Effects of chromosomal rearrangements on human-chimpanzee molecular evolution

Many chromosomes are rearranged between humans and chimpanzees while others remain colinear. It was recently observed, based on over 100 genes, that the rates of protein evolution are substantially higher on rearranged than on colinear chromosomes during human-chimpanzee evolution. This finding led to the conclusion, since debated in the literature, that chromosomal rearrangements had played a key role in human-chimpanzee speciation. Here we re-examine this important conclusion by employing larger a data set (over 7000 genes), as well as alternative analyses. We show that the higher rates of protein evolution on rearranged chromosomes observed in the earlier study are not reproduced by our survey of the larger data set. We further show that the conclusion of the earlier study is likely confounded by two factors introduced by the relatively limited sample size: (1) nonuniform distribution of genes in the genome, and (2) stochastic noise in substitution rates inherent to short lineages such as the human-chimpanzee lineage. Our results offer a general cautionary note on the importance of controlling for hidden factors in studies involving bioinformatic surveys.     

C2360, a nuclear protein expressed in human proliferative cytotrophoblasts, is a representative member of a novel protein family with a conserved coiled coil-helix-coiled coil-helix domain

In this study, we describe the identification of nine novel genes isolated from a unique human first-trimester cDNA library generated from the placental bed. One of these clones, called C2360 and located on chromosome 10q22, was selected as it showed restricted expression in placental bed tissue as well as in JEG3 choriocarcinoma cells with absent expression in adult tissues. We show that the expression is restricted to first-trimester proliferative trophoblasts of the proximal column and show that C2360 is a nuclear protein. No detectable transactivation potential was observed for different domains of the protein. Secondary structure prediction showed that C2360 is a representative member of a eukaryotic family of proteins with a low conservation at the amino acid level, but with strong conservation at the structural level, sharing the general domain (coiled coil 1)-(helix 1)-(coiled coil 2)-(helix 2), or CHCH domain. Each alpha-helix within this domain contains two cysteine amino acids, and these intrahelical cysteines are separated by nine amino acids (C-X(9)-C motif). The fixed position within each helix indicated that both helices could form a hairpin structure stabilized by two interhelical disulfide bonds. Other proteins belonging to the family include estrogen-induced gene 2 and the ethanol-induced 6 protein. The conserved motif was found in yeast, plant, Drosophila, Caenorhabditis elegans, mouse, and human proteins, indicating that the ancestor of this protein family is of eukaryotic origin. These results indicate that C2360 is a representative member of a multifamily of proteins, sharing a protein domain that is conserved in eukaryotes.     

The basolateral sorting signals of the thyrotropin and luteinizing hormone receptors: an unusual family of signals sharing an unusual distal intracellular localization, but unrelated in their structures

The mechanisms of the basolateral targeting of G protein-coupled receptors remain largely unknown. Mutagenesis experiments have allowed us to identify the basolateral sorting signals of the TSH and LH receptors expressed in Madin-Darby canine kidney cells and thyroid follicular FRT cells. Unexpectedly these signals (amino acids 731-746 and 672-689, respectively) share an unusual localization in the distal part of the intracellular domain of the receptors at a marked distance from the membrane. When grafted onto the p75-neurotropin receptor, these signals redirect this normally apically expressed protein to the basolateral cell surface. They are independent of the endocytosis signal. The basolateral sorting signals of TSH, LH, and FSH receptors do not exhibit primary sequence homology with each other or with any other known signal. Furthermore, circular dichroism studies show that the three signals exhibit distinct secondary structures. The TSH receptor has a stable helical structure, the LH receptor has both helix and beta-sheet structures, and the FSH receptor sorting signal has a main random coil structure. This means that even in closely-related receptors different secondary structures can be found for basolateral signals unrelated to internalization signals. This observation contrasts with what is known about basolateral signals related to internalization signals for which a common beta-turn structure has been described. Deletion of the basolateral sorting signals results in apical targeting of the receptors, suggesting the existence of apical sorting information. However, a soluble form of the TSH receptor, which harbors all N- and putative O-linked oligosaccharides, is secreted in a nonpolarized fashion. This implies that apical sorting information must be located elsewhere, either in the transmembrane or in the intracellular domains of the receptor.     

S-Nitrosohemoglobin: an allosteric mediator of NO group function in mammalian vasculature

Since the discovery of NO as the endothelium-derived relaxing factor, there has been considerable interest in how NO interacts with hemoglobin (Hb). Numerous investigations have highlighted the possibility that rather than operating as a sink to consume NO, the vasculature can operate as a delivery mechanism for NO. The principal hypothesis proposed to explain this phenomenon is that Hb can transport NO on the conserved cysteine residue beta93 and deliver that NO to the tissues in an allosterically dependent manner. This proposal has been termed the S-Nitrosohemoglobin (SNO-Hb) Hypothesis. This review addresses the experimental evidence that led to development of this hypothesis and examines much of the research that resulted from its generation. Specifically it covers the evidence concerning NO in the vasculature, the SNO-Hb Hypothesis itself, the biochemical and biophysical data relating to NO and Hb interactions, SNO-Hb in human physiology, and alternative vascular forms of NO. Finally a model of NO in the vasculature in which SNO-Hb forms the central core is proposed.     

Evaluation of hydrodynamic drag on experimental fouling-release surfaces, using rotating disks

Fouling by biofilms significantly increases frictional drag on ships' hulls. A device, the friction disk machine, designed to measure torque on rotating disks, was used to examine differences among experimental fouling-release coatings in the drag penalty due to accumulated biofilms. Penalties were measured as the percentage change in the frictional resistance coefficient Cf. Drag penalties due to microfouling ranged from 9% to 29%, comparable to previously reported values. An antifouling control coating showed a smaller drag penalty than the fouling-release coatings. There were also significant differences among the fouling-release coatings in drag due to biofilm formation. These results indicate that the friction disk machine may serve as a valuable tool for investigating the effects of experimental coatings, both antifouling and fouling-release, on microfouling and associated drag penalties.     

Proteomic analysis of resistance mediated by Rcm 2.0 and Rcm 5.1, two loci controlling resistance to bacterial canker of tomato

Two quantitative trait loci from Lycopersicon hirsutum, Rcm 2.0 and Rcm 5.1, control resistance to Clavibacter michiganensis subsp. michiganensis, the causal agent of bacterial canker of tomato. Lines containing Rcm 2.0 and Rcm 5.1 and a susceptible control line were compared at 72 and 144 h postinoculation, using 2-dimensional gel electrophoresis to identify proteins regulated in response to C. michiganensis subsp. michiganensis infection. A total of 47 proteins were subjected to tandem mass spectrometry. Database queries with resulting spectra identified tomato genes for 26 proteins. The remaining 21 proteins were either identified in other species or possessed no homology to known proteins. Spectra were interpreted to deduce peptide amino acid sequences that were then used to query publicly available data. This approach identified tomato genes or expressed sequence tags for 44 of the proteins analyzed. Three superoxide dismutase (SOD) enzymes were differentially regulated among genotypes, and patterns of hydrogen peroxide accumulation were genotype- and tissue-specific, indicating a role for oxidative stress in response to C. michiganensis subsp. michiganensis. Steady-state mRNA and protein levels for SOD, thioredoxin M-type, S-adenosylhomocysteine hydrolase, and pathogenesis-related proteins demonstrated similar patterns of differential regulation. Lines containing Rcm 2.0 and Rcm 5.1 accumulate different proteins and steady-state mRNAs in response to inoculation, suggesting that the two loci may confer resistance through distinct mechanisms.     

Increased attention to spatial context increases both place field stability and spatial memory

The hippocampal formation is critical for the acquisition and consolidation of memories. When recorded in freely moving animals, hippocampal pyramidal neurons fire in a location-specific manner: they are "place" cells, comprising a hippocampal representation of the animal's environment. To explore the relationship between place cells and spatial memory, we recorded from mice in several behavioral contexts. We found that long-term stability of place cell firing fields correlates with the degree of attentional demands and that successful spatial task performance was associated with stable place fields. Furthermore, conditions that maximize place field stability greatly increase orientation to novel cues. This suggests that storage and retrieval of place cells is modulated by a top-down cognitive process resembling attention and that place cells are neural correlates of spatial memory. We propose a model whereby attention provides the requisite neuromodulatation to switch short-term homosynaptic plasticity to long-term heterosynaptic plasticity, and we implicate dopamine in this process.     

New synaptic bouton formation is disrupted by misregulation of microtubule stability in aPKC mutants

The Baz/Par-3-Par-6-aPKC complex is an evolutionarily conserved cassette critical for the development of polarity in epithelial cells, neuroblasts, and oocytes. aPKC is also implicated in long-term synaptic plasticity in mammals and the persistence of memory in flies, suggesting a synaptic function for this cassette. Here we show that at Drosophila glutamatergic synapses, aPKC controls the formation and structure of synapses by regulating microtubule (MT) dynamics. At the presynapse, aPKC regulates the stability of MTs by promoting the association of the MAP1Brelated protein Futsch to MTs. At the postsynapse, aPKC regulates the synaptic cytoskeleton by controlling the extent of Actin-rich and MT-rich areas. In addition, we show that Baz and Par-6 are also expressed at synapses and that their synaptic localization depends on aPKC activity. Our findings establish a novel role for this complex during synapse development and provide a cellular context for understanding the role of aPKC in synaptic plasticity and memory.