On the sex chromosome trivalent in some Lepidoptera females

In four of the moth species investigated, viz. Witlesia murana, Scoparia arundinata (Pyraloidea), Bactra furfurana and B. lacteana (Tortricoidea) the metaphase plates of the first meiotic division of their oocytes show a trivalent in addition to the normal bivalents. It evidently has its rise in a transverse break in one of the conjugated chromosomes. Two sex chromatin bodies can be seen in the female somatic cells of three of these species, whereas other species with a normal XY bivalent have only one. These two sex chromatin bodies are unequal in size, and their sizes bear approximately the same relation to each other as do those of the two smaller chromosomes of the trivalent. The broken chromosome is evidently the Y chromosome. The sex chromosome designation for the four above-mentioned species is thus XY₁Y₂ for the females and XX for the males. The sex chromosomes of the four species are among the biggest of the respective complements. This supports the view that the big chromosome to be found in several Lepidoptera species is the sex chromosome. It seems that in animals with holokinetic chromosomes an excessive fragmentation is hindered, at least in the case of the sex chromosomes, by its deleterious effect on the balance of sex-determining genes.Dedicated to Doctor Sally Hughes-Schrader on the occasion of her seventy-fifth birthday.     

Lysis of Trypanosoma brucei by a toxic subspecies of human high density lipoprotein

Trypanosoma brucei brucei is an important pathogen of domestic cattle in sub-Saharan Africa and is closely related to the human sleeping sickness parasites, Trypanosoma brucei gambiense and Trypanosoma brucei rhodesiense. However, T. b. brucei is non-infectious to humans. The restriction of the host range of T. b. brucei results from the sensitivity of the parasite to lysis by toxic human high density lipoproteins (HDL) (Rifkin, M. R. (1978) Proc. Natl. Acad. Sci. U.S.A. 75, 3450-3454). We show in this report that trypanosome lytic activity is not a universal feature of all human HDL particles but rather that it is associated with a minor subclass of HDL. We have purified the lytic activity about 8,000-fold and have identified and characterized the subspecies of HDL responsible for trypanosome lysis. This class of HDL has a relative molecular weight of 490,000, a buoyant density of 1.21-1.24 g/ml, and a particle diameter of 150-210 A. It contains apolipoproteins AI, AII, CI, CII, and CIII, and monoclonal antibodies against apo-AI and apo-AII inhibit trypanocidal activity. In addition to these common apolipoproteins, the particles also contain at least three unique proteins, as measured by sodium dodecyl sulfate-polyacrylamide gel electrophoresis under nonreducing conditions. Treatment of the particles with dithiothreitol resulted in the disappearance of two of the proteins and abolished trypanocidal activity. Two-dimensional gel electrophoresis showed that these proteins were a disulfide-linked trimer of 45,000, 36,000, and 13,500-Da polypeptides and dimers of the 36,000- and 13,500-Da polypeptides or of 65,000- and 8,500-Da polypeptides. Studies on the lysis of T. b. brucei by the purified particle suggest that the lytic pathway may involve the uptake of the trypanocidal subspecies of HDL by endocytosis.     

Using genetic variation to disentangle the complex relationship between food intake and health outcomes

Diet is considered as one of the most important modifiable factors influencing human health, but efforts to identify foods or dietary patterns associated with health outcomes often suffer from biases, confounding, and reverse causation. Applying Mendelian randomization in this context may provide evidence to strengthen causality in nutrition research. To this end, we first identified 283 genetic markers associated with dietary intake in 445,779 UK Biobank participants. We then converted these associations into direct genetic effects on food exposures by adjusting them for effects mediated via other traits. The SNPs which did not show evidence of mediation were then used for MR, assessing the association between genetically predicted food choices and other risk factors, health outcomes. We show that using all associated SNPs without omitting those which show evidence of mediation, leads to biases in downstream analyses (genetic correlations, causal inference), similar to those present in observational studies. However, MR analyses using SNPs which have only a direct effect on the exposure on food exposures provided unequivocal evidence of causal associations between specific eating patterns and obesity, blood lipid status, and several other risk factors and health outcomes.     

Disruption of gastrulation and heparan sulfate biosynthesis in EXT1-deficient mice

Mutations in the EXT1 gene are responsible for human hereditary multiple exostosis type 1. The Drosophila EXT1 homologue, tout-velu, regulates Hedgehog diffusion and signaling, which play an important role in tissue patterning during both invertebrate and vertebrate development. The EXT1 protein is also required for the biosynthesis of heparan sulfate glycosaminoglycans that bind Hedgehog. In this study, we generated EXT1-deficient mice by gene targeting. EXT1 homozygous mutants fail to gastrulate and generally lack organized mesoderm and extraembryonic tissues, resulting in smaller embryos compared to normal littermates. RT-PCR analysis of markers for visceral endoderm and mesoderm development indicates the delayed and abnormal development of both of these tissues. Immunohistochemical staining revealed a visceral endoderm pattern of Indian hedgehog (Ihh) in wild-type E6.5 embryos. However, in both EXT1-deficient embryos and wild-type embryos treated with heparitinase I, Ihh failed to associate with the cells. The effect of the EXT1 deletion on heparan sulfate formation was tested by HPLC and cellular glycosyltransferase activity assays. Heparan sulfate synthesis was abolished in EXT1 -/- ES cells and decreased to less than 50% in +/- cell lines. These results indicate that EXT1 is essential for both gastrulation and heparan sulfate biosynthesis in early embryonic development.     

Cell surface, heparin-like molecules are required for binding of basic fibroblast growth factor to its high affinity receptor.

The role of low affinity, heparin-like binding sites for basic fibroblast growth factor (bFGF) was investigated in CHO cells mutant in their metabolism of glycosaminoglycans. Heparan sulfate-deficient mutants transfected to express a cloned mouse FGF receptor cDNA are not able to bind bFGF. It is demonstrated that free heparin and heparan sulfate can reconstitute a low affinity receptor that is, in turn, required for the high affinity binding of bFGF. These studies suggest that the low affinity receptor is an accessory molecule required for binding of bFGF to the high affinity site. Such an obligatory interaction of low and high affinity FGF receptors suggests a physiological role for heparin-like, low affinity receptors and constitutes a novel mechanism for the regulation of growth factor-receptor interactions.     

Mitochondrial Dysfunction Plus High-Sugar Diet Provokes a Metabolic Crisis That Inhibits Growth

The Drosophila mutant tko^25t exhibits a deficiency of mitochondrial protein synthesis, leading to a global insufficiency of respiration and oxidative phosphorylation. This entrains an organismal phenotype of developmental delay and sensitivity to seizures induced by mechanical stress. We found that the mutant phenotype is exacerbated in a dose-dependent fashion by high dietary sugar levels. tko^25t larvae were found to exhibit severe metabolic abnormalities that were further accentuated by high-sugar diet. These include elevated pyruvate and lactate, decreased ATP and NADPH. Dietary pyruvate or lactate supplementation phenocopied the effects of high sugar. Based on tissue-specific rescue, the crucial tissue in which this metabolic crisis initiates is the gut. It is accompanied by down-regulation of the apparatus of cytosolic protein synthesis and secretion at both the RNA and post-translational levels, including a novel regulation of S6 kinase at the protein level.