Bipolar spindle assembly in the vertebrate oocyte relies on a self-organization chromosome-dependent pathway. Upon fertilization, the male gamete provides a centrosome, and the first and subsequent embryonic divisions occur in the presence of duplicated centrosomes that act as dominant microtubule organizing centres (MTOCs). The transition from meiosis to embryonic mitosis involves a necessary adaptation to integrate the dominant chromosome-dependent pathway with the centrosomes to form the bipolar spindle. Here, we took advantage of the Xenopus laevis egg extract system to mimic in vitro the assembly of the first embryonic spindle and investigate the respective contributions of the centrosome and the chromosome-dependent pathway to the kinetics of the spindle bipolarization. We found that centrosomes control the transition from the meiotic to the mitotic spindle assembly mechanism. By defining the kinetics of spindle bipolarization, the centrosomes ensure their own positioning to each spindle pole and thereby their essential correct inheritance to the two first daughter cells of the embryo for the development of a healthy organism.

T.C. was supported by a Formación de Personal Investigador (FPI) fellowship (Ministerio de Economıa y Competitividad) [grant number BES-2010-031355]. This work was supported by the Ministerio de Economıa y Competitividad [grant numbers ́ BFU2009-10202 and BFU2012-37163]. We acknowledge the support of the Spanish Ministerio de Economıa y Competitividad programme ́ ‘Centro de Excelencia Severo Ochoa 2013–2017’ [grant number SEV-2012-0208]