Centriole biogenesis in early murine development

Centrosomes are the major microtubule organising centre of most cells. A centrosome consists of a pair of perpendicular centrioles surrounded by a cloud of pericentriolar material. Centrioles must be duplicated once per cell cycle to ensure each daughter cell inherits the correct number of centrioles. In somatic cells this process is controlled by centriole replication proteins including SAS-6 and Plk4. Centrioles have an unusual life-cycle in early mouse development. Both the sperm and the egg lack centrioles. Therefore the first few divisions in mouse embryos take place without centrioles. New centrioles are then formed ‘de novo’ in early developing embryos. In this thesis the molecular basis for this unusual scenario is examined. Firstly, a transgenic mouse model was used to confirm centrioles are formed de novo at the mouse blastocyst stage. This model was then used to examine the influence of centriole emergence on microtubule organisation. Secondly, overexpression of the centriole replication protein Plk4 was found to drive precocious formation of centriole-like structures in all stages of oocyte and embryo examined, which cause abnormal spindles. However, this does not appear to affect embryo development or chromosome segregation. Finally, overexpression of the downstream centriole component SAS-6 was also found to drive the formation of foci in embryos but strikingly, SAS-6 fails to arrange into centriole-like foci in immature or mature unfertilised oocytes. These experiments document the presence of an inducible de novo centriole formation pathway in mammalian oocytes and embryos, and show that the pathway is more resistant to activation prior to fertilisation