Alcohol promotes in vitro chondrogenesis in embryonic facial mesenchyme

Ethanol is a well-recognized teratogen in vertebrates that can perturb the development of the facial primordia and various other embryonic structures. However,the mechanisms underlying alcohol's effects on embryogenesis are currently unclear. Recent evidence suggests that the cranial neural crest, which forms the entire facial skeleton, may be a particularly sensitive target of ethanol teratogenicity. In the present study we have examined the influence of in vitro ethanol exposure on cartilage differentiation in micromass cultures of mesenchymal cells isolated from the various facial primordia (maxillary, mandibular, frontonasal, and hyoid processes) of the stage 24 chick embryo. In all four populations of facial mesenchyme, exposure to 1-1.5% ethanol promoted marked increases in Alcian blue-positive cartilage matrix formation, a rise in 35SO4 accumulation into matrix glycosaminoglycans, and enhanced expression of cartilage-characteristic type II collagen and aggrecan gene transcripts. In frontonasal and mandibular mesenchyme cultures, which undergo extensive spontaneous cartilage formation, ethanol treatment quantitatively elevated both matrix production and cartilage-specific gene transcript expression. In cultures of maxillary process and hyoid arch mesenchyme, which form little or no cartilage spontaneously, ethanol exposure induced the formation of chondrogenic cell aggregates and the appearance of aggrecan and type II collagen mRNAs. These actions were not restricted to ethanol, since tertiary butanol treatment also enhanced cartilage differentiation in facial mesenchyme cultures. Our findings demonstrate a potent stimulatory effect of alcohol on the differentiation of prechondrogenic mesenchyme of the facial primordia. Further analysis of this phenomenon might yield insight into the developmental mechanisms underlying the facial dysmorphologies associated with embryonic ethanol exposure.