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Polarization occurs in all organisms and is fundamental to specifying various cell fates and achieving functional potential. In one-cell C. elegans embryos, polarization, characterized by a first asymmetric division, establishes the anterior-posterior axis. The sperm-donated centrosome initiates polarization by triggering a series of changes at the posterior-cortex, namely destabilizing the actomyosin cytoskeleton, inducing cortical flows and localizing cytoplasmic determinants like PAR proteins. Studies have shown the centrosome need not be closely associated with the cortex to cue polarity, but increased centrosome-cortex distance has been correlated to severe polarity defects. Additionally, contact with the posterior-cortex is normally observed during polarization. However, the exact dynamics, specifically timing and duration, of centrosome-cortex interaction remain controversial. PAM-1 is a puromycin-sensitive aminopeptidase believed to anchor the centrosome to the posterior-cortex. In pam-1 mutants, which lack the essential puromycin-sensitive aminopeptidase, the centrosome prematurely departs from the cortex and becomes mislocalized, culminating in a failure to establish polarity. Confocal microscopy and time-lapse imaging of wild-type (WT) and pam-1 mutant strains, both with GFP-tagged chromosomes and centrosomes, provided some insight. Compared to centrosomes in WT, pam-1 centrosomes contact the cortex for significantly shorter durations of time, while also occurring earlier during the cell-cycle. Using pseudocleavage, a harbinger of polarity, to determine whether duration or timing had greater significance, it became apparent that longer durations produced higher likelihoods of pseudocleavage. This allows us to hypothesize a model whereby the centrosome can cue polarity initiation from afar but centrosome-cortex contact is necessary to sustain the polarization process. Future work involves synthesizing WT and pam-1 strains with γ-tubulin::GFP and PAR-6::GFP to analyze how varying centrosome behavior affects localization of PAR-6 to the anterior-cortex.
Parikh, Devayu A., "Comparing Centrosome Behavior in Wild-Type and pam-1 Mutant One-Celled Caenorhabditis elegans Embryos" (2015). Biology Summer Fellows. 16.