Analysis of trophic structure of two carnivore assemblages by means of guild identification

We evaluated the existence of trophic guild structure, considering seasonal and annual variation, in two terrestrial carnivore assemblages: one from Santa Cruz province (Argentinean Patagonia, composed by six carnivore species), and the other from Doñana National Park (SW Spain, composed by five carnivore species). To identify trophic guilds, we first studied seasonal and annual diets of predators, calculated trophic overlap among species pairs, and then constructed overlap matrices (similarity matrices). We determined guild membership objectively by entering the similarity matrices into the clustering technique unweighted pair-group method with arithmetic averaging. Carnivores from both assemblages were grouped, respectively, into four feeding guilds. Lagomorphs and rodents promoted the formation of two feeding guilds in both study sites, although the taxonomic composition of predator species that composed them was different. The ungulates-edentates feeding guild was only present at Santa Cruz, whereas the birds and reptiles feeding guild was only present at Doñana. Invertebrates and fruits were the base for the formation of a guild composed by species of the same taxonomic origin both in Santa Cruz and Doñana. Guild structure of Santa Cruz and Doñana assemblages did not exhibit seasonal or annual variation, although the specific guild composition changed over the two studied periods for both assemblages. This structure probably responded to discontinuities in resource spectra in Santa Cruz and fluctuations in rabbit abundance in Doñana. Our results support the hypothesis that establishes that guilds are originated by opportunistic convergence of species on abundant and energetically rewarding resources.     

Purification of CMP-N-acetylneuraminic acid synthetase from bovine anterior pituitary glands

CMP-beta-N-acetylneuraminic acid (CMP-neuNAc) is the substrate for the sialylation of glycoconjugates by sialyltransferases in microbes and higher eukaryotes. CMP-neuNAc synthetase catalyzes the formation of this substrate, CMP-neuNAc, from CTP and neuNAc. In this report we describe the purification of CMP-neuNAc synthetase from bovine anterior pituitary glands. The enzyme was purified by ion exchange, gel filtration, and affinity chromatography. The protein was homogeneous on SDS-PAGE with a molecular weight of 52 kDa, a subunit size similar to that of the E.coli K1 (48.6 kDa). The identity of the 52 kDa protein band was confirmed by native gel electrophoresis in that the position of the enzyme activity in gel slices coincided with the position of major bands in the stained gel. Photoaffinity labeling with 125I-ASA-CDP ethanolamine resulted in the modification of a 52 kDa polypeptide that was partially protected against modification by the substrate CTP. Enzyme activity in crude fractions could be adsorbed onto an immunoadsorbent prepared from antibody against the purified 52 kDa protein. Taken together these data suggest that the 52 kDa polypeptide purified by this procedure described in this report is indeed CMP-neuNAc synthetase. The active enzyme chromatographed on a gel filtration column at 158 kDa suggesting it exists in its native form as an oligomer.     

Ovarian 3-hydroxy-3-methylglutaryl-CoA reductase in Blattella germanica (L.): pattern of expression and critical role in embryogenesis

In the ovary of adult Blattella germanica, the enzyme 3-hydroxy-3-methylglutaryl-CoA reductase (HMG-CoA reductase) is highly expressed in mid-late vitellogenesis, suggesting a functional link of the mevalonate pathway with choriogenesis. The inhibitor of HMG-CoA reductase, fluvastatin, applied in females in late vitellogenesis, inhibits the activity of the enzyme in the ovary and in the developing embryos within the ootheca. This does not affect choriogenesis or ootheca formation but reduces the number of larvae per ootheca. Our results suggest that fluvastatin is incorporated into the oocytes and has delayed inhibitory effects on the oviposited eggs. HMG-CoA reductase is essential for embryogenesis, but not for chorion formation.     

Non-cell autonomous requirement for the bloodless gene in primitive hematopoiesis of zebrafish

Vertebrate hematopoiesis occurs in two distinct phases, primitive (embryonic) and definitive (adult). Genes that are required specifically for the definitive program, or for both phases of hematopoiesis, have been described. However, a specific regulator of primitive hematopoiesis has yet to be reported. The zebrafish bloodless (bls) mutation causes absence of embryonic erythrocytes in a dominant but incompletely penetrant manner. Primitive macrophages appear to develop normally in bls mutants. Although the thymic epithelium forms normally in bls mutants, lymphoid precursors are absent. Nonetheless, the bloodless mutants can progress through embryogenesis, where red cells begin to accumulate after 5 days post-fertilization (dpf). Lymphocytes also begin to populate the thymic organs by 7.5 dpf. Expression analysis of hematopoietic genes suggests that formation of primitive hematopoietic precursors is deficient in bls mutants and those few blood precursors that are specified fail to differentiate and undergo apoptosis. Overexpression of scl, but not bmp4 or gata1, can lead to partial rescue of embryonic blood cells in bls. Cell transplantation experiments show that cells derived from bls mutant donors can differentiate into blood cells in a wild-type host, but wild-type donor cells fail to form blood in the mutant host. These observations demonstrate that the bls gene product is uniquely required in a non-cell autonomous manner for primitive hematopoiesis, potentially acting via regulation of scl.     

The D' measure of overall gametic disequilibrium between pairs of multiallelic loci

Abstract The D ' coefficient is one of the most commonly used measures of the extent of gametic disequilibrium between multiallelic loci. It has been suggested that the range of the D ' measure of overall disequilibrium between pairs of multiallelic loci depends on allele frequencies, except under some very restricted conditions. Nevertheless, the problem of dependence of the range of D ' has not been characterized under a wide set of possible polymorphisms. Evaluation of the utility of D ' as a measure of the strength of overall disequilibrium between all possible pairs of alleles at two multiallelic loci requires better knowledge of its range than is currently available. In this work, the conditions of polymorphism under which the range of D ' is frequency independent are given. It is found that the range of D ' is more often independent of allelic frequencies than is commonly thought. Furthermore, the range of D ' undergoes only small fluctuations as a function of the polymorphisms at the loci. Numerical cases and microsatellite data from humans are used for illustration. These observations indicate that the D ' coefficient is a useful tool for the estimation and comparison of the extent of overall disequilibrium across pairs of multiallelic loci.     

Zinc uptake by human placental microvillous membrane vesicles

Zinc uptake by syncytiotrophoblast microvillous membrane vesicles (SMMV) from human placentas was characterized and the effects of maternal serum zinc levels at term and of gestational age on kinetic parameters were evaluated. Zinc uptake at pH 7.2 was rapid for the first 2 min, followed by a slower increase, approaching equilibrium after 30 min. Uptake was saturable at a zinc concentration of 30 micromol/L, higher than the upper range of the physiological serum zinc level. Kinetic analysis of uptake at 1 min in SMMV from term placenta showed similar Km values (mean: 6.9+/-0.6 micromol/L) for different levels of maternal serum zinc. However, Vmax was higher (p < 0.05) in SMMV from mothers with serum zinc lower than 7.6 micromol/L compared to those with higher serum zinc levels (35.8+/-1.6 and 26.6+/-1.6 nmol 65Zn/mg protein/min, respectively). Km values were similar in term (>37 wk of gestation) and preterm (20-25 wk of gestation) placentas, whereas Vmax was higher (p < 0.05) in the preterm (34.3+/-1.6 nmol Zn/mg protein/min) compared to term placentas from mothers with serum zinc levels above 7.6 micromol/L. These results suggest that whereas afffinity for zinc was not altered with gestational age or maternal serum zinc levels, zinc-uptake capacity in human placenta is influenced both by gestational age and by low levels of maternal serum zinc in order to ensure an adequate maternal-fetal zinc transfer.     

p53-inducible human homologue of Drosophila seven in absentia (Siah) inhibits cell growth: suppression by BAG-1.

The Drosophila seven in absentia (sina) gene is required for R7 photoreceptor cell formation during Drosophila eye development, where it functions within the Ras/Raf pathway and targets other proteins for degradation via associations with a ubiquitin-conjugating enzyme. Recently, a mammalian sina homologue was reported to be a p53-inducible gene in a myeloid leukemia cell line. To explore the function of human SINA-homologous (Siah) proteins, expression plasmids encoding Siah-1A were transiently transfected into 293 epithelial cells and GM701 fibroblast cells, resulting in growth arrest without induction of apoptosis. We discovered that BAG-1, a ubiquitin-like Hsp70/Hsc70-regulating protein, is a negative regulator of Siah-1A. Siah-1A was identified as a BAG-1-binding protein via yeast two-hybrid methods. Specific interaction of BAG-1 with Siah-1A was also demonstrated by in vitro binding experiments using glutathione S-transferase fusion proteins and co-immunoprecipitation studies. Siah-1A-induced growth arrest in 293 and GM701 cells was abolished by co-transfection of wild-type BAG-1 with Siah-1A but not by a C-terminal deletion mutant of BAG-1 that fails to bind Siah-1A. Over-expression of BAG-1 significantly inhibited p53-induced growth arrest in 293 cells without preventing p53 transactivation of reporter gene plasmids. BAG-1 also prevented growth arrest following UV-irradiation-induced genotoxic injury without interfering with accumulation of p53 protein or p21(waf-1) expression. BAG-1 functions downstream of p53-induced gene expression to inhibit p53-mediated suppression of cell growth, presumably by suppressing the actions of Siah-1A. We suggest that Siah-1A may be an important mediator of p53-dependent cell-cycle arrest and demonstrate that Siah-1A is directly inhibited by BAG-1.