DISSECTING THE REGULATION AND FUNCTION OF THE CAP PROTEIN LON-1 IN BMP SIGNALING AND BODY SIZE IN C. ELEGANS
Access to this document is restricted. Some items have been embargoed at the request of the author, but will be made publicly available after the "No Access Until" date.
During the embargo period, you may request access to the item by clicking the link to the restricted file(s) and completing the request form. If we have contact information for a Cornell author, we will contact the author and request permission to provide access. If we do not have contact information for a Cornell author, or the author denies or does not respond to our inquiry, we will not be able to provide access. For more information, review our policies for restricted content.
BMPs, or Bone Morphogenetic Proteins, are evolutionarily conserved signaling molecules in the TGF-beta superfamily. The BMP signaling pathway informs cell behavior both during development and in homeostasis, and misregulation of this pathway in humans is associated with defects in the skeletal, neurological, and cardiovascular systems, as well as cancer. Canonical signal transduction occurs when the extracellular BMP ligand binds Type I and Type II receptors on the cell membrane. The Type II receptor then phosphorylates the Type I receptor, which in turn leads to the phosphorylation of R-Smad transcription factors in the cytosol. The R-Smads can then form a complex with co-Smads and enter the nucleus to regulate downstream targets of the pathway. BMP signaling must be tightly regulated to ensure specificity, and a number of modulators work to affect the localization, timing, and intensity of signaling.This thesis focuses on C. elegans, where all core pathway members have conserved homologs. BMP signaling is not required for viability in C. elegans, but affects a number of processes including body size and mesoderm patterning. C. elegans also has several modulators of BMP signaling, including LON-1, whose expression is also regulated by the BMP signaling pathway. LON-1 is a secreted protein in the CAP (Cysteine-rich secretory protein, Antigen 5, and Pathogenesis-related 1) superfamily, an ancient protein family that has members present across all kingdoms of life. In C. elegans, LON-1 is a negative regulator of body size and BMP signaling, but its mechanism of action is not fully understood. I have found that LON-1 requires its CAP domain for its function in regulating body size and BMP signaling, and worked with collaborators to show that LON-1 can bind small molecules including sterols in vitro, a feature shared with other CAP family proteins. Furthermore, mutating conserved residues within the CAP domain affects LON-1 function both in vivo and in vitro. These findings suggest that LON-1 may function by interacting with sterols. I also investigated the mechanism by which BMP signaling regulates lon-1 expression. Using lon-1 transcriptional reporters, I identified a BMP-responsive element (BRE) in the lon-1 promoter, and showed that deletion of the BRE region in the endogenous lon-1 locus impacts the regulation and function of LON-1. I further showed that the regulation of lon-1 expression is developmental stage specific, and that different components of the BMP pathway contribute differently to the regulation of lon-1. My work suggests that the BMP signaling pathway directly regulates lon-1 expression, and uncovers previously unappreciated complexities in the BMP signaling pathway.