A full Bayesian hierarchical mixture model for the variance of gene differential expression

Background  

In many laboratory-based high throughput microarray experiments, there are very few replicates of gene expression levels. Thus, estimates of gene variances are inaccurate. Visual inspection of graphical summaries of these data usually reveals that heteroscedasticity is present, and the standard approach to address this is to take a log₂ transformation. In such circumstances, it is then common to assume that gene variability is constant when an analysis of these data is undertaken. However, this is perhaps too stringent an assumption. More careful inspection reveals that the simple log₂ transformation does not remove the problem of heteroscedasticity. An alternative strategy is to assume independent gene-specific variances; although again this is problematic as variance estimates based on few replications are highly unstable. More meaningful and reliable comparisons of gene expression might be achieved, for different conditions or different tissue samples, where the test statistics are based on accurate estimates of gene variability; a crucial step in the identification of differentially expressed genes.     

Degradation of cuticle during larval-pupal and pupal-adult development of the housefly, Musca domestica

Abstract. The patterns of changes in cuticle weight, its chitin content and chitinase activity have been studied during postembryonic development of the housefly, Musca domestica L. During pupariation the larval cuticle loses weight. During the early part of this weight-loss the decline in chitin content parallels the overall change in cuticle weight. A simultaneous elevation in chitinase activity suggests that at this time the larval cuticle is being enzymatically degraded. Later weight loss may be due to sclerotization. No significant changes in cuticle weight or its chitin content occur in pharate cuticle until one day before eclosion. However, a peak of chitinase activity found at mid-late pupal stage suggests the timing of pupal cuticle breakdown.     

Age-related thermodynamic and mechanical properties of the rat collagen

The age peculiarities of cross-linking degree, thermodynamic and mechanic properties of rat tail tendon collagen fibres were investigated. It is shown that during the period from 1 to 3 months the melting temperature decreases and the enthalpy difference increases, from 3 to 24 months the melting temperature increases and the enthalpy difference decreases. The strength of fibres increases during the whole life. The maximal relative extension increases during the first 12 months and tends to decrease in after-life. The Young's module in the elastic deformation region decreases during the period from 1 to 3 months, then increases. It is shown tht those changes in fibre properties may be connected with the age dynamics of collagen cross-linking degree observed here: its decreasing during the period from 1 to 3 months and its following continuous increasing in after-life.