Length control of primary cilia: analysis of monociliate and multiciliate PtK1 cells

Lengths of primary cilia in cultured PtK1 cells, on both a population basis and within individual (multiciliate) cells, have been compared. The latter examines the degree of discrepancy between cilia arising within the same cell and using a common precursor pool, on the hypothesis that a better correlation would be expected between cilia issuing from the same centrosome than between those in the population in general. To obtain accurate et plentiful measurements, a 'flow-fixation' technique was devised, which flattens the long primary cilia of cultured PtK1 cells (a kidney epithelial cell line from Potorous tridactylus, the kangaroo rat), prior to immunostaining with an antibody directed against detyrosinated tubulin (ID5). Comparisons of the flow-fixed measurements with a through-focus procedure for upright cilia in conventionally fixed cultures showed reasonable agreement, but not as closely as with measurements made on the living cells using the edge-on method of Roth et al. (J. Cell Sci. 89 (1988) 457). The incidence of multiciliation of confluent PtK1 cells cultures was approximately 5%, of which the majority were biciliates. Although shaft length in general varied considerably, biciliates and multiciliates showed a greater internal consistency, with discrepancies of < 25% in 70% of the cases. On both accounts, this consistency is far poorer than in, for comparison, Chlamydomonas, where its two flagella were < 5% different in length and within 10% tolerance throughout the whole population. Thus, length of primary cilia in PtK1 cell populations is considerably less stringently controlled than in PtK1 cells bearing 9 + 2 cilia, but those issuing from a single multiciliated cell tend to show better correspondence.