Linker histone protects linker DNA on only one side of the core particle and in a sequence-dependent manner

The protection against micrococcal nuclease digestion afforded to chromatosomal DNA by the presence of a linker histone (H1(o)) has been quantitatively measured in two reconstituted systems. We have used chromatosomes reconstituted at two distinct positions on a DNA fragment containing the 5S rRNA gene from Lytechinus variegatus and at a specific position on a sequence containing Gal4- and USF-binding sites. In all cases, we find asymmetric protection, with approximately 20 bp protected on one side of the core particle and no protection on the other. We demonstrated through crosslinking experiments that the result is not due to any sliding of the histone core caused by either linker histone addition or micrococcal nuclease cleavage. Because the core particle is itself a symmetric object, the preferred asymmetric location of a linker histone must be dictated by unknown elements in the DNA sequence.

Interaction of liver methionine adenosyltransferase with hydroxyl radical

Liver methionine adenosyltransferase (MAT) plays a critical role in the metabolism of methionine converting this amino acid, in the presence of ATP, into S-adenosylmethionine. Here we report that hydrogen peroxide (H2O2), via generation of hydroxyl radical, inactivates liver MAT by reversibly and covalently oxidizing an enzyme site. In vitro studies using pure liver recombinant enzyme and mutants of MAT, where each of the 10 cysteine residues of the enzyme subunit were individually changed to serine by site-directed mutagenesis, identified cysteine 121 as the site of molecular interaction between H2O2 and liver MAT. Cysteine 121 is specific to the hepatic enzyme and is localized at a "flexible loop" over the active site cleft of MAT. In vivo studies, using wild-type Chinese hamster ovary (CHO) cells and CHO cells stably expressing liver MAT, demonstrate that the inactivation of MAT by H2O2 is specific to the hepatic enzyme, resulting from the modification of the cysteine residue 121, and that this effect is mediated by the generation of the hydroxyl radical. Our results suggest that H2O2-induced MAT inactivation might be the cause of reduced MAT activity and abnormal methionine metabolism observed in patients with alcoholic liver disease.

[The characteristics of macular branch retinal vein occlusion]

OBJECTIVE

The study was designed for the analysis on data of 51 patients with macular branch retinal vein occlusion (McBRVO) and the comparison between them and 210 patients (214 eyes) with major branch retinal vein occlusion (MjBRVO).

METHODS

Fluorescein angiography, ophthalmoscope and slit-lamp were used for the examination of the venous obstructive site and the locations of artery and vein.

RESULTS

(1) The incidence of McBRVO was 19.5% (51/261) in branch retinal vein occlusion. (2) The site of occlusion: the incidence of McBRVO at supero-temporal branches was 72.5% (37/51) and the incidence of MjBRVO was 73.4% (157/214). (3) The involved branch at the first macular branch accounted for 39.6%, the second branch 58.3%, and the third branch 2.1%. The artery anterior to the vein at arteriovenous crossing at the obstructive site accounted for 93.0% in the McBRVO group and 95.0% in the MjBRVO group. (4) The complications and visual prognosis: The incidence of cystoid macular edema was 20.0% in McBRVO group and that was 28.5% in the MjBRVO group. No neovascularization was found in the McBRVO group, while 37.9% neovascular formation was found in the MjBRVO group. The visual acuity recovered to 0.5 or better was in 88.2% in the McBRVO group, while 57.0% in the MjBRVO group (P < 0.005).

CONCLUSION

There are no significant differences in sex, age, laterality, pathogenesis as well as occlusion site between the McBRVO and MjBRVO groups, but the visual prognosis is better in the former than that in the latter group.

Sex-specific and non-sex-specific oligomerization domains in both of the doublesex transcription factors from Drosophila melanogaster

The doublesex gene of Drosophila melanogaster encodes the alternatively spliced, sex-specific transcription factors DSXM and DSXF. These factors regulate male- and female-specific transcription of many genes. For example, female-specific transcription of the yolk protein 1 gene is regulated by DSXM repression in males and DSXF activation in females. In this study we used in vitro interaction assays and the in vivo yeast two-hybrid method to identify and examine oligomerization domains of the DSX proteins. A 66-amino-acid segment common to both proteins (amino acids 39 to 104) contains a sequence-specific DNA binding domain and an oligomerization domain (OD1). The OD1 domain oligomerizes up to at least a pentamer, but only dimers bound to a palindromic regulatory site in the yolk protein 1 gene are detected. Both subunits of the OD1 dimer are in contact with DNA. Another segment of each protein (amino acids 350 to 412 for DSXF and 350 to 427 for DSXM) contains a second oligomerization domain (OD2F and OD2M, respectively). The OD2 domains have both sex-specific and non-sex-specific sequences which are necessary for oligomerization. On the basis of sequence analysis, we predict that OD2 oligomerizes through coiled-coil interactions. We speculate that the common function of OD1 and OD2 is to oligomerize the full-length proteins, whereas their specialized functions are to form a dimeric DNA binding unit and a sex-specific transcriptional activation or repression unit.

Analysis of basic fibroblast growth factor in rats with inherited retinal degeneration

In RCS rats, photoreceptors degenerate between postnatal days 20 and 60, secondary to a genetic defect expressed in the neonatal retinal pigmented epithelium (RPE). Previous work has shown delay of the photoreceptor degeneration in this model by intraocular injection of basic fibroblast growth factor (bFGF). Evidence is presented here, from bFGF immunostaining and Northern analysis of bFGF mRNA, for reduced bFGF expression in uncultured RPE of dystrophic RCS pups. It is also shown that in the mutant eyes angiogenesis in the underlying choroid, which normally occurs between postnatal days 7 and 10, is markedly delayed, with irregular distribution of vessels, consistent with a reduction in this known angiogenesis factor. Mutational analysis of the bFGF transcript and gene by denaturing gradient gel electrophoresis and Southern analysis did not, however, reveal abnormalities in the coding sequence of this gene in RCS rats.

[Examination and analysis on keratometry and axis of myopia]

In this study, we applied SYSTAT software package to deal with the data, measured the keratometric values and axes of 276 patients with myopia (523 eyes), analyzed on the data of keratometry and astigmatism, correlations between the myopic degree and keratometric value and between the former and length of axis, and pathogenesis of myopia. The results revealed that the vertical corneal refractive power was stronger than the horizontal value, the vertical corneal refractive power in high and superhigh myopia was greater than that in mild and medium myopia, the axial lengths are significantly different among mild, medium, high and superhigh myopia (P < 0.01), and the myopic degree is correlated with the keratometric value and axial length. We can conclude that keratometry and axis are two main factors for the formation of myopia.

Three protein binding sites form an enhancer that regulates sex- and fat body-specific transcription of Drosophila yolk protein genes

Transcription of the Drosophila yolk protein (Yp) genes is regulated by the somatic sex determination pathway. A gene at the bottom of this pathway, doublesex, encodes the female-specific DSXF and male-specific DSXM proteins that bind to and regulate transcription from several sites in the Yp genes. We report site-directed mutagenesis, protein binding and germline transformation experiments that identify and characterize the activity of a single binding site (dsxA) for the doublesex proteins and two binding sites for other regulatory proteins. A single copy of the three sites is sufficient to direct the sex and fat body specificities of Yp transcription. The sites form an enhancer with two strongly synergistic enhancer elements. One element (22 bp) consists of dsxA and an overlapping site, bzip1, that binds the DmC/EBP (slbo) protein, a member of the bZIP family of transcriptional activators. The other element is an 11 bp binding site (ref1) for an unknown protein. Tissue-specific activation requires strong cooperation between the ref1 site and the bzip1 or dsxA sites. Sex specificity is regulated exclusively by the dsxA site which connects the sex determination pathway to the target gene through DSXM repression and DSXF activation.

Integrating sex- and tissue-specific regulation within a single Drosophila enhancer

We have investigated the integration of sex- and tissue-specific transcriptional regulation in Drosophila. A single copy of the o-r enhancer from yolk protein genes directs female- and fat body-specific transcription. It consists of four protein-binding sites: dsxA, which binds male (DSXM) and female (DSXF) proteins encoded by the doublesex gene; aef1, which binds the AEF1 repressor; bzip1, which binds the DmC/EBP activator encoded by the slbo gene; and ref1, which binds an unknown activator. Multimeric and mutated binding sites were used in protein binding, germ-line transformation, and genetic experiments to examine the independent and combinatorial activities of the proteins and DNA sites. DSXF activates from dsxA by sterically excluding AEF1 repressor from the aef1 site and synergistically activating transcription together with a protein at bzip1. Sex specificity in fat bodies arises from the opposite effect of DSXM, which represses activity of the protein at bzip1. Tissue specificity is regulated by all four DNA sites. Separately, bzip1 and ref1 activate transcription in ovarian somatic cells and all nongonadal tissues, respectively, whereas together they activate only in fat bodies. The aef1 site represses ectopic transcription in ovaries and dsxA antirepresses this activity in fat bodies. Thus, in the organism, ref1 and bzip1 act combinatorially to direct the fundamental tissue specificity, aef1 and dsxA modulate this tissue specificity, and dsxA adds sex specificity.

Hepatic stimulator substance protects against acute liver failure induced by carbon tetrachloride poisoning in mice

Hepatic stimulator substance was extracted from the liver of weanling Sprague-Dawley rats according to the method of LaBrecque. Quang-Ming mice were injected with carbon tetrachloride to induce acute liver failure. Hepatic stimulator substance suppressed the elevation of ALT and AST induced by carbon tetrachloride in a dose-dependent manner. Hepatic histological changes indicated that hepatic stimulator substance reduced the severity of hepatic lesion induced by carbon tetrachloride and reversed carbon tetrachloride-induced reduction of hepatic mitochondrial succinic dehydrogenase activity. In attempting to elucidate the mechanism or mechanisms of this protective effect, we found that hepatic stimulator substance significantly restored the carbon tetrachloride-induced decrease of hepatocyte plasmalemma and mitochondrial and microsomal membrane fluidity. Hepatic stimulator substance also decreased the malondialdehyde content of carbon tetrachloride-intoxicated mice; restored the liver-reduced glutathione content, which was lowered by carbon tetrachloride intoxication; stimulated liver regeneration, as shown by enhanced DNA synthesis; and increased the 3H-thymidine incorporation into DNA of hepatocytes. We propose that hepatic stimulator substance protects the liver against acute liver failure induced by carbon tetrachloride poisoning, probably by an antioxidative effect on hepatocyte membrane lipid peroxidation, which was increased by free radicals produced from carbon tetrachloride. In addition, hepatic stimulator substance stimulates hepatocyte proliferation. These protective mechanisms may act in concert to protect against carbon tetrachloride injury.

[A study of the protective mechanism of hepatic stimulator substance against experimental acute liver failure in mice]

In our previous work we have demonstrated a protective effect of hepatic stimulator substance (HSS) on experimental hepatic injury in mice. The underlying mechanism of this effect was further investigated with the following results: (1) HSS could significantly increase the CCl4-induced decrease of membrane fluidity of hepatic plasmalemma, mitochondria and microsomes to the control level. (2) HSS could decrease the liver melondialdehyde contents of CCl4-intoxicated mice. (3) HSS could restore the liver glutathione contents lowered by CCl4-intoxication. (4) HSS stimulated regeneration of liver, enhanced DNA synthesis of hepatocytes and increased 3H-TdR incorporation into DNA. According to the results mentioned above, we proposed that HSS should have an antioxidative effect on the hepatic membrane lipid peroxidation which was increased by free radicals produced by CCl4. In addition, HSS might increase antioxidative ability of hepatocyte and stimulate the proliferation of hepatocytes. These protective mechanisms might act in a concordant manner.

[Protective effect of hepatic stimulator substance against experimental acute liver failure in mice]

A hepatic stimulator substance (HSS) was extracted from the liver of male weanling SD rats according to the method of LaBrecque. The mice were injected with carbon tetrachloride or D-galactosamine to induce hepatic injuries and the protective effect of HSS on thus induced hepatic damage was investigated. The results were as follows: (1) HSS could suppresses the elevation of sGPT and sGOT induced by carbon tetrachloride intoxication in a dose-dependent manner. (2) Hepatic histological findings indicated that the degree of CCl4 or D-galactosamine-induced hepatic lesions could be lessened by HSS. (3) CCl4-induced reduction of hepatic mitochondrial succinic dehydrogenase activity could be restored by HSS. (4) Insulin-glucagon enhanced the survival of D-galactosamine intoxicated mice and stimulated hepatocyte proliferation, thus showing less pronounced hepatic damage.