Comparative analysis of follicle morphology and oocyte diameter in four mammalian species (mouse, hamster, pig, and human)

Abstract

Background: Laboratory animals are commonly used for evaluating the physiological properties of the mammalian ovarian follicle and the enclosed oocyte. The use of different species to determine the morphological relationship between the follicle and oocyte has led to a recognizable pattern of follicular stages, but differences in follicle size, oocyte diameter and granulosa cell proliferation are not consistent across the different species. In an effort to better understand how these differences are expressed across multiple species, this investigation evaluates oocyte and follicle diameters and granulosa cell proliferation in the mouse, hamster, pig, and human.

Methods: Histological sections of ovaries from the mouse, hamster, pig, and human were used to calculate the diameter of the oocyte and follicle and the number of granulosa cells present at pre-determined stages of follicular development. A statistical analysis of these data was performed to determine the relationship of follicular growth and development within and between the species tested.

Results: These data have revealed that the relationships of the features listed are tightly regulated within each species, but they vary between the species studied.

Conclusion: This information may be useful for comparative studies conducted in different animal models and the human.

Figure 1

Follicle Selection. Depiction of a representative Graafian follicle (pig) at the largest cross-sectional diameter (a), and a representative preantral follicle (hamster) at the midsection (b) and examples of diameter measurements with and without inclusion of the thecal layer, (c,d) respectively.

Figure 2

Follicular Stages of Maturation. Depiction of representative primordial (pig) (a), primary (pig) (b), preantral (hamster) (c), incipient antral (mouse) (d), small antral (hamster) (e) and Graafian (pig) (f) follicles.

Figure 3

Follicular Growth in Maturational Stages. Semi-log bar graph of follicle diameter versus follicular stage, * indicates values from previously published data for reference [11], and therefore do not include error bars. Values are the mean ± standard error.

Figure 4

Oocyte Growth in Maturational Stages. Bar graph of oocyte diameter versus follicular stage, * indicates values from previously published data for reference [12], and therefore do not include error bars. Values are the mean ± standard error.

Figure 5

Granulosa Cell Proliferation. Regression analysis of granulosa cell count compared to follicle diameter for primary, secondary, and incipient antral follicles in each of the four species.