Expression of fertilin and CD9 in bovine trophoblast and endometrium during implantation

Abstract

The superficial placentation of cattle involves the development of fetal binucleate cells that arise from the chorion and migrate between adjacent cell tight junctions to fuse with maternal epithelium. Thus, the temporal and spatial patterns of expression of the cell migration, adhesion, and fusion molecules fertilin and CD9 were investigated in bovine trophoblast and endometrium. Bovine fertilin α and fertilin β messenger RNA sequences were amplified by reverse transcriptase-polymerase chain reaction in testis (positive control), peri-implantation (Days 18, 19, and 21), and postimplantation (Days 35-40) trophoblast RNA, but not in caruncular endometrium (Day 40). Northern blot analysis indicated that the transcript hybridizing to fertilin α in trophoblast RNA was approximately 4.0 kilobases (kb), whereas in testis, 2 transcripts of approximately 3.3 and 3.8 kb were indicated. The transcript hybridizing to the fertilin β probe was also larger in trophoblast than in testis (∼3.8 vs. 2.4 kb, respectively). In situ hybridization revealed that fertilin β mRNA was expressed by trophoblast cells, including binucleate cells. Immunohistochemical study of CD9, a member of the transmembrane-4-superfamily which is thought to be involved in sperm-egg fusion, showed that CD9 was present on the apical surface of uterine epithelium and in a subpopulation of binucleate cells of the trophoblast. Immunoprecipitation followed by Western blot analysis showed association between CD9 and integrin α3 in endometrium. The results support the hypothesis that fertilin and CD9 are involved in bovine binucleate cell migration and fusion.