Vocal Tract Articulation in Zebra Finches

Background

Birdsong and human vocal communication are both complex behaviours which show striking similarities mainly thought to be present in the area of development and learning. Recent studies, however, suggest that there are also parallels in vocal production mechanisms. While it has been long thought that vocal tract filtering, as it occurs in human speech, only plays a minor role in birdsong there is an increasing number of studies indicating the presence of sound filtering mechanisms in bird vocalizations as well.

Methodology/Principal Findings

Correlating high-speed X-ray cinematographic imaging of singing zebra finches (Taeniopygia guttata) to song structures we identified beak gape and the expansion of the oropharyngeal-esophageal cavity (OEC) as potential articulators. We subsequently manipulated both structures in an experiment in which we played sound through the vocal tract of dead birds. Comparing acoustic input with acoustic output showed that OEC expansion causes an energy shift towards lower frequencies and an amplitude increase whereas a wide beak gape emphasizes frequencies around 5 kilohertz and above.

Conclusion

These findings confirm that birds can modulate their song by using vocal tract filtering and demonstrate how OEC and beak gape contribute to this modulation.     

T Cell Specific Adapter Protein (TSAd) Interacts with Tec Kinase ITK to Promote CXCL12 Induced Migration of Human and Murine T Cells

Background

The chemokine CXCL12/SDF-1α interacts with its G-protein coupled receptor CXCR4 to induce migration of lymphoid and endothelial cells. T cell specific adapter protein (TSAd) has been found to promote migration of Jurkat T cells through interaction with the G protein β subunit. However, the molecular mechanisms for how TSAd influences cellular migration have not been characterized in detail.

Principal Findings

We show that TSAd is required for tyrosine phosphorylation of the Lck substrate IL2-inducible T cell kinase (Itk). Presence of Itk Y511 was necessary to boost TSAd''s effect on CXCL12 induced migration of Jurkat T cells. In addition, TSAd''s ability to promote CXCL12-induced actin polymerization and migration of Jurkat T lymphocytes was dependent on the Itk-interaction site in the proline-rich region of TSAd. Furthermore, TSAd-deficient murine thymocytes failed to respond to CXCL12 with increased Itk phosphorylation, and displayed reduced actin polymerization and cell migration responses.

Conclusion

We propose that TSAd, through its interaction with both Itk and Lck, primes Itk for Lck mediated phosphorylation and thereby regulates CXCL12 induced T cell migration and actin cytoskeleton rearrangements.     

Controlling angiogenesis by two unique TGF-β type I receptor signaling pathways

Genetic studies in mice and humans have revealed a pivotal function for transforming growth factor-beta (TGF-β) in vascular development and maintenance of vascular homeostasis. Mice deficient for various TGF-β signaling components develop an embryonic lethality due to vascular defects. In patients, mutations in TGF-β receptors have been linked to vascular dysplasia like Hereditary Hemorrhagic Telangiectasia (HHT) and pulmonary arterial hypertension (PAH). Besides indirect effects by regulating the expression of angiogenic regulators, TGF-β also has potent direct effects on endothelial cell growth and migration, and we have proposed that TGF-β regulates the activation state of the endothelium via two opposing type I receptor/Smad pathways, activin receptor-like kinase (ALK)1 and ALK5. TGF-β is also critical for the differentiation of mural precursors into pericytes and smooth muscle cells. Furthermore, defective paracrine TGF-β signaling between endothelial and neighboring mural cells may be responsible for a leaky vessel phenotype that is characteristic of HHT. In this review, we discuss our current understanding of the TGF-β signaling pathway and its regulation of endothelial and vascular smooth muscle cell function.     

Removal of acidic residues of the prodomain of PCSK9 increases its activity towards the LDL receptor

Proprotein convertase subtilisin/kexin type 9 (PCSK9) binds to the low density lipoprotein receptor (LDLR) at the cell surface and mediates intracellular degradation of the LDLR. The amino-terminus of mature PCSK9, residues 31–53 of the prodomain, has an inhibitory effect on this function of PCSK9, but the underlying mechanism is not fully understood. In this study, we have identified two highly conserved negatively charged segments (residues 32–40 and 48–50, respectively) within this part of the prodomain and performed deletions and substitutions to study their importance for degradation of the LDLRs.Deletion of the acidic residues of the longest negatively charged segment increased PCSK9’s ability to degrade the LDLR by 31%, whereas a modest 8% increase was observed when these residues were mutated to uncharged amino acids. Thus, both the length and the charge of this part of the prodomain were important for its inhibitory effect. Deletion of the residues of the shorter second negatively charged segment only increased PCSK9’s activity by 8%. Substitution of the amino acids of both charged segments to uncharged residues increased PCSK9’s activity by 36%. These findings indicate that the inhibitory effect of residues 31–53 of the prodomain is due to the negative charge of this segment. The underlying mechanism could involve the binding of this peptide segment to positively charged structures which are important for PCSK9’s activity. One possible candidate could be the histidine-rich C-terminal domain of PCSK9.     

Regulatory control and the costs and benefits of biochemical noise

Experiments in recent years have vividly demonstrated that gene expression can be highly stochastic. How protein concentration fluctuations affect the growth rate of a population of cells is, however, a wide-open question. We present a mathematical model that makes it possible to quantify the effect of protein concentration fluctuations on the growth rate of a population of genetically identical cells. The model predicts that the population's growth rate depends on how the growth rate of a single cell varies with protein concentration, the variance of the protein concentration fluctuations, and the correlation time of these fluctuations. The model also predicts that when the average concentration of a protein is close to the value that maximizes the growth rate, fluctuations in its concentration always reduce the growth rate. However, when the average protein concentration deviates sufficiently from the optimal level, fluctuations can enhance the growth rate of the population, even when the growth rate of a cell depends linearly on the protein concentration. The model also shows that the ensemble or population average of a quantity, such as the average protein expression level or its variance, is in general not equal to its time average as obtained from tracing a single cell and its descendants. We apply our model to perform a cost-benefit analysis of gene regulatory control. Our analysis predicts that the optimal expression level of a gene regulatory protein is determined by the trade-off between the cost of synthesizing the regulatory protein and the benefit of minimizing the fluctuations in the expression of its target gene. We discuss possible experiments that could test our predictions.     

Leakage-free rapid quenching technique for yeast metabolomics

Accurate determination of intracellular metabolite levels requires reliable, reproducible techniques for sampling and sample treatment. Quenching in 60% (v/v) methanol at −40°C is currently the standard method for sub-second arrest of metabolic activity in microbial metabolomics but there have been contradictory reports in the literature on whether leakage of metabolites from the cells occurs. We have re-evaluated this method in S. cerevisiae using a comprehensive, strictly quantitative approach. By determining the levels of a large range of metabolites in different sample fractions and establishing mass balances we could trace their fate during the quenching procedure and confirm that leakage of metabolites from yeast cells does occur during conventional cold methanol quenching, to such an extent that the levels of most metabolites have been previously underestimated by at least twofold. In addition, we found that the extent of leakage depends on the time of exposure, the temperature and the properties of the methanol solutions. Using the mass balance approach we could study the effect of different quenching conditions and demonstrate that leakage can be entirely prevented by quenching in pure methanol at ≤−40°C, which we propose as a new improved method. Making use of improved data on intracellular metabolite levels we also re-evaluated the need of sub-second quenching of metabolic activity and of removing the extracellular medium. Our findings have serious implications for quantitative metabolomics-based fields such as non-stationary ¹³C flux analysis, in vivo kinetic modeling and thermodynamic network analysis.

Tetradecylthioacetic acid prevents the inflammatory response in two-kidney, one-clip hypertension

ANG II promotes inflammation through nuclear factor-kappaB (NF-kappaB)-mediated induction of cytokines and reactive oxygen species (ROS). The aim of the present study was to examine the effect of tetradecylthioacetic acid (TTA), a modified fatty acid, on NF-kappaB, proinflammatory markers, ROS, and nitric oxide (NO) production in two-kidney, one-clip (2K1C) hypertension. The 2K1C TTA-treated group had lower blood pressure (128 +/- 3 mmHg) compared with 2K1C nontreated (178 +/- 5 mmHg, P < 0.001). The p50 and p65 subunits of NF-kappaB were higher in the clipped kidney (0.44 +/- 0.01 and 0.22 +/- 0.01, respectively) compared with controls (0.25 +/- 0.03 and 0.12 +/- 0.02, respectively, P < 0.001). In the 2K1C TTA-treated group, these values were similar to control levels. The same pattern of response was seen in the nonclipped kidney. In 2K1C hypertension, cytokines plasma were higher than in control: TNF-alpha was 13.5 +/- 2 pg/ml (P < 0.03), IL-1beta was 58.8 +/- 10 pg/ml (P = 0.003), IL-6 was 210 +/- 33 pg/ml (P < 0.001), and monocyte chemoattractant protein-1 was 429 +/- 21 pg/ml (P = 0.04). In the 2K1C TTA-treated group, these values were similar to controls, and the same pattern was seen in the clipped kidney. Clipping increased 8-iso-PGF-2alpha (P < 0.01) and decreased NO production (P < 0.01 vs. control) in the urine. TTA treatment normalized these values. NO production was also lower in clipped and nonclipped kidney (P < 0.001). After TTA treatment, these values were similar to controls. The results indicate that TTA has a potent anti-inflammatory effect in 2K1C by inhibition of p50/p65 NF-kappaB subunit activation, reduction of cytokines production and ROS, and enhanced NO production.     

Two novel type II receptors mediate BMP signalling and are required to establish left-right asymmetry in zebrafish

Ligands of the transforming growth factor β (TGFβ) superfamily, like Nodal and bone morphogenetic protein (BMP), are pivotal to establish left-right (LR) asymmetry in vertebrates. However, the receptors mediating this process are unknown. Here we identified two new type II receptors for BMPs in zebrafish termed bmpr2a and bmpr2b that induce a classical Smad1/5/8 response to BMP binding. Morpholino-mediated knockdown of bmpr2a and bmpr2b showed that they are required for the establishment of concomitant cardiac and visceral LR asymmetry. Expression of early laterality markers in morphants indicated that bmpr2a and bmpr2b act upstream of pitx2 and the nodal-related southpaw (spaw), which are expressed asymmetrically in the lateral plate mesoderm (LPM), and subsequently regulate lefty2 and bmp4 in the left heart field. We demonstrated that bmpr2a is required for lefty1 expression in the midline at early segmentation while bmpr2a/bmpr2b heteromers mediate left-sided spaw expression in the LPM. We propose a mechanism whereby this differential interpretation of BMP signalling through bmpr2a and bmpr2b is essential for the establishment of LR asymmetry in the zebrafish embryo.