The Necessity of Geminin for Pluripotency and Neural Lineage

by Golnaz Aghazadeh Tabrizi
Doctoral thesis
Date of Examination:2012-12-13
Date of issue:2013-08-21
Advisor:Prof. Dr. Michael Kessel
Referee:Prof. Dr. Matthias Dobbelstein
Referee:Prof. Dr. Ahmed Mansouri
Persistent Address: http://dx.doi.org/10.53846/goediss-4005

 

 

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Abstract

English

Pluripotent mouse embryonic stem cells (ESCs) are in vitro derivatives of the early mouse embryo. They can self-renew infinitely, and have the ability to differentiate into embryonic lineages including the germ line. ESCs have the ability to give rise to all tissues of a mouse if added early in embryogenesis. They possess a specific transcriptional network, an “open” chromatin state and a rapid cell cycle. Our research group is interested to study the link between cell fate determination and cell cycle regulation, using the Geminin protein as an anchor. Geminin plays a central role in controlling the fidelity of DNA replication, and more recently additional functions in the regulation of proteins involved in patterning and differentiation were recognized. It is highly expressed in the early embryo and in pluripotent cells, and its genetic inactivation is lethal after the first few cell divisions. We have generated ESCs, in which the Geminin gene can be inactivated by the addition of the small molecule tamoxifen. We found that Geminin is essential for self-renewal of pluripotent cells, and that the absence of Geminin causes reduction of pluripotency markers. The loss of Geminin altered the differentiation capacity of the ESCs; they could not give rise to the neural lineage anymore, but instead differentiated into the alternative mesendodermal lineage. Geminin turned out to be redundant in differentiated, somatic cells, but was necessary for their reprogramming to pluripotent cells. We could show that its function is targeted on the Sox2 gene, a key transcription factor of the pluripotency circuit, essential for the maintenance of pluripotency. The Sox2 enhancer requires Geminin for activity, and becomes epigenetically repressed in its absence. In conclusion, we introduce Geminin as a required factor for totipotency, pluripotency and the early neural lineage.
Keywords: Geminin; Pluripotency; reprogramming; Epigenetics; Sox2
 
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