RFX2 is a candidate downstream amplifier of A-MYB regulation in mouse spermatogenesis

<p>Abstract</p> <p>Background</p> <p>Mammalian spermatogenesis involves formation of haploid cells from the male germline and then a complex morphological transformation to generate motile sperm. Focusing on meiotic prophase, some tissue-specific transcription factors are known (A-MYB) or suspected (RFX2) to play important roles in modulating gene expression in pachytene spermatocytes. The current work was initiated to identify both downstream and upstream regulatory connections for <it>Rfx2</it>.</p> <p>Results</p> <p>Searches of pachytene up-regulated genes identified high affinity RFX binding sites (X boxes) in promoter regions of several new genes: <it>Adam5</it>, <it>Pdcl2</it>, and <it>Spag6</it>. We confirmed a strong promoter-region X-box for <it>Alf</it>, a germ cell-specific variant of general transcription factor TFIIA. Using <it>Alf </it>as an example of a target gene, we showed that its promoter is stimulated by RFX2 in transfected cells and used ChIP analysis to show that the promoter is occupied by RFX2 in vivo. Turning to upstream regulation of the <it>Rfx2 </it>promoter, we identified a cluster of three binding sites (MBS) for the MYB family of transcription factors. Because testis is one of the few sites of <it>A-myb </it>expression, and because spermatogenesis arrests in pachytene in <it>A-myb </it>knockout mice, the MBS cluster implicates <it>Rfx2 </it>as an <it>A-myb </it>target. Electrophoretic gel-shift, ChIP, and co-transfection assays all support a role for these MYB sites in <it>Rfx2 </it>expression. Further, <it>Rfx2 </it>expression was virtually eliminated in <it>A-myb </it>knockout testes. Immunohistology on testis sections showed that A-MYB expression is up-regulated only after pachytene spermatocytes have clearly moved away from the tubule wall, which correlates with onset of RFX2 expression, whereas B-MYB expression, by contrast, is prevalent only in earlier spermatocytes and spermatogonia.</p> <p>Conclusion</p> <p>With an expanding list of likely target genes, RFX2 is potentially an important transcriptional regulator in pachytene spermatocytes. <it>Rfx2 </it>itself is a good candidate to be regulated by A-MYB, which is essential for meiotic progression. If <it>Alf </it>is a genuine RFX2 target, then <it>A-myb</it>, <it>Rfx2</it>, and <it>Alf </it>may form part of a transcriptional network that is vital for completion of meiosis and preparation for post-meiotic differentiation.</p

Mathematical Formulations of Hebbian Learning

Several formulations of correlation-based Hebbian learning are reviewed. On the presynaptic side, activity is described either by a firing rate or by presynaptic spike arrival. The state of the postsynaptic neuron can be described by its membrane potential, its firing rate, or the timing of backpropagating action potentials (BPAPs). It is shown that all of the above formulations can be derived from the point of view of an expansion. In the absence of BPAPs potentials, it is natural to correlate presynaptic spikes with the postsynaptic membrane potential. Time windows of spike time dependent plasticity arise naturally, if the timing of postsynaptic spikes is available at the site of the synapse as it is the case in the presence of BPAPs. With an appropriate choice of parameters, Hebbian synaptic plasticity has intrinsic normalization properties that stabilizes postsynaptic firing rates and leads to subtractive weight normalization

OBSERVATION OF AN ISOKINETIC TEMPERATURE AND COMPENSATION EFFECT FOR HIGH TEMPERATURE CRUDE OIL FOULING

The initial fouling rates of four crude oils were determined at a nominal bulk temperature of 315 °C, an initial heated wall shear stress of 13 Pa, and initial surface temperatures between 375 and 445 °C. These initial fouling rates ranged from 1.3(10-6) to 7.8(10-5) m2 K/kJ. Corresponding Arrhenius plots were linear with the initial fouling rates passing through an isokinetic temperature of 407.5 °C. A plot of the natural logarithm of the preexponential factors (7.6(104) – 5.2(1015) m2 K/kJ) versus the apparent activation energies (128 – 269 kJ/mol) was also linear, confirming the validity of the isokinetic temperature and the presence of the compensation effect. Below the isokinetic temperature, the relative fouling rates were Crude Oil C \u3e Crude Oil A \u3e Crude Oil D \u3e Crude Oil B; above the isokinetic temperature, the relative fouling rates were reversed (Crude Oil B \u3e Crude Oil D \u3e Crude Oil A \u3e Crude Oil C). Chemical characterization of a fouling deposit suggested that the dominant fouling mechanism at these conditions was coking with significant contributions from sedimentation (iron sulfide) and corrosion (~340 μm/yr) of the 304 stainless steel test material

OBSERVATION OF AN ISOKINETIC TEMPERATURE AND COMPENSATION EFFECT FOR HIGH TEMPERATURE CRUDE OIL FOULING

The initial fouling rates of four crude oils were determined at a nominal bulk temperature of 315 °C, an initial heated wall shear stress of 13 Pa, and initial surface temperatures between 375 and 445 °C. These initial fouling rates ranged from 1.3(10-6) to 7.8(10-5) m2 K/kJ. Corresponding Arrhenius plots were linear with the initial fouling rates passing through an isokinetic temperature of 407.5 °C. A plot of the natural logarithm of the preexponential factors (7.6(104) – 5.2(1015) m2 K/kJ) versus the apparent activation energies (128 – 269 kJ/mol) was also linear, confirming the validity of the isokinetic temperature and the presence of the compensation effect. Below the isokinetic temperature, the relative fouling rates were Crude Oil C \u3e Crude Oil A \u3e Crude Oil D \u3e Crude Oil B; above the isokinetic temperature, the relative fouling rates were reversed (Crude Oil B \u3e Crude Oil D \u3e Crude Oil A \u3e Crude Oil C). Chemical characterization of a fouling deposit suggested that the dominant fouling mechanism at these conditions was coking with significant contributions from sedimentation (iron sulfide) and corrosion (~340 μm/yr) of the 304 stainless steel test material

Excitation of EMIC waves detected by the Van Allen Probes on 28 April 2013

Abstract We report the wave observations, associated plasma measurements, and linear theory testing of electromagnetic ion cyclotron (EMIC) wave events observed by the Van Allen Probes on 28 April 2013. The wave events are detected in their generation regions as three individual events in two consecutive orbits of Van Allen Probe-A, while the other spacecraft, B, does not detect any significant EMIC wave activity during this period. Three overlapping H+ populations are observed around the plasmapause when the waves are excited. The difference between the observational EMIC wave growth parameter (Eh) and the theoretical EMIC instability parameter (Sh) is significantly raised, on average, to 0.10 ± 0.01, 0.15 ± 0.02, and 0.07 ± 0.02 during the three wave events, respectively. On Van Allen Probe-B, this difference never exceeds 0. Compared to linear theory (Eh\u3eSh), the waves are only excited for elevated thresholds

Theory of Interaction of Memory Patterns in Layered Associative Networks

A synfire chain is a network that can generate repeated spike patterns with millisecond precision. Although synfire chains with only one activity propagation mode have been intensively analyzed with several neuron models, those with several stable propagation modes have not been thoroughly investigated. By using the leaky integrate-and-fire neuron model, we constructed a layered associative network embedded with memory patterns. We analyzed the network dynamics with the Fokker-Planck equation. First, we addressed the stability of one memory pattern as a propagating spike volley. We showed that memory patterns propagate as pulse packets. Second, we investigated the activity when we activated two different memory patterns. Simultaneous activation of two memory patterns with the same strength led the propagating pattern to a mixed state. In contrast, when the activations had different strengths, the pulse packet converged to a two-peak state. Finally, we studied the effect of the preceding pulse packet on the following pulse packet. The following pulse packet was modified from its original activated memory pattern, and it converged to a two-peak state, mixed state or non-spike state depending on the time interval

Guaranteed and Prospective Galactic TeV Neutrino Sources

Recent observations, particularly from the HESS Collaboration, have revealed rich Galactic populations of TeV gamma-ray sources, including a collection unseen in other wavelengths. Many of these gamma-ray spectra are well measured up to ~10 TeV, where low statistics make observations by air Cerenkov telescopes difficult. To understand these mysterious sources, especially at much higher energies--where a cutoff should eventually appear--new techniques are needed. We point out the following: (1) For a number of sources, it is very likely that pions, and hence TeV neutrinos, are produced; (2) As a general point, neutrinos should be a better probe of the highest energies than gamma rays, due to increasing detector efficiency; and (3) For several specific sources, the detection prospects for km^3 neutrino telescopes are very good, about 1-10 events/year, with low atmospheric neutrino background rates above reasonable energy thresholds. Such signal rates, as small as they may seem, will allow neutrino telescopes to powerfully discriminate between models for the Galactic TeV sources, with important consequences for our understanding of cosmic-ray production.Comment: 12 pages, 5 figures; minor changes to match published versio

Sparse and Dense Encoding in Layered Associative Network of Spiking Neurons

A synfire chain is a simple neural network model which can propagate stable synchronous spikes called a pulse packet and widely researched. However how synfire chains coexist in one network remains to be elucidated. We have studied the activity of a layered associative network of Leaky Integrate-and-Fire neurons in which connection we embed memory patterns by the Hebbian Learning. We analyzed their activity by the Fokker-Planck method. In our previous report, when a half of neurons belongs to each memory pattern (memory pattern rate $F=0.5$), the temporal profiles of the network activity is split into temporally clustered groups called sublattices under certain input conditions. In this study, we show that when the network is sparsely connected ($F<0.5$), synchronous firings of the memory pattern are promoted. On the contrary, the densely connected network ($F>0.5$) inhibit synchronous firings. The sparseness and denseness also effect the basin of attraction and the storage capacity of the embedded memory patterns. We show that the sparsely(densely) connected networks enlarge(shrink) the basion of attraction and increase(decrease) the storage capacity

Prelude to THEMIS tail conjunction study

A close conjunction of several satellites (LANL, GOES, Polar, Geotail, and Cluster) distributed from the geostationary altitude to about 16 &lt;I&gt;R&lt;sub&gt;E&lt;/sub&gt;&lt;/I&gt; downstream in the tail occurred during substorm activity as indicated by global auroral imaging and ground-based magnetometer data. This constellation of satellites resembles what is planned for the THEMIS (Time History of Events and Macroscopic Interactions during Substorms) mission to resolve the substorm controversy on the location of the substorm expansion onset region. In this article, we show in detail the dipolarization and dynamic changes seen by these satellites associated with two onsets of substorm intensification activity. In particular, we find that dipolarization at ~16 &lt;I&gt;R&lt;sub&gt;E&lt;/sub&gt;&lt;/I&gt; downstream in the tail can occur with dawnward electric field and without plasma flow, just like some near-Earth dipolarization events reported previously. The spreading of substorm disturbances in the tail coupled with complementary ground observations indicates that the observed time sequence on the onsets of substorm disturbances favors initiation in the near-Earth region for this THEMIS-like conjunction

Cosmic histories of star formation and reionization: An analysis with a power-law approximation

With a simple power-law approximation of high-redshift ($\gtrsim3.5$) star formation history, i.e., $\dot{\rho}_*(z)\propto [(1+z)/4.5]^{-\alpha}$, we investigate the reionization of intergalactic medium (IGM) and the consequent Thomson scattering optical depth for cosmic microwave background (CMB) photons. A constraint on the evolution index $\alpha$ is derived from the CMB optical depth measured by the {\it Wilkinson Microwave Anisotropy Probe} (WMAP) experiment, which reads $\alpha\approx2.18\lg{\mathscr{N}_{\gamma}}-3.89$, where the free parameter $\mathscr{N}_\gamma$ is the number of the escaped ionizing ultraviolet photons per baryon. Moreover, the redshift for full reionization, $z_f$, can also be expressed as a function of $\alpha$ as well as $\mathscr{N}_{\gamma}$. By further taking into account the implication of the Gunn-Peterson trough observations to quasars for the full reionization redshift, i.e., $6\lesssim z_f \lesssim7$, we obtain $0.3\lesssim\alpha\lesssim1.3$ and $80\lesssim\mathscr{N}_{\gamma}\lesssim230$. For a typical number of $\sim4000$ of ionizing photons released per baryon of normal stars, the fraction of these photons escaping from the stars, $f_{\rm esc}$, can be constrained to within the range of $(2.0-5.8)$.Comment: 10 pages, 4 figures, accepted for publication in JCA