Metabolism of low molecular weight collagen by chondrocytes obtained from histologically distinct zones of the chick embryo tibiotarsus.

Primary monolayer cultures of chondrocytes from different zones of the chick embryo tibiotarsus incorporate ~- [~H]proline into collagen which is secreted by the cells in equal amounts into two extracellular pools-a cell matrix (Ma-collagen) pool and a culture medium (CM-collagen) pool.Rates of total collagen synthesis, in nanomoles of protein-bound hydroxyproline per h per lo6 cells, were 1.1 in cultures of cells obtained from the zone of rapidly dividing chondrocytes, 1.3 in cultures from the zone of elongated chondrocytes, and 1.0 in cultures from the zone of hypertrophying chondrocytes.The major collagen product formed by all cultures was type I1 collagen which was composed of pro-al(II), pCal(II), p~cul(II), and al(I1) chains in the CM-collagen pools, and of p~al(I1) and al(I1) chains in the Ma-collagen pools.A low molecular weight collagen (Mr = 59,000) was observed only in the CM-collagen pools where it was found in increasing proportions in passing from the rapidly dividing to the elongated to the hypertrophying chondrocyte cultures.The M, = 59,000 collagen was secreted from the cells more slowly than the type 11 procollagen and was not metabolized further in the culture medium under conditions in which the conversion of type II procollagen to type I1 collagen occurred.Inhibition of procollagen peptidase activities by EDTA blocked the procollagen to collagen conversion but did not prevent the formation of M, = 59,000 collagen or result in the accumulation of a precursor of the M, = 59,000 collagen.When intact cartilage segments were cultured with ~-[~H]proline, the M, = 59,000 collagen was synthesized only by the cartilage from the zone of hypertrophying chondrocytes, suggesting that this collagen is a marker for the final stage of chondrocyte differentiation in the developing tibiotarsus.When chondrocytes from the earlier stages of differentiation were grown in monolayers, they underwent differentiative changes which resulted in their production of the M, = 59,000 collagen.In the developing tibiotarsus of the chick embryo, rapidly dividing chondrocytes withdraw from the cell cycle and progress through a series of changes in their morphologies and their biological activities before they hypertrophy and finally