THE SHAPING OF PHARYNGEAL CARTILAGES DURING EARLY DEVELOPMENT OF THE ZEBRAFISH

In zebrafish the cartilages of the pharynx develop during late embryog enesis and grow extensively in the larva before eventually being repla ced by bone. Here we examine chondrocyte arrangements, shapes, numbers , and divisions in the young hyoid cartilages. We observe two distinct developmental phases, morphogenesis and growth. The first phase gener ates stereotypically oriented chondrocyte stacks that might form by in tercalations among cells within the precartilage condensations. In mut ants that have deformed cartilages the orientation of the stacks is ch anged, and we propose that their correct formation underlies the corre ct initial shaping of the organ. The following period of rapid, nearly isometric cartilage growth occurs by divisions of chondrocytes that a re largely located near the joints, and appears to be under quite sepa rate regulation. (C) 1998 Academic Press.