A 34 kD selenoprotein purified from rat testis was identified as a specific sperm nuclei glutathione peroxidase (snGPx) with similar properties to phospholipid hydroperoxide glutathione peroxidase (PHGPx). The determination of its primary structure by analysis of its first N‐terminal amino acids, database search, polymerase chain reaction, and sequencing of the cDNA showed that it differs from PHGPx in its N‐terminal sequence. This sequence, which is encoded for by an alternative exon in the first intron of the PHGPx gene, shows more than 50% homology to the protamine sequences and contains a nuclear localization signal. In rats, snGPx is highly expressed in the nuclei of the late spermatids where it is the only selenoprotein present. Its appearance coincides with the reorganization of DNA, which leads to highly condensed chromatin stabilized by cross‐linked protamine thiols. In selenium‐depleted rats where the concentration of snGPx had decreased to one‐third of the normal level, chromatin condensation was severely disturbed. We provided evidence that snGPx acts as a protamine thiol peroxidase responsible for disulfide cross‐linking by reduction of reactive oxygen species. Its dual function in chromatin condensation and the protection of sperm DNA against oxidation is necessary to ensure male fertility and sperm quality.
Although it has been known for over more than forty years that selenium is essential for the mammalian organism, our knowledge of the metabolism and the functions of the element is still incomplete. In order to investigate some of the still unanswered questions, several studies have been carried out on rats. The animals were either supplied with adequate amounts of selenium or were depleted by feeding with a seleniumdeficient diet over longer periods of time, sometimes for several generations. By combining methods for trace element analysis, tracer techniques and various biochemical procedures, the distribution of selenium was determined among tissues, tissue fractions, certain types of cells, subcellular compartments and proteins. In this way information was obtained on the regulation of selenium and on new selenium-containing proteins and their sites of action. Our main findings in these two areas of research will be presented and discussed.
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Mit Wistar‐Ratten im Alter von etwa 3 Monaten wurde ein in vitro‐Fertilisationsmodell erstellt. Die Befruchtung führten wir mit Brinster‐Medium bei einem pH von 7,8 und einer Osmolarität von 280–320 m Osmol/kg durch. Die Inkubationen er‐folgten bei 37°C und 5 % CO
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in Luft. Zur Eizellgewinnung wurden die Weibchen mit 10 IU PMSG und 30 IU HCG im Abstand von 48 Stunden stimuliert und nach weiteren 15 Stunden die Eizellen aus den eweiterten Eileiterampullen gewonnen. Die Insemination erfolgte mit epidydimalen Spermatoroen in vorgewärmtem Medium unter Paraffin‐öl in einer Konzentration von 1 × 106 Spermatozoen/ml. Nach 6 Stunden setzten wir die Eizellen in das Kultivierungsmedium, welches dem Befruchtungsmedium entsprach, um. Anhand der 2–Zellstadien wurde 48 Stunden nach Insemination die Befruchtungs‐rate ermittelt. Nach Zugabe von spermatozoenantikörperhaltigen Sewn — die Immunisierung erfolgte mit ganzen Rattenspermatozoen in Freund'schen Adjuvans zu gleichen Teilen (vlv) — zu den in vitro‐Fertilisationskulturen in einer Konzentration von 10 %, konnte im Vergleich zu der Kontrollgruppe (Immunisierung mit Freund'schen Adjuvans) eine statistisch signifikante Reduktion der in vitro‐Befruchtungsraten erzielt werden. Somit ist die Beeinflussung von spermatozoenantikörperhaltigen Sewn in vitro bei der Ratte, wie bereits bei der Maus beschrieben, möglich. Für den Menschen ergibt sich dadurch ein interessantes Denkmodell zur passiven Immunisierung mit Sperma‐toroen‐Antikörpern, welche in unserem Labor derreit als monoklonale Antikörper hergestellt werden.
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