Interphase microtubules in cultured cells: Long or short?

The question about microtubule length in interphase cells has become actual now, because parametres of dynamic instability of the plus end of microtub ules measured in vivo cannot account for a rapid turnover of long microtubu les. This problem may be solved assuming that microtubules rapidly turnover via depolymerization from the minus end and/or the real length of microtub ules is much shorter than the considered one. We traced microtubules radiating from the centrosome in epitelial cells (PK and FBT) and in fibroblasts (MEF and L) in the area of 4,0 x 5,5 x 1,5 mu m with centrioles in its center and microtubules in a large portion of the cytoplasm in PK cells. The number of microtubules analysed around the centr osome was no less than 200 for each cell line. In all cell lines studied, microtubules radiating from the centrosome were typically no longer than 1 mu m, and about 1/3 of microtubules were 0,2-0,4 mu m long. Only 2,5-8% of microtubules radiating from the centrosome run o ut of the area studied. The mean length of microtubules surrounding the cen trosome in all cell lines examined was 0,4-0,8 mu m. The average length of microtubules attached to the centrosome was less than that of free microtub ules. Thus, almost all microtubules around the centrosome are short, and on ly a few attached microtubules can reach the cell periphery. The reconstruc tion of cytoplasmic microtubules in PK cell was undertaken in an area of 10 x 35 mu m. In the lamella, the mean length of microtubules is about 1,6 mu m and the majority of microtubules are 0,5 to 1,5 mu m long. The results o btained support the hypothesis [1] that the majority of microtubules in int erphase cell are not associated with the centrosome.