Polarity of marginal-band microtubules in vertebrate erythrocytes.

Erythrocytes from three different vertebrate species (bullfrog, mudpuppy, and stinkpot) were isolated, and the polarity of the marginal-band microtubules was determined using a modification of the method described by Heidemann and McIntosh [12]. A considerable part of each marginal band was examined in serial sections to see whether any changes in the polarity pattern occurred along the length of the band. On the basis of analyses of over 45 marginal bands, the following observations were made: (i) different polarity patterns were present within a given species; (ii) the polarity pattern seen in one cross-section of the marginal band remained the same along its entire length; no evidence for a limited zone of overlap was obtained; (iii) centrioles were found in erythrocytes from all three species. The data on the polarity patterns and the presence of centrioles in erythrocytes are compatible with a model recently proposed for the organization of marginal-band microtubules in blood clams that invokes the activity of a microtubule organizing center [20]. We suggest that a modification of the process of marginal-band formation described in that model can account for our observations on the polarity of marginal-band microtubules.