DETECTION AND CHARACTERIZATION OF AN ACTIVITY WHICH ALIGNS MESODERMALCELLS INTO PARALLEL ARRAYS

A cell line of mesodermal origin, FS9, was found to release a Cell Ori enting Factor into its culture medium. In contrast with the random mig ration of controls, the orienting activity causes migrating mesenchyma l cells to form an orderly 'halo' surrounding tissue explants; individ ual cells and their cytoskeletons are elongated and parallel to each o ther but at right angle to the explant. No effect on the rate of cell movement was apparent. The orienting activity could be quantified by c ounting the number of cells found within strings radiating at right an gles to a single tissue explant in the presence of FS9 conditioned med ium or by using NIH image analysis. A dose dependent relationship with half maximal activity occurring at a 25% dilution of conditioned medi um was observed. Cells that migrated randomly in the absence of condit ioned medium became oriented within 4 h of exposure to 50% conditioned medium. Conversely, when the conditioned medium was removed, parallel alignment was rapidly lost. The orienting activity was found in condi tioned media from a variety of mesodermal derivatives. Transformation of Balb/c 3T3 cells using EJ-ras oncogene led to augmented production of the activity. Furthermore, insulin was required in serum-free mediu m to support its production. Laminin, fibronectin and collagen and a r ange of pure cytokines, neither promoted nor inhibited orientation. Ce ll alignment was also unaffected by treatments which interfered with c ell-substrate interactions and motility including the addition of the RGD peptide or anti-integrin beta 1 and beta 3 antibodies. A protein i s likely to be involved since the activity was heat and trypsin sensit ive and non-dialysable. The possibility is discussed that the orientin g activity is a novel protein(s) which alters intercellular interactio ns to promote the formation of an aligned pattern by migrating mesench ymal cells.