Identifying and characterizing regulators of a bone morphogenetic protein cell signaling pathway in Caenorhabditis elegans

Cell-to-cell communication pathways ensure proper development of organisms. One group of signaling pathways that animals use is the bone morphogenetic protein (BMP) family. BMPs play significant roles in embryogenesis, development of skeletal and cardiovascular systems, among many others. Misregulation of BMP signaling leads to various diseases and thus needs to be tightly regulated. An understanding of how this pathway is itself controlled and performs diverse functions throughout the lifetime of living organisms is not very well understood. To identify new regulators of the BMP signaling pathway we used the roundworm C. elegans. DBL-1/BMP signaling is a dose dependent regulator of body size. Over expression of DBL-1 makes animal longer and suppression of the pathway reduces animal body size. Using genetic and imaging tools, we identified a group of genes called dumpy (dpy) that genetically interact with DBL-1/BMP signaling. Most of the identified dpy genes code for extracellular matrix components and/or are associated with body size regulation. We showed that loss of some dpy genes suppresses expression of the DBL-1 ligand and DBL-1 signaling activity. Using RNA sequencing, we identified genes that are differentially regulated by the DBL-1 signaling pathway; many of which regulate body size. Furthermore, we identified two dpy genes, dpy-2 and dpy-9, that have stage-specific interactions with the DBL-1 signaling pathway. Additionally, we characterized the interaction between DBL-1 pathway and dpy-24/blmp-1. BLMP-1 is a transcription regulator and controls some organismal traits that the DBL-1 pathway also affects. We showed DBL-1 signaling and BLMP-1 regulate each other. We also identified a physical interaction between BLMP-1 and the SMADs, downstream regulator of DBL-1 pathway using yeast-two hybrid system. Using bioinformatics and qPCR analysis, we showed that the interaction between SMADs and BLMP-1 is required to regulate some common downstream target genes. Lastly, we performed epistasis studies and identified that the DBL-1 signaling pathway and BLMP-1 work partially independently to regulate body size and work together to regulate brood size. Collectively, we identified additional regulators and interactors of the DBL-1 signaling pathway, and our findings provide insights about a new molecular mechanism by which DBL-1 pathway regulate certain organism traits.