Subcircuits of Deep and Superficial CA1 Place Cells Support Efficient Spatial Coding across Heterogeneous Environments

1. Download : Download high-res image (204KB)
2. Download : Download full-size image

     

Ligand-induced asymmetry as observed through fluorophore rotations and free energy couplings: application to neurophysin

Changes that occur in subunit neurophysin structure upon ligand binding were explored by two methods. First, the thermal coefficient of the viscosity around the subunit tyrosine was monitored, which yields information on the environmental flexibility and free rotational space of the fluorophore. Initially, it was determined that the environmental flexibility and the free space around each subunit tyrosine are unperturbed upon dimerization. Binding of the tripeptide analogue of oxytocin causes the once homologous environments of the subunit tyrosines to become drastically different such that one moves onto a closely packed environment whereas the other moves into a region of larger free space. Even though the subunits as seen by each tyrosine are very different, the specific binding sites as seen by the ligands are similar. It was also found that ligand binding is stabilized by ring stacking and that energy transfer occurs between the tyrosine of the ligand and the neurophysin subunit tyrosine. Second, changes in subunit structure upon ligation were also followed by the determination of the order of free energy coupling between ligand binding and oligomerization, which tells how each ligand affects the subunit affinity. Since the binding of ligand is cooperative and induces dimer formation, there is second-order coupling between ligand binding and dimerization and the binding of the second ligand is responsible for the increase in subunit affinity.     

Anti-idiotypic antibodies as probes of cell surface receptors

Summary Anti-idiotypic antibodies have proven to have unique applications as probes in both functional and biochemical studies of cell surface receptors. Anti-idiotypic receptor antibodies have been prepared to antibodies which bind to purified ligand, as in the case of insulin, retinol-binding protein, the mammalian reovirus receptor, and the neutrophil chemotatic receptor, and to natural ligand analogs, such as the beta-adrenergic antagonist alprenolol. These systems have documented the usefulness of anti-idiotypic antibodies in the quantitation and modulation of specific membrane receptors on a variety of cell types. Anti-idotypic antibodies have also been utilized for the isolation of specific membrane receptors, e.g., reovirus and B-1 H globulin receptors. Some anti-idiotypic receptor antibodies, e.g., insulin and reovirus systems, have been shown to mimic the physiological properties of ligand upon binding to cellular receptors. These antibodies enable a new dimension of both receptor based cellular studies and therapeutic regimens. This review focuses on the past use of anti-idiotypic antibodies as probes of cell surface receptors, and on the methodologies required for the successful application of anti-idiotypic antibodies for use in further membrane receptor studies, and of the genes which encode and regulate these receptors. We also discuss the use of anti-idiotypic antibodies in the understanding of and therapeutic approach to receptor related diseases.Dr. Gaulton received the NRSA Viral Oncology Training Grant t# CA 09031.     

Optimization of somatic cell injection in the perspective of nuclear transfer in goldfish

Background  

Nuclear transfer has the potential to become one strategy for fish genetic resources management, by allowing fish reconstruction from cryopreserved somatic cells. Survival rates after nuclear transfer are still low however. The part played by unsuitable handling conditions is often questioned, but the different steps in the procedure are difficult to address separately. In this work led on goldfish (Carassius auratus), the step of somatic cells injection was explored. Non-enucleated metaphase II oocytes were used as a template to explore the toxicity of the injection medium, to estimate the best location where the cell should be injected, and to assess the delay necessary between cell injection and oocyte activation.     

Deletion of the trichodiene synthase gene of Fusarium venenatum: two systems for repeated gene deletions.

The trichodiene synthase (tri5) gene of Fusarium venenatum was cloned from a genomic library. Vectors were created in which the tri5 coding sequence was replaced with the Neurospora crassa nitrate reductase (nit3) gene and with the Aspergillus nidulans acetamidase (amdS) gene flanked by direct repeats. The first vector was utilized to transform a nitrate reductase (niaD) mutant of F. venenatum to prototrophy, and the second vector was utilized to confer acetamide utilization to the wild-type strain. Several of the transformants lost the capacity to produce the trichothecene diacetoxyscirpenol and were shown by hybridization analysis to have gene replacements at the tri5 locus. The nit3 gene was removed by retransformation with a tri5 deletion fragment and selection on chlorate. The amdS gene was shown to excise spontaneously via the flanking direct repeats when spores were plated onto fluoroacetamide.     

Phorophyte size and soil profiles differentially correlate with community structure among hemiepiphytes and nomadic vines

Tropical non-self-supporting plants such as hemiepiphytes and nomadic vines are model organisms for disentangling biotic and environmental correlates which influence their occupancy patterns. We inventoried >4000 individuals from >3000 trees ranging from 1 to 200 cm diameter at breast height (DBH) in a northeastern Amazonian upland forest to address how tree (phorophyte) size, edaphic factors and recruitment strategy influence occupancy, diversity, and compositional patterns of two vascular non-self-supporting plant functional groups. Hemiepiphytes germinate on phorophytes prior to establishing soil connections, whereas nomadic vines initiate their life cycle on the forest floor and subsequently climb phorophytes for crown access, abandoning roots replaced by adventitious connections which may reach the ground. Our results show that larger phorophytes (≥30 cm DBH) supported more species for both hemiepiphytes and nomadic vines. However, nomadic vines' occupancy probabilities saturated faster at smaller stem sizes than that of hemiepiphytes indicating differential preferences for stem sizes among the two functional groups. For smaller phorophytes (<30 cm DBH), soil correlations were stronger with nomadic vines than hemiepiphytes, whereas no significant differences were detected among functional groups in relation to edaphic factors for larger (≥ 30 cm DBH) ones. Finally, a small core group of species showed disproportionately greater abundances among large phorophytes suggesting that autogenic processes differentially promote survivability. Such interactions among phorophyte size and edaphic factors may result from the contrasting ecological requirements of hemiepiphytes and nomadic vines at the recruitment stage, demonstrating the necessity for elaborate demographic-based studies to better understand these complex plant–plant interactions. Abstract in Spanish is available with online material     

N-(β-iodoethy)trifluoroacetamide: A new reagent for the aminoethylation of thiol groups in proteins

β-Iodoethyltrifluoroacetamide was prepared and evaluated for use in the aminoethylation of sulfhydryl groups in proteins. Lysozyme, ribonuclease A, chymotrypsinogen A, and soybean trypsin inhibitor were reduced using dithiothreitol in 6 m guanidine hydrochloride. The reduced proteins were then treated with the reagent. Conversion of cysteinyl to aminoethylcysteinyl residues averaged 97%; no destruction of nontarget residues was observed.     

A Simple Method for Collecting and Mounting Ribboned Serial Sections of Epoxy Embedded Specimens

A simple and rapid method of handling ribboned serial sections of epoxy embedded specimens is described. Ribbons are cut from a block having the leading and trailing sides coated with contact cement. A scoop made from polyethylene tubing is used to remove a ribbon of sections from the boat of a glass or diamond knife and to transfer it to a pool of water on a microscope slide. Many ribbons (comprising hundreds of sections) can be mounted on a single slide. This method requires the construction of only one simple, inexpensive tool, the polyethylene scoop, and otherwise utilizes only items commonly available in the laboratory.