The transition from egg to embryo in C. elegans involves fertilisation, meiosis, exit from meiosis and the establishment of the anteroposterior (AP) axis. These last two processes may be connected - many mutants with meiotic defects, including several that affect ubiquitin-mediated proteolysis, have polarity defects. Now, Bruce Bowerman and colleagues report that PAM-1, a puromycin-sensitive aminopeptidase that might act in conjunction with the proteasome to degrade ubiquitin-tagged proteins, is required for both meiotic exit and AP polarity in one-cell worm embryos (see ). The researchers show that meiotic exit is delayed and the AP axis is not specified in pam-1 mutants. As inactivation of the B-type cyclin CYB-3 rescues the first (but not the second) of these defects, PAM-1 may regulate CYB-3 during meiotic exit but presumably targets other proteins to regulate polarity. The researchers conclude that PAM-1 contributes to the proteolytic machinery that triggers cell-cycle progression and the establishment of AP polarity in the early worm embryo, and possibly in other embryos.
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