The polarization of fibroblasts in early primary cultures is independent of microtubule integrity

Fibroblasts in culture apparently require an intact system of microtubules in order to adopt and maintain a polarized morphology. In contrast, the polarization of a number of epithelial cell types has been shown to be microtubule-independent. Reconciliation of these apparently contradictory data is difficult, however, because the epithelial cells were studied in short-term primary cultures while the fibroblasts were studied in secondary or longer-term cultures. To clarify the situation we have examined the effects of the microtubule-disrupting drugs, colcemid and nocodazole, on the polarization of a single cell type, the chick heart fibroblast (HF), maintained in both primary (1°) and secondary (2°) cultures. Immunofluorescence observations of both types of culture showed that in control medium the cells contained abundant microtubules, which were absent if the cells were cultured in medium containing either colcemid or nocodazole. The effects of microtubule-disrupting drugs on the polarization of the cells were quantified using two measures of cell shape, elongation and dispersion, both of which increase with increasing polarization. The results show that microtubule-disrupting drugs do not have a significant effect on the polarization of HF spreading in 1 ° culture but significantly reduce the polarization of HF spreading in 2° cultures. The effects of microtubule disruption on HF that had been maintained in 1° culture for 6h, 24 h or 48 h were also quantified. These measurements demonstrate that the polarization of HF in 1° culture becomes increasingly sensitive to microtubule disruption over this period until, after 48 h, they are as sensitive as HF in 2° cultures to microtubule disruption. The results show that the polarization of HF, cultured immediately after their isolation from the parent tissue is, like that of some epithelial cells, microtubule-independent but that during the first 48 h in culture these fibroblasts change in such a way that their polarization becomes microtubuledependent.