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Antisense Knockdown of Cyclin E does not affect the Midblastula Transition in Xenopus laevis Embryos
Michael K. Slevin, Gillian Lyons-Levy, Daniel L. Weeks and Rebecca S. Hartley
volume 4 | issue 10
october 2005Pages: 1396 - 1402
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In Xenopus laevis embryos cyclin E protein remains constitutively high throughout the first 12 cell cycles following fertilization until the onset of the midblastula transition (MBT) (after the 12th cell cycle) when it undergoes a dramatic reduction. The disappearance of cyclin E at the MBT occurs independently of active cell cycle progression, zygotic transcription, protein synthesis and the nuclear to cytoplasmic ratio. This has suggested that cyclin E is part of an autonomous maternal timer that regulates the onset of the MBT. To determine how constitutively high levels of cyclin E are maintained prior to the MBT and to investigate if the reduction in cyclin E protein affects the timing of the MBT, we have knocked down endogenous cyclin E mRNA using an N,N-diethyl-ethylene-diamine (DEED) modified antisense oligonucleotide (ODN) targeted to its open reading frame (ORF). We report that maintenance of high levels of cyclin E protein before the MBT is due to a balance between ongoing translation and proteolytic degradation. In support of our antisense experiments, polysome analysis demonstrates that cyclin E mRNA is associated with the translated fraction prior to the MBT. Furthermore, knockdown of cyclin E was not associated with defects in the timing of developmental events. Our data suggests that cyclin E is not required for the later cell cycles of embryonic development and that the pathway effecting downregulation of cyclin E rather then cyclin E degradation itself may be part of a maternal timer that affects the onset of the MBT. 2
We now provide open access to journal articles published online for one year or more. This article may be downloaded at the following link:
Download PDF If the document does not open, please right-click on the link (control-click on a Macintosh) and select the option to save the file to disk.