1,082 research outputs found
A comparative molecular approach to mesodermal patterning in basal deuterostomes: the expression pattern of Brachyury in the enteropneust hemichordate Ptychodera flava
This work concerns the formation of mesoderm in the development of an enteropneust hemichordate, Ptychodera flava, and the expression of the Brachyury gene during this process. Brachyury expression occurs in two distinct phases. In the embryo, Brachyury is transcribed during gastrulation in the future oral and anal regions of the gut, but transcripts are no longer detected by 2 weeks of development. Brachyury expression is not detected during the 5 months of larval planktonic existence. During this time, the adult coeloms begin to develop, originating as coalescences of cells that appear to delaminate from the wall of the gut. Brachyury expression cannot be detected again until metamorphosis, when transcripts appear in the mesoderm of the adult proboscis, collar and the very posterior region of the trunk. It is also expressed in the posterior end of the gut. At no time is Brachyury expressed in the stomochord, the putative homologue of the chordate notochord. These observations illuminate the process of maximal indirect development in Ptychodera and, by comparison with patterns of Brachyury expression in the indirect development of echinoderms, their sister group, they reveal the evolutionary history of Brachyury utilization in deuterostomes
Phylogenetic Analysis of the Formin Homology 2 Domain
Formin proteins are key regulators of eukaryotic actin filament assembly and elongation, and many species possess multiple formin isoforms. A nomenclature system based on fundamental features would be desirable, to aid the rapid identification and characterization of novel formins. In this article, we attempt to systematize the formin family by performing phylogenetic analyses of the formin homology 2 (FH2) domain, an independently folding region common to all formins, which alone can influence actin dynamics. Through database searches, we identify 101 FH2 domains from 26 eukaryotic species, including 15 in mice. Sequence alignments reveal a highly conserved yeast-specific insert in the “knob loop” region of the FH2 domain, with unknown functional consequences. Phylogenetic analysis using minimum evolution (ME), maximum parsimony (MP), and maximum likelihood (ML) algorithms strongly supports the existence of seven metazoan groups. Yeast FH2 domains segregate from all other eukaryotes, including metazoans, other fungi, plants, and protists. Sequence comparisons of non-FH2 regions support relationships between three metazoan groups (Dia, DAAM, and FRL) and examine previously identified coiled-coil and Diaphanous auto-regulatory domain sequences. This analysis allows for a formin nomenclature system based on sequence relationships, as well as suggesting strategies for the determination of biochemical and cellular activities of these proteins
A l'origine des grands animaux, un petit ver tout nu
Les premiers multicellulaires, marins et
invértebrés, sont apparus avant le
début du Cambrien, il y a 544 millions
d'années. Quarante millions d'années
plus tard, les branches principales du
règne animal Ă©taient probablement dĂ©jĂ
présentes, à l’exception des espèces
terrestres. Durant « l'explosion
cambrienne » apparaissent done tous
les plans de base des animaux actuels.
Comment expliquer l'Ă©mergence de
cette extraordinaire diversité? La clé du
mystère se cache sans doute dans les
processus génétiques qui contrôlent le
développement embryonnaire
Dynamic detection of electron spin accumulation in ferromagnet-semiconductor devices by ferromagnetic resonance
A distinguishing feature of spin accumulation in ferromagnet-semiconductor
devices is precession of the non-equilibrium spin population of the
semiconductor in a magnetic field. This is the basis for detection techniques
such as the Hanle effect, but these approaches become less effective as the
spin lifetime in the semiconductor decreases. For this reason, no electrical
Hanle measurement has been demonstrated in GaAs at room temperature. We show
here that by forcing the magnetization in the ferromagnet (the spin injector
and detector) to precess at the ferromagnetic resonance frequency, an
electrically generated spin accumulation can be detected from 30 to 300 K. At
low temperatures, the distinct Larmor precession of the spin accumulation in
the semiconductor can be detected by ferromagnetic resonance in an oblique
field. We verify the effectiveness of this new spin detection technique by
comparing the injection bias and temperature dependence of the measured spin
signal to the results obtained using traditional methods. We further show that
this new approach enables a measurement of short spin lifetimes (< 100 psec), a
regime that is not accessible in semiconductors using traditional Hanle
techniques.Comment: 4 figure
Reconstruction of Family-Level Phylogenetic Relationships within Demospongiae (Porifera) Using Nuclear Encoded Housekeeping Genes
Background: Demosponges are challenging for phylogenetic systematics because of their plastic and relatively simple morphologies and many deep divergences between major clades. To improve understanding of the phylogenetic relationships within Demospongiae, we sequenced and analyzed seven nuclear housekeeping genes involved in a variety of cellular functions from a diverse group of sponges.
Methodology/Principal Findings: We generated data from each of the four sponge classes (i.e., Calcarea, Demospongiae, Hexactinellida, and Homoscleromorpha), but focused on family-level relationships within demosponges. With data for 21 newly sampled families, our Maximum Likelihood and Bayesian-based approaches recovered previously phylogenetically defined taxa: Keratosap, Myxospongiaep, Spongillidap, Haploscleromorphap (the marine haplosclerids) and Democlaviap. We found conflicting results concerning the relationships of Keratosap and Myxospongiaep to the remaining demosponges, but our results strongly supported a clade of Haploscleromorphap+Spongillidap+Democlaviap. In contrast to hypotheses based on mitochondrial genome and ribosomal data, nuclear housekeeping gene data suggested that freshwater sponges (Spongillidap) are sister to Haploscleromorphap rather than part of Democlaviap. Within Keratosap, we found equivocal results as to the monophyly of Dictyoceratida. Within Myxospongiaep, Chondrosida and Verongida were monophyletic. A well-supported clade within Democlaviap, Tetractinellidap, composed of all sampled members of Astrophorina and Spirophorina (including the only lithistid in our analysis), was consistently revealed as the sister group to all other members of Democlaviap. Within Tetractinellidap, we did not recover monophyletic Astrophorina or Spirophorina. Our results also reaffirmed the monophyly of order Poecilosclerida (excluding Desmacellidae and Raspailiidae), and polyphyly of Hadromerida and Halichondrida.
Conclusions/Significance: These results, using an independent nuclear gene set, confirmed many hypotheses based on ribosomal and/or mitochondrial genes, and they also identified clades with low statistical support or clades that conflicted with traditional morphological classification. Our results will serve as a basis for future exploration of these outstanding questions using more taxon- and gene-rich datasets
Translocation as a strategy to rehabilitate the queen conch (Strombus gigas) population in the Florida Keys
Queen conch (Strombus gigas) stocks in the Florida Keys once supported commercial and recreational fisheries, but overharvesting has decimated this once abundant snail. Despite a ban on harvesting this species since 1985, the local conch population has not recovered. In addition, previous work has reported that conch located in nearshore Keys waters are incapable of spawning because of poor gonadal condition, although reproduction does occur offshore. Queen conch in other areas undergo ontogenetic migrations from shallow, nearshore sites to offshore habitats, but conch in the Florida Keys are prevented from doing so by Hawk Channel. The present study was initiated to determine the potential of translocating nonspawning nearshore conch to offshore sites in order to augment the spawning stock. We translocated adult conch from two nearshore sites to two offshore sites. Histological examinations at the initiation of this study confirmed that nearshore conch were incapable of reproduction, whereas offshore conch had normal gonads and thus were able to reproduce. The gonads of nearshore females were in worse condition than those of nearshore males. However, the gonadal condition of the translocated nearshore conch improved, and these animals began spawning after three months offshore. This finding suggests that some component of the nearshore environment (e.g., pollutants, temperature extremes, poor food or habitat quality) disrupts reproduction in conch, but that removal of nearshore animals to suitable offshore habitat can restore reproductive viability. These results indicate that translocations are preferable to releasing hatchery-reared juveniles because they are more cost-effective, result in a more rapid increase in reproductive output, and maintain the genetic integrity of the wild stock. Therefore, translocating nearshore conch to offshore spawning aggregations may be the key to expediting the recovery of queen conch stocks in the Florida Keys
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A microRNA cluster in the Fragile-X region expressed during spermatogenesis targets FMR1.
Testis-expressed X-linked genes typically evolve rapidly. Here, we report on a testis-expressed X-linked microRNA (miRNA) cluster that despite rapid alterations in sequence has retained its position in the Fragile-X region of the X chromosome in placental mammals. Surprisingly, the miRNAs encoded by this cluster (Fx-mir) have a predilection for targeting the immediately adjacent gene, Fmr1, an unexpected finding given that miRNAs usually act in trans, not in cis Robust repression of Fmr1 is conferred by combinations of Fx-mir miRNAs induced in Sertoli cells (SCs) during postnatal development when they terminate proliferation. Physiological significance is suggested by the finding that FMRP, the protein product of Fmr1, is downregulated when Fx-mir miRNAs are induced, and that FMRP loss causes SC hyperproliferation and spermatogenic defects. Fx-mir miRNAs not only regulate the expression of FMRP, but also regulate the expression of eIF4E and CYFIP1, which together with FMRP form a translational regulatory complex. Our results support a model in which Fx-mir family members act cooperatively to regulate the translation of batteries of mRNAs in a developmentally regulated manner in SCs
Myonuclear Domain Flexibility Challenges Rigid Assumptions on Satellite Cell Contribution to Skeletal Muscle Fiber Hypertrophy
Satellite cell-mediated myonuclear accretion is thought to be required for skeletal muscle fiber hypertrophy, and even drive hypertrophy by preceding growth. Recent studies in humans and rodents provide evidence that challenge this axiom. Specifically, Type 2 muscle fibers reliably demonstrate a substantial capacity to hypertrophy in the absence of myonuclear accretion, challenging the notion of a tightly regulated myonuclear domain (i.e., area that each myonucleus transcriptionally governs). In fact, a “myonuclear domain ceiling”, or upper limit of transcriptional output per nucleus to support hypertrophy, has yet to be identified. Satellite cells respond to muscle damage, and also play an important role in extracellular matrix remodeling during loading-induced hypertrophy. We postulate that robust satellite cell activation and proliferation in response to mechanical loading is largely for these purposes. Future work will aim to elucidate the mechanisms by which Type 2 fibers can hypertrophy without additional myonuclei, the extent to which Type 1 fibers can grow without myonuclear accretion, and whether a true myonuclear domain ceiling exists
Fusion and Beyond: Satellite Cell Contributions to Loading-Induced Skeletal Muscle Adaptation
Satellite cells support adult skeletal muscle fiber adaptations to loading in numerous ways. The fusion of satellite cells, driven by cell-autonomous and/or extrinsic factors, contributes new myonuclei to muscle fibers, associates with load-induced hypertrophy, and may support focal membrane damage repair and long-term myonuclear transcriptional output. Recent studies have also revealed that satellite cells communicate within their niche to mediate muscle remodeling in response to resistance exercise, regulating the activity of numerous cell types through various mechanisms such as secretory signaling and cell–cell contact. Muscular adaptation to resistance and endurance activity can be initiated and sustained for a period of time in the absence of satellite cells, but satellite cell participation is ultimately required to achieve full adaptive potential, be it growth, function, or proprioceptive coordination. While significant progress has been made in understanding the roles of satellite cells in adult muscle over the last few decades, many conclusions have been extrapolated from regeneration studies. This review highlights our current understanding of satellite cell behavior and contributions to adaptation outside of regeneration in adult muscle, as well as the roles of satellite cells beyond fusion and myonuclear accretion, which are gaining broader recognition
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