CTCF-binding sites within the H19 ICR differentially regulate local chromatin structures and cis-acting functions

It is generally assumed that CTCF-binding sites are synonymous with the demarcation of expression domains by promoting the formation of chromatin loops. We have proposed earlier, however, that such features may be context-dependent. In support of this notion, we show here that chromatin loop structures, impinging on CTCF-binding sites 1/2 and 3/4 at the 5′ and 3′-ends, respectively, within the maternal allele of the H19 imprinting control region (ICR), differ significantly. Although abrogation of CTCF binding to the maternal H19 ICR allele results in loss of chromatin loops in the 3′-region, there is a dramatic gain of long-range chromatin loops impinging on the 5′-region. As the degree of occupancy of its four CTCF-binding sites discriminates between the chromatin insulator and replication timing functions, we submit that the CTCF-binding sites within the H19 ICR are functionally diverse and organize context-dependent higher order chromatin conformations.     

The magnesium content of the trabecular bone in diabetic subjects

Trabecular bone samples, obtained in vivo from the iliac crest, were examined for their magnesium content by atomic absorption spectrophotometry after ashing. A significant decrease was found in jevunile-type diabetics and in maturity-type patients treated with insuline as compared to non-diabetic controls. The possibility of a long-term effect of daily insulin injections is discussed.     

Differences in the life histories of twoCochlearia species

Cochlearia bavarica Vogt andC. pyrenaica Dc. are closely related and highly endangered species in Bavaria (SE Germany).Cochlearia bavarica (2n=36) is a hybrid ofC. pyrenaica (2n=12) andC. officianalis (2n=24) stabilized by polyploidy.Cochlearia officinalis does not occur in Bavaria. The question being addressed is whether the present non-overlapping distribution of the two Bavarian species, both of which are restricted to calcareous springs with a continuous water supply or drainage ditches, is due to competitive exclusion or to subtle differences of ecological requirements. I did not find any evidence for the second case, i.e. niche differentiation, because both species occurred in all the habitat types that I could define by floristic and ecological criteria. The population structures of bothC. bavarica andC. pyrenaica vary in parallel with different habitat types. Both species have the greatest reproductive output (viable seeds) and the highest population densities in habitats with high light availability and/or low interspecific competition. Thus, I expected that one of the two species might be competitively superior over the other, but that it would fail to reach all its potential sites of occurrence. Cochlearia bavarica individuals (dry mass =5.75 g) grow significantly larger thanC. pyrenaica individuals (3.62 g;P<0.05) and produce more, larger and heavier seeds, possibly due to hybrid vigour. Flowering individuals ofC. bavarica also allocate more biomass to vegetative structures thanC. pyrenaica. The analysis of population dynamics reveals a higher life expectancy and reproductive output inC. bavarica. The calculated population growth rates although negative over the observation period in both species, suggest a significantly higher fitness ofC. bavarica (λ=0.66) compared withC. pyrenaica (λ=0.44). Thus, our data are in line with the competitive exclusion hypothesis andCochlearia bavarica appears as an example of a species with hybridogenous origin possessing higher fitness than its progenitor. However, considering the rarity of both species it seems at present unlikely that the former will displace the latter over a large distributional region.