In vitro analysis of the spatial organization of chondrogenic regions of avian mandibular mesenchyme.

The mechanism(s) which control patterning in the face remain elusive, due in large part to the absence of morphologically identifiable controlling regions such as the AER of the limb bud. In order to identify the controlling region(s) and timing of patterning in the face, an investigation was launched to determine the spatial organization of tissues within this region, beginning with the chondrogenic zones of the avian (chick and quail) mandible. The mandibles from HH stage 23/24 chick and equivalent stage quail embryos were initially bisected in three planes giving rostral or caudal, proximal or distal, and medial or lateral halves. The mesenchyme from these various regions was isolated, plated out in high density micromass cultures, and grown for 4 days. Additionally, further cultures were grown, consisting of mandibular mesenchyme subdivided into quarters along the long axis of the mandible (e.g., rostro-proximal quarter) as well as the bisecting of medial or lateral halves (e.g., medial-rostral quarter). Nodule number and area were determined by morphometric analysis for each culture as well as whole mandible controls. The demarcation between chondrogenic and non-chondrogenic regions was dramatic. Of the bisected halves, proximal and lateral were the most chondrogenic with the lateral subdivision displaying much more cartilage than whole mandible. The nodules of the lateral cultures fused into a sheet of cartilage. In contrast mesenchyme from the medial half was virtually non-chondrogenic. When ranked by the amount of chondrogenesis, the order was, lateral > proximal = whole = core > distal > caudal > rostral > periphery >> medial. Interestingly, when subdivided further an altered pattern appeared.(ABSTRACT TRUNCATED AT 250 WORDS)