Figure 3.—

spd-3(oj35) embryos are defective in mitotic spindle alignment. In the single-cell embryo, the centrosomes are associated with the paternal pronucleus designating the posterior of the embryo, while the maternal pronucleus is usually located in the anterior (a and g). The pronuclei migrate toward each other, meeting near the posterior (b and h, centrosomes are marked by asterisks). In wild-type embryos, the pronuclear/centrosome complex then rotates 90°, aligning the mitotic spindle along the anterior/posterior axis to coordinate with the axis of polarity (c, centrosomes marked by asterisks). This rotation fails in the oj35 embryo, resulting in a mitotic spindle aligned transverse to the anterior/posterior axis (i, centrosomes marked by asterisks). The cleavage plane bisects the spindle (d and j), resulting in a proper asymmetric division in wild type (e) but not in oj35 embryos (k). In wild-type embryos, astral microtubules interact with the cell cortex and appear to be captured and stabilized (f). In oj35 embryos, astral microtubules appear to grow along the cortex (l) and are excessive in length. Bar, 10 μm. Tubulin is visualized with α-tubulin n357 (Amersham Pharmacia Biotech).