Vascular endothelial growth factor (VEGF) mRNA splice variants are differentially expressed in human blastocysts

The aim of our study was to detect and characterize mRNA expression of VEGF isoforms VEGF(121), VEGF(145), VEGF(165), VEGF(189), and VEGF(206) in human blastocysts. We recently demonstrated VEGF mRNA expression during human preimplantation embryo development, and further information regarding the alternatively spliced mRNAs resulting in freely secreted proteins or proteins bound to cell surface heparan-sulphate proteoglycans is needed to better understand the process of angiogenesis during implantation. Human blastocysts unsuitable for transfer obtained from the IVF programme at Stanford University were examined by reverse transcription/hemi-nested polymerase chain reaction for their expression of VEGF mRNA splice variants. VEGF mRNA was expressed in 17 out of 19 (89%) blastocysts. Of the 17 blastocysts, VEGF(121) mRNA was detected in 88%, VEGF(145) mRNA in 100%, VEGF(165) mRNA in 71%, and VEGF(189) mRNA in 24% of blastocysts. There was co-expression of mRNA for VEGF(121) and VEGF(145) only in 29% blastocysts, of mRNA for VEGF(165) and VEGF(145) only in 12%, and of mRNA for VEGF(121), VEGF(145) and VEGF(165) in 59% blastocysts, VEGF(206) mRNA could not be detected. In conclusion, we demonstrated that blastocysts express the mRNAs encoding for the free VEGF proteins, enabling the implanting embryo to immediately induce angiogenesis at the implantation site.