A Non-Synonymous HMGA2 Variant Decreases Height in Shetland Ponies and Other Small Horses

The identification of quantitative trait loci (QTL) such as height and their underlying causative variants is still challenging and often requires large sample sizes. In humans hundreds of loci with small effects control the heritable portion of height variability. In domestic animals, typically only a few loci with comparatively large effects explain a major fraction of the heritability. We investigated height at withers in Shetland ponies and mapped a QTL to ECA 6 by genome-wide association (GWAS) using a small cohort of only 48 animals and the Illumina equine SNP70 BeadChip. Fine-mapping revealed a shared haplotype block of 793 kb in small Shetland ponies. The HMGA2 gene, known to be associated with height in horses and many other species, was located in the associated haplotype. After closing a gap in the equine reference genome we identified a non-synonymous variant in the first exon of HMGA2 in small Shetland ponies. The variant was predicted to affect the functionally important first AT-hook DNA binding domain of the HMGA2 protein (c.83G>A; p.G28E). We assessed the functional impact and found impaired DNA binding of a peptide with the mutant sequence in an electrophoretic mobility shift assay. This suggests that the HMGA2 variant also affects DNA binding in vivo and thus leads to reduced growth and a smaller stature in Shetland ponies. The identified HMGA2 variant also segregates in several other pony breeds but was not found in regular-sized horse breeds. We therefore conclude that we identified a quantitative trait nucleotide for height in horses.     

Activity of Mg2+-ATPase and cytochrome c-Oxidase in microsporocytes and anther wall during microsporogenesis inLarix europaea D.C.

Studies have been made on the activity of two mitochondrial enzymes, Mg²⁺ ATPase (E.C.3.6.1.3.) and cytochrome c-oxidase (E.C.I.9.3.2.) in microsporocytes and somatic cells of anther in larch. The material for study were homogeneous fractions of microsporocytes from 15 stages of meiosis and the attendant anther somatic cells. The results have demonstrated that cells undergoing meiosis exhibit considerable mitochondrial metabolic activity. It is characterized by considerable variations in the activity level of both enzymes studied. The level and dynamics of variations of Mg²⁺-ATPase and cytochrome c-oxidase activity in microsporocytes are clearly different from those in the anther somatic cells. The cytochrome c-oxidase activity in microsporocytes throughout microsporogenesis is higher compared with that in the anther wall cells, whereas the Mg²⁺-ATPase activity in microsporocytes averagesca. one half that in the anther somatic cells The dynamics of activity variations of the enzymes under study suggests enhanced mitochondrial metabolism in the period of middle diplotene and young dyad. This result supports the thesis following from our earlier studies that the middle diplotene and young dyad constitute specific metabolic switches in microsporogenesis in larch.     

The mechanism of extrachromosomal homologous DNA recombination in plant cells

Summary By cotransfecting plasmids carrying particular mutations in the -glucuronidase (GUS) gene into Nicotiana plumbaginifolia protoplasts and by monitoring the recombination rates using a recently developed transient assay, we were able to obtain insights into the mechanism of extrachromosomal recombination operating in plant cells. An exchange of flanking markers takes place in over 90% of the recombination events. In most of the remaining cases two consecutive, independent single crossover events occur. These events involve the same DNA substrate and lead to two successive exchanges of flanking markers, thus mimicking a presumed double crossover intermediate. A comparison of the outcome of our experiments with the predictions of two recombination models originally proposed for mammalian cells indicates that extrachromosomal recombination in plant cells is best described by the single strand annealing model. According to this model all recombination events result in an exchange of flanking markers. Our results rule out the double strand break repair model which predicts that flanking markers are exchanged in only half of all events.     

Homologous recombination in plant cells is enhanced by in vivo induction of double strand breaks into DNA by a site-specific endonuclease.

Induction of double strand breaks (DSBs) is coupled to meiotic and mitotic recombination in yeast. We show that also in a higher eukaryote induction of DSBs is directly correlated with a strong enhancement of recombination frequencies. We cotransfected Nicotiana plumbaginifolia protoplasts with a plasmid carrying a synthetic I-SceI gene, coding for a highly sequence specific endonuclease, together with recombination substrates carrying an I-SceI-site adjacent to their homologous sequences. We measured efficiencies of extrachromosomal recombination, using a well established transient beta-glucuronidase (GUS) assay. GUS enzyme activities were strongly increased when a plasmid carrying the I-SceI gene in sense but not in antisense orientation with respect to the promoter was included in the transfections. The in vivo induced DSBs were detected in the recombination substrates by Southern blotting, demonstrating that the yeast enzyme is functional in plant cells. At high ratios of transfected I-SceI-genes to I-SceI-sites the majority of the I-SceI-sites in the recombination substrates are cleaved, indicating that the induction of the DSBs is the rate limiting step in the described recombination reaction. These results imply that in vivo induction of transient breaks at specific sites in the plant genome could allow foreign DNA to be targeted to these sites via homologous recombination.     

Immunochemical and biological studies of antigens isolated from a strain of Bacteroides fragilis

Phenol/water-extracted lipopolysaccharide and a fraction HM, extracted with acetate buffer pH 2.0, from Bacteroides fragilis strain 62/73 are antigenically different as shown by immunodiffusion, passive haemagglutination, haemagglutination inhibition and preliminary chemical investigations. Biological activity, assessed with the local Shwartzmann reaction, was demonstrated for the lipopolysaccharide whereas antigen HM was almost inactive in this test. HM is immunogenic in rabbits. Antibodies against HM were detected in seven out of ten sera of healthy humans.     

Familial translocation t(1p-;21q+) associated with Down's syndrome

Summary Familial occurrence of 1/21 translocation in connection with trisomy 21 was described. The possibilities of inheritance of further chromosome rearrangements arising during the gametogenesis of persons with this translocation were considered.