Model experiment of magnetic field amplification in laser-produced plasmas via the Richtmyer-Meshkov instability

A model experiment of magnetic field amplification (MFA) via the Richtmyer-Meshkov instability (RMI) in supernova remnants (SNRs) was performed using a high-power laser. In order to account for very-fast acceleration of cosmic rays observed in SNRs, it is considered that the magnetic field has to be amplified by orders of magnitude from its background level. A possible mechanism for the MFA in SNRs is stretching and mixing of the magnetic field via the RMI when shock waves pass through dense molecular clouds in interstellar media. In order to model the astrophysical phenomenon in laboratories, there are three necessary factors for the RMI to be operative: a shock wave, an external magnetic field, and density inhomogeneity. By irradiating a double-foil target with several laser beams with focal spot displacement under influence of an external magnetic field, shock waves were excited and passed through the density inhomogeneity. Radiative hydrodynamic simulations show that the RMI evolves as the density inhomogeneity is shocked, resulting in higher MFA

Auto-regulation of the Sohlh1 gene by the SOHLH2/SOHLH1/SP1 complex: implications for early spermatogenesis and oogenesis.

Tissue-specific basic helix-loop-helix (bHLH) transcription factor proteins often play essential roles in cellular differentiation. The bHLH proteins SOHLH2 and SOHLH1 are expressed specifically in spermatogonia and oocytes and are required for early spermatogonial and oocyte differentiation. We previously reported that knocking out Sohlh2 causes defects in spermatogenesis and oogenesis similar to those in Sohlh1-null mice, and that Sohlh1 is downregulated in the gonads of Sohlh2-null mice. We also demonstrated that SOHLH2 and SOHLH1 can form a heterodimer. These observations led us to hypothesize that the SOHLH2/SOHLH1 heterodimer regulates the Sohlh1 promoter. Here, we show that SOHLH2 and SOHLH1 synergistically upregulate the Sohlh1 gene through E-boxes upstream of the Sohlh1 promoter. Interestingly, we identified an SP1-binding sequence, called a GC-box, adjacent to these E-boxes, and found that SOHLH1 could bind to SP1. Furthermore, chromatin-immunoprecipitation analysis using testes from mice on postnatal day 8 showed that SOHLH1 and SP1 bind to the Sohlh1 promoter region in vivo. Our findings suggest that an SOHLH2/SOHLH1/SP1 ternary complex autonomously and cooperatively regulates Sohlh1 gene transcription through juxtaposed E- and GC-boxes during early spermatogenesis and oogenesis

SOHLH2/SOHLH1 heterodimer regulates the <i>Sohlh1</i> promoter through a restricted upstream region.

<p>(A) Reporter assay using the pGL3-Basic vector containing the −1036 bp mouse <i>Sohlh1</i> promoter (200 ng), a pCAG-Sohlh2 expression vector (0 to 40 ng), a pCAG-Sohlh1 expression vector (0 to 40 ng), and a pRL-CMV normalization vector (0.1 ng). Results show the <i>Sohlh1</i> promoter-driven firefly luciferase activity relative to CMV promoter-driven Renilla luciferase activity. (B) Reporter assays using pGL3-Basic vectors containing various lengths of the mouse <i>Sohlh1</i> promoter (200 ng), a pCAG-Sohlh2 expression vector (200 ng), a pCAG-Sohlh1 expression vector (200 ng), and a pRL-CMV normalization vector (0.1 ng). Results show the firefly/Renilla luciferase activity relative to that obtained with the −1036 bp promoter fragment, which was arbitrarily set at 1. Error bars represent the S.E.M. of the means of 3–5 separate experiments done in triplicate. <i>P</i> values were calculated by Student's <i>t</i>-test. *<i>P</i><0.05. SOHLH2 and SOHLH1 regulate the activity of the mouse <i>Sohlh1</i> promoter through a region −154 to −321 bp upstream from its translational start site.</p

SOHLH2 and SOHLH1 form homodimers.

<p>(A) Western blots of lysates of HEK293 cells overexpressing SOHLH2, FLAG-SOHLH2, and SOHLH2-Myc, using anti-SOHLH2, anti-FLAG, and anti-Myc antibodies. (B) Western blots of lysates of HEK293 cells overexpressing SOHLH1, FLAG-SOHLH1, and SOHLH1-Myc, using anti-SOHLH1, anti-FLAG, and anti-Myc antibodies. (C) Lysates of HEK293 cells overexpressing FLAG-SOHLH2, SOHLH2-Myc, or SOHLH2 were immunoprecipitated with anti-FLAG agarose beads and subjected to western blotting using an anti-Myc antibody. Arrow: an SOHLH2-Myc band. Pre-immunoprecipitation lysates were used as input. (D) Lysates of HEK293 cells overexpressing FLAG-SOHLH1, SOHLH1-Myc, or SOHLH1 were immunoprecipitated with anti-FLAG agarose beads and subjected to western blotting using an anti-Myc antibody. Arrow: an SOHLH1-Myc band. Pre-immunoprecipitation lysates were used as input. Anti-FLAG agarose was loaded to indicate the IgG heavy chain (dashed arrow) and IgG light chain (arrowhead) bands.</p

Binding of SOHLH1 and SP1 to the <i>Sohlh1</i> promoter region <i>in vivo</i>.

<p>Binding of SOHLH1 and SP1 to the <i>Sohlh1</i> promoter region <i>in vivo</i> was examined by ChIP assay using P8 testes. The <i>Sohlh1</i> promoter region (−371 to −284) and the control region far upstream of the <i>Sohlh1</i> promoter (−8946 to −8834) were quantitated by Real-time PCR from chromatin fractions immunoprecipitated with anti-SOHLH1 antibody, anti-SP1 antibody, or control rabbit IgG. Fold enrichment represents the quantity of the region immunoprecipitated with anti-SOHLH1 (A) or anti-SP1 (B) relative to that immunoprecipitated with control rabbit IgG. Values are expressed as means ±S.E.M. of three technical replicates. <i>P</i> values were calculated by Student's <i>t</i>-test. *<i>P</i><0.03.</p

The three <i>Sohlh1</i>-promoter E-boxes are not equal in regulating <i>Sohlh1</i>.

<p>Reporter assays using the pGL3-Basic vector with various mutations of the E-boxes in the <i>Sohlh1</i> promoter, along with pCAG-Sohlh1 and pCAG-Sohlh2 expression vectors (200 ng each). Results show the firefly/Renilla luciferase activity relative to that of the −1036 bp intact promoter, which was arbitrarily set at 1. Error bars represent the S.E.M. of the means of 3–6 separate experiments done in triplicate. <i>P</i> values were calculated by Student's <i>t</i>-test. *<i>P</i><0.05.</p

Interaction of SP1 to the SOHLH proteins.

<p>(A) Lysates of HEK293 cells overexpressing SP1 and FLAG-SOHLH1 or SOHLH1 were immunoprecipitated with anti-FLAG agarose beads and analyzed by western blotting using anti-SOHLH1 or anti-SP1 antibodies. Arrowhead: FLAG-SOHLH1. Dashed arrow: SOHLH1. (B) Lysates of HEK293 cells overexpressing SP1 and FLAG-SOHLH2 or SOHLH2 were immunoprecipitated with anti-FLAG agarose beads and analyzed by western blotting using anti-SOHLH2 or anti-SP1 antibodies. Arrowhead: FLAG-SOHLH2. Dashed arrow: SOHLH2. Arrow: IgG heavy chain. Pre-immunoprecipitation lysate was used as input.</p

Conserved regulatory regions of the mouse and rat <i>Sohlh1</i> gene.

<p>The underlined E- and GC-box sequences are conserved between the mouse and rat. These E- and GC-box sequences are also found in the <i>Sohlh1</i> promoter region of the chimpanzee and human (not shown).</p