Galectin LEC-6 interacts with glycoprotein F57F4.4 to cooperatively regulate the growth of Caenorhabditis elegans.

To study the endogenous counterpart of LEC-6, a major galectin in Caenorhabditis elegans, the proteomic analysis of glycoproteins captured by an immobilized LEC-6 column was performed using the nano liquid chromatography-tandem mass spectrometry (LC-MS/MS) technique. A protein recovered in a significant amount was determined to be either F57F4.3 or F57F4.4, although the method used could not determine which protein was the actual counterpart. Because the knockdown of the F57F4.3/4 genes in C. elegans is reported to cause growth retardation, we performed a double knockdown of the lec-6 and F57F4.3/4 genes. Although the RNA-mediated interference (RNAi) of lec-6 led to no obvious phenotype, the RNAi of both the lec-6 and F57F4.3/4 genes led to a significant reduction in growth rate when compared to the RNAi of F57F4.3/4 alone. Furthermore, to clarify which protein, F57F4.3 or F57F4.4, was responsible for the retarded growth, the levels of the F57F4.3/4 proteins expressed in a C. elegans wild type and a mutant lacking part of the F57F4.3 gene were compared. The levels of protein expressed by the wild type and the mutant were not significantly different, suggesting that the F57F4.3 protein contributes very little to growth retardation and that the major glycoprotein that interacts with LEC-6 is the F57F4.4 protein. These results suggest that binding with LEC-6 supports the function of F57F4.4 and that their cooperative functioning regulates the growth of C. elegans.