Reduction in corpora lutea number in obese melanocortin-4-receptor-deficient mice - PubMed (original) (raw)

Reduction in corpora lutea number in obese melanocortin-4-receptor-deficient mice

Mara Sandrock et al. Reprod Biol Endocrinol. 2009.

Abstract

Obese melanocortin-4-receptor-deficient (MC4R-/-) male mice are reported to have erectile dysfunction, while homozygous MC4R-/- female mice are apparently fertile. A recently established obese mouse strain, carrying an inactivating mutation in the MC4R gene, revealed difficulties in breeding for the homozygous female mice. This prompted us to determine the presence of follicles and corpora lutea (CL) in ovaries of MC4R-/- mice aged 3-6 months in comparison to wild type (MC4R+/+) littermates. Serial sections of formaldehyde-fixed ovaries of mice with vaginal signs of estrus and metestrus were assessed for the number of healthy and regressing follicles and CL. The number of CL, as an estimate for the ovulation rate, decreased to zero during aging in MC4R-/- mice. The number of small- (diameter 100-200 micrometer) and large-sized follicles namely antral follicles (diameter >200 micrometer) were slightly increased in MC4R-/- compared to MC4R+/+ mice. Greater differences were found in very large to cystic follicles, which were more numerous in MC4R-/- mice. The number of regressing antral follicles was higher in the MC4R-/- group compared to the MC4R+/+ group. This was associated with a wide range in the number of collapsed zonae pellucidae as the last remnants of regressed follicles. A conspicuous hypertrophy of the interstitial cells was noted in 6-month-old MC4R-/- mice. In conclusion, cystic follicles and the reduction in CL number point to a decreased ovulation rate in obese MC4R-/- mice.

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Figures

Figure 1

Figure 1

Ovaries of 6-month-old MC4R-deficient mice differ in morphology compared to MC4R+/+ mice. The figure shows representative ovary sections of mice with a mixed genetic C3H/B6 background. Under a B6 background, identical morphological changes were observed although less frequent. A and B: Ovaries of MC4R-/- mice (A) contain a cystic follicle (star) and no CL, while MC4R+/+ ovaries (B) show many CL (arrowheads). H.E. Scale bars: 200 μm. C and D: Collapsed zonae pellucidae as remnants of regressed follicles (arrows) are more obvious in MC4R-/- mice (C) compared to MC4R+/+ mice (D). PAS reaction. Scale bars: 50 μm. E and F: Interstitial gland cells are hypertrophied in MC4R-/- ovaries (E) compared to MC4R+/+ ovaries (F). H.E. Scale bars: 25 μm.

Figure 2

Figure 2

Decrease in the number of CL in ovaries of MC4R-/- mice. The number of CL was determined in completely dissected H.E. stained ovaries. Compared with MC4R+/+ mice the number of CL is significantly lower in MC4R-/- mice at a mixed C3H/B6 (1st cohort) and at a B6 background (2nd cohort). A: The difference in the 1st cohort appears to increase with animal age in months. B: shows the data broken down into animals with vaginal signs of estrus and metestrus. Data are presented as box-and-whisker plots with median (line), interquartile range (box), minimum and maximum range (whisker) and outliers (cross); n indicates the number of animals; * indicates significant differences with p value ≤ 0.05.

Figure 3

Figure 3

Increase in the number of regressing antral follicles in ovaries of MC4R-/- mice. The ovaries of MC4R-/- and MC4R+/+ mice at a mixed C3H/B6 background (1st cohort) were serially sectioned and either H.E.-stained for counting regressing antral follicles in (A) or PAS-stained for counting zonae pellucidae in (B), the latter at an interval of 168 μm. The final number was calculated for either the whole ovary (A) or for a one millimeter thick ovarian section (B). A: Significantly more regressing antral follicles are counted in MC4R-/- mice compared to MC4R+/+ mice with vaginal signs of estrus and metestrus. B: The range in the number of collapsed zonae pellucidae is strikingly wider in MC4R-/- than in MC4R+/+ mice. Data are depicted as box-and-whisker plots with outliers; n indicates the number of animals; * highlights significant differences (p ≤ 0.05)

Figure 4

Figure 4

Hypertrophy of interstitial gland cells in ovaries of MC4R-deficient mice as measurable decrease in nuclear density. To determine whether hypertrophy of interstitial gland cells (Fig. 1E) occurs to a measurable extent, the nuclear density was determined per 100 μm2-sized areas of interstitial gland cells. Statistically significantly less nuclei are counted in 6-month-old MC4R-deficient C3H/B6 mice than in MC4R+/+ littermates. Data are presented as box-and-whisker plots with outliers; n indicates the number of mice; * highlights significant differences (p ≤ 0.05).

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