Development of cytotrophoblast columns from explanted first-trimester human placental villi: Role of fibronectin and integrin alpha 5 beta 1

Human first-trimester floating mesenchymal villi explanted onto gels of col lagen I or Matrigel were observed to undergo de novo development of anchori ng sites. These consisted of cytotrophoblast columns that formed by prolife ration of stem villous cytotrophoblast cells, as revealed by whole-mount an d thin-section microscopy and incorporation of bromodeoxyuridine into DNA. Column formation occurred exclusively at the distal tips of the villi, No c olumn formation was observed in tissue explanted onto agarose. On Matrigel, the developing columns penetrated downwards into the matrix, whereas on co llagen I, cytotrophoblast sheets spread across the surface of the gel and m erged to form a shell, The developing columnar cytotrophoblast up-regulated integrins alpha 1 beta 1 and alpha 5 beta 1 and produced an extracellular matrix containing oncofetal fibronectin, as in vivo. Function-blocking anti bodies were used to investigate the role of the integrin-fibronectin intera ction in anchoring villus development on collagen I. Antibodies to fibronec tin and the integrin subunits alpha 5 and beta 1, added at 24 h, all change d the pattern of cytotrophoblast outgrowth, Anti-fibronectin caused cell ro unding within the cytotrophoblast sheet and increased the population of sin gle cells at its periphery. Anti-integrin alpha 5 caused rounding and redis tribution of cells within the outgrowth. In the presence of anti-integrin b eta 1, cell-collagen interactions within the sheet were destabilized, often leading to the appearance of an annulus of aggregated cells at the periphe ry. These results show that 1) mesenchymal villi retain the potential to fo rm anchoring sites until at least the end of the first trimester, 2) adhesi on to a permissive extracellular matrix stimulates cytotrophoblast prolifer ation and differentiation along the extravillous lineage, 3) integrin alpha 5 beta 1-fibronectin interactions contribute significantly to anchorage of the placenta to uterine extracellular matrix. We suggest that as the devel oping placenta ramifies, new sites of anchorage form whenever peripheral vi lli contact decidua. This process is predicted to contribute to the stabili ty of the placental-decidual interface.