Abrupt shortening of bird W chromosomes in ancestral Neognathae

As a result of suppressed recombination, heterogametic sex chromosomes (either Y or W) are usually assumed to gradually shorten over evolutionary time as a way to remove accumulated mutations. However, suppressed recombination removes the most obvious mechanism for excising portions of sex chromosomes. We examined ratios of W/Z chromosome size across 224 bird species from 146 genera. Much of the data were obtained from a previous study (Rutkowska et al. 2012. Biology Letters 8 : 636–638), who, similar to ourselves, found no gradual decrease in W chromosome length over evolutionary time. However, we show an abrupt decrease in W chromosome length at or just after the phylogenetic split between the two extant bird superorders, Paleognathae and Neognathae, indicating that the key to understanding sex chromosome evolution may have little to do with gradual suppression of recombination.     

Dynamic regulation of histone H3 lysine (K) acetylation and deacetylation during prolonged oxygen deprivation in a champion anaerobe

Molecular and Cellular Biochemistry - Neurodegenerative diseases, such as Parkinson’s disease, represent a biggest challenge for medicine, imposing high social and economic impacts. As a...     

The regulation of heat shock proteins in response to dehydration in <Emphasis Type="Italic">Xenopus laevis</Emphasis>

African clawed frogs (Xenopus laevis) endure bouts of severe drought in their natural habitats and survive the loss of approximately 30% of total body water due to dehydration. To investigate molecular mechanisms employed by X. laevis during periods of dehydration, the heat shock protein response, a vital component of the cytoprotective stress response, was characterized. Using western immunoblotting and multiplex technology, the protein levels of HSP27, HSP40, HSP60, HSP70, HSC70, and HSP90 were quantified in the liver, skeletal muscle, kidney, lung, and testes from control frogs and those that underwent medium or high dehydration (~16 or ~30% loss of total body water). Dehydration increased HSP27 (1.45–1.65-fold) in the kidneys and lungs, and HSP40 (1.39–2.50-fold) in the liver, testes, and skeletal muscle. HSP60 decreased in response to dehydration (0.43–0.64 of control) in the kidneys and lungs. HSP70 increased in the liver, lungs, and testes (1.39–1.70-fold) during dehydration, but had a dynamic response in the kidneys (levels increased 1.57-fold with medium dehydration, but decreased to 0.56 of control during high dehydration). HSC70 increased in the liver and kidneys (1.20–1.36-fold), but decreased in skeletal muscle (0.27–0.55 of control) during dehydration. Lastly, HSP90 was reduced in the kidney, lung, and skeletal muscle (0.39–0.69 of control) in response to dehydration, but rose in the testes (1.30-fold). Overall, the results suggest a dynamic tissue-specific heat shock protein response to whole body dehydration in X. laevis.