Exogenous platelet-activating factor stimulates cell proliferation in mouse pre-implantation embryos prior to the fourth cell cycle and shows isoform-specific stimulatory effects

Abstract

Mouse embryos secrete molecules homologous to platelet-activating factor (PAF), termed embryo-derived PAF (EPAF), which act in an autocrine/paracrine fashion to stimulate embryonic development in vitro. Mouse EPAF is thought to consist predominantly of hexadecyl (C16) and octadecyl (C18) PAF-like components. Mouse pre-implantation embryos cultured with exogenous PAF from the early cleavage stages exhibit increased blastocyst cell numbers and rates of mitosis around the 8-cell stage. We investigated whether exogenous PAF could specifically stimulate embryonic cell proliferation prior to the blastocyst stage in the mouse and also compared the biological activities of the C16 and C18 PAF isoforms as follows. Embryos were cultured for either 24 h or 120 h from the 2-cell stage and their total cell numbers were determined or their development assessed in terms of their incidence of successful zona-hatching respectively. In each case, embryos were cultured in unsupplemented medium or in medium supplemented with either C16 or C18 PAF (0.5 μM). Compared with controls, culture with C16 PAF produced a significant stimulation of mean total per number per embryo and a significant increase in the incidence of successful zona-hatching, whilst culture with C18 PAF had no significant effect. We then cultured 1-cell zygotes for 48 h in unsupplemented medium or medium supplemented with either an equimolar mixture of C16 and C18 PF or with either C16 or C18 PF alone (each at 0.2 μM). Embryos were also scored for cell number at 4 h and 30 h of culture. Although no significant effect on mean cell number per embryo was seen following 4 h or 30 h of culture with a mixed C16/C18 PAF preparation, culture for 48 h with a mixed C16/C18 PAF preparation or with C16 PAF alone produced a significant increase in mean cell number per embryo compared with controls - an effect that is likely to be receptor-mediated, since culture with an equivalent concentration of C18 PAF had no significant effect compared with controls. We have demonstrated that mouse zygotes/embryos can respond in a specific manner to exogenous hexadecyl PAF in terms of increased rates of cell proliferation prior to cavitation, and must be capable of doing so at some time between the first and third, and also between the second and fourth, cell cycles. Such embryos presumably express one or more classes of functional PAF-receptor molecule during this period (i.e. as early as during the 1-, 2- or 4-cell stages). We have also demonstrated that embryonic response to exogenous PAF is significantly isoform-specific, which may reflect differences between the two isoforms either in affinity for binding to putative embyronic PAF-receptor molecules or in their ability to elicit a stimulatory response following binding. This observation calls into question the use of preparations containing a mixture of hexadecyl and octadecyl PAF isoforms, particularly in dose-response studies, in the mouse.

Effect of the microenvironment and embryo density on developmental characteristics and gene expression profile of bovine preimplantative embryos cultured in vitro

“…According to their biological process, genes associated with small molecule transport and signal transduction are also enriched in blastocysts derived from WOW environment. That would be accompanied by the accumulation of auto-and paracrine factors in the WOW system as proposed before (Thibodeaux et al 1993, Stoddart et al 1996, O'Neill 1997, Stoddart et al 2001.…”

The effect of paracrine/autocrine interactions on the in vitro culture of bovine preimplantation embryos

“…Exposure of early cattle embryos to PAF led to a significant depression in blastocyst rate on day 7, suggesting an adverse effect on preimplantation development, in contradiction to the report that exogenous PAF increases murine embryo development in a concentration-dependent manner (Stoddart et al 2001). However, the depression in cavitation rate in the bovine embryo may occur as a result of prolonged compaction (Van Soom et al 1997).…”

“…A 1.909 mmol stock of PAF/l (C16 isoform) (Stoddart et al 2001) was prepared in ethanol and diluted in SOFaaBSA to give a range of concentrations (0.5 -20 mM). Controls were also prepared in which the corresponding volumes of ethanol were added to SOFaaBSA (0.026-1.04% (v/v) ethanol).…”

“…It can act in an autocrine and/or paracrine manner to improve murine embryo development (Stoddart et al 1996, O'Neil 1997, especially at low embryo culture densities (O'Neill 1998). Supplementation of culture medium with the biologically active C16 isoform of PAF (Stoddart et al 2001) increases implantation rate (Ryan et al 1990a), placental mass (Ryan et al 1990a) and the viability of embryos for uterine transfer (O'Neill et al 1989). Furthermore, PAF can increase mitosis (Roberts et al 1993) and reduce apoptosis (O'Neill 1998), blastocyst cell number (Stoddart et al 1996, O'Neill 1997 and the oxidative metabolism of glucose and lactate (Ryan et al 1989(Ryan et al , 1990b.…”

Heterogeneity in the sn-1 carbon chain of platelet-activating factor glycerophospholipids determines pro- or anti-apoptotic signaling in primary neurons

“…The sn-1 ether linkage is not required for PAFR interaction but does increase potency several hundred-fold (1). The sn-1 carbon chain length and degree of unsaturation is implicated in activation of different PAFR signaling pathways (10,(13)(14)(15).…”