In female gametogenesis, oocyte competence develops through complex processes beginning with embryonic formation and ending with metaphase II oocyte ovulation. During ovulation, the oocyte is enclosed into a lineage of ovarian somatic cells and pregranulosa cells
and then grows into a primordial follicle. The primordial follicle pool, an embryonic product of the most mammal species including human, represents the female's ovarian reserve. Hence, the embryo quality is mainly decided by the competence of the oocyte selected for fertilization.
It is likely that SLCTs derive from primitive pregranulosa cells
and therefore represent a pseudo-male gonadal genesis in the ovary.
Primordial follicles consist of an immature GV oocyte arrested at prophase I, which is encapsulated by pregranulosa cells
. Activation of primordial follicles to primary follicles is marked by a morphological change of pregranulosa cells
from squamous to cuboidal.
Primordial follicle consists of an oocyte surrounded by a layer of few somatic cells, the pregranulosa cells
. The fate of each follicle is controlled by different mechanisms involving endocrine and paracrine factors.
The primordial follicles were defined as an oocyte encapsulated by squamose pregranulosa cells
, primary follicles as those with one layer of cuboidal granulosa cells and preantral follicles as those with two and more layers of cuboidal granulosa cells.
Normally, inactive primordial follicles undergo arrest at prophase I and contain nongrowing oocytes and squamous pregranulosa cells
supported by a basal lamina.