Stress activation and genomic impact of Tnt1 retrotransposons in Solanaceae.

Tnt1 elements are a superfamily of LTR-retrotransposons distributed in the Solanaceae plant family and represent good model systems for studying regulatory and evolutionary controls established between hosts and transposable elements. Tnt1 retrotransposons tightly control their activation, by restricting expression to specific conditions. The Tnt1A element, originally discovered in tobacco, is expressed in response to stress, and its activation by microbial factors is followed by amplification, demonstrating that factors of pathogen origin can generate genetic diversity in plants. The Tnt1A promoter has the potential to be activated by various biotic and abiotic stimuli but a number of these are specifically repressed in tobacco and are revealed only when the LTR promoter is placed in a heterologous context. We propose that a tobacco- and stimulus-specific repression has been established in order to minimize activation in conditions that might generate germinal transposition. In addition to tight transcriptional controls, Tnt1A retrotransposons self-regulate their activity through gradual generation of defective copies that have reduced transcriptional activity. Tnt1 retrotransposons found in various Solanaceae species are characterized by a high level of variability in the LTR sequences involved in transcription, and have evolved by gaining new expression patterns, mostly associated with responses to diverse stress conditions. Tnt1A insertions associated with genic regions are initially favored but seem subsequently counter-selected, while insertions in repetitive DNA are maintained. On the other hand, amplification and loss of insertions may result from more brutal occurrences, as suggested by the large restructuring of Tnt1 populations observed in tobacco compared to each of its parental species. The distribution of Tnt1 elements thus appears as a dynamic flux, with amplification counterbalanced by loss of insertions. Tnt1 insertion polymorphisms are too high to reveal species relationships in the Nicotiana genus, but can be used to evaluate species relationships in the Lycopersicon and Capsicum genera. This also demonstrates that the behavior of Tnt1 retrotransposons differs between host species, most probably in correlation to differences in expression conditions and in the evolutionary and environmental history of each host.

Humoral hypercalcemia of hepatocellular carcinoma associated with elevated levels of parathyroid-hormone-related-peptide.

Parathyroid-hormone-related-peptide (PTHrP) has been shown to be important in the pathogenesis of hypercalcemia of malignancy. The malignancies most commonly associated with hypersecretion of PTHrP include squamous cell carcinoma and breast cancer. The pathogenesis of hypercalcemia associated with hepatocellular carcinoma was evaluated in this study. Two male patients with hepatocellular carcinoma were found to have severe hypercalcemia at initial presentation. PTHrP was measured with radioimmunoassay in these two patients before treatment as well as in nine other patients with hepatocellular carcinoma but without hypercalcemia. The levels were markedly elevated in the two patients with hypercalcemia (29.3 and 32.1 pM), but were less than 5 pM in the nine patients without hypercalcemia. These results suggest that PTHrP was important in the pathogenesis of hypercalcemia associated with hepatocellular carcinoma in these men.

Postcensal estimates for local areas using current samples with census as the source of sampling frame.

"Two techniques for direct postcensal local area estimation are introduced in this paper. Compared with existing techniques for postcensal local area estimation, the proposed techniques are not subject to any bias due to the assumption of constancy of certain statistical relationships between the variable of interest and the symptomatic or associated variables established at a certain point in time (typically a census)." The author notes that "application of the proposed techniques calls for recognition of an integrated design approach at the early planning stage, incorporating considerations of survey designs for the census and the postcensal sample surveys, maintenance and upkeep of the census sampling frame, data analysis and local area estimation requirements simultaneously. When the current samples are continuous and overlap each other, a third technique for postcensal local area estimation is also proposed. An example illustrating these techniques in estimating postcensal district population in Hong Kong is given." (summary in FRE)

The distribution of copia-type retrotransposons and the evolutionary history of tomato and related wild species.

Retrotransposons are mobile genetic elements that amplify throughout the genome and may be important contributors of genetic diversity. Their distribution is influenced by element behaviour and host-driven controls. We analysed the distribution of three copia-type retrotransposons, ToRTL1, T135 and Tnt1 using sequence-specific amplification polymorphism in self-compatible (SC) and incompatible (SI) species of Solanum subsection Lycopersicon, and genetically mapped polymorphic insertions in S. lycopersicum (tomato). The majority of polymorphic insertions (61%) are located in centromeric regions of the tomato genome. A significant positive relationship was detected between insertion polymorphisms and mating system, independent of selection as most insertions were found to be neutral. As insertion patterns successfully inferred interspecific relationships of Solanum subsection Lycopersicon, our results suggest that the distribution of ToRTL1, T135 and Tnt1 may essentially be determined by selection removing strongly deleterious insertions, with genetic drift and mating system, but not recombination rate, playing important roles.

Parathyroid hormone-activated phosphoinositide degradation and calcium channels in human dermal fibroblasts.

Previous studies have shown that there are two types of parathyroid hormone (PTH) receptors on human dermal fibroblasts. We evaluate the effects of PTH on intracellular cyclic AMP, calcium and phosphoinositides in order to define the effector systems of the PTH receptors. The results show that PTH stimulates cyclic AMP accumulation in the human dermal fibroblasts with half-maximal effect at 1-5 nM. PTH also increases intracellular calcium as measured by the technique using Fura-2 fluorescent dye and stimulates phosphoinositide degradation as evaluated by column chromatography. The half-maximal effect on AMP occurred at 5 nM, while those effect on calcium and phosphoinositide turnover occurred at 500 nM of PTH. The results show that cyclic AMP, intracellular calcium and phosphoinositides are second messengers for PTH in human dermal fibroblasts. These results provide further evidence to support the concept of heterogeneity of the PTH receptor and its effector system.