MICROINJECTION OF ANTIFIBRONECTIN ANTIBODIES IN THE CHICKEN BLASTODERM - INHIBITION OF MESOBLAST CELL-MIGRATION BUT NOT OF CELL INGRESSION AT THE PRIMITIVE STREAK

The involvement of fibronectin in adhesion and migration of individual mesoblast cells during chicken gastrulation was examined after microi njection of functional and nonfunctional antifibronectin antibodies in the blastoderm during the period of rapid migration of mesoblast cell s. The injection of affinity-purified polyclonal antihuman fibronectin antibody (total IgG or Fab fragment) or of monoclonal antichicken cel lular fibronectin caused a thickening of the primitive streak, which w as composed of loosely connected cells. This effect was most evident a t the level of Hensen's node, and very few mesoblast cells were observ ed migrating in the space between upper layer and deep layer. The obvi ous explanation of this effect was that the de-epithelialization of up per layer cells persisted in the presence of antibodies, but ingressed cells failed to emigrate from the primitive streak. Immunostaining of microinjected antibodies showed binding to the basement membrane, to the cell surface of mesoblast cells that had migrated before microinje ction occurred, and to the cell surface of deep layer cells. Cells tha t ingressed and detached in the course of reincubation of the embryo p ossessed little immunolabelling along their cell surface. The results suggest that the failure of ingressed cells to emigrate from the primi tive streak and to form mesoblast was due (1) to alterations in adhesi on between newly ingressed primitive streak cells, which had the abili ty to detach but possessed relatively little fibronectin along their c ell surfaces and a small number of cell protrusions, and (2) probably to a lack of adhesion of detached cells to the basement membrane, whic h was blocked by the presence of antifibronectin antibodies. We conclu de that the presence of fibronectin in the basement membrane is requir ed for emigration of ingressed cells and migration of mesoblast cells to occur. Once migration has commenced, fibronectin is also deposited along the cell surface of migrating cells, a factor that may increase their mutual adhesion. (C) 1993 Wiley-Liss, Inc.