Résumé
Of the numerous processes under the regulation of differential protein phosphorylation, mitotic transit has recently attracted intense examination with the isolation of a 34000 Mr kinase as an active component of the maturation promoting factor (MPF) in oocytes and its identification as an homolog of the yeast cell division cycle gene product cdc2, and the histone 1 kinase from mammalian cells (1, 2, 3). This kinase, now known as p34cdc2 is itself regulated by multiple dephosphorylation and phosphorylation and its association with two or more cyclin proteins (for reviews see 4, 5, 6). However, whilst more and more reports seemed to converge to make p34cdc2 an universal control switch driving the different events associated with mitotic induction, we found that microinjection of this kinase in a highly purified and active form was insufficient to induce interphase somatic mammalian cells to enter mitosis (7). The present report will detail aspects of the potential functions of this kinase and other regulatory molecules which bring further insights on the role of differential protein phosphorylation in the regulation of mammalian cell mitosis. Our approach has involved microneedle microinjection to examine the consequences on the progression through the cell cycle, cell morphology and cytoarchitecture of artificially elevating or inactivating different kinase and phosphatase pathways in synchronized mammalian cells. We have examined in particular a crucial point in mitosis, prophase entry, focussing on the role of p34cdc2 kinase, src kinase and the requirement of a distinct pathway involving inactivation of the cAMP-dependent protein kinase.