Monastrol and STLC treatment of S. compressa zygotes. (A-C) Zygotes were not sensitive to monastrol treatment during interphase (16 h AF); (A) 0.2% DMSO (B) 25 μM monastrol, (C) 50 μM monastrol. Note that the interphase zygotes in B and C exhibit elongated nuclei, indicating that they developed slightly faster than the control zygote in A. However, differences in developmental timing between treatments were not routinely observed. (D-F) Formation of monasters in mitosis (24 h AF); (D) 0.2% DMSO, (E) 25 μM monastrol, (F) 5 μM STLC. (G-I) Multipolar spindles (24 h AF); (G) 25 μM monastrol, (H) 50 μM monastrol, (I) 0.5 μM STLC. (J-L) Cytaster formation; (J) 25 μM monastrol (24 h AF), (K) 50 μM monastrol (24 h AF), (L) 100 μM monastrol (48 h AF). Cytasters were observed scattered throughout the cytoplasm. Hours in parentheses indicate times at which zygotes were fixed. MTs are depicted in green, condensed chromatin is depicted in red, and overlap between MTs and condensed chromatin is depicted in yellow. Median optical sections, 10–20 μm in total thickness, are shown. Scale bars equal 10 μm.