Expression patterns of sirtuin genes in porcine preimplantation embryos and effects of sirtuin inhibitors on in vitro embryonic development after parthenogenetic activation and in vitro fertilization

We examined the expression patterns of porcine sirtuin 1 to 3 (Sirt1-3) genes in preimplantation embryos derived from parthenogenetic activation (PA), in vitro fertilization (IVF) and somatic cell nuclear transfer (SCNT). We also investigated the effects of sirtuin inhibitors (5 mM nicotinamide [NAM] and 100 μM sirtinol) on embryonic development of PA and IVF embryos under in vitro culture (IVC). The expression patterns of Sirt1-3 mRNA in preimplantation embryos of PA, IVF, and SCNT were significantly (P < 0.05) decreased from metaphase stage of oocyte to blastocyst stage. Especially, the expressions of Sirt1-3 in SCNT blastocysts were significantly (P < 0.05) lower and Sirt2 in PA blastocyst was significantly higher compared with the IVF blastocysts. Treatment with sirtuin inhibitors during IVC resulted in significantly (P < 0.05) decreased blastocyst formation and total cell number of blastocyst derived from PA (NAM: 29.4% and 29.6, sirtinol: 31.0% and 30.3, and control: 40.9% and 41.7, respectively) and IVF embryos (NAM: 10.4% and 30.9, sirtinol: 6.3% and 30.5, and control: 16.7% and 42.8, respectively). There was no significant difference in cleavage rate in both PA and IVF embryos. The early and expanded blastocyst formations at Day 7 were significantly lower in the sirtuin inhibitors-treated groups than the control. It was demonstrated that sirtuin inhibitor (NAM) influenced the percentage of blastocyst formation and total cell number of PA derived blastocyst when NAM was added during day 4 to 7 (22.1% and 32.4) or day 0 to 7 (23.1% and 31.6) of IVC compared with the control (41.8% and 41.5). No significant difference in cleavage rates appeared among the groups. The blastocysts derived from PA embryos treated with sirtuin inhibitors showed lower (P < 0.05) expressions of POU5F1 and Cdx2 genes. Also, Sirt2 mRNA expression was significantly decreased in sirtinol treated group and Sirt3 mRNA expression was also significantly decreased in both NAM and sirtinol treated groups compared with the control. In conclusion, these results suggest that sirtuins may have a physiological and important role in embryonic development of porcine preimplantation embryos by regulating essential gene expressions of developing embryos. These findings could have implications for understanding the role of sirtuins during embryo development and for improving SCNT and related techniques.

A follicular fluid factor inhibiting Xenopus oocyte maturation

A factor was isolated from bovine follicular fluid (FF) that blocked progesterone-induced maturation of Xenopus oocytes. The factor was purified by ultrafiltration through PM-10 membrane, gel filtration on Sephadex G-25 column, gel permeation chromatography on Superose 12 column and reversed-phase HPLC on Partisil ODS-3 column. The active factor is a peptide with an estimated Mr of 8000 and it effectively blocked progesterone-induced maturation of Xenopus oocytes at a concentration of 100 micrograms/ml. On the other hand, it did not influence the spontaneous maturation of isolated cumulus-enclosed or denuded mouse oocytes. The present findings suggest that the FF factor may be an inhibitor or antagonist of progesterone action.

Inhibition of progesterone-mediated maturation of oocytes of Xenopus laevis by oocyte maturation inhibitor from pig follicular fluid: development of a routine assay for the inhibitor with Xenopus oocytes

We describe an assay for oocyte maturation inhibitor (OMI) using the progesterone-mediated maturation of Xenopus oocytes. The test fraction used was a partially purified fraction from pig follicular fluid, which gave consistent inhibition of maturation in the pig oocyte assay. In the toad assay, oocytes (30-50) from each toad were pretested to determine whether satisfactory maturation was achieved because widespread animal variation was observed. Toads whose oocytes showed greater than 60% maturation in the pretest could be used directly. Toads whose oocytes showed less than 60% maturation were injected with pregnant mares serum gonadotropin (PMSG) in order to increase progesterone-mediated maturation. The dose and time after injection of PMSG before harvesting oocytes, dose and duration of progesterone exposure, and order of exposure of oocytes to OMI and progesterone were important variables. Opposing effects of OMI and progesterone were seen in oocytes from toads receiving 60 IU PMSG. In the routine assay we use animals whose oocytes show greater than 60% maturation in the pretest or animals treated with 12 IU of PMSG 4 to 7 days before use. Oocytes are exposed to the OMI fraction for 1 hr, progesterone is added, and incubations continued until controls reach maximum maturation (5 to 8 hr). The inhibition of toad oocyte maturation by OMI is reversible. The toad and mammalian oocyte assays were compared using more highly purified fractions of OMI and gave identical results.