Expression and production of stathmin in growth plate chondrocytes is cell-maturation dependent

Growth plate cartilage is comprised of linear columns of chondrocytes with the least differentiated cells at one end and the terminally differentiated cells at the other end. Rat costochondral chondrocytes can be divided into the resting cell zone (reserve cell zone), which contains relatively immat ure chondrocytes (RC cells), and the phenotypically more mature prehypertro phic and upper hypertrophic cell zones, which together may be termed the gr owth zone chondrocytes (GC cells). When grown separately in monolayer cultu re, they continue to express their zone-specific phenotype, providing a mod el for assessing cell-maturation-dependent Expression of molecules associat ed with differentiation. Stathmin (also called prosolin, Op18, p19, 19K, an d others) is a highly conserved, phosphorylated cytosolic protein with appa rent ubiquitous expression. Although its exact function is unknown, stathmi n is considered to be a messenger phosphorylated protein, it plays a role i n tubulin stability, and it may participate in both general and specific re gulatory pathways. One uniform observation is that the expression of stathm in protein decreases in all cells as they become more terminally differenti ated in culture. There have been no published data regarding stathmin expre ssion and production in chondrocytes. This study was based on the hypothesi s that stathmin exists in chondrocytes and that the mRNA and protein levels decline in the CC cell with respect to the RC cell. Stathmin mRNA levels w ere determined and quantitated by reverse transcription-polymerase chain re action (RT-PCR) and northern blots. Protein levels were determined using im munoblots. It was found that stathmin exists in chondrocytes and that RC ce lls express approximately twice the level of mRNA and protein to that found in GC cells. The results support the hypothesis and suggest that the level of stathmin expression and production in culture is related to the level o f differentiation of RC and GC cells in vivo. (C) 2000 Wiley-Liss, Inc.