Secretion of a novel class of iFABPs in nematodes: coordinate use of the Ascaris/Caenorhabditis model systems.

A novel fatty acid binding protein, As-p18, is secreted into both the perivitelline and perienteric fluids of the parasitic nematode, Ascaris suum, and at least eight potential homologues of As-p18 have been identified in the Caenorhabditis elegans genome. The products of the three most closely related homologues are fatty acid binding proteins (LBP-1, LBP-2 and LBP-3) which contain putative secretory signals. Phylogenetic analysis revealed that these secreted fatty acid binding proteins comprise a distinct gene class within the fatty acid binding protein family and are possibly unique to nematodes. To examine the potential sites of As-p18 secretion, the expression of the putative promoters of the C. elegans homologues was examined with GFP reporter constructs. The developmental expression of lbp-1 was identical to that of As-p18 and consistent with the secretion of LBP-1 from the hypodermis to the perivitelline fluid. The expression patterns of lbp-2 and lbp-3 were consistent with the secretion of LBP-2 and LBP-3 from muscle into the perienteric fluid later in development. These studies demonstrate that at least some perivitelline fluid proteins appear to be secreted from the hypodermis prior to the formation of the cuticle and, perhaps more importantly, that this coordinate C. elegans/A. suum approach may be potentially useful for examining a number of key physiological processes in parasitic nematodes.