The patterns on chondrogenesis of cells from facial primordia of chick embryos in micromass culture.

Chondrogenesis of mesenchymal cells from the frontonasal mass, mandibles and maxillae of stage-24 chick embryos has been investigated in micromass (high-density) cultures. Distinct differences in the amount and pattern of cartilage differentiation are found. In cultures of frontonasal mass cells, a central sheet of cartilage develops; in cultures of mandible cells, less cartilage differentiates and nodules form; while in cultures of maxillae cells, virtually no chondrogenesis takes place. The same patterns of cartilage are found in cultures established from stage-20 embryos. At stage 28, frontonasal mass cultures form cartilage nodules and the number of nodules in mandible cultures is markedly decreased. There are striking parallels between the chondrogenic patterns of cells from the face and limb buds in micromass culture. The frontonasal mass cell cultures of stage-20 and -24 chick embryos resemble those established from the progress zone of limb buds. The progress zone is an undifferentiated region of the limb in which positional cues operate. Cultures established from the frontonasal mass of stage-28 chick embryos and from the mandibles of all stages resemble cultures of whole limb buds. These contain a mixture of committed and uncommitted cells. Ectoderm from facial primordia locally inhibits chondrogenesis in micromass cultures and this could provide a positional cue. The differences in chondrogenic potential of cells from facial primordia may underlie the specific retinoid effects on the frontonasal mass.