Die Testes spezifische Expression von Bromodomänen-Proteinen und Untereinheiten des Polycomb-Repressiven-Komplexes sowie deren mögliche Funktionen während der Spermatogenese in Mammalia

Die Spermatogenese ist ein sehr konservierter Prozess von der Fliege bis zu Mammalia, bei dem aus diploiden Spermatogonien haploide Spermatiden entstehen. Bei der Spermatogenese von Mammalia endet die Transkription in frühen, runden Spermatiden. Die für die Spermiogenese benötigten Transkripte werde...

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Bibliographic Details
Main Author: Gonzalez, Nicola Helena
Contributors: Rathke, Christina (Dr.) (Thesis advisor)
Format: Dissertation
Language:German
Published: Philipps-Universität Marburg 2015
Biologie
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Table of Contents: Spermatogenesis is a controlled process in which diploid spermatogonia develop into haploid spermatids. It is also highly conserved among many organisms. In mammalian spermatogenesis, transcription ends in round spermatids. Due to this, transcripts that are required for spermiogenesis have to be transcribed in round spermatids and are translationally repressed until they are needed. In contrast to mammals, transcription of translationally repressed mRNAs takes place in early spermatocytes of Drosophila melanogaster. In Drosophila, a testis-specific transcription factor TFIID is hypothesized to transcribe post-meiotic relevant mRNAs in association with testis-specific TATA-box binding-protein-associated factors (tTAFs). The Polycomb repressive complex 1 (PRC1) is assumed to be responsible for repressing spermiogenesis-relevant genes until they are transcribed in early spermatocytes. In these cells, PRC1 is supposed to be removed from the promoter of post-meiotic relevant genes by tTAFs and is recruited to the nucleolus. Additionally to the removal of PRC1, it is postulated that tTAFs are involved in transcription activation of these genes. Furthermore, three testis-specific bromodomain proteins (tBRD-1, tBRD-2, tBRD-3) have been identified which partially co-localize with subunits of PRC1 and tTAFs in spermatocytes of Drosophila. Based on these findings in Drosophila, it has been hypothesized that tBRDs are involved in transcriptional initiation in spermatocytes. It is obscure, whether PRC1 and PRC2 also exist in mammalian testes. So far, BRDT is the only known BRD-protein considered to play a role during transcription initiation and chromatin reorganization throughout spermiogenesis. The first aim of this study was to evaluate classical BRD-proteins in mammalian testes. The results revealed that the transcripts of Brd2, Brd8 and Tif1α are significantly enriched in round spermatids and that these BRD-proteins are localized in the same germ cells as active RNA-polymerase II is. Two BRD-proteins (BRD3, SMARCA2) showed the same expression pattern as hyperacetylated H4 and transition protein 1. Whereby active RNA-polymerase II served as a marker for transcription. Hyperacetylated H4 as well as transition protein 1 were used to indicate the upcoming histone-to-protamine transition. Summing up these results, in addition to BRDT three further BRD-proteins (BRD2, BRD8 and TIF1α) were detected that could be involved in transcription of meiotic and post-meiotic relevant genes. Two other BRD-proteins (BRD3, SMARCA2) were found which could play a role during chromatin reorganization throughout histone-to-protamine transition. The second aim was to analyze if classical subunits of the PRC1 and PRC2 are present in the testes of mice and men. In mice, transcripts of some PRC1-subunits (Ring1, Bmi1, Scmh1, Cbx2, and Cbx8) and PRC2-subunits (Ezh2, Eed, Suz12) were detected in testes. Due to the transcription pattern of these subunits within different germ cells of mice, it is assumed that the subunits RING1, BMI1 and SCMH1 are part of PRC1 and EZH2, EED and SUZ12 could be part of the PRC2. Since some PRC- and BRD-transcripts are significantly enriched in meiotic and post-meiotic germ cells, it is assumed that PRC1 and PRC2 are newly synthesized in these germ cells in order to repress all spermatogenesis relevant genes and therefore stop transcription during spermatid differentiation.