MATURATION OF MYOGENIC AND CHONDROGENIC CELLS IN THE PRESOMITIC MESODERM OF THE CHICK-EMBRYO

The establishment of cells with myogenic or chondrogenic potential is temporally and spatially separated from terminal differentiation in th e developing chick embryo. Both cell types arise from tissue adjacent to the neural tube and notochord, the paraxial mesoderm. A cell cultur e system was developed in order to study the maturation and differenti ation of myogenic and chondrogenic cells along the length of the parax ial mesoderm at different stages of development. Somite and segmental plate cells obtained from 36- to 52-h (stages 10-15) embryos were plat ed as a monolayer on substrata of gelatin, fibronectin, or laminin. A substratum of gelatin plus fibronectin was most effective in supportin g adhesion and differentiation. Maximal increase in number of cells in somite cultures occured 24 h earlier than that in segmental plate cul tures. Fewer skeletal muscle cells and chondroblasts were present in c ultures prepared from progressively more caudal regions of the paraxia l mesoderm and from younger embryos. Some cells present within the som ites and the rostral two-thirds of the stage 13 segmental plate differ entiated without replication after placement in culture. Only the prog eny of cells from its caudal third, and from stage 10 somites and segm ental plates, differentiated under these conditions. The results sugge st that some myogenic and chondrogenic cells obtain the ability to dif ferentiate under these in vitro conditions after stage 10 of developme nt, as they occupy more rostral positions within the segmental plate r elative to the addition of cells at its caudal end. Although some stag e 13 segmental plate cells form skeletal muscle and cartilage directly after removal from the embryo, differentiation is not observed in ovo until these cells are incorporated into somites, a minimum of 10 h la ter. Three-dimensional tissue interactions, and/or cell-cell interacti ons, while not required for segmental plate cells to undergo myogenesi s and chondrogenesis, may play a role in regulating the timing of term inal differentiation within the embryo. (C) 1994 Academic Press, Inc.