Evidence for the existence of a functional helical myocardial band

Characterization of local and global contractile activities in the myocardium is essential for a better understanding of cardiac form and function. The spatial distribution of regions that contribute the most to cardiac function plays an important role in defining the pumping parameters of the myocardium like ejection fraction and dynamic aspects such as twisting and untwisting. In general, myocardium shortening, tangent to the wall, and ventricular wall thickening are important parameters that characterize the regional contribution within the myocardium to the global function of the heart. We have calculated these parameters using myocardium displacement fields, which were captured through the displacement-encoding with stimulated echoes (DENSE) MRI technique in three volunteers. High spatial resolution of the acquired data revealed transmural changes of thickening and tangential shortening with high fidelity in beating hearts. By filtering myocardium regions that showed a tangential shortening index of <0.23, we were able to identify the complete or a portion of a macrostructure composed of connected regions in the form of a helical bundle within the left ventricle mass. In this study, we present a representative case that shows the complete morphology of a helical myocardial band as well as two other cases that present ascending and descending portions of the helical myocardial band. Our observation of a helical functional band based on dynamics is in agreement with diffusion tensor MRI observations and gross dissection studies in the arrested heart.     

Evidence for the possible existence of a second polarization-vision pathway in the locust brain

For spatial orientation and navigation, many insects derive compass information from the polarization pattern of the blue sky. The desert locust Schistocerca gregaria detects polarized light with a specialized dorsal rim area of its compound eye. In the locust brain, polarized-light signals are passed through the anterior optic tract and tubercle to the central complex which most likely serves as an internal sky compass. Here, we suggest that neurons of a second visual pathway, via the accessory medulla and posterior optic tubercle, also provide polarization information to the central complex. Intracellular recordings show that two types of neuron in this posterior pathway are sensitive to polarized light. One cell type connects the dorsal rim area of the medulla with the medulla and accessory medulla, and a second type connects the bilaterally paired posterior optic tubercles. Given the evidence for a role of the accessory medulla as the master clock controlling circadian changes in behavioral activity in flies and cockroaches, our data open the possibility that time-compensated polarized-light signals may reach the central complex via this pathway for time-compensated sky-compass navigation.     

Evidence for the existence of a secondary pathway for fibril growth during the aggregation of tau

The mechanism of amyloid fibril formation by proteins has been classically described by the nucleation-dependent polymerization (NDP) model, which makes certain predictions regarding the kinetics of fibrillation. All proteins whose aggregation conforms to the NDP model display a t(2) time dependence for their initial reaction profile. However, there are proteins whose aggregation reactions have kinetic signatures of a flat lag phase followed by an exponential rise in fibril mass, which does not conform to the NDP model. Amyloid fibril formation by tau, a microtubule-associated protein whose aggregation to form neurofibrillary tangles is implicated in Alzheimer's disease and other tauopathies, in the presence of inducers such as heparin and fatty acid micelles, has always been traditionally described by a ligand-induced NDP model. In this study, the existence of a secondary pathway for fibril growth during the aggregation of the functional, repeat domain of tau in the presence of heparin has been established. Both kinetic and accessory evidence are provided for the existence of this pathway, which is shown to augment the primary homogeneous nucleation pathway. From the kinetic data, the main secondary pathway that is operative appears to be fibril fragmentation but other pathways such as branching or secondary nucleation may also be operative.     

Evidence supporting the existence of a host cell surface receptor for Trypanosoma cruzi

Membrane fragments from trypomastigote forms of Trypanosoma cruzi inhibited the association of intact trypomastigotes with rat heart myoblasts whereas a similar preparation from non-invasive epimastigotes did not. Furthermore, killed trypomastigotes bound to the host cell surface and prevented the attachment of living organisms. Conversely, the extent of association of killed parasites with the host cells was reduced by the presence of living flagellates. These results suggest the presence of a distinct structure(s) on the surface of rat heart myoblasts to which infective forms of T. cruzi can bind.     

Evidence for the existence of a new receptor for CGRP,which is not CRLR

Receptors for calcitonin gene-related peptide (CGRP), a neuropeptide known to be the most potent vasodilator, are abundantly expressed in cerebellum. A monoclonal antibody to cerebellar CGRP receptors specifically detects a 66 kDa protein from rat cerebellum and other rat and human tissues, but not from SK-N-MC cells which express calcitonin receptor-like receptor (CRLR), a recently described component of CGRP receptors. In contrast, mRNA expression for CRLR was abundant in SK-N-MC cells, but it was undetectable in rat cerebellum. Furthermore, the antibody could not detect any immunoreactive protein in HEK 293 cells transiently transfected with CRLR and receptor activity-modifying protein 1 (RAMP(1)) indicating the possible existence of another CGRP receptor, which does not involve CRLR. Due to the absence of biochemical or structural data on the existence of a CGRP(2) receptor and the new data provided in this paper, we suggest to identify the two CGRP receptors as CGRP-A and CGRP-B.     

CNS - endocrine pancreas system. IV. Evidence for the existence of a direct hypothalamic-vagal descending pathway

Influence of TRH, T3 and cGMP on the volume of thyrotropic cells nuclei in rat pituitary in vitro has been examined. A significant increase of the volume of thyrotropic cells nuclei in the culture exposed to TRH, in another one exposed to cGMP and in the third one exposed to both TRH and cGMP together have been observed. The mean volume of cells nuclei within the group exposed to T3 was significantly lower, when compared to the control. T3 inhibited the TRH-induced increase of the volume of thyrotrophs nuclei. The obtained results suggest that the role of cGMP and T3 in the regulation of the thyrotropic cell function are independent and rather opposed. Since TRH increases the level of cAMP in the anterior pituitary, additive effect of TRH and exogenous cGMP support the assumption that both the cyclic nucleotides within the thyrotropic cell act in the same direction.     

Evidence for a disease-resistance pathway in rice similar to the NPR1-mediated signaling pathway in Arabidopsis

The Arabidopsis NPR1/NIM1 gene is a key regulator of systemic acquired resistance (SAR). Over-expression of NPR1 leads to enhanced resistance in Arabidopsis. To investigate the role of NPR1 in monocots, we over-expressed the Arabidopsis NPR1 in rice and challenged the transgenic plants with Xanthomonas oryzae pv. oryzae (Xoo), the rice bacterial blight pathogen. The transgenic plants displayed enhanced resistance to Xoo. RNA blot hybridization indicates that enhanced resistance requires expression of NPR1 mRNA above a threshold level in rice. To identify components mediating the resistance controlled by NPR1, we used NPR1 as bait in a yeast two-hybrid screen. We isolated four cDNA clones encoding rice NPR1 interactors (named rTGA2.1, rTGA2.2, rTGA2.3 and rLG2) belonging to the bZIP family. rTGA2.1, rTGA2.2 and rTGA2.3 share 75, 76 and 78% identity with Arabidopsis TGA2, respectively. In contrast, rLG2 shares highest identity (81%) to the maize liguleless (LG2) gene product, which is involved in establishing the leaf blade-sheath boundary. The interaction of NPR1 with the rice bZIP proteins in yeast was impaired by the npr1-1 and npr1-2 mutations, but not by the nim1-4 mutation. The NPR1-rTGA2.1 interaction was confirmed by an in vitro pull-down experiment. In gel mobility shift assays, rTGA2.1 binds to the rice RCH10 promoter and to a cis-element required sequence-specifically for salicylic acid responsiveness. This is the first demonstration that the Arabidopsis NPR1 gene can enhance disease resistance in a monocot plant. These results also suggest that monocot and dicot plants share a conserved signal transduction pathway controlling NPR1-mediated resistance.     

Evidence for the existence of an oligomeric, non-DNA-binding complex of the progesterone receptor in the cytoplasm

Steroid receptors are found as a hetero-oligomeric complex in cell extracts. Due to the dynamic interaction between receptor-associated proteins and receptors, it is difficult to study the oligomeric complex in living cells. Here this was attempted in cells in which the interaction was stabilized by introducing molybdate into the cells or by incubating the cells at low temperature. The complex was studied with an antibody (aD) recognizing only the dissociated form of the chicken progesterone receptor (PR) and with antibodies (PR22, PR6). Recognizing also oligomeric forms of the receptor. When wild-type chicken PR was transfected, all antibodies showed nuclear staining. Molybdate or cold treatment of cells resulted in cytoplasmic accumulation of the PR as detected with PR22/PR6. aD, however, stained predominantly the nuclear PR in treated cells. These findings suggest that when the oligomeric complex of the PR is stabilized in intact cells in vivo and then crosslinked with paraformaldehyde, a portion of the cytoplasmic receptor is seen as an oligomeric complex, whereas, in the nucleus, most, if not all receptor molecules are in dissociated form.     

Evidence for a two-step mechanism involved in assembly of functional signal recognition particle receptor

The signal recognition particle (SRP) and SRP receptor act sequentially to target nascent secretory proteins to the membrane of the ER. The SRP receptor consists of two subunits, SR alpha and SR beta, both tightly associated with the ER membrane. To examine the biogenesis of the SRP receptor we have developed a cell-free assay system that reconstitutes SR alpha membrane assembly and permits both anchoring and functional properties to be assayed independently. Our experiments reveal a mechanism involving at least two distinct steps, targeting to the ER and anchoring of the targeted molecule on the cytoplasmic face of the membrane. Both steps can be reconstituted in vitro to restore translocation activity to ER microsomes inactivated by alkylation with N-ethyl-maleimide. The characteristics elucidated for this pathway distinguish it from SRP-dependent targeting of secretory proteins, SRP-independent ER translocation of proteins such as prepromellitin, and direct insertion mechanisms of the type exemplified by cytochrome b5.