Impact of Heat Stress Exposure During Meiotic Maturation on Oocyte, Surrounding Cumulus Cell, and Embryo RNA Populations

Abstract

Abstract. To determine if reductions in developmental competence related to heat stress exposure were correlated with perturbations in certain RNA populations, poly(A) RNA, total RNA, RNA size distribution, and the abundance of transcripts (cyclin B1, GDF9, BMP15, poly(A) polymerase, HSP70, 18S & 28S rRNA) were examined in oocytes matured at 38.5 or 41 C. Performing in vitro fertilization resulted in embryos for examining RNA. Relative to germinal vesiclestage oocytes, total amount of poly(A) RNA decreased similarly in oocytes matured at 38.5 or 41 C. Total RNA did not change during meiotic maturation or up through the 4 to 8-cell stage of embryonic development. Blastocyst-stage embryos had more total RNA; those originating from heat-stressed oocytes had more than those from nonheat-stressed oocytes. Oocytes and 4 to 8-cell embryos had similar RIN values and ratios for rRNA, 18S/fast region, and 18S/inter region. Values obtained for blastocyst-stage embryos were similar to those obtained for cumulus cell RNA, which did not change during maturation. Culture at 41 C for the first 12 h of meiotic maturation had no impact on RNA size distribution or transcripts examined from oocytes, surrounding cumulus or resultant 4 to 8-cell embryos. Interestingly, however, RNA from blastocysts originating from heat-stressed oocytes had lower 18S/fast region and 18S/inter region ratios compared to other developmental stages and cumulus cells. Although biological significance of these RNA changes is unclear, differences at the molecular level in embryos from heat-stressed oocytes emphasize the importance of minimizing stress exposure during meiotic maturation, if the intent is to obtain developmentally-competent embryos. Key words: Cumulus, Heat stress, Microcapillary electrophoresis, Oocyte, RNA (J. Reprod. Dev. 57: [481][482][483][484][485][486][487][488][489][490][491] 2011) griculturally-important females exposed to environmental heat stress experience reduced fertility [1][2][3][4]. In cattle, this is largely due to hyperthermia [5][6][7] whereby rectal temperatures may reach or exceed 41 C [5,[8][9][10][11][12]. Effects of environmental heat stress to reduce female fertility are pronounced during or near estrus [13][14][15]. This corresponds to the time period when the female is receptive to mating and the oocyte within the Graafian follicle resumes meiosis and progresses to metaphase II (MII; meiotic maturation) in preparation for fertilization. Hyperthermia during this time has been associated with reductions in early embryonic development [16] and increases in embryonic loss near the time of placental attachment [17].The negative impact of hyperthermia during estrus may be attributable to indirect effects on the maternal environment [reviewed by 18] and/or due to direct effects on the cumulus-oocyte complex. Direct exposure of the cumulus-oocyte complex to 41 C during meiotic maturation reduces early embryo development after fertilization by 30 to 65% [19][20][21][22][23][24][25] similar to consequences observed when e...

Developmental competence and expression pattern of bubaline (Bubalus bubalis) oocytes subjected to elevated temperatures during meiotic maturation in vitro

“…Also, Payton et al [52] did not find any significant difference in the relative abundance of BMP15 and GDF9 in germinal vesicle stage and matured oocytes on exposure to 41°C for first 12 h of in vitro maturation. However, the heat-induced perturbations occurring at molecular level during maturation are inherited by later stage embryos even after fertilization [53].…”

Heat stress effects on the cumulus cells surrounding the bovine oocyte during maturation: altered matrix metallopeptidase 9 and progesterone production

“…To validate some of the microarray results, the relative abundance of five transcripts identified as differentially expressed in the cumulus surrounding the control and heatstressed oocytes was examined using cumulus-derived cDNA from a different experimental effort described by Payton et al (2011). In that study, intact cumulus-oocyte complexes were randomly allotted to culture at 38.5 8C for 0 (i.e.…”

Factors affecting the in vitro embryo production in cattle associated to ovum pick up sistem

“…On the other hand, some findings provided evidence for bovine HSO to mature faster than non-heat-stressed counterparts (Edwards et al, 2005;Schrock et al, 2007; Andreu- Vazquez et al, 2010). In agreement with our results, oocytes heat-stressed during the germinal vesicle stage (bovine: Payton et al, 2004;mouse: LaRosa and Downs, 2007) or during maturation (bovine: Ju et al, 2005;Schrock et al, 2007;Edwards et al, 2009;Zhandi et al, 2009;Rispoli et al, 2011;Payton et al, 2011) have shown competence in overcoming the first cellular division similar to that found in non-HSO. In addition, we observed that HS treatment improved the ability of the oocytes to form blastocysts.…”