Cyclic AMP and cell differentiation in amphibian embryonic explants

Conflicting results have been published concerning the effects of cyclic nucleotides on amphibian cell differentiation. Here we report the effects of cyclic adenosine monophosphate (cAMP) and dibutyryl-cyclic adenosine monophosphate (db-cAMP) on isolated explants from late blastulae of Ambystoma mexicanum and Xenopus laevis. Both cAMP and db-cAMP (10(-4)-10(-9) M) promote 'neuralizing' differentiation in Ambystoma explants. Xenopus explants treated with the nucleotides (10(-4), 10(-6), 10(-8) M) LiCl or heparan sulphate only give rise to ciliated aggregates or dissociation. The results confirm observations that different amphibian species react in different ways to activating chemicals.     

X-linked agammaglobulinemia (XLA): A genetic tyrosine kinase (Btk) disease

X-linked agammaglobulinemia is a heritable immunodeficiency disease caused by a differentiation abnormality, resulting in the virtual absence of B Iymphocytes and plasma cells. The affected gene encodes a cytoplasmic protein tyrosine kinase, Bruton's agammaglobulinemia tyrosine kinase, designated Btk. Btk and the other family members, Tec, Itk and Bmx, contain five regions, four of which are common structural and functional modules that are found in other signaling proteins. Mutations affect all domains of the gene, but amino acid substitutions seem to be confined to certain regions. More than 150 unique mutations have been identified and are collected in a mutation database, BTKbase. Here we discuss the three-dimensional structural implications of such mutations and their putative functional role. Of special interest are mutations affecting the pleckstrin homology domain, as Btk is the only disease-associated protein so far reported to carry mutations in this particular module.     

In vivo treatment with interferon-gamma during early pregnancy in mice induces strong expression of major histocompatibility complex class I and II molecules in uterus and decidua but not in extra-embryonic tissues.

Allopregnant (NFR/N [Swiss-derived] H-2q females x 57/Bl H-2b males) and syngeneically pregnant (NFR/N x NFR/N) mice were subjected to daily injections (10(5) U/mouse/day, from Day 5.5 of gestation) of recombinant rat or mouse interferon-gamma (IFNg) in order to investigate its ability to induce extra-embryonic major histocompatibility complex (MHC) expression and antipaternal immune reactions if administered during the first part of the gestation period. In addition, a limited number of IFNg-treated embryo-transferred NFR/N mice carrying C57/B1 embryos (representing a complete allogenic pregnancy) were investigated. Mouse and rat IFNg caused the same type of histological and physiological changes, and most of the experiments were performed by using rat IFNg. Several IFNg-treated mice (irrespective of type of mating) showed a drop in weight and a high rate of resorptions at Day 12.5 of gestation. This interference with pregnancy appeared not to be caused by immunological reactions against the feto-placental unit (no leukocyte infiltration and no significant effect on serum levels of antipaternal antibodies in preimmunized allopregnant IFNg-treated mice). Immunohistochemical stainings of cryosectioned tissues at Day 9.5 of pregnancy revealed that IFNg treatment caused a strong induction of MHC class I and class II expression on most cells in the uterus and on several cells in the maternal decidua, while there was a complete absence of detectable MHC class I and class II expression in the extra-embryonic tissues. Characteristic for a Day 12.5 placenta of an IFNg-treated mouse (including embryo-transferred mice) was a strongly MHC class II-induced maternal decidua and a completely MHC class II-negative fetal placenta. The pattern of IFN-induced MHC class I expression was similar to that of class II, with the exception of class I expression on scattered cells within the basal zone. Thus, the present study provides immunohistological evidence that IFNg administered in vivo during the first part of gestation is not capable of inducing MHC expression on murine extra-embryonic cells despite an extremely high expression of MHC molecules on decidual cells in intimate contact with extra-embryonic tissues. It is likely that the resistance to IFNg-mediated induction of MHC expression on extra-embryonic cells is of basic importance for the protection of mammalian semi-allogeneic fetuses.     

The use of hair as an indicator of occupational 14C contamination

This paper presents a study in which the specific activity of ¹⁴C in hair has been investigated as an easily determined bio-indicator of the integrated ¹⁴C exposure (over several months). The study includes 28 Swedish workers handling ¹⁴C-labelled compounds, or working in a ¹⁴C-enriched environment. Hair samples from personnel at a Swedish nuclear power plant showed very low levels of ¹⁴C contamination, if any. In contrast, personnel at the investigated research departments showed ¹⁴C levels in hair of up to 60% above the natural specific activity of ¹⁴C. Much higher levels, up to 80 times the natural specific activity of ¹⁴C, were found in hair from individuals working at a pharmaceutical research laboratory. This contamination was, however, not solely an internal contamination. There were indications that most of the ¹⁴C in the hair originated from airborne ¹⁴C-compounds, which were adsorbed onto the hair. The difficulties in removing this external ¹⁴C contamination prior to analysis are discussed, as are the possibilities of using accelerator mass spectrometry to analyse various types of samples for retrospective dose assessment.     

Autoneuralization in the amphibian ectoderm--a species-specific and stage-specific phenomenon

Ectoderm from Ambystoma is especially prone to undergo 'autoneuralization'. This assertion has led to the maxim that ectoderm from this species is unsuitable for studying cell differentiation. Here we report that the degree of neuralization in cultured explants is stage-dependent. Control explants from blastulae (stage 8-9) show no neuralization, while explants treated with LiCl (10 mM) give rise to neuralization in about 70% of the cases. This difference between control and experiment decreases during gastrulation, in late gastrulae (stage 12) it is more or less negligible. Ectoderm from Cynops pyrrhogaster reacts like that of Ambystoma when exposed to LiCl, but like Triturus ectoderm it is insensitive to cyclic nucleotides.     

Employment of hydrolytic enzymes in the study of the level of DNA methylation

A new method for the determination of the level of DNA methylation was established. The method involves enzymatic hydrolysis of DNA by nuclease P1 and bacterial alkaline phosphatase, and separation of the resulting deoxyribonucleosides by HPLC. By this method, DNA was hydrolysed completely to the five deoxyribonucleosides and the complete base composition was determined. Pairing bases were shown to occur in similar amounts, and analysis could be performed on as little as 1 microgram of DNA with a high degree of reproducibility. Among other enzymes hitherto used in order to hydrolyze DNA, micrococcal nuclease, phosphodiesterase II and nuclease P1 have been shown to cause deamination of deoxyadenosine, while deoxyribonuclease I, phosphodiesterase I and bacterial alkaline phosphatase have been shown to be sensitive to contamination by RNA, and to release 5-methyldeoxycytidine at a slower rate than the other four deoxyribonucleosides. Neither of these effects was seen with the new method.     

Omeprazole and ranitidine, antisecretagogues with different modes of action, are equally effective in causing hyperplasia of enterochromaffin-like cells in rat stomach

Female rats were treated for 28 days with high doses of the gastric acid secretion inhibitors omeprazole and ranitidine. Omeprazole, which is long-acting, was given orally once daily. Ranitidine, which is short-acting, was given by continuous infusion (via osmotic minipumps, implanted subcutaneously). The aim was to produce a similar degree of acid inhibition with the two drugs. The inhibition of acid secretion over the day and night was more pronounced in the omeprazole-treated rats (maximal inhibition 100%, minimum 85%) than in those receiving ranitidine (mean 70%). In both groups, there was a great increase in plasma gastrin, somewhat greater after omeprazole than after ranitidine. The gastrin concentration in the antrum was almost doubled by both treatments and there was a moderate increase in the number of antral gastrin cells in the omeprazole-treated rats. The number of enterochromaffin-like (ECL) cells (per visual field) increased in the oxyntic mucosa to the same extent (greater than 100%) in the ranitidine- and omeprazole-treated rats. Apart from the gastrin cells in the antrum and the ECL cells in the corpus no other gastric endocrine cell type seemed to respond to treatments with antisecretagogues. We conclude that, regardless of the type of antisecretagogue used, effective and long-term suppression of gastric acid secretion results in sustained hypergastrinemia and increased number of ECL cells. Conceivably therefore, the ECL cell hyperplasia reflects the trophic effect of gastrin.     

Changes in the distributions of epiphytic lichens in southern Sweden using a new statistical method

Past studies on changes in species distribution have mainly been based on analysis of range boundaries. In contrast, the method used here evaluates shifts in species' geographic centroids within a predefined area. We used presence/absence data on epiphytic lichens collected 1986 and 2003 from 64 sites in southern Sweden. A centroid was calculated each year, for each lichen species and substrate. The distance of centroid movement was evaluated in a permutation procedure. In total, 56 lichen species on 22 tree species were involved in the analyses, yielding 30 cases that had sufficient sample sizes both years to be evaluated. Out of these, three exhibited a significant movement of their centroid. The shift of lichen centroids of Hypogymnia physodes (L.) Nyl. and Vulpicida pinastri (Scop.) J.-E. Mattsson & M. J. Lai on the tree species Juniperus communis L. was 50 and 151 km with the direction 27° and 48°, respectively. For Hypogymnia physodes on Pinus sylvestris L., corresponding values were 41 km and 30°. The northnortheast shifts of these species in Sweden could be a response to a warming climate.     

Household salt for retrospective dose assessments using OSL: signal integrity and its dependence on containment,sample collection,and signal readout

The aim of this work was to determine how a latent optically stimulated luminescence (OSL) signal in irradiated household salt is preserved under various ambient conditions, from the time of exposure to the time of signal readout. The following parameters were examined: optical fading in fluorescent light and under darkroom conditions (red light), thermal stability of the OSL signal during storage in a light-tight container, optical fading in representative container types, and sensitization effects of the OSL signal in exposed household salt. Furthermore, the influence of grain mixing within the saltshaker or salt container was studied by determining the dose gradient within typical salt packages. Finally, the signal integrity of salt irradiated under field conditions in a village in Belarus contaminated by Chernobyl fallout was investigated. The results show that the OSL signal in household salt is preserved in large cardboard box containers, but not in white plastic salt containers or in small portion bags used in, e.g., fast food restaurants. Furthermore, the continuous wave blue OSL signal in household salt does not fade significantly during storage up to 140 days. On the contrary, the signal appears to slowly increase during storage (“inverse fading”). Field tests of two different salt containers (with and without black tape to block light) located in Belarussian households confirmed that the signal is preserved in white plastic salt containers when they are covered with extra light-shielding material.