Physicochemical characterization of progressive changes in the Xenopus laevis egg envelope following oviductal transport and fertilization

Previous studies have shown that the Xenopus laevis egg envelope exists in three forms with differing ultrastructural, macromolecular, and sperm penetrability properties. The coelomic envelope (CE) is derived from eggs released from the ovary into the body cavity of the female, the vitelline envelope (VE) from eggs which have passed through the oviduct, and the fertilization envelope (FE) from fertilized eggs. In the present study, the physicochemical characteristics of these three envelope types were differentiated. Investigation of envelope solubility, deformability, sulfhydryl reactivity, and hydrophobic dye and ferritin binding capacity demonstrated that profound physicochemical changes occur in envelope conversions CE----VE----FE. The physical strength of the envelopes, as evidenced by deformability studies, ranked FE greater than CE greater than VE. These differences were not accountable by differences in the number of disulfide bonds, although the CE sulfhydryl groups were significantly less accessible than those in the VE or FE. All three envelope forms were hydrophilic in nature, exhibiting little ability to bind 1-anilino-8-naphthalenesulfonic acid. The CE bound greater amounts of ferritin in comparison to the VE and FE, indicating the presence of a basic domain, presumably in the 43-kDa glycoprotein, which is lost upon proteolysis to 41 kDa during the CE----VE conversion. The envelope integrity of all three forms was maintained by both noncovalent and covalent (disulfide) bonds. Measurements of the effect of pH on envelope solubilization indicated the involvement of an ionizable group with pKa of 8.0 in maintaining envelope structure.     

The geometry of taking flight: Limb morphometrics in Mesozoic theropods

Theropoda was one of the most successful dinosaurian clades during the Mesozoic and has remained a dominant component of faunas throughout the Cenozoic, with nearly 10,000 extant representatives. The discovery of Archaeopteryx provides evidence that avian theropods evolved at least 155 million years ago and that more than half of the tenure of avian theropods on Earth was during the Mesozoic. Considering the major changes in niche occupation for theropods resulting from the evolution of arboreal and flight capabilities, we have analyzed forelimb and hindlimb proportions among nonmaniraptoriform theropods, nonavian maniraptoriforms, and basal avialans using reduced major axis regressions, principal components analysis, canonical variates analysis, and discriminant function analysis. Our study is the first analysis on theropod limb proportions to apply phylogenetic independent contrasts and size corrections to the data to ensure that all the data are statistically independent and amenable to statistical analyses. The three ordination analyses we performed did not show any significant groupings or deviations between nonavian theropods and Mesozoic avian forms when including all limb elements. However, the bivariate regression analyses did show some significant trends between individual elements that suggested evolutionary trends of increased forelimb length relative to hindlimb length from nonmaniraptoriform theropods to nonavian maniraptoriforms to basal avialans. The increase in disparity and divergence away from the nonavian theropod body plan is well documented within Cenozoic forms. The lack of significant groupings among Mesozoic forms when examining the entire theropod body plan concurrently suggests that nonavian theropods and avian theropods did not substantially diverge in limb proportions until the Cenozoic. J. Morphol. 276:152–166, 2015. © 2014 Wiley Periodicals, Inc.     

A major effect quantitative trait locus for whirling disease resistance identified in rainbow trout (Oncorhynchus mykiss)

Whirling disease, caused by the pathogen Myxobolus cerebralis, leads to skeletal deformation, neurological impairment and under certain conditions, mortality of juvenile salmonid fishes. The disease has impacted the propagation and survival of many salmonid species over six continents, with particularly negative consequences for rainbow trout. To assess the genetic basis of whirling disease resistance in rainbow trout, genome-wide mapping was initiated using a large outbred F(2) rainbow trout family (n=480) and results were confirmed in three additional outbred F(2) families (n=96 per family). A single quantitative trait locus (QTL) region on chromosome Omy9 was identified in the large mapping family and confirmed in all additional families. This region explains 50-86% of the phenotypic variance across families. Therefore, these data establish that a single QTL region is capable of explaining a large percentage of the phenotypic variance contributing to whirling disease resistance. This is the first genetic region discovered that contributes directly to the whirling disease phenotype and the finding moves the field closer to a mechanistic understanding of resistance to this important disease of salmonid fish.     

Assessing population structure: F(ST) and related measures

Although F(ST) is widely used as a measure of population structure, it has been criticized recently because of its dependency on within-population diversity. This dependency can lead to difficulties in interpretation and in the comparison of estimates among species or among loci and has led to the development of two replacement statistics, F'(ST) and D. F'(ST) is the normal F(ST) standardized by the maximum value it can obtain, given the observed within-population diversity. D uses a multiplicative partitioning of diversity, based on the effective number of alleles rather than on the expected heterozygosity. In this study, we review the relationships between the three classes of statistics (F(ST), F'(ST) and D), their estimation and their properties. We illustrate the relationships between the statistics using a data set of estimates from 84 species taken from the last 4 years of Molecular Ecology. As with F(ST), unbiased estimators are available for the two new statistics D and F'(ST). Here, we develop a new unbiased F'(ST) estimator based on G(ST), which we call G'(ST). However, F'(ST) can be calculated using any F(ST) estimator for which the maximum value can be obtained. As all three statistics have their advantages and their drawbacks, we recommend continued use of F(ST) in combination with either F'(ST) or D. In most cases, F'(ST) would be the best choice among the latter two as it is most suited for inferences of the influence of demographic processes such as genetic drift and migration on genetic population structure.     

Synthesis and biodistribution studies of technetium-99m-labeled aminopeptidase N inhibitor conjugates

Probestin is a potent aminopeptidase N (APN) inhibitor. Four probestin conjugates containing a tripeptide chelator (N₃S) and a PEG₂ linker were synthesized and radiolabeled with Tc-99m. The number of –COOH groups on the chelator was altered to increase the excretion of the radiotracer from blood stream via the renal-urinary pathway and to decrease its hepatobiliary uptake. Biodistribution of the radiolabeled conjugates was evaluated in healthy CF-1? mice at 1 h post-injection. The results revealed that the Tc-99m labeled probestin conjugate preferentially (>85% injected dose) excreted via the renal route when an aspartic acid residue was added to the linker (conjugate 4). These results suggest that the pharmacokinetic properties of probestin-based APN-targeted agents could be optimized by adding an appropriate amino acid residue in between the linker and the payload.     

Reversing mother's curse revisited

Because of maternal mtDNA inheritance, mtDNA mutations detrimental only in males are not expected to be selected against, an effect termed the "mother's curse." However, if there is positive-assortative mating, equivalent to what was called "inbreeding" by Wade and Brandvain (2009), then selection can act to reduce the frequency of these male-specific detrimental mtDNA mutants. On the other hand, as shown here negative-assortative mating, or "outbreeding, " paradoxically can result in an increase in the frequency of male-specific detrimental mtDNA mutants. The implications of these findings are briefly discussed.     

New ground for organic catalysis: a ring-opening polymerization approach to hydrogels

Herein, we describe an organocatalytic living polymerization approach to network and subsequent hydrogel formation. Cyclic carbonate-functionalized macromolecules were ring-opened using an alcoholic initiator in the presence of an organic catalyst, amidine 1,8-diazabicyclo[5.4.0]undec-7-ene. A model reaction for the cross-linking identified monomer concentration-dependent reaction regimes, and enhanced kinetic control was demonstrated by introducing a co-monomer, trimethylene carbonate. The addition of the co-monomer facilitated near-quantitative conversion of monomer to polymer (>96%). Resulting poly(ethylene glycol) networks swell significantly in water, and an open co-continuous (water-gel) porous structure was observed by scanning electron microscopy. The organocatalytic ring-opening polymerization of cyclic carbonate functional macromonomers using alcoholic initiators provides a simple, efficient, and versatile approach to hydrogel networks.     

Organocatalytic ring opening polymerization of trimethylene carbonate

A variety of organocatalysts has been surveyed in the ring opening polymerization of trimethylene carbonate. Excellent control was found for several of these catalysts yielding well-defined polycarbonates with molecular weights up to 50,000 g mol(-1), polydispersities below 1.08, and high end-group fidelity. Melt or bulk polymerization was accomplished without loss of control of molecular weight or polydispersity, and random ester-carbonate bulk polymerizations were also demonstrated. Furthermore, by combining disparate polymerization techniques using bifunctional initiators, the mild polymerization conditions allow for the preparation of new block copolymers. Hydrogen-bond activation of monomer and initiator/propagating species is proposed as the underlying mechanism, which can be tuned to mitigate adverse side reactions.