Cytoplasmic MTs Behavior in A. gossypii Figure 4. Bik1 promotes cMT growth in A. gossypii. (A) Anti- -tubulin immunostainings in bik1 and wild-type cells. Pictures correspond to stacks of 5Z planes with 0.75- m distance. (B) 1Z plane time-lapse microscopy of bik1 and wild-type cells expressing GFP-Tub1. Here, we focused on growth (arrows), pause (*), and shrinkage (arrowheads) of cMTs. (C) Quantiﬁcation of cMT length in bik1 cells. The average WT cMT polymerization rate is shown as reference (black line). (D) Quantiﬁcation of SPB position in bik1 and WT hyphae. SPBs are categorized into two classes: SPB situated in the white cortical zones and SPB situated in the center of the cell (gray zone). Bars, 5 m. parts as described in Figure 4D and classiﬁed the SPBs in two categories: 1) SPB located in the center of the cell (gray zone) and 2) SPB situated near the cortex (white zones). For Table 1. Measurement of cMT length in WT and mutant A. gossypii strains Wild type bik1 kip2 kip3 Avg. MT length 5.46 1.67 1.33 6.9 Max, MT length 26.5 9.5 5.53 25.6 No. of MTs 335 489 438 397 Measurements are in micrometers and were done on anti- -tubulin immunostaining pictures. Vol. 21, November 1, 2010 these quantiﬁcations, we only focused on SPBs belonging to G1 nuclei: 54.2% of SPBs in wild type (GFP-TUB1) are prox- imal to the cortex, whereas this is the case for only 20.8% of the SPBs in bik1 . As mentioned, in wild-type A. gossypii cells long cMTs were sliding along the cell cortex, pulling on SPBs and nuclei and bringing them close to the cortex (see the SPB move- ment in Figure 3Ac: t36 – 60 s). These sliding events were not observed in bik1 mutants. In budding yeast, cMT sliding depends on the MT motor dynein, in association with its activator dynactin. In Agbik1 mutant, sliding does not occur because cMTs are probably too short to be subjected to cortical forces (probably involving dynein). This phenotype also could also suggest that Bik1 by helping to maintain lateral contact of cMTs with the plasma membrane protects them from pausing or depolymerizing as shown in mam- malian cells (Komarova et al., 2002). Together, our results suggest that long cMTs are required to maintain SPBs and 3685