Clusters of alpha satellite on human chromosome 21 are dispersed far onto the short arm and lack ancient layers.

Human alpha satellite (AS) sequence domains that currently function as centromeres are typically flanked by layers of evolutionarily older AS that presumably represent the remnants of earlier primate centromeres. Studies on several human chromosomes reveal that these older AS arrays are arranged in an age gradient, with the oldest arrays farthest from the functional centromere and arrays progressively closer to the centromere being progressively younger. The organization of AS on human chromosome 21 (HC21) has not been well-characterized. We have used newly available HC21 sequence data and an HC21p YAC map to determine the size, organization, and location of the AS arrays, and compared them to AS arrays found on other chromosomes. We find that the majority of the HC21 AS sequences are present on the p-arm of the chromosome and are organized into at least five distinct isolated clusters which are distributed over a larger distance from the functional centromere than that typically seen for AS on other chromosomes. Using both phylogenetic and L1 element age estimations, we found that all of the HC21 AS clusters outside the functional centromere are of a similar relatively recent evolutionary origin. HC21 contains none of the ancient AS layers associated with early primate evolution which is present on other chromosomes, possibly due to the fact that the p-arm of HC21 and the other acrocentric chromosomes underwent substantial reorganization about 20 million years ago.

Overexpression of melanopsin in the retina restores visual function in Royal College of Surgeons rats.

Retinitis pigmentosa (RP) is a pathological condition leading to progressive visual decline resulting from continual loss of photoreceptor cells and outer nuclear layers of the retina. The aim of the present study was to explore whether melanopsin was able to restore retinal function and inhibit its degeneration by acting in a similar manner to channel rhodopsins. Royal College of Surgeons rats, which were used as an animal model of inherited retinal degeneration, were subjected to sub-retinal injection with melanopsin overexpression vector (AV­OPN4­GFP). Immunohistochemical and western blot analyses were used to detect the distribution and protein expression of melanopsin in the retina, revealing that melanopsin was gradually reduced with increasing age of the rats, which was due to loss of dendritic axons of intrinsically photosensitive retinal ganglion cells. Animals injected into both eyes were subjected to a behavioral open-field test, revealing that melanopsin overexpression reduced the loss of light sensitivity of the rats. In a flash electroretinography experiment, the b­wave and response to light flash stimuli at three and five weeks following injection with AV­OPN4­GFP were higher compared to those in eyes injected with AV­GFP (P<0.05). In conclusion, the present study showed that during retinal degeneration, the expression of melanopsin was significantly decreased, while vector-mediated overexpression of melanopsin delayed the loss of visual function in rats.

Glucagon replacement via micro-osmotic pump corrects hypoglycemia and alpha-cell hyperplasia in prohormone convertase 2 knockout mice.

Prohormone convertase 2 (PC2) plays an essential role in the processing of proglucagon to mature active glucagon in pancreatic alpha-cells (J Biol Chem 276:27197-27202, 2001). Mice lacking PC2 demonstrate multiple defects, including chronic mild hypoglycemia and dramatic hyperplasia of the pancreatic alpha-cells. To define the contribution of mature glucagon deficiency to the hypoglycemia and alpha-cell hyperplasia, we have attempted to correct the defects by delivery of exogenous glucagon by micro-osmotic pumps. Intraperitoneal delivery of 0.5 microg glucagon/h in PC2(-/-) mice resulted in the normalization of blood glucose concentrations. Islet remodeling through the loss of hyperplastic alpha-cells was evident by day 11 after pump implantation; by 25 days postimplantation, PC2(-/-) islets were indistinguishable from wild-type islets. These rapid changes were brought about by induction of apoptosis in the alpha-cell population. Morphological normalization of islets was also accompanied by marked downregulation of endogenous preproglucagon gene expression, but with little or no change in the level of preproinsulin gene expression. Exogenous glucagon delivery also normalized hepatic expression of the gluconeogenic enzyme PEPCK. These results demonstrate that the lack of mature glucagon in PC2(-/-) mice is responsible for the aberrant blood glucose levels, islet morphology, and gene expression, and they confirm the role of glucagon as a tonic insulin antagonist in regulating glycemia.