Acentrosomal

Acentrosomal refers to cellular processes and structures that lack a centrosome, the typical primary microtubule organizing center found in many animal cells. In acentrosomal divisions, the spindle forms without a centrosome, relying instead on chromatin-mediated microtubule nucleation and non-centrosomal organizing centers to establish a bipolar spindle.

In animal oocytes, especially during meiosis, centrosomes are absent or inactivated, and spindle assembly is driven by the chromosomes themselves. Chromatin-associated factors and the Ran-GTP gradient promote microtubule nucleation around chromosomes, while motor proteins organize these microtubules into a functional spindle. The augmin complex can recruit γ-tubulin ring complexes to existing microtubules to generate new minus ends, supporting robust spindle formation without centrosomes.

Plants and some other eukaryotes also perform acentrosomal spindle assembly, as they lack canonical centrosomes and rely on multiple non-centrosomal MTOCs or chromatin-anchored nucleation to build the spindle apparatus during mitosis and meiosis.

Acentrosomal mechanisms are a focus of study for understanding how accurate chromosome segregation is achieved in the absence of centrosomes and for insights into fertility and developmental biology. Errors in acentrosomal spindle assembly can contribute to aneuploidy in oocytes and have implications for evolution and species differences in mitotic machinery.