Mechanical properties of the compass depressors of the sea-urchin Paracentrotus lividus (Echinodermata, Echinoidea) and the effects of enzymes, neurotransmitters and synthetic tensilin-like protein

The compass depressors (CDs) of the sea-urchin lantern are ligaments consisting mainly of discontinuous collagen fibrils associated with a small population of myocytes. They are mutable collagenous structures, which can change their mechanical properties rapidly and reversibly under nervous control. The aims of this investigation were to characterise the baseline (i.e. unmanipulated) static mechanical properties of the CDs of Paracentrotus lividus by means of creep tests and incremental force-extension tests, and to determine the effects on their mechanical behaviour of a range of agents. Under constant load the CDs exhibited a three-phase creep curve, the mean coefficient of viscosity being 561±365 MPa.s. The stress-strain curve showed toe, linear and yield regions; the mean strain at the toe-linear inflection was 0.86±0.61; the mean Young's modulus was 18.62±10.30 MPa; and the mean tensile strength was 8.14±5.73 MPa. Hyaluronidase from Streptomyces hyalurolyticus had no effect on creep behaviour, whilst chondroitinase ABC prolonged primary creep but had no effect on secondary creep or on any force-extension parameters; it thus appears that neither hyaluronic acid nor sulphated glycosaminoglycans have an interfibrillar load transfer function in the CD. Acetylcholine, the muscarinic agonists arecoline and methacholine, and the nicotinic agonists nicotine and 1-[1-(3,4-dimethyl-phenyl)-ethyl]-piperazine produced an abrupt increase in CD viscosity; the CDs were not differentially sensitive to muscarinic or nicotinic agonists. CDs showed either no, or no consistent, response to adrenaline, L-glutamic acid, 5-hydroxytryptamine and γ-aminobutyric acid. Synthetic echinoid tensilin-like protein had a weak and inconsistent stiffening effect, indicating that, in contrast to holothurian tensilins, the echinoid molecule may not be involved in the regulation of collagenous tissue tensility. We compare in detail the mechanical behaviour of the CD with that of mammalian tendon and highlight its potential as a model system for investigating poorly understood aspects of the ontogeny and phylogeny of vertebrate collagenous tissues.(undefined)info:eu-repo/semantics/publishedVersio

Signaling pathways downstream of P2 receptors in human neutrophils

Extracellular nucleotides stimulate human neutrophils by activating the purinergic P2Y2 receptor. However, it is not completely understood which types of G proteins are activated downstream of this P2 receptor subtype. We investigated the G-protein coupling to P2Y2 receptors and several subsequent signaling events. Treatment of neutrophils with pertussis toxin (PTX), a Gi protein inhibitor, caused only ∼75% loss of nucleotide-induced Ca2+ mobilization indicating that nucleotides cause Ca2+ mobilization both through Gi-dependent and Gi-independent pathways. However, the PLC inhibitor U73122 almost completely inhibited Ca2+ mobilization in both nucleotide- and fMLP-stimulated neutrophils, strongly supporting the view that both the PTX-sensitive and the PTX-insensitive mechanism of Ca2+ increase require activation of PLC. We investigated the dependence of ERK phosphorylation on the Gi pathway. Treatment of neutrophils with PTX caused almost complete inhibition of ERK phosphorylation in nucleotide or fMLP activated neutrophils. U73122 caused inhibition of nucleotide- or fMLP-stimulated ERK phosphorylation, suggesting that although pertussis toxin-insensitive pathways cause measurable Ca2+ mobilization, they are not sufficient for causing ERK phosphorylation. Since PLC activation leads to intracellular Ca2+ increase and PKC activation, we investigated if these intracellular events are necessary for ERK phosphorylation. Exposure of cells to the Ca2+ chelator BAPTA had no effect on nucleotide- or fMLP-induced ERK phosphorylation. However, the PKC inhibitor GF109203X was able to almost completely inhibit nucleotide- or fMLP-induced ERK phosphorylation. We conclude that the P2Y2 receptor can cause Ca2+ mobilization through a PTX-insensitive but PLC-dependent pathway and ERK phosphorylation is highly dependent on activation of the Gi proteins

α-thalassaemia

Alpha-thalassaemia is inherited as an autosomal recessive disorder characterised by a microcytic hypochromic anaemia, and a clinical phenotype varying from almost asymptomatic to a lethal haemolytic anaemia

Recessive Antimorphic Alleles Overcome Functionally Redundant Loci to Reveal TSO1 Function in Arabidopsis Flowers and Meristems

Arabidopsis TSO1 encodes a protein with conserved CXC domains known to bind DNA and is homologous to animal proteins that function in chromatin complexes. tso1 mutants fall into two classes due to their distinct phenotypes. Class I, represented by two different missense mutations in the CXC domain, leads to failure in floral organ development, sterility, and fasciated inflorescence meristems. Class II, represented by a nonsense mutation and a T-DNA insertion line, develops wild-type–like flowers and inflorescences but shows severely reduced fertility. The phenotypic variability of tso1 alleles presents challenges in determining the true function of TSO1. In this study, we use artificial microRNA, double mutant analysis, and bimolecular fluorescence complementation assay to investigate the molecular basis underlying these two distinct classes of phenotypes. We show that the class I mutants could be converted into class II by artificial microRNA knockdown of the tso1 mutant transcript, suggesting that class I alleles produce antimorphic mutant proteins that interfere with functionally redundant loci. We identified one such redundant factor coded by the closely related TSO1 homolog SOL2. We show that the class I phenotype can be mimicked by knocking out both TSO1 and its homolog SOL2 in double mutants. Such antimorphic alleles targeting redundant factors are likely prevalent in Arabidopsis and maybe common in organisms with many sets of paralogous genes such as human. Our data challenge the conventional view that recessive alleles are always hypomorphic or null and that antimorphic alleles are always dominant. This study shows that recessive alleles can also be antimorphic and can produce a phenotype more severe than null by interfering with the function of related loci. This finding adds a new paradigm to classical genetic concepts, with important implications for future genetic studies both in basic research as well as in agriculture and medicine

A Global Perspective on Trends in Nature-Based Tourism

Falling attendance at United States and Japanese national parks has led to claims of a pervasive shift away from nature-based recreation. A global analysis, however, now suggests that while visit rates are declining slightly in some richer countries, elsewhere nature tourism is booming

When Less Is Best: Female Brown-Headed Cowbirds Prefer Less Intense Male Displays

Sexual selection theory predicts that females should prefer males with the most intense courtship displays. However, wing-spread song displays that male brown-headed cowbirds (Molothrus ater) direct at females are generally less intense than versions of this display that are directed at other males. Because male-directed displays are used in aggressive signaling, we hypothesized that females should prefer lower intensity performances of this display. To test this hypothesis, we played audiovisual recordings showing the same males performing both high intensity male-directed and low intensity female-directed displays to females (N = 8) and recorded the females' copulation solicitation display (CSD) responses. All eight females responded strongly to both categories of playbacks but were more sexually stimulated by the low intensity female-directed displays. Because each pair of high and low intensity playback videos had the exact same audio track, the divergent responses of females must have been based on differences in the visual content of the displays shown in the videos. Preferences female cowbirds show in acoustic CSD studies are correlated with mate choice in field and captivity studies and this is also likely to be true for preferences elucidated by playback of audiovisual displays. Female preferences for low intensity female-directed displays may explain why male cowbirds rarely use high intensity displays when signaling to females. Repetitive high intensity displays may demonstrate a male's current condition and explain why these displays are used in male-male interactions which can escalate into physical fights in which males in poorer condition could be injured or killed. This is the first study in songbirds to use audiovisual playbacks to assess how female sexual behavior varies in response to variation in a male visual display

Synthesis of two SAPAP3 isoforms from a single mRNA is mediated via alternative translational initiation

In mammalian neurons, targeting and translation of specific mRNAs in dendrites contribute to synaptic plasticity. After nuclear export, mRNAs designated for dendritic transport are generally assumed to be translationally dormant and activity of individual synapses may locally trigger their extrasomatic translation. We show that the long, GC-rich 5′-untranslated region of dendritic SAPAP3 mRNA restricts translation initiation via a mechanism that involves an upstream open reading frame (uORF). In addition, the uORF enables the use of an alternative translation start site, permitting synthesis of two SAPAP3 isoforms from a single mRNA. While both isoforms progressively accumulate at postsynaptic densities during early rat brain development, their levels relative to each other vary in different adult rat brain areas. Thus, alternative translation initiation events appear to regulate relative expression of distinct SAPAP3 isoforms in different brain regions, which may function to influence synaptic plasticity

Loss-of-Function Mutations in PTPN11 Cause Metachondromatosis, but Not Ollier Disease or Maffucci Syndrome

Metachondromatosis (MC) is a rare, autosomal dominant, incompletely penetrant combined exostosis and enchondromatosis tumor syndrome. MC is clinically distinct from other multiple exostosis or multiple enchondromatosis syndromes and is unlinked to EXT1 and EXT2, the genes responsible for autosomal dominant multiple osteochondromas (MO). To identify a gene for MC, we performed linkage analysis with high-density SNP arrays in a single family, used a targeted array to capture exons and promoter sequences from the linked interval in 16 participants from 11 MC families, and sequenced the captured DNA using high-throughput parallel sequencing technologies. DNA capture and parallel sequencing identified heterozygous putative loss-of-function mutations in PTPN11 in 4 of the 11 families. Sanger sequence analysis of PTPN11 coding regions in a total of 17 MC families identified mutations in 10 of them (5 frameshift, 2 nonsense, and 3 splice-site mutations). Copy number analysis of sequencing reads from a second targeted capture that included the entire PTPN11 gene identified an additional family with a 15 kb deletion spanning exon 7 of PTPN11. Microdissected MC lesions from two patients with PTPN11 mutations demonstrated loss-of-heterozygosity for the wild-type allele. We next sequenced PTPN11 in DNA samples from 54 patients with the multiple enchondromatosis disorders Ollier disease or Maffucci syndrome, but found no coding sequence PTPN11 mutations. We conclude that heterozygous loss-of-function mutations in PTPN11 are a frequent cause of MC, that lesions in patients with MC appear to arise following a “second hit,” that MC may be locus heterogeneous since 1 familial and 5 sporadically occurring cases lacked obvious disease-causing PTPN11 mutations, and that PTPN11 mutations are not a common cause of Ollier disease or Maffucci syndrome

Trichomonas Transmembrane Cyclases Result from Massive Gene Duplication and Concomitant Development of Pseudogenes

Trichomonas vaginalis is the only medically important protist (single-cell eukaryote) that is sexually transmitted. The ∼160-Mb Trichomonas genome contains more predicted protein-encoding genes (∼60,000) than the human genome. To begin to understand why there are so many copies of some genes, we chose here to study a large family of genes encoding unique transmembrane cyclases. Our most important results include the following. More than 100 transmembrane cyclase genes do not result from chromosomal duplications, because for the most part only the coding regions of the genes, rather than flanking sequences, are duplicated. Almost half of the transmembrane cyclase genes are pseudogenes, and these pseudogenes are polymorphic among laboratory strains of Trichomonas. Messenger RNAs for numerous transmembrane cyclases are expressed simultaneously, and representative cyclase domains have adenylyl cyclase activity. In summary, the large family of Trichomonas genes encoding transmembrane adenylyl cyclases results from massive gene duplication and concomitant development of pseudogenes

Evolution of a Signaling Nexus Constrained by Protein Interfaces and Conformational States

Heterotrimeric G proteins act as the physical nexus between numerous receptors that respond to extracellular signals and proteins that drive the cytoplasmic response. The Gα subunit of the G protein, in particular, is highly constrained due to its many interactions with proteins that control or react to its conformational state. Various organisms contain differing sets of Gα-interacting proteins, clearly indicating that shifts in sequence and associated Gα functionality were acquired over time. These numerous interactions constrained much of Gα evolution; yet Gα has diversified, through poorly understood processes, into several functionally specialized classes, each with a unique set of interacting proteins. Applying a synthetic sequence-based approach to mammalian Gα subunits, we established a set of seventy-five evolutionarily important class-distinctive residues, sites where a single Gα class is differentiated from the three other classes. We tested the hypothesis that shifts at these sites are important for class-specific functionality. Importantly, we mapped known and well-studied class-specific functionalities from all four mammalian classes to sixteen of our class-distinctive sites, validating the hypothesis. Our results show how unique functionality can evolve through the recruitment of residues that were ancestrally functional. We also studied acquisition of functionalities by following these evolutionarily important sites in non-mammalian organisms. Our results suggest that many class-distinctive sites were established early on in eukaryotic diversification and were critical for the establishment of new Gα classes, whereas others arose in punctuated bursts throughout metazoan evolution. These Gα class-distinctive residues are rational targets for future structural and functional studies