Chitin is a homopolymer of -1, 4 linked N-acetyl-glucosamine synthesized by chitin synthase. In arthropods, chitin is found in the exoskeleton, the tubular trachea system and the gut epithelia. In nematodes, chitin is only conclusively known to be present in the eggshell. We studied chitin localization in C. elegans and analyzed the roles of chitin synthase genes.For chitin detection, we engineered a labeled fusion protein carrying a chitin-specific binding domain from Bacillus circulans chitinase A1. Using this probe, we discovered elaborate chitin localization patterns in the pharynx besides detecting chitin in the eggshell. Chitin was detected in the entire lumen wall of the buccal capsule, and formed three longitudinal bundles in the corpus regions consistent with being localized to the three lobes of the pharynx lumen. In the terminal bulb, chitin was detected as an intense ragged band that corresponds to the grinder.There are two predicted chitin synthase genes, T25G3.2 and F48A11.1, in the C. elegans genome, and they are named
chs-1 and
chs-2 respectively. Reducing
chs-1 gene activity by RNAi led to eggs that were fragile and permeable to small molecules, and in the most severe case, absence of embryonic cell division. Complete loss of function in a
chs-1 deletion also resulted in embryos that failed to divide and lacked chitin in their eggshells. However, the pharynx chitin was unaffected by the
chs-1 deletion. Knocking down
chs-2 by RNAi resulted in eggs that hatched normally but most of the L1 larvae failed to develop further and appeared to be starved. These arrested L1 larvae usually had an irregular and enlarged grinder.Taking together the data from the chitin localization and gene function analyses, we conclude that
chs-1 is required for eggshell chitin while
chs-2 is responsible for pharyngeal chitin. This agrees with RNA in situ data that showed
chs-1 RNA expression in the ovary (Y. Kohara, p.c.) and with promoter analysis that
chs-2::GFP reporter is expressed in the pharynx. Studies in parasitic nematodes suggest that a
chs-1 ortholog is responsible for the production of eggshell chitin (Harris, et al., MBP, 111:351-62, 2000). By molecular cloning, we have identified
chs-2 orthologs in these nematodes. This suggests that distinct roles of chitin in the eggshell and pharynx are likely conserved among nematodes and controlled by
chs-1 and
chs-2 orthologs respectively.