Effects of thyroxine and 3,5,3'-triiodothyronine in brown adipose tissue of rats

Rats of both sexes were either cold acclimated (6 +/- 1 degree C) or treated with thyroxine (T4) or 3,5,3'-triiodothyronine (T3) (500 micrograms/kg body wt daily s.c. for 3 weeks). Wet weight, total proteins, lipids and nucleic acids in the interscapular brown adipose tissue (IBAT) were measured. Values obtained with T4 treatment were similar to those obtained with T3 treatment. T3 is the main thyroidal hormone in the rat and it is formed from T4 deiodination in liver and kidney. As T4-treated rats have not received T3 directly and its IBAT has a similar composition to that of T3-treated rats, it is concluded that peripheral T4 deiodination is governed by the plasma T4 levels. Total proteins and DNA content were similar in cold-acclimated and T3- or T4-treated rats, which is interpreted as thyroidal hormones having an action at these levels.     

Brown adipose tissue thermogenesis above the lower critical temperature

Heat-acclimated rats show lighter IBAT deposit with different gross composition and lower GDP-binding than controls at thermoneutrality. A thermal disactivation of the tissue is then inferred. Cafeteria regime increased IBAT mass and GDP-binding when offered to rats at a thermoneutral ambient temperature. These results indicate that BAT thermogenesis at thermoneutrality is not the lowest one of the tissue and that diet-induced thermogenesis can take place even at thermoneutrality.     

The rabbit alpha-like globin gene cluster is polymorphic both in the sizes of BamHI fragments and in the numbers of duplicated sets of genes

The alpha-like globin gene cluster in rabbits contains embryonic zeta- globin genes, an adult alpha-globin gene, and theta-globin genes of undetermined function. The basic arrangement of genes, deduced from analysis of cloned DNA fragments, is 5'-zeta 0-zeta 1-alpha 1-theta 1- zeta 2-zeta 3-theta 2-3'. However, the pattern of restriction fragments containing zeta- and theta-globin genes varies among individual rabbits. Analysis of BamHI fragments of genomic DNA from 24 New Zealand white rabbits revealed eight different patterns of fragments containing zeta-globin genes. The large BamHI fragments containing genes zeta 0 and zeta 1 are polymorphic in length, whereas a 1.9-kb fragment containing the zeta 2 gene and the 3.5-kb fragment containing the zeta 3 gene do not vary in size. In contrast to this constancy in the size of the restriction fragments, the copy number of the zeta 2 and zeta 3 genes does vary among different rabbits. No length polymorphism was detected in the BamHI fragments containing the theta-globin genes, but again the copy number varies for restriction fragments containing the theta 2 gene. The alpha 1- and theta 1-globin genes are located in a nonpolymorphic 7.2-kb BamHI fragment. The combined data from hybridization with both zeta and theta probes shows that the BamHI cleavage pattern does not vary within the region 5'-alpha 1-theta 1- zeta 2-zeta 3-theta 2-3', but the pattern genomic blot-hybridization patterns for the progeny of parental rabbits with different zeta-globin gene patterns shows that the polymorphic patterns are inherited in a Mendelian fashion. Two different haplotypes have been mapped based on the genomic blot-hybridization data. The variation in the alpha-like globin gene cluster in the rabbit population results both from differences in the copy number of the duplication block containing the zeta-zeta-theta gene set and from the presence or absence of polymorphic BamHI sites.      

Assignment of orthologous relationships among mammalian alpha-globin genes by examining flanking regions reveals a rapid rate of evolution

In order to study the relationships among mammalian alpha-globin genes, we have determined the sequence of the 3' flanking region of the human alpha 1 globin gene and have made pairwise comparisons between sequenced alpha-globin genes. The flanking regions were examined in detail because sequence matches in these regions could be interpreted with the least complication from the gene duplications and conversions that have occurred frequently in mammalian alpha-like globin gene clusters. We found good matches between the flanking regions of human alpha 1 and rabbit alpha 1, human psi alpha 1 and goat I alpha, human alpha 2 and goat II alpha, and horse alpha 1 and goat II alpha. These matches were used to align the alpha-globin genes in gene clusters from different mammals. This alignment shows that genes at equivalent positions in the gene clusters of different mammals can be functional or nonfunctional, depending on whether they corrected against a functional alpha-globin gene in recent evolutionary history. The number of alpha-globin genes (including pseudogenes) appears to differ among species, although highly divergent pseudogenes may not have been detected in all species examined. Although matching sequences could be found in interspecies comparisons of the flanking regions of alpha- globin genes, these matches are not as extensive as those found in the flanking regions of mammalian beta-like globin genes. This observation suggests that the noncoding sequences in the mammalian alpha-globin gene clusters are evolving at a faster rate than those in the beta-like globin gene clusters. The proposed faster rate of evolution fits with the poor conservation of the genetic linkage map around alpha-globin gene clusters when compared to that of the beta-like globin gene clusters. Analysis of the 3' flanking regions of alpha-globin genes has revealed a conserved sequence approximately 100-150 bp 3' to the polyadenylation site; this sequence may be involved in the expression or regulation of alpha-globin genes.      

Is It Possible to Improve Memory Function by Upregulation of the Cholesterol 24S-Hydroxylase (CYP46A1) in the Brain?

We previously described a heterozygous mouse model overexpressing human HA-tagged 24S-hydroxylase (CYP46A1) utilizing a ubiquitous expression vector. In this study, we generated homozygotes of these mice with circulating levels of 24OH 30–60% higher than the heterozygotes. Female homozygous CYP46A1 transgenic mice, aged 15 months, showed an improvement in spatial memory in the Morris water maze test as compared to the wild type mice. The levels of N-Methyl-D-Aspartate receptor 1, phosphorylated-N-Methyl-D-Aspartate receptor 2A, postsynaptic density 95, synapsin-1 and synapthophysin were significantly increased in the hippocampus of the CYP46A1 transgenic mice as compared to the controls. The levels of lanosterol in the brain of the CYP46A1 transgenic mice were significantly increased, consistent with a higher synthesis of cholesterol. Our results are discussed in relation to the hypothesis that the flux in the mevalonate pathway in the brain is of importance in cognitive functions.     

2-Aminobenzoxazole-appended coumarins as potent and selective inhibitors of tumour-associated carbonic anhydrases

We have carried out the design, synthesis, and evaluation of a small library of 2-aminobenzoxazole-appended coumarins as novel inhibitors of tumour-related CAs IX and XII. Substituents on C-3 and/or C-4 positions of the coumarin scaffold, and on the benzoxazole moiety, together with the length of the linker connecting both units were modified to obtain useful structure-activity relationships. CA inhibition studies revealed a good selectivity towards tumour-associated CAs IX and XII (K_i within the mid-nanomolar range in most of the cases) in comparison with CAs I, II, IV, and VII (K_i > 10 µM); CA IX was found to be slightly more sensitive towards structural changes. Docking calculations suggested that the coumarin scaffold might act as a prodrug, binding to the CAs in its hydrolysed form, which is in turn obtained due to the esterase activity of CAs. An increase of the tether length and of the substituents steric hindrance was found to be detrimental to in vitro antiproliferative activities. Incorporation of a chlorine atom on C-3 of the coumarin moiety achieved the strongest antiproliferative agent, with activities within the low micromolar range for the panel of tumour cell lines tested.     

Polymorphism in allergens

Allergens are antigens that elicit an IgE-mediated immune response; they originate from diverse sources such as pollens, mites, molds, mammal exudates, insects and food. Allergenic molecules can contain several antigenic determinants, termed epitopes. Allergenic proteins have been discovered with polymorphisms, i.e., a mixture of similar molecules with minor variations in their amino acid sequences. These are called isoallergens or allergenic variants depending on the degree of similarity. Polymorphism may be defined by the presence of several alleles of the same gene or as families of related genes. Polymorphisms can have an important effect on the epitopes recognized by T lymphocytes, monoclonal antibodies and IgE of allergic patients. Individual polymorphisms can affect the basal level of allergenicity as well as the cross-reactivity with other allergens. The use of isoforms with low or total absence of IgE binding capacity but with high capacity to stimulate T cell response has been suggested as an alternative to the conventional immunotherapy for allergic diseases. Standardization of allergenic compounds can be affected by the differing proportions of isoforms in allergenic sources from different regions.