Elucidating the function of Lnc1, a phospholipase B

Alison J. Albee1, Linya Li1, Eileen T. O'Toole2, Thomas H. Giddings, Jr.2, and Susan K. Dutcher1

1) Department of Genetics, Washington University School of Medicine, St. Louis, MO, 63110 2) Boulder Laboratory for 3D Electron Microscopy of Cells, Department of Molecular, Cellular, and Developmental Biology, University of Colorado, Boulder, CO 80309

Basal bodies are complex, microtubule-based structures that are part of the microtubule organizing center (MTOC) of cells. Basal bodies also template cilia and recruit proteins needed for ciliary assembly. Cilia (also known as flagella) are found on almost every cell type of the human body and numerous human diseases are associated with ciliary defects that include male infertility, polycystic kidney disease, and Bardet-Biedl Syndrome. Phylogenetic profile comparison methods of ciliated organisms have identified Lnc1 as a protein found primarily in ciliated organisms. It is also among a small, but growing set of proteins that localize to the MTOC and the nucleolus during interphase, but is absent from the mitotic nucleus, which indicates its localization may be cell cycle regulated. Lnc1 is a member of a conserved family of phospholipase B proteins. Phospholipases cleave phospholipids to generate second messengers for a variety of signaling pathways, phospholipid synthesis, and membrane remodeling. Although Lnc1 lacks the conserved phospholipase catalytic site, it has phospholipase activity in vitro, which suggests it may have a novel catalytic site. Knockdown of Lnc1 in Chlamydomonas reinhardtii using RNA interference leads to increased numbers of cytoplasmic microtubules, short flagella, and the absence of the distal striated fiber that connects the basal bodies to each other. Surprisingly, MTOCs isolated from RNAi::LNC1 cells nucleate microtubules at lower tubulin concentrations than wild-type MTOCs. This is not associated with increased gamma-tubulin recruitment to the MTOCs, and suggests Lnc1 may be involved in a novel microtubule nucleation pathway.

e-mail address of presenting author: aalbee@genetics.wustl.edu