Variations in the hypotarsus morphology of birds and their evolutionary significance

Crown group (neornithine birds) exhibit a great variation in the morphology of the hypotarsus, a structure on the proximal end of the tarsometatarsus, which guides the tendons of the flexor muscles of the toes. Hypotarsus morphology is of significance for the identification of fossil taxa, and several extant groups show characteristic patterns that are of phylogenetic interest. So far, however, the diversity of hypotarsus morphologies has been little studied, and there are no comprehensive studies across all neornithine birds. In particular, the identities of the involved canals and sulci remain elusive, and some confusion exists about their correct homologies. In this study, hypotarsus morphologies are for the first time surveyed among all extant birds, and basic patterns are characterized. Instances are identified, in which particular hypotarsus morphologies are correlated with certain locomotion types, inferences are made about possible ancestral morphologies, and some patterns of phylogenetic interest are discussed.     

Abstracts from the 3rd Annual A-CURE Symposium

Background

Patients after aortic coarctation (CoA) repair show impaired aortic bioelasticity and altered left ventricular (LV) mechanics, predisposing diastolic dysfunction. Our purpose was to assess aortic bioelasticity and LV properties in CoA patients who underwent endovascular stenting or surgery using cardiovascular magnetic resonance (CMR) imaging.

Methods

Fifty CoA patients (20.5 ± 9.5 years) were examined by 3-Tesla CMR. Eighteen patients had previous stent implantation and 32 had surgical repair. We performed volumetric analysis of both ventricles (LV, RV) and left atrium (LA) to measure biventricular volumes, ejection fractions, left atrial (LA) volumes, and functional parameters (LAEF_Passive, LAEF_Contractile, LAEF_Reservoir). Aortic distensibility and pulse wave velocity (PWV) were assessed. Native T1 mapping was applied to examine LV tissue properties. In twelve patients post-contrast T1 mapping was performed.

Results

LV, RV and LA parameters did not differ between the surgical and stent group. There was also no significant difference for aortic distensibility, PWV and T1 relaxation times. Aortic root distensibility correlated negatively with age, BMI, BSA and weight (p < 0.001). Native T1 values correlated negatively with age, weight, BSA and BMI (p < 0.001). Lower post-contrast T1 values were associated with lower aortic arch distensibility and higher aortic arch PWV (p < 0.001).

Conclusions

CoA patients after surgery or stent implantation did not show significant difference of aortic elasticity. Thus, presumably other factors like intrinsic aortic abnormalities might have a greater impact on aortic elasticity than the approach of repair. Interestingly, our data suggest that native T1 values are influenced by demographic characteristics.

     

Melanosome diversity and convergence in the evolution of iridescent avian feathers—Implications for paleocolor reconstruction

Some of the most varied colors in the natural world are created by iridescent nanostructures in bird feathers, formed by layers of melanin‐containing melanosomes. The morphology of melanosomes in iridescent feathers is known to vary, but the extent of this diversity, and when it evolved, is unknown. We use scanning electron microscopy to quantify the diversity of melanosome morphology in iridescent feathers from 97 extant bird species, covering 11 orders. In addition, we assess melanosome morphology in two Eocene birds, which are the stem lineages of groups that respectively exhibit hollow and flat melanosomes today. We find that iridescent feathers contain the most varied melanosome morphologies of all types of bird coloration sampled to date. Using our extended dataset, we predict iridescence in an early Eocene trogon (cf. Primotrogon) but not in the early Eocene swift Scaniacypselus, and neither exhibit the derived melanosome morphologies seen in their modern relatives. Our findings confirm that iridescence is a labile trait that has evolved convergently in several lineages extending down to paravian theropods. The dataset provides a framework to detect iridescence with more confidence in fossil taxa based on melanosome morphology.     

Phosphorylation by cdc2-CyclinB1 kinase releases cytoplasmic dynein from membranes

Movement of various cargoes toward microtubule minus ends is driven by the microtubule motor cytoplasmic dynein (CD). Many cargoes are motile only during certain cell cycle phases, suggesting that CD function may be under cell cycle control. Phosphorylation of the CD light intermediate chain (DLIC) has been suggested to play a crucial role in modulating CD function during the Xenopus embryonic cell cycle, where CD-driven organelle movement is active in interphase but greatly reduced in metaphase. This down-regulation correlates with hyperphosphorylation of DLIC and release of CD from the membrane. Here we investigate the role of the key mitotic kinase, cdc2-cyclinB1, in this process. We show that DLIC within the native Xenopus CD complex is an excellent substrate for purified Xenopus cdc2-glutathione S-transferase (GST) cyclinB1 (cdc2-GSTcyclinB1) kinase. Mass spectrometry of native DLIC revealed that a conserved cdc2 site (Ser-197) previously implicated in the metaphase modulation of CD remains phosphorylated in interphase and so is unlikely to be the key regulatory site. We also demonstrate that incubating interphase membranes with cdc2-GSTcyclinB1 kinase results in substantial release of CD from the membrane. These data suggest that phosphorylation of DLIC by cdc2 kinase leads directly to the loss of membrane-associated CD and an inhibition of organelle movement.     

Structural and functional properties of aldose xylose reductase from the D-xylose-metabolizing yeast Candida tenuis

The primary structure of the aldose xylose reductase from Candida tenuis (CtAR) is shown to be 39% identical to that of human aldose reductase (hAR). The catalytic tetrad of hAR is completely conserved in CtAR (Tyr51, Lys80, Asp46, His113). The amino acid residues involved in binding of NADPH by hAR (D.K. Wilson, et al., Science 257 (1992) 81-84) are 64% identical in CtAR. Like hAR the yeast enzyme is specific for transferring the 4-pro-R hydrogen of the coenzyme. These properties suggest that CtAR is a member of the aldo/keto reductase superfamily. Unlike hAR the enzyme from C. tenuis has a dual coenzyme specificity and shows similar specificity constants for NADPH and NADH. It binds NADP(+) approximately 250 times less tightly than hAR. Typical turnover numbers for aldehyde reduction by CtAR (15-20 s(-1)) are up to 100-fold higher than corresponding values for hAR, probably reflecting an overall faster dissociation of NAD(P)(+) in the reaction catalyzed by the yeast enzyme.     

The import pathway of human and Thermoplasma 20S proteasomes into HeLa cell nuclei is different from that of classical NLS-bearing proteins

Wild-type proteasomes of human erythrocytes and the archaeon Thermoplasma acidophilum compete with each other for transport into nuclei of digitonin-permeabilized HeLa cells in the presence of an energy-regenerating system and rabbit reticulocyte lysate. 'NLS'-mutated Thermoplasma proteasomes were also able to compete with human proteasomes in the same assay, although with lower efficiency. Furthermore, in contrast to the other archaeal and bacterial cell lysates tested, the Thermoplasma cytosol efficiently supported nuclear import of human and Thermoplasma proteasomes. However, the same lysate could barely direct the nuclear transport of BSA-NLSsv40 peptide conjugates or the classical NLS-bearing protein, nucleoplasmin. Finally, additional importin alpha/beta significantly decreased the import efficiency of both human and Thermoplasma proteasomes. Taken together, these results suggest that nuclear import of proteasomes may use a novel pathway that is different from that of classical NLS-bearing proteins.     

Folding and self-assembly of the domains of betaB2-crystallin from rat eye lens

betaB2-Crystallin from vertebrate eye lens forms domain-swapped dimers, with subunits consisting of two all-beta domains connected by an eight-residue extended linker peptide. Topologically, the two domains show great similarity; however, they differ widely in their stability. As shown by urea-induced equilibrium unfolding experiments, the isolated monomeric C-terminal domain is more stable than complete betaB2. In contrast, the N-terminal domain exhibits marginal stability only in its dimeric state; upon subunit dissociation, at low protein concentration, unfolding takes place. The folding and association of intact betaB2 follows a sequential uni-bimolecular mechanism according to N2 <==> 2 I <==> 2U, whereas the isolated domains may be quantitatively described by the two-state model (N <==> U).     

A novel A-isoform-like inositol 1,4,5-trisphosphate 3-kinase from chicken erythrocytes exhibits alternative splicing and conservation of intron positions between vertebrates and invertebrates

Based on the partial peptide sequence of inositol 1,4, 5-trisphosphate 3-kinase purified with 135 000-fold enrichment from chicken erythrocytes, cDNA-fragments were cloned by RT-PCR using degenerate oligonucleotides. Subsequent hybridization screening of an embryonic chicken cDNA library and 5'-RACE yielded a cDNA-contig of 2418 bp, encoding a 452 amino acid protein. The amino acid sequence shows the highest degree of homology with A-isoforms of inositol 1,4,5-trisphosphate 3-kinase (65% identities), whereas homology towards B and C isoforms was lower (57% and 52% amino acid identities respectively). These findings reveal a new tissue-specific pattern of A-isoform expression, a form which so far has only been found in brain and testes.Two overlapping lambda-genomic clones for chicken inositol 1,4,5-trisphosphate 3-kinase, isolated by hybridization screening, covered 18 499 bp of genomic sequence. This contig included four exons: three of them were present in all cDNA clones, whereas one was only represented in a single cDNA clone. In addition, the sequence of the latter differed from the other cDNAs by an in-frame deletion of 72 bp within the coding region for the catalytic domain of the enzyme. This divergent cDNA suggests the existence of alternative splice products, at least in embryonic tissue.A comparison of the position of introns, with the respective introns known from the corresponding gene from Caenorhabditis elegans, revealed a high degree of conservation of intron positions between vertebrates and invertebrates. Functional data for the enzyme suggests that the conserved exons represent defined functional protein modules.