A search for factors specifying tonotopy implicates DNER in hair-cell development in the chick's cochlea

The accurate perception of sound frequency by vertebrates relies upon the tuning of hair cells, which are arranged along auditory organs according to frequency. This arrangement, which is termed a tonotopic gradient, results from the coordination of many cellular and extracellular features. Seeking the mechanisms that orchestrate those features and govern the tonotopic gradient, we used expression microarrays to identify genes differentially expressed between the high- and low-frequency cochlear regions of the chick (Gallus gallus). Of the three signaling systems that were represented extensively in the results, we focused on the notch pathway and particularly on DNER, a putative notch ligand, and PTPζ, a receptor phosphatase that controls DNER trafficking. Immunohistochemistry confirmed that both proteins are expressed more strongly in hair cells at the cochlear apex than in those at the base. At the apical surface of each hair cell, the proteins display polarized, mutually exclusive localization patterns. Using morpholinos to decrease the expression of DNER or PTPζ as well as a retroviral vector to overexpress DNER, we observed disturbances of hair-bundle morphology and orientation. Our results suggest a role for DNER and PTPζ in hair-cell development and possibly in the specification of tonotopy.     

Effect of loading rate on mechanical properties and fracture morphology of spider silk

Spider silks have been shown to have impressive mechanical properties. In order to assess the effect of extension rate, both quasi-static and high-rate tensile properties were determined for single fibers of major (MA) and minor (MI) ampullate single silk from the orb weaving spider Nephila clavipes . Low rate tests have been performed using a DMA Q800 at 10(-3) s(-1), while high rate analysis was done at 1700 s(-1) utilizing a miniature Kolsky bar apparatus. Rate effects exhibited by both respective silk types are addressed, and direct comparison of the tensile response between the two fibers is made. The fibers showed major increases in toughness at the high extension rate. Mechanical properties of these organic silks are contrasted to currently employed ballistic fibers and examination of fiber fracture mechanisms are probed via scanning electron microscope, revealing a globular rupture surface topography for both rate extremums.     

Waves on Reissner's membrane: a mechanism for the propagation of otoacoustic emissions from the cochlea

Sound is detected and converted into electrical signals within the ear. The cochlea not only acts as a passive detector of sound, however, but can also produce tones itself. These otoacoustic emissions are a striking manifestation of the cochlea's mechanical active process. A controversy remains of how these mechanical signals propagate back to the middle ear, from which they are emitted as sound. Here, we combine theoretical and experimental studies to show that mechanical signals can be transmitted by waves on Reissner's membrane, an elastic structure within the cochlea. We develop a theory for wave propagation on Reissner's membrane and its role in otoacoustic emissions. Employing a scanning laser interferometer, we measure traveling waves on Reissner's membrane in the gerbil, guinea pig, and chinchilla. The results are in accord with the theory and thus support a role for Reissner's membrane in otoacoustic emissions.     

Time Space Translation: A Hox Mechanism for Vertebrate A-P Patterning

The vertebrate A-P axis is a time axis. The head is made first and more and more posterior levels are made at later and later stages. This is different to the situation in most other animals, for example, in Drosophila. Central to this timing is Hox temporal collinearity (see below). This occurs rarely in the animal kingdom but is characteristic of vertebrates and is used to generate the primary axial Hox pattern using time space translation and to integrate successive derived patterns (see below). This is thus a different situation than in Drosophila, where the primary pattern guiding Hox spatial collinearity is generated externally, by the gap and segmentation genes.     

NITPICK: peak identification for mass spectrometry data

Background  

The reliable extraction of features from mass spectra is a fundamental step in the automated analysis of proteomic mass spectrometry (MS) experiments.     

PA,a stress-induced short cut to switch-on ethylene signalling by switching-off CTR1?

Constitutive triple response 1 (CTR1) is a protein kinase that represses plant responses to ethylene. Recently, we have shown that CTR1 function is negatively regulated by the lipid second messenger phosphatidic acid (PA) in vitro.¹ PA was shown to inhibit (1) CTR1''s protein kinase activity, (2) the intramolecular interaction between N-terminus and kinase domain, and (3) the interaction of CTR1 with the ethylene receptor ETR1. PA typically accumulates within minutes in response to biotic or abiotic stresses, which are known to induce ethylene formation. Although long-term treatment with ethephon does stimulate PA accumulation, our results show no fast increase in PA in response to ethylene. A speculative model is presented which explains how stress-induced PA formation could switch on downstream ethylene responses via interaction of the lipid with CTR1.Key words: lipid signaling, phosphatidic acid, ethylene, constitutive triple response 1, plant stress signaling, protein kinase, phospholipase D