The hidden duplication past of Arabidopsis thaliana

Analysis of the genome sequence of Arabidopsis thaliana shows that this genome, like that of many other eukaryotic organisms, has undergone large-scale gene duplications or even duplications of the entire genome. However, the high frequency of gene loss after duplication events reduces colinearity and therefore the chance of finding duplicated regions that, at the extreme, no longer share homologous genes. In this study we show that heavily degenerated block duplications that can no longer be recognized by directly comparing two segments because of differential gene loss, can still be detected through indirect comparison with other segments. When these so-called hidden duplications in Arabidopsis are taken into account, many homologous genomic regions can be found in five to eight copies. This finding strongly implies that Arabidopsis has undergone three, but probably no more, rounds of genome duplications. Therefore, adding such hidden blocks to the duplication landscape of Arabidopsis sheds light on the number of polyploidy events that this model plant genome has undergone in its evolutionary past.     

The volumetric measurement of gastric emptying and gastric secretion by a radioisotope method

Most methods of measurement of gastric emptying rely on the serial estimation of intragastric volume and do not separately account for the volume of fluid which has been added to the meal by gastric secretion, duodenal reflux, or swallowed saliva. The volume emptied is therefore underestimated. A method of measuring gastric emptying using [¹²⁵I]RIHSA and the Volémetron is presented. The volume of fluid added to the meal is taken into consideration in this method, giving a more accurate reflection of gastric emptying. Using this method in the dog, emptying was found to be linear rather than exponential.Supported by South African Medical Research Council grant M14/71/51.     

Mass spectrometry study of a transferrin-based protein drug reveals the key role of protein aggregation for successful oral delivery

A recently designed human growth hormone/transferrin fusion protein (GHT) remains one of the very few examples of a protein capable of eliciting measurable therapeutic response after oral administration. To better understand the underlying factors that resulted in this rare success of nonparenteral protein drug delivery, we analyzed proteolytic stability and receptor binding properties of this protein, the key factors in overcoming the primary barriers to successful oral delivery. Analysis of GHT by a combination of size exclusion chromatography and mass spectrometry revealed that a significant protein population exists in an oligomeric (GHTx) state in addition to the anticipated monomer (GHT1). These states of GHT were evaluated for their survivability in stomach-like conditions, as well as their ability to bind transferrin receptor (TfR). Our results reveal an exceptional stability of GHTx, as well as the preserved ability to bind TfR, a critical first step in crossing the epithelial-intestinal barrier through receptor-mediated transcytosis.