Cystatins are natural protease inhibitors of the cathepsin B, L, H, F, S and Z cysteine protease families. They control the activity of these proteases through binding to the active site and forming a tight but reversible protein-protein complex. The N-terminal region and the two hairpin loops of the cystatin proteins are arranged in a wedge-shaped edge that is highly complimentary to the active-site cleft of the target enzymes. The function of the cysteine proteases is influenced by their interactions with their specific protein inhibitors as it is believed that an imbalance in these interactions may disturb their normal function within cells or defined biological processes. We previously reported that the C. elegans cathepsin L-like enzyme,
Ce-cpl-1, has multiple functions but its function in early embryogenesis is essential as it is specifically involved in yolk processing. The C. elegans cathepsin Z-like enzyme,
Ce-cpz-1, has also multifunctional roles during C. elegans development, in particular during molting. The C. elegans genome has two cystatin-like inhibitors,
Ce-cli-1 (R01B10.1) and
Ce-cli-2 (K08B4.6). We characterized a loss of function
cli-1(allele
ok1256) mutation which results in almost complete sterility of the worms but otherwise healthy adult hermaphrodites. The homozygous
cli-1(
ok1256) mothers (n=200) were able to produce only 0-10 fertile embryos over a 5 days period compared to ~280 in wild type control worms. The sterility in the mutant worms appears to be due to the disruption in the maturation of the oocytes. The target cysteine enzyme in this process is not as yet known but it potentially is involved in the processing of yolk proteins. Interestingly, during embryonic development
cli-1 is expressed in intestinal, hypodermal and pharyngeal cells in various stages of embryonic development. The protein was also present in several cells of the developing embryos as well as in eggshells. In adult hermaphrodites, the CLI-1 protein is not only present in the immature oocytes but also in the pharynx, vulva muscles and the hypodermis. The localization results imply that the inhibitor has also a significant role in regulating enzymes that are destined to function in these cells. Based on the co-localization of the inhibitor and the Ce-CPL-1 enzyme in the above cells we predict that Ce-CLI-1 is regulating the established functions of CPL-1 during worm development. The characterization of
cli-2 is in progress.