Figure 4. 4R-Tau induced mitotic phenotypes in larval eye imaginal discs and brains.

(A) Larval eye discs from wild-type (n = 8) and 4R-Tau (n = 9) flies were analyzed for S phase (using a PCNA-EmGFP transgene)⁶⁶ and M phase (using pH3 staining) (Scale bar = 50 μm). The double arrow indicates the SMW. (B) Quantification of pH3-positive mitotic cells within the SMW in wild-type and 4R-Tau expressing eye discs (mean ± SD). (C) Quantification of S phase cells within the SMW in wild-type and 4R-Tau expressing eye discs (mean ± SD). (D) Spindle morphology in wild-type mitotic cells reveals the presence of normal bipolar spindles (arrows) while in 4R-Tau expressing eye discs, a large portion of the mitotic cells display a monopolar spindle configuration (arrowheads) (Scale bar = 10 μm). (E) Mitotic index in wild-type and 4R-Tau expressing third instar larval brains (n = 8 for each genotypes, mean ± SD) indicates an accumulation of pH3-positive cells. (F,G) Images of mitotic figures in wild-type and 4R-Tau-expressing larval brains. (F) In wild-type, metaphase cells show the presence of a well-focused bipolar spindle and at anaphase the segregation of two equal DNA masses at opposite poles. (G) In 4R-Tau expressing ganglion mother cells, the metaphase spindle has only one well-focused pole and at anaphase the two DNA masses appear to be unequal and asynchronous in their movement towards opposite poles (arrowhead). Furthermore, most cells display a monopolar configuration. Circular mitotic figures showing an increased DNA content are also observed (Scale bar = 10 μm). (H) Quantification of the mitotic phases in wild type (n = 1171, mean ± SEM) and 4R-Tau (n = 1985, mean ± SEM) expressing larval brains reveals a high frequency of dividing cells with a monopolar spindle configuration.