Stages of oogenesis
in Lytechinus
varigetaus. (a) Oocytes attached to the somatic cells
of the ovary. (B) previtellogenic primary oocytes. (C-E)
Vitellogenic growth phase of the oogenesis. (E-I) Full
grown oocytes complete meiosis with the large germinal
vesicle moving asymmetrically to the cell periphery, where
it breaks down and extrudes two polar bodies to produce a
haploid mature egg that is now ready for fertilization.
Scale bar = 50 microns. nc = nucleolus; gv = germinal
vesicle; pbs = polar bodies; pn = pronucleus. Image
courtesy of Gary Wessel, Brown Univ.
Oogenesis involves the progressive elaboration of the
oocyte, and includes transport of
yolk
proteins into the oocyte, the
localization
of mRNAs, and the production and translocation of
cortical granules, which lie immediately
beneath the plasma membrane, and are crucial for events
following fertilization.
