Analysis of the novel excretory cell expressed ECP-1 protein and its proposed ECP-1/IFC-2 fusion protein EXC-2 in the nematode Caenorhabditis elegans

The multigene family of cytoplasmic intermediate filament (IF) proteins in C. elegans covers eleven members, of which four (IFA-1 to IFA-3, IFB-1), which form an obligate heteropolymeric IF system, are essential for development. The six other C. elegans IF proteins IFB-2, IFC-1, IFC-2, IFD-1, IFD-2 and IFP-1 are co-expressed in the intestinal terminal web during different developmental stages, reveal various differently penetrant RNAi phenotypes and form another heteropolymeric IFB-2/IFCDP-1 IF system in C. elegans. Interestingly, the alternatively spliced IFC-2 variant, called EXC-2, was recently found also to be needed for a normal excretory system maturation in C. elegans. In order to better understand the IFC-2 function in the nematode tissue, we retrieved from the WormBase its multiple predicted alternatively spliced transcripts and analysed them using the molecular, immunofluorescence and RNAi approaches. We found that the 21-exon long genomic fragment encodes, besides the two different intestinal IFC-2a and IFC-2b IF proteins, also the novel excretory cell/IF unrelated protein ECP-1 and probably also the large ECP-1/IFC-2 fusion protein EXC-2, which all seem to be tissue-specific regulated from different promoters. Our analyses provide a framework for investigating interactions between the novel ECP-1, EXC-2 and some other proteins, including IFs, which show a similar excretory canal phenotype and are essential for development of the C. elegans excretory cells.