Triiodothyronine bound to red blood cells is not available for transport through the blood-brain barrier

Many steroid and thyroid hormones and some drugs are bound by circulating red cells. Red cell-bound ligand may not be physiologically inert, as recent studies show that red cell-bound drug is available for uptake by brain. To investigate whether triiodothyronine (T₃) is available for uptake by brain in vivo from the circulating red cell pool, the present investigations measure the effects of human erythrocytes on rat brain uptake of [¹²⁵I]T₃ in vivo. The fraction of circulating T₃ available for uptake in vivo in the presence of 0, 2, 5, 10, 22, or 44% red cells was essentially identical to the fraction of [¹²⁵I]T₃ unbound in vitro. Therefore, [¹²⁵I]T₃ bound to red cells obtained from normal volunteers is not available for uptake by brain in vivo.     

Genetics of resistance to ethidium bromide in the petite-negative yeast Hansenula wingei

Summary A mutant of Hansenula wingei, resistant to ethidium bromide (EB) on glucose medium, was analyzed for both meiotic and mitotic segregation. EB resistance on glucose was found to be recessive and due to mutation of two linked nuclear genes, called etb1 and etb2, which are separated by 18 centimorgans. A linked, pleiotropic, glycerol-negative gene (glp) increases the already high frequency of mitotic segregation of these EB resistant loci from the heterozygous diploid about 7-fold. Genetic analysis of six genes has defined only two linkage groups indicating that H. wingei has a small number of chromosomes. This is in agreement with cytological observations by C. Robinow which show that in H. wingei the haploid chromosome number is four.     

Phylogeny,extinction and conservation: embracing uncertainties in a time of urgency

Evolutionary studies have played a fundamental role in our understanding of life, but until recently, they had only a relatively modest involvement in addressing conservation issues. The main goal of the present discussion meeting issue is to offer a platform to present the available methods allowing the integration of phylogenetic and extinction risk data in conservation planning. Here, we identify the main knowledge gaps in biodiversity science, which include incomplete sampling, reconstruction biases in phylogenetic analyses, partly known species distribution ranges, and the difficulty in producing conservation assessments for all known species, not to mention that much of the effective biological diversity remains to be discovered. Given the impact that human activities have on biodiversity and the urgency with which we need to address these issues, imperfect assumptions need to be sanctioned and surrogates used in the race to salvage as much as possible of our natural and evolutionary heritage. We discuss some aspects of the uncertainties found in biodiversity science, such as the ideal surrogates for biodiversity, the gaps in our knowledge and the numerous available phylogenetic diversity-based methods. We also introduce a series of cases studies that demonstrate how evolutionary biology can effectively contribute to biodiversity conservation science.