miRNA functions in pluripotency and spermatogenesis
by Lukasz Smorag
Date of Examination:2012-10-18
Date of issue:2013-10-23
Advisor:Dr. Dasaradha Venkata Krishna Pantakani
Referee:Prof. Dr. Wolfgang Engel
Referee:Prof. Dr. Sigrid Hoyer-Fender
Referee:Prof. Dr. Michael Kessel
Referee:Prof. Dr. Ahmed Mansouri
Referee:Prof. Dr. Tomas Pieler
Referee:Prof. Dr. Peter Schu
Persistent Address:
http://dx.doi.org/10.53846/goediss-4091
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Abstract
English
For quite a long time, non-coding RNAs (ncRNAs) were discriminated and considered as an evolutionary error. In light of this opinion, discovery of small ncRNAs, in particular microRNA (miRNA), which can regulate the gene expression post-transcriptionally, was a surprise. Computational and experimental approaches revealed the presence of miRNA in almost all living organisms, including plants and Homo sapiens. Growing body of evidence suggests that miRNAs play a crucial role in different aspects of life, ranging from regulation of single cell metabolism through controlling of cell fate and development of multicellular organisms. The present thesis is aimed at understanding the function of miRNAs in pluripotent stem cells and in spermatogenesis. In the first part of this thesis, we studied the role of miRNA-290 cluster, a pluripotency-related miRNA cluster, during differentiation of embryonic stem cells (ESCs). Our results show that miRNA-290 family members are not sufficient to prevent the loss-of-pluripotency during induced differentiation of ESCs. However, inhibition of these miRNAs was found to facilitate the differentiation process. In addition, overexpression of miR-290 cluster in ESCs resulted in prevention of differentiation towards mesoderm and germ cells, possibly through modulation of Wnt-signaling pathway. Collectively, these results support the assumption that miRNA-290 members are included in regulation of differentiation fate of ESCs. In the second part of this thesis, we identified that ESCs but not germline derived pluripotent stem cells retain high expression levels of miRNA-302 cluster, another pluripotency-related miRNA clusters. Further, we found out subtle differences in expression levels of germ cell marker genes between ESCs and germline derived pluripotent cell types such as multipotent adult germline stem cells (maGSCs) and embryonic germ cells (EGCs). Interestingly expression of germ cell marker genes was negatively correlated with expression of miRNA-302 family members. In agreement with these observations overexpression of miRNA-302 cluster in maGSCs resulted in downregulation of germ cell marker genes. Taken together, our results highlight that miRNA-302 cluster regulates differentiation of ESCs to the germ cell lineage. In the third part of this thesis, we made an attempt to establish the miRNA signature of various stage-specific germ cells. Towards this end, we generated a double transgenic mouse model (Stra8/EGFP and Sycp3/DsRed), which helped us to obtain pure germ cell populations from mouse testis. Next, we compared miRNA expression profiles between spermatogonial stem cells (SSCs), pre-meiotic (green) and meiotic (red) cells. Through this study, we identified that stage-specific miRNAs, i.e., miRNA-221, -203 and -34b-5p regulate their corresponding targets such as c-Kit, Rbm44 and Cdk6 to orchestrate the spermatogenesis process. To sum up this study, we described spatiotemporal expression pattern of miRNAs and their possible functions during spermatogenesis. In the present study, we also identified two novel pluripotent cell-specific miRNAs: miR-135b and miR-363. The function of these novel pluripotency-related miRNAs is under investigation. Furthermore, using our double transgenic mouse model, we identified several uncharacterized meiotic cell-specific genes. Currently, the molecular and biochemical characterization of these genes and their functions during meiosis is under the way.
Keywords: miRNAs; pluripotency; spermatogenesis