Effects of maternal undernutrition during early pregnancy on apoptosis regulators in the ovine fetal ovary

Abstract

This study aimed to determine whether reduced fetal ovary folliculogenesis in ewes undernourished during early/midpregnancy is associated with altered ovarian cell proliferation and/or the expression of apoptosis-regulating genes. Groups of ewes (n 5 11-19) were fed either 100% (high; H) or 50% (low; L) of metabolisable energy requirements for live-weight maintenance during selected windows of gestation. All animals were killed at days 50, 65 or 110 of gestation. Between mating and slaughter, control animals were fed the H ration, while animals of other subgroups were fed the L ration from (a) mating to slaughter at 50, 65 or 110 days; (b) 0 to 30 days; (c) 31 to 50 or 65 days; or (d), in the day 110 slaughter group only, from 66 to 110 days. Bouin's-fixed fetal ovaries were examined for (a) Ki67 immunoexpression (proliferation) and (b) Bax and Mcl-1 (apoptosis-regulating genes) expression by in situ hybridisation (day 110) and immunohistochemistry (days 50, 65 and 110). At day 50, maternal nutrition had no effect on Ki67, predominant in germ cells, or Bax and Mcl-1, predominant in the oocytes. Restricted maternal food intake from 0 to 30 days significantly reduced staining for Ki67 in germ cells at day 65 (P < 0.05) but increased staining in granulosa cells at day 110 (P < 0.05). In animals fed the L ration for 110 days, primordial follicle Bax and Mcl-1 were significantly increased (Bax: P < 0.01; Mcl-1: P < 0.05). Granulosa cell Bax was also increased (P < 0.05). When the L ration was fed from 66 to 110 days, granulosa cell Bax (P < 0.05) and primordial follicle Mcl-1 (P < 0.01) were also significantly increased. In the fetal ovarian vasculature, animals underfed for 0-110 days had significantly elevated perivascular Mcl-1 (P < 0.001) and endothelial Bax expression (P < 0.05). Moreover, at day 110, endothelial Mcl-1 was increased by underfeeding from 0 to 30 days (P < 0.05). These data indicate that maternal undernutrition alters proliferation and the expression of apoptosis-regulating genes in the developing fetal ovary. The precise mechanism depends on the window of maternal food restriction.

Epigenetics and developmental programming of welfare and production traits in farm animals

“…Where endpoints were assessed in fetal life, the consensus is one of delayed germ cell degeneration or delayed ovarian follicular development, as measured by elaboration of the granulosa cell layer (Borwick et al 1997;Rae et al 2001). Altered proliferation and apoptosis within the developing ovary may be the root cause (Lea et al 2006;GrazulBilska et al 2009). In all cases, the effects of maternal undernutrition were independent of fetal body growth.…”

Cellular proliferation and vascularization in ovine fetal ovaries: effects of undernutrition and selenium in maternal diet

“…However, inconsistent results of the effects of nutrient restriction on total fetal weight (i.e., differences due to fetal sex were not reported) at the end of pregnancy in sheep have been reported, showing a decrease or no effect on fetal weight (Rae et al 2001, Osgerby et al 2002, Redmer et al 2004, Lea et al 2006, Luther et al 2007). Similar to our findings, a lack of effect of maternal dietary restriction or environmental pollutants on ovine fetal ovarian weight has been reported by others (Rae et al 2001, Osgerby et al 2002, Murdoch et al 2003, Fowler et al 2008.…”

“…Both undernutrition and overnutrition of pregnant ewes negatively affect fetal growth and development (Redmer et al 2004, Luther et al 2005, 2007. In fact, cellular proliferation in fetal ovaries is regulated by numerous fetal and maternal factors including factors originating from maternal diet (Lea et al 2006). Moreover, Se has been demonstrated to diminish cellular proliferation, neo-angiogenesis, and other cellular functions in several tissues including cancerous tissues and digestive tract (Clark et al 1996, Ganther 1999, Combs 2001, Combs & Lu 2001, Zeng & Combs 2008.…”

Developmental programming of reproduction and fertility: what is the evidence?

“…Since these periods of nutrient restriction were calculated to correspond with foetal ovarian differentiation, meiosis I and folliculogenesis, respectively, it follows that different developmental mechanisms are sensitive to maternal undernutrition. In support, further studies following the same nutritional regimen as Rae et al (2001 and have shown that underfeeding from 0 to 110 days or from 65 to 110 days alters the expression of ovarian genes that regulate apoptosis, whereas undernutrition during the first 30 days of gestation reduces germ cell proliferation at day 65 but increased granulosa cell proliferation at day 110 (Lea et al, 2006). Thus it is likely that both of these mechanisms contribute to the impact of maternal undernutrition on folliculogenesis in the female foetal ovary.…”

“…Foetal undernutrition during the first 95 days may also reduce the subsequent adults' ovulatory function (3; Rae et al, 2001 and, most likely through direct effects on folliculogenesis (3; Rae et al, 2001). Undernutrition restricted to only the first 30 days of gestation in sheep may have a similar effect when examined at 65 or 110 days in the sheep (4; Lea et al, 2006). Increased ovarian DNA damage has also been observed following early (d28) to mid (d80) undernutrition in sheep (5; Murdoch et al, 2003).…”