Bone Morphogenetic Protein (BMP) pathway controls body length in C. elegans by repressing the transcription of its downstream target,
lon-1 gene. The
lon-1 product subsequently blocks endoreduplication in hypodermis. In the absence of the BMP signal,
lon-1 is active, resulting in worms of shorter body length. In
lon-1(
e185) mutant, un-repressed endoreduplication leads to longer worms. Meanwhile, the
lon-1 gene product, LON-1, shows physical interaction with a BMP facilitator, CRM-1, in yeast-2-hybrid assay, and it is detected in the hypodermal membrane fraction by specific antibody. When the body length of
dbl-1 (
nk3);
lon-1 (
e185) double mutant showed an intermediate phenotype, it raises the possibility that
lon-1 might antagonize
dbl-1 activity, which has not been defined. Since
lon-1 is also required to repress endoreduplication, the elimination of
lon-1 function may have a dual and potentially opposite effect acting extracellularly and intracellularly, and the body length could not be used as the sole indicator of BMP signal activity. We dissociate the two different effects by introducing a novel
p4klon-1::gfp transcriptional reporter to assess its extracellular regulatory role on BMP signal. The green fluorescence in the hypodermis would change inversely to the BMP signal. Our data shows that BMP signal decreases in
lon-1 (
e185) mutant, with an intestinal BMP transcriptional reporter
pspp-9::gfp signal as reference, indicating that
lon-1 might be a positive regulator of BMP pathway. In the yeast-2-hybrid system, SCP-CRISP domain of LON-1 protein could interact with Cysteine-Rich (CR) domain of CRM-1 protein. We therefore hypothesize that the membrane bound LON-1 protein might complex with CRM-1 and DBL-1, which augments the presentation of the DBL-1 to its receptor. To demonstrate the complex formation of LON-1, CRM-1 and DBL-1, these three genes will be expressed in the Drosophila S2 cell line and followed by co-immunoprecipitation assay. Using the
lon-1 transcriptional reporter to monitor the BMP signal, we expect to have the
lon-1 overexpressing worms with an enhanced BMP signaling activity will show a weaker green fluorescent signal. (This study is supported by Research Grants Council, Hong Kong).