Centrosomes are the main microtubule. organizing centers in animal cells. During meiosis and mito- sis, two centrosomes form the poles that direct the assembly of a bipolar spindle, thus ensuring the accurate segregation of chromosomes. Cells cannot tolerate the presence of more than two active centrosomes during meiosis or mitosis because doing so results in the formation of multipolar spindles, infidelity in chromosome segregation, and aneuploidy. Here, we show that fertilization or Spisula solidissima oocytes results in cells that contain three active centrosomes, two maternal and one paternal. During meiosis I, the paternal centrosomeis ability to nucleate microtubules is selectively shut off while maternal centrosomes remain competent to nucleate micro- tubules and assemble asters in the same cytoplasm. We propose that embryos can identify paternal vs. maternal centrosomes and can control them differentially.
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