortices gradually lose their ability to respond to calcium but retention of calcium sensitivity is considerably aided by inclusion of ATP in the media; ATP has no apparent effect on discharge of the KCl cortices. The glycine cortices, as opposed to the KCl cortices, exhibited variation in calcium sensitivity during the breeding season and in the number of vesicles which would not break down in response to added calcium (referred to as refractory vesicles). The question of which type of cortex preparation most closely simulates the in vivo situation is discussed, and the view is presented that the glycine cortices most closely resemble the in vivo situation.     

Topographical difference in taste organ density and its sensitivity of frog tongue

Distribution density of the taste disks of the fungiform papillae in the frog tongue was larger at the proximal portion than at the apical and middle portions. The number of myelinated afferent nerve fibres and taste cells per cm2 area of the tongue increased in the order of proximal greater than middle greater than apical portion. The amplitudes of gustatory neural responses for 0.5 M NaCl, 0.5 M KCl, 0.5 M NH4Cl, 0.05 M CaCl2, 1 mM acetic acid and 1 mM quinine-HCl (Q-HCl) were significantly larger with lingual stimulation of the proximal region than with the stimulation of the apical region. With these stimuli the mean ratio of the apical response to the proximal response was 1.00:1.54. On the other hand, this ration with deionized water was 1.00:5.00. The mean magnitudes of receptor potentials in taste cells for 1 mM acetic acid and 10 mM Q-HCl were the same among the apical, middle and proximal portions of the tongue. The mean magnitudes of receptor potentials for 0.5 M NaCl were significantly larger at the apical portion than at the other portions, whereas those for deionized water tended to be the largest at the proximal portion. It is concluded that the larger magnitude of the gustatory neural responses at the proximal portion of the tongue is due to morphological and physiological properties of the taste organ.     

Mutants of Group D1Salmonella Carrying the Somatic Antigen of Group A Organisms: Isolation and Serological Characterization

O antigen mutants were obtained from Salmonella durban, a group D(1) organism, by treatment with N-methyl-N'-nitro-N-nitrosoguanidine. Serological studies demonstrated that the mutants lost the O-9 antigen factor of the parent organism but acquired the O-2 factor specific to group A Salmonella. Lipopolysaccharides of the mutant strains contained paratose which determines the specificity of O-2 factor. Tyvelose, present in the wild-type lipopolysaccharide, was not found in the mutants. H antigens and other biological characteristics of the mutant strains were the same as those of the wild-type organism. The present finding implies that group A Salmonella species might be derived from group D(1) organisms.     

Direct control by calcium of 25-hydroxycholecalciferol-1-hydroxylase activity in chick kidney mitochondria

Kidney mitochondria were isolated from rachitic chicks and their activity in the metabolism of 25-OH-D₃ was studied in relation to the amount of calcium added $\text{in vitro}$. The addition of 0.050.2 mM calcium to a mitochondrial suspension caused a marked and dose-related stimulation of 1-hydroxylation. A sharp decline in the activity was induced by higher concentrations (0.3-0.5 mM) of calcium. The rate of 24-hydroxylation was not influenced by calcium. In these effects, calcium was relatively specific among various divalent cations. These data strongly suggest that calcium is directly involved in the regulation of the vitamin D activation in kidney mitochondria.