Control of pluripotency during the oocyte-to-embryo transition in caenorhabditis elegans

Abstract

The germline of Caenorhabditis elegans has been used as a model system to study the control of pluripotency in germ cells: through the mean of a genetic screen, from which most of the results of this thesis derived, different factors involved in the control of pluripotency in growing oocytes have been found. It is interesting to note that all the factors identified in the screen are cytoplasmic RNA-binding proteins (RBPs) involved in different aspects of post-transcriptional gene regulation. Post-transcriptional gene regulation can therefore be considered the main mechanism through which a “quiescent” pluripotent state is maintained in oocytes until after fertilization. The oocyte-to-embryo transition has been shown to occur in the absence of polymerase II-dependent transcription, a fact which better clarifies the general importance of RBPs in this developmental context. This study has been the first one to provide the example of a factor, LIN-41, which regulates pluripotency specifically in developing oocytes. lin-41 mutant oocytes lose their germline identity, enter an embryonic and pluripotent state and terminally differentiate into somatic cells. Although LIN-41 was already known in C. elegans to be involved in a somatic developmental pathway, it appears to regulate different targets in the two developmental contexts. Not only lin-41 mutants, but also another class of mutants has been identified in the screen and started to be characterized. The oocytes of the mutants belonging to this class prematurely enter an embryonic state, but, despite that, they are not able to fully acquire pluripotent features and to differentiate into somatic cells. Overall this thesis has been able to shed some light on the factors and, at least in part, the post-transcriptional mechanisms controlling pluripotency during the oocyte-to-embryo transition.