Melanophore appearance in wild and red tilapia embryos

Red tilapia has aroused interest in many countries for its commercial potential. This tilapia strain combines a desirable coloration and appearance with other advantageous farming characteristics. To study the early appearance of melanophore pigmentation in tilapia, a red tilapia strain originating from Thailand and a wild type coloration of Oreochromis niloticus were used as broodstock to produce artificially wild x wild and red x red progenies. The larvae were assessed periodically up to the first feeding and were recorded. Wild type fish showed a regular appearance of stellate melanophores. In the red strain, the pattern of chromatophores varies from total absence of black spotting to different degrees of macromelanophore distribution. Comparison between red and wild types showed that these two tilapia can be easily scored at day 7. Further, we present indications that the pigmentation over the body develops independently of the initial degree of pigmentation.     

Identification of the tuberous sclerosis complex-2 tumor suppressor gene product tuberin as a target of the phosphoinositide 3-kinase/akt pathway

The S/T-protein kinases activated by phosphoinositide 3-kinase (PI3K) regulate a myriad of cellular processes. Here, we show that an approach using a combination of biochemistry and bioinformatics can identify substrates of these kinases. This approach identifies the tuberous sclerosis complex-2 gene product, tuberin, as a potential target of Akt/PKB. We demonstrate that, upon activation of PI3K, tuberin is phosphorylated on consensus recognition sites for PI3K-dependent S/T kinases. Moreover, Akt/PKB can phosphorylate tuberin in vitro and in vivo. We also show that S939 and T1462 of tuberin are PI3K-regulated phosphorylation sites and that T1462 is constitutively phosphorylated in PTEN(-/-) tumor-derived cell lines. Finally, we find that a tuberin mutant lacking the major PI3K-dependent phosphorylation sites can block the activation of S6K1, suggesting a means by which the PI3K-Akt pathway regulates S6K1 activity.     

Analysing protein-protein interactions with the yeast two-hybrid system

Plant research is moving into the post-genomic era. Proteomic-based strategies are now being developed to study functional aspects of the genes predicted from the various genome-sequencing initiatives. All biological processes depend on interactions formed between proteins and the mapping of such interactions on a global scale is providing interesting functional insights. One of the techniques that has proved itself invaluable in the mapping of protein-protein interactions is the yeast two-hybrid system. This system is a sensitive molecular genetic approach for studying protein-protein interactions in vivo. In this review we will introduce the yeast two-hybrid system, discuss modifications of the system that may be of interest to the plant science community and suggest potential applications of the technology.     

Perceived contrast following adaptation: the role of adapting stimulus visibility

The issue of whether contrast adaptation can reduce the perceived contrast of gratings oriented orthogonal to the adapting stimulus to a greater extent than parallel gratings has been the subject of considerable debate (Snowden and Hammett, 1992; Ross and Speed, 1996). We compared the reductions in perceived contrast of various test gratings oriented parallel and orthogonal to the adapting stimulus across a range of spatial frequencies (2.25-9 c/deg) and adaptation contrasts (0.19-1.0). Our results show that when the adapting stimulus is low in contrast, parallel adaptation effects are always greater than the effects of orthogonal adaptation. When the adapting contrast is increased, however, the difference between parallel and orthogonal effects is reduced. Further increases in adapting contrast can produce a situation where cross-orientation adaptation effects exceed iso-orientation effects. This was observed at low spatial frequencies (2.25 and 4.5 c/deg) only. The difference in the pattern of results obtained at low and high spatial frequencies can be explained in terms of the adapting stimulus visibility. We conclude that cross-orientation adaptation effects can be greater than iso-orientation effects, but only when the adapting stimulus is highly suprathreshold.     

The yersiniae--a model genus to study the rapid evolution of bacterial pathogens

Yersinia pestis, the causative agent of plague, seems to have evolved from a gastrointestinal pathogen, Yersinia pseudotuberculosis, in just 1,500-20,000 years--an 'eye blink' in evolutionary time. The third pathogenic Yersinia, Yersinia enterocolitica, also causes gastroenteritis but is distantly related to Y. pestis and Y. pseudotuberculosis. Why do the two closely related species cause remarkably different diseases, whereas the distantly related enteropathogens cause similar symptoms? The recent availability of whole-genome sequences and information on the biology of the pathogenic yersiniae have shed light on this paradox, and revealed ways in which new, highly virulent pathogens can evolve.