Absence of centrioles in the first and second meiotic spindles of mouse oocytes

TLDR

Centrioles are present in oogonia and early oocytes up to the pachytene stage but disappear in later meiotic stages. During germinal vesicle breakdown, electron‑dense fibrillar foci near the nucleus generate microtubules that assemble into asters functioning as spindle poles for both meiotic divisions. The spindle poles contain multiple, variable‑number centers, demonstrating that centrioles are not required for spindle formation.

Abstract

ABSTRACT Centrioles are present in oogonia and oocytes of hamsters, mice, rats, gerbils and man up to the pachytene stage. In subsequent meiotic stages, centrioles are absent. At the time of germinal vesicle breakdown in the mouse several foci composed of electron-dense fibrillar material from which microtubules radiate appear near the nucleus. These fibrillar aggregates, referred to as microtubule foci, form small asters and collectively perform the role of the spindle pole during the two meiotic divisions. There are multiple centres at each pole and their number may vary. Thus, centrioles are not obligatory organelles of the spindle apparatus.