Possible involvement of crosstalk cell-adhesion mechanism by endometrial CD26/dipeptidyl peptidase IV and embryonal fibronectin in human blastocyst implantation.

When human blastocysts hatch through the zona pellucida, gaining the ability to adhere to the endometrium, crosstalk between the embryo and the uterus may represent a successful outcome of their synchronized development and differentiation. CD26/dipeptidyl peptidase IV is known as a marker molecule of the implantation phase endometrium. To study the role of CD26 in implantation, 35 human hatched blastocysts were prepared by enzymatic treatment of expanded blastocysts that had been grown on schedule from frozen-thawed surplus embryos at the 2- or 4-cell stage. The blastocysts were placed on CD26-overexpressing or mock-transfected control monolayer cell cultures. The CD26-overexpression caused significantly higher blastocyst adhesion rate (53.3% versus 25.0%, P < 0.05) and significantly larger outgrowth area of trophectoderm (1.7-fold, P < 0.05). The second part of the present study was to show the expression of fibronectin, a CD26 ligand, in human preimplantation embryos, using the same donated resources. Fibronectin mRNA was detected by RT-PCR from the single hatched blastocyst (2/2) and from the single early blastocyst (3/6) but not from the single morula (0/5) samples. An indirect immunofluorescence technique verified the localization of fibronectin on the surface of the blastocyst. These results indicate that the adhesion mechanism by endometrial CD26 and embryonal fibronectin may be involved in human blastocyst implantation.