ScienceDaily (July 23, 2010) — When searching for long-lost treasure, sometimes all you need is a good flashlight.
Such a "flashlight," developed at the Marine Biological Laboratory's (MBL) Josephine Bay Paul Center, has been used to illuminate a long-neglected cellular component -- the nucleolinus -- and confirm its role in cell division. MBL scientists Mark Alliegro and Mary Anne Alliegro, and MBL visiting investigator Jonathan Henry of University of Illinois, Urbana, present their discoveries regarding the nucleolinus in a paper in Proceedings of the National Academy of Sciences.
The nucleolinus is a structure observed in the nucleus of many cells, including invertebrate egg cells and some mammalian cells. While it was discovered more than 150 years ago, and other scientists have proposed that is involved in cell division, difficulties in visualizing the nucleolinus inside most cells have kept that hypothesis dormant.
When the nucleolinus is damaged with an infrared laser, a fertilized Spisula egg cell (bottom right) does not proceed through cell division, and its cell division apparatus (blue and yellow) is malformed. The top left cell shows proper cell division in a fertilized egg with an undamaged nucleolinus. (Credit: Mary Anne Alliegro, Marine Biological Laboratory)
"Our paper reintroduces (a cell component) that was discovered and forgotten long ago," Mark Alliegro says. "When we saw a couple of interesting things about the nucleolinus, I asked, 'What does it do?' I went to the library and quickly found out that nobody knew."
He and his colleagues went on to develop a probe that binds to specific nucleolinar molecules in egg cells of the surf clam Spisula solidissima. Using the label to keep an eye on the nucleolinus, they found that it was associated with structures required for cell division. Follow-up experiments in which the nucleolinus was targeted by a laser resulted in failed cell division and disruption of structures necessary for the process.
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Rediscovery of the nucleolinus, a dynamic RNA-rich organelle associated with the nucleolus, spindle, and centrosomes
-Author Affiliations
- aJosephine Bay Paul Center, The Marine Biological Laboratory, Woods Hole, MA 02543; and
- bDepartment of Cell and Developmental Biology, University of Illinois, Urbana, IL 61801
- Communicated by Lynn Margulis, University of Massachusetts, Amherst, MA, June 24, 2010 (received for review April 6, 2010)
Abstract
The nucleolinus is an RNA-rich compartment, closely apposed to or embedded within the nucleolus. Discovered over 150 y ago, fewer than two dozen articles have been published on the nucleolinus, probably because complex histochemical stains are required for its visualization in the great majority of cells. The nucleolinus has been reported in invertebrate oocytes, mammalian and amphibian epithelial cells, neurons, and several transformed cell lines. A prominent nucleolinus, clearly visible with transmitted light microscopes at 10× magnification, is present in each oocyte of the surf clam, Spisula solidissima. We observed a consistent relationship between the nucleolinus and the developing meiotic apparatus following Spisula oocyte activation. Through sonication and sucrose gradient fractionation of purified oocyte nuclei, we isolated nucleolini, extracted their RNA, and prepared an in situ riboprobe (NLi-1), which is associated specifically with the nucleolinus, confirming its unique composition. Other in situ observations revealed a NLi-1 and nucleolinar association with the developing spindle and centrosomes. Laser microsurgery that targeted the nucleolinus resulted in failed meiotic cell division in parthenogenetically activated oocytes and failed mitosis in fertilized oocytes. Although the nucleolinus may be a forgotten organelle, its demonstrated role in spindle formation suggests it deserves renewed attention.
Footnotes
- 1To whom correspondence should be addressed. E-mail: malliegro@mbl.edu.
- Author contributions: M.A.A., J.J.H., and M.C.A. designed research; M.A.A., J.J.H., and M.C.A. performed research; M.A.A., J.J.H., and M.C.A. contributed new reagents/analytic tools; M.A.A., J.J.H., and M.C.A. analyzed data; and M.A.A., J.J.H., and M.C.A. wrote the paper.
- The authors declare no conflict of interest.
- Data deposition: The sequence reported in this paper has been deposited in the GenBank database (accession no. HM004235).
- This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1008469107/-/DCSupplemental.
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