Microarray technologies are useful to mine the transcriptome of FCs expressed in follicles associated with competent oocytes and could be used to improve embryo selection with the objective of successful single embryo transfer.

No abstract

Embryo selection efficiency in human IVF procedure is still suboptimal as shown by low pregnancy rates with single embryo transfer (SET). Bidirectional communication between the oocyte and follicular cells (FC) is essential to achieve developmental competence of the oocyte. Differences in the gene expression profile of FCs from follicles leading to pregnancy could provide useful markers of oocyte developmental competence. FCs were recovered by individual follicle puncture. FC expression levels of potential markers were assessed by Q-PCR with an intra-patient and an inter-patient analysis approach. Using gene expression, a predictive model of ongoing pregnancy was investigated. Using intra-patient analysis, four candidate genes, phosphoglycerate kinase 1 (PGK1), regulator of G-protein signalling 2 (RGS2), regulator of G-protein signalling 3 (RGS3) and cell division cycle 42 (CDC42) showed a difference between FCs from follicles leading to a pregnancy or developmental failure. The best predictors for ongoing pregnancy were PGK1 and RGS2. Additionally, inter-patient analysis revealed differences in FC expression for PGK1 and CDC42 between follicles leading to a transferred embryo with positive pregnancy results and those with negative results. Both inter-patient and intra-patient approaches must be taken into consideration to delineate gene expression variations in the context of follicular competence. A predictor model using biomarkers could improve the efficiency of predicting developmental competence of oocytes. These new approaches provide useful tools in the context of embryo selection and in the improvement of pregnancy rates with SET.

We report here that intracellular pH (pH(i)) in cleavage-stage human embryos (2-8-cell) is regulated by at least two mechanisms: the HCO(3)(-)/Cl(-) exchanger (relieves alkalosis) and the Na(+)/H(+) antiporter (relieves acidosis). The mean pH(i) of cleavage-stage embryos was 7.12 +/- 0.008 (n = 199) with little variation between different stages. Embryos demonstrated robust recovery from alkalosis that was appropriately Cl(-)-dependent, indicating the presence of the HCO(3)(-)/Cl(-) exchanger. This was further confirmed by measuring the rate of intracellular alkalinization upon Cl(-) removal, which was markedly inhibited by the anion transport inhibitor, 4,4'-diisocyanatostilbene-2,2'-disulphonic acid, disodium salt. The set-point of the HCO(3)(-)/Cl(-) exchanger was between pH(i) 7.2 and 7.3. Embryos also exhibited Na(+)-dependent recovery from intracellular acidosis. Na(+)/H(+) antiporter activity appeared to regulate recovery up to about pH(i) 6.8; this recovery was HCO(3)(-)-independent and amiloride-sensitive, with a pH(i) set-point of approximately 6.8-6.9. A second system that was both Na(+)- and HCO(3)(-)-dependent appeared to mediate further recovery from acidosis up to about pH(i) 7.1. Thus, pH(i) of early human preimplantation embryos appears to be regulated by opposing mechanisms (HCO(3)(-)/Cl(-) exchanger, Na(+)/H(+) antiporter, and possibly a third acid-alleviating transporter that was both Na(+)- and HCO(3)(-)-dependent) resulting in the maintenance of pH(i) within a narrow range.