Ovarian responses to undernutrition in pregnant ewes, USA

Abstract

In most mammals oogonia proliferate by mitosis and begin meiotic development during fetal life. Previous studies indicated that there is a delay in the progression to the first stage of meiotic arrest in germ cells of female fetuses of undernourished ewes. We report that underfeeding (50% NRC requirement beginning on Day 28 of pregnancy) provokes an increase in oxidative base lesions within DNA of mid-gestational (Day 78) fetal oogonia; this condition was associated with up-regulation of the tumor suppressor/cell-cycle arrest modulator p53, antiapoptotic factor Bcl-2, and base-excision repair polymerase beta. Fetal ovarian weights and germ cell concentrations were not altered by nutrient deprivation. Ovaries of ewes on control diets (100% NRC) contained more tertiary follicles than their restricted counterparts; however, peripheral venous estradiol-17beta was not different between groups. There was no effect of treatment on p53 accumulation in maternal oocytes. Luteal structure-function was not perturbed by undernutrition. No fetal losses were attributed to the dietary restriction. It is proposed that DNA of interphase fetal oogonia is vulnerable to oxidative insults perpetrated by a nutritional stress to the dam, and that multiple/integrated adaptive molecular response mechanisms of cell-cycle inhibition (providing the time required for base repairs) and survival hence sustain the genomic integrity and population stability of the germline.

Figure 1

Light microscopic morphology of fetal ovaries. A low-power view of the ovarian surface epithelium (OSE) and cortex are shown in the upper left panel. High-power views of healthy oogonia (O), an apoptotic oogonium (AO), and pregranulosa cells (GC) are illustrated in the lower left panel. A mid-power view of oogonial clusters/cords is depicted in the right panel. Scale bars = 5 μm.

Figure 2

Fluorescence intensity scores of oogonia/oocytes: A, fetal 8-oxoguanine; B, fetal p53; C, fetal Bcl-2; D, fetal polymerase β; E, fetal apoptosis (DNA fragmentation); F, maternal p53 (fetal control, n = 4; fetal restricted, n = 5; maternal control, n = 7; maternal restricted, n = 6). Asterisks indicate pairwise increases (P < 0.01). Values for negative controls (not subtracted from the data shown) were < 45. Representative photomicrographs of p53-immunostained oogonia of control (left panel) and restricted (center panel) fetuses are shown in the inset (note the contrast in magnitudes of nuclear fluorescence); a negative preabsorption control cell (restricted fetus) is shown in the right panel.