Intra-nuclear microtubules and a mitotic spindle orientation checkpoint

Cells of the fission yeast Schizosaccharomyces pombe have a checkpoint mechanism that reportedly monitors the orientation of the mitotic spindle. Astral microtubules in pre-anaphase spindles are thought to contact the contractile actin ring at the plasma membrane in order to rotate the spindle and to sense spindle orientation. Here, we show that these microtubules are actually inside the nuclear envelope.