Archives of Histology and Cytology
Online ISSN : 1349-1717
Print ISSN : 0914-9465
ISSN-L : 0914-9465
Oocyte Follicle Cells Association during Development of Human Ovarian Follicle. A Study by High Resolution Scanning and Transmission Electron Microscopy
Pietro M. MOTTASayoko MAKABETomonori NAGUROSilvia CORRER
Author information
JOURNAL FREE ACCESS

1994 Volume 57 Issue 4 Pages 369-394

Details
Abstract

Morphodynamics of oocyte follicle cells association during the development of human ovarian follicles were studied by transmission electron microscopy and high resolution scanning electron microscopy including the ODO method.
For this study primordial, primary, growing preantral and antral follicles were systematically analysed in a total of 20 adult and fetal (3-8 months and at term) ovaries.
In early stages of follicle development (primordial and primary stages) the flattened and/or polyhedral cells, closely associated with the growing oocyte, project an increasing number of microvillous processes. These are in apposition with the oolemma, and form bulbous terminals presenting attachment zones such as zonula adherens, desmosomes and communicating junctions (gap junctions). “Focal contacts” between oolemma, and lateral microvillous extensions of follicle cells were also present.
Unusual forms of contact between follicle cell microvilli and oocytes in the early stages of growing primordial and primary follicles were also observed. These consist of long, thin extensions penetrating into the oocyte through deep invaginations of the oolemma. The aid of high resolution SEM of specimens subjected to the ODO method clearly reveals their 3-D arrangement within the ooplasm. They appear as long tortuous microvilli coming very close to the nucleus, and in their course are closely associated with a variety of organelles such as Golgi vesicles, endoplasmic reticulum membranes and nascent forms of smooth endoplasmic reticulum.
Using integrated observations by TEM and SEM, there may be as many as 3-5 “intraooplasmic processes” even in only one plane of fracture of an oocyte. Therefore, if the total volume of the oocyte and associated cells is considered, their amounts appear to be higher than previously reported. Thus, they have to be considered as normal devices of deep contact between the ooplasm and associated follicle cell extensions.
The presence of such structures within the ooplasm in early developing follicles well coincides with the great increase in volume of the oocyte. Although it is commonly believed that the activation of the growing oocyte may depend on the numerous contacts between the oolemma and follicle cells (mostly via gap junctions), the finding of these additional intraoocytic extensions suggests that they may in someway contribute to the initiation of growth in the human. In fact, these microvilli penetrate deep into the ooplasm, much like a sword in its sheath. After contacting numerous oocytes' organelles, they come close to the nucleus, where they might transfer, more extensively and easily, a variety of ions or molecules (as signals), including nutrients. In turn, they may mediate or integrate a parallel activation on specific oocyte organelles and their cohort of enzymes.
In later stages of follicle development (pluristratified and antral follicles provided with a thick and complete zona pellucida), these intraooplasmic microvilli were very rarely observed. In large antral follicles close to ovulation, the bulbous processes of follicle cells contacting the oolemma were noted, and the attachement zones (zonula adherens, desmosome) and gap junctions appeared very numerous. All these junctions disappear by being disrupted, at the time of ovulation, by active retraction of follicle cell extensions.
The long exposure of specimens to the ODO maceration method allowed full observation of the real 3-D surface pattern of follicular cells and their extensions, including those of the so-called corona radiata. In fact, through the chemical dissolution of liquor folliculi and zona pellucida, these cells, which were mainly pear shaped, showed a characteristic apical polarization of their numerous microvilli toward the oocyte. As a rule, these unusual microvilli measured 7-10μm in length and the apical surface of a single corona cell toward the zone/oocyte formed up to

Content from these authors
© International Society of Histology and Cytology
Previous article Next article
feedback
Top