I first heard of Oedogonium, a freshwater green alga, in a video made by Jeremy Pickett-Heaps, which Sveta gave me for a present.  I subsequently found myself reading his book on green algae, hoping to learn something about cell division in the rest of the eukaryotic world.  Cell division in Oedogoniales seems about as different from cell division in animals as possible.  I wondered if I would ever see them alive, and then recalled that there’s a stream running through the OIMB campus.  It turns out to be well populated with Oedogonium. 

Everything I know about this organism I learned from Pickett-Heaps book.  Two movies below show mitosis and cytokinesis.  Chromosome condensation, alignment, and separation are easily visible using DIC; mitosis is followed by formation of a nascent septum between the daughter nuclei; but prior to mitosis, the cell forms a “division ring” at an invisible gap in the wall just behind the apex.  After mitosis, the gap ruptures abruptly, and the division ring unfolds rapidly into a new section of wall; as the cell expands, the septum is positioned beneath the basal-most portion of the new wall section.

The contrast with animal cells could hardly be more pronounced: the cell division plane in Oedogonium is pre-defined by the structure of the cell wall, rather than by the midplane of the mitotic apparatus as in animal cells.  The midplane does define the position of the septum, but the septum, as described by Pickett-Heaps and colleagues, is formed by a phycoplast, in which microtubules form a parallel array between the nuclei, and associate with vesicles that assemble a partition from inside out, rather than a cleavage furrow pinching from outside in.  Finally, the septum with daughter nuclei on each side migrates to the true division plane.