The Nucleolinus: A disappearing, forgotten, and (maybe) misnamed organelle

It is common knowledge that many of the cell components we study today were discovered more than a century ago. Some have been renamed due to a newer understanding of their physiology or composition, and in some cases the old terminology is abandoned. It is unusual, however, to find a structure that has not been renamed but simply forgotten. This appears to be the case for the nucleolinus, discovered at least 150 years ago and studied by Agassiz, Haekel, Montgomery, and others until it virtually dropped from the literature in the early 1970s. The nucleolinus was thought to have a role in cell division, but with little knowledge of its composition and no molecular markers (until recently) available for its study, we do not know if the nucleolinus is a ubiquitous structure or an antiquated descriptor. This brief article relates most of what we know about the nucleolinus and where to find more information. Our growing knowledge concerning the role of the closely allied nucleolus in cell cycle regulation suggests that renewed study of the nucleolinus will yield important information about the biogenesis and evolution of the cell division apparatus.